Multiple Choice Questions 501-600

 

Key Code: B

All of the following statements regarding infections caused by enterohemorrhagic
Escherichia coli are correct, EXCEPT

A) Bloody diarrhea and fever usually occur within 24 hours
B) Range of manifestations may vary from mild diarrhea to hemolysis and renal failure
C) Greatest incidence of infection is in children under 5 years of age
D) Most cases are attributed to undercooked meat
E) Hemolytic uremic syndrome is a life-threatening sequela

Answer: A
(Year Posted:UI  501)

 

Key Code: M

Which one of the following statements about an Hfr cell is correct?

A) Forms as the result of imprecise excision of the F plasmid from the chromosome
B) Usually cannot mediate conjugation
C) Can spontaneously revert to an F+
D) A and B
E) A and C

Answer: C

(Year Posted: 2001 UI  502)

 

Key Code: M

A cell may become competent after which one of the following?

A) New gene expression triggered by quorum sensing of a competence factor
B) Adsorption of a bacteriophage
C) Introduction of a plasmid harboring a composite transposon
D) Uptake of homologous DNA
E) None of the above

Answer: A

(Year Posted:UI  503)

 

Key Code: M

All of the following statements concerning the Gram stain are correct, EXCEPT

A) Escherichia coli stains red because its cell wall has a thin peptidoglycan layer
B) Streptococcus pyogenes stains blue because its cell wall has a thick peptidoglycan laye
C) Mycobacterium tuberculosis stains blue because its cell wall has a thick lipid layer
D) Mycoplasma pneumoniae is not visible by Gram stain because it lacks a cell wal
E) Only Gram-positive cells in the late lag and exponential phases of growth stain reliably with the Gram stain

Answer: C

(Year Posted:UI  504)

 

Key Code: B

All of the following are associated with infections caused by both Clostridium tetani and Clostridium botulinum, EXCEPT

A) Potent neurotoxins
B) Toxi-infections
C) Spastic paralysis
D) A and B
E) A, B and C

Answer: C

(Year Posted: UI  505)

 

Key Code: M

The coagulase test, in which bacteria cause plasma to clot, can be used to distinguish which one of the following pairs of organisms?

A) Staphylococcus aureus from Staphylococcus saprophyticus
B) Staphylococcus aureus from Staphylococcus epidermidis
C) Staphylococcus epidermidis from Staphylococcus saprophyticus
D) A and B
E) A, B and C

Answer: D

(Year Posted:UI  506)

 

Key Code: M

The use of selective bacteriological media are indicated in which one of the following situations?

A) When the pathogen is likely to be present in low numbers and might be missed by overgrowth by endogenous bacteria in the clinical specimen
B) When the pathogen may be killed by metabolic products of endogenous bacteria growing on the medium
C) When the pathogen is suspected to be Gram-negative
D) A and B
E) A, B and C

Answer: D

(Year Posted:UI  507)

 

Key Code: B

Which one of the following groups of organisms represent the three most common bacterial causes of childhood diarrhea in the United States?

A) Salmonella spp., Shigella sonnei and Campylobacter jejuni
B) Campylobacter jejuni, enterotoxigenic Escherichia coli and Salmonella spp.
C) Shigella flexneri, Shigella sonnei and Shigella boydii
D) Salmonella spp., Shigella sonnei and enterotoxigenic Escherichia coli
E) Shigella sonnei, Campylobacter jejuni and enteropathogenic Escherichia coli

Answer: A

(Year Posted:UI  508)

 

Key Code: B, Key Code: M

All of the following statements about Mycobacterium tuberculosis or the disease it causes are correct, EXCEPT

A) The organism is resistant to drying, many disinfectants and alkali
B) The acid-fast stain can be useful in the diagnosis of tuberculosis
C) Cultures from sputum samples become positive after 1-2 days of incubation
D) Cord factor is produced by virulent organisms
E) The cell wall has a high content of lipid (about 40-60% by dry weight)

Answer: C

(Year Posted:UI  509)

 

Key Code: M, Key Code: N

Which one of the following mechanisms of antibiotic resistance could be conferred by plasmid-borne gene?

A) Specification of an altered protein product that is not sensitive to the antibiotic
B) Modification of the antibiotic
C) Modification of the target of the antibiotic
D) A and B
E) A, B and C

Answer: E

(Year Posted:UI  510)

 

Key Code: M

DNAses present in the extracellular environment can abolish which one of the following processes?

A) Transduction
B) Transposition
C) Transformation
D) Conjugation
E) B and D

Answer: C

(Year Posted:UI  511)

 

Key Code: M

The DNA found in an individual specialized transducing phage particle is usually derived from which one of the following

A) Phage origin only
B) Plasmid origin only
C) Bacterial origin only
D) Bacterial and phage origin
E) None of the above

Answer: D

(Year Posted:UI  512)

 

Key Code: M, Key Code: N, Key Code: I

Which one of the following statements concerning the mode of action of endotoxin (lipopolysaccharide) is CORRECT?

A) Degrades lecithin in eukaryotic cell membranes
B) Inactivates elongation factor 2
C) Lyses red blood cells
D) Causes the release of acute phase cytokines such as IL-1 and TNF-a
E) Kills B- and T-lymphocytes

Answer: D

(Year Posted:UI  513)

 

Key Code: M, Key Code: N

Which one of the following antibiotics acts by directly preventing the cross-linking of the glycan chains of peptidoglycan?

A) Vancomycin
B) Cycloserine
C) Bacitracin
D) Penicillin
E) Polymyxin

Answer: D

(Year Posted:UI  514)

 

Key Code: B

Your patient has subacute bacterial endocarditis caused by a member of the viridans group of streptococci. Which one of the following sites is most likely to be the source of the organism?

A) Skin
B) Rectum
C) Oropharynx
D) Urethra
E) Colon

Answer: C

(Year Posted:UI  515)

 

Key Code: B

A 45-year old female with acute leukemia has recently received chemotherapy. She presents to the ER with fever and pain at the I.V. catheter site. On exam you notice pus at the catheter site. She has a leukocytosis (elevated WBC count). Which one of the following organisms would MOST LIKELY be recovered from her blood cultures?

A) Staphylococcus epidermidis
B) Staphylococcus saprophyticus
C) A viridans streptococcus
D) Escherichia coli
E) Enterococcus faecium

Answer: A

(Year Posted:UI  516)

 

Key Code: B

Six hours after consumption of potato salad at a July 4th picnic, several family members presented to the ER with the abrupt onset of nausea, vomiting and diarrhea. Which one of the following is the MOST LIKELY causative pathogen?

A) Bacillus cereus
B) Enterococcus faecalis
C) Staphylococcus aureus
D) Escherichia coli
E) Clostridium perfringens

Answer: C

(Year Posted:UI  517)

 

Key Code: M, Key Code: B, Key Code: N

Which one of the following statements concerning Mycoplasma pneumoniae is CORRECT?

A) Lacks a cell wall and contains both DNA and RNA
B) Cannot be cultivated on routine laboratory media (e.g., BAP)
C) Is the most common cause of pneumonia in healthy young adults
D) Erythromycin is the drug of choice for treatment
E) All of the above

Answer: E

(Year Posted:UI  518)

 

Key Code: B

Which one of the following is the most common cause of "culture-negative" endocarditis?

A) Haemophilus influenzae
B) Haemophilus aegyptus
C) Haemophilus aphrophilus
D) Haemophilus ducrey
E) Haemophilus parainfluenzae

Answer: C

(Year Posted:UI  519)

 

Key Code: B

All of the following signs and symptoms are associated with cystitis, EXCEPT

A) Dysuria
B) Hematuria
C) Flank pain
D) >100,000CFU bacteria/ml of urine
E) Urinary frequency

Answer: C

(Year Posted:UI  520)

 

Key Code: M

All of the following statements concerning anaerobic bacteria are correct, EXCEPT

A) They generate energy by respiration
B) They grow best in the complete absence of air
C) They lack superoxide dismutase
D) They lack catalase
E) Medically-important anaerobes are somewhat aerotolerant

Answer: A

(Year Posted:UI  521)

 

Key Code: B, Key Code: N

Which one of the following is suggestive of an anaerobic infection?

A) Infections related to the use of aminoglycoside antibiotics
B) Infections adjacent to a mucosal surface
C) Foul-smelling discharge
D) B and C only
E) A, B and C

Answer: E

(Year Posted:UI  522)

 

Key Code: M, Key Code: M

All of the following statements concerning enterococci are correct, EXCEPT

A) Important cause of endogenous infections
B) Important cause of nosocomial infections
C) Members of the normal microbiota of the large bowel
D) Multiple resistance to antibiotics
E) Enterococcus faecium causes the majority of enterococcal infections

Answer: E

(Year Posted:UI  523)

 

Key Code: M

Which one of the following occurs in an F+ x F- mating?

A) The recipient usually remains F-
B) Cell to cell contact and participation of the F pilus is required
C) Chromosomal DNA is transferred to the recipient at a high frequency
D) a and b
E) b and c

Answer: B

(Year Posted:UI  524)

 

Key Code: M

A transposon can be found on which one of the following?

A) Plasmid DNA
B) Bacteriophage DNA
C) Chromosomal DNA
D) A and B
E) A, B and C

Answer: E

(Year Posted:UI  525)

Key Code: B

Which one of the following bacteria is MOST commonly associated with the formation of struvite stones?

A) Proteus mirabilis
B) Escherichia coli
C) Enterococcus spp.
D) Pseudomonas aeruginosa
E) Staphylococcus saprophyticus

Answer: A

(Year Posted:UI  526)

 

Key Code: B

All of the following are features of Clostridium perfringens food poisoning, EXCEPT

A) Enterotoxin-producing type A causes a mild self-limiting gastroenteritis
B) Beta-toxin-producing type C causes necrotizing bowel disease
C) The consumption of only a few vegetative cells is necessary to cause either disease
D) The enterotoxin is released during sporulation of type A organisms in the gut
E) The lack of intestinal trypsin or the consumption of food containing trypsin- inhibitors are contributing factors to necrotizing bowel disease

Answer: C

(Year Posted: 2001 UI  527)

 

Key Code: M, Key Code: B

All of the following statements concerning Haemophilus influenzae are correct, EXCEPT

A) It is a coccobacillus
B) It is non-motile and non-spore forming
C) It requires blood components for optimal growth
D) All Haemophilus influenzae infections can be prevented by immunization
E) Haemophilus influenzae is one of the three leading causes of bacterial meningitis

Answer: D

(Year Posted: 2001 UI  528)

 

Key Code: B

Refer to the case history below to answer questions

A 65-year old man comes to his physician complaining of a chronic cough for more than two months. Now he sees blood in the sputum. He further reports that he often wakes at night with severe night sweats, feels tired most of the time and has lost about 15 pounds. He tearfully reports that he is living alone as his wife passed away 18 months ago. Physical examination is unremarkable except for the pulmonary examination in which rales are heard. Radiographic findings show the presence of cavitary disease in the right upper lobe of the lungs. Sputum samples are sent for microbiological workup of suspected tuberculosis. Microbiological findings confirm this.

Tissue destruction in TB is due primarily to

A) mycobacterial leukocidin
B) mycobacterial cytotoxin
C) immediate hypersensitivity
D) delayed-type hypersensitivity

Answer: D

What is the most likely origin of the organisms responsible for this man's disease?

A) exogenous, from a tick bite
B) exogenous, from an infected person's sputum
C) endogenous, from normal flora
D) endogenous, from a reactivation of a primary lesion

Answer: D

This man's active disease would be treated with two or more antibiotics in order to

A) take advantage of synergistic effects
B) prevent the emergence of strains resistant to one antibiotic
C) inhibit bacteria located in different body compartments
D) inhibit different bacterial species that contribute to this disease

Answer: B

Vaccination against this disease is practiced in many parts of the world. The vaccine is BEST described as

A) live, attenuated
B) whole cell, killed
C) subunit, purified outer membrane protein
D) capsular material
E) cord factor

Answer: A

(Year Posted: 2001 UI  529)

 

Key Code: M

A chemical substance that is found in bacterial spores, but NOT in vegetative cells is

A) diaminopimelic acid
B) dipicolinic acid
C) ketodeoxyoctonoic acid
D) D-glutamate
E) D-alanine

Answer: B

(Year Posted: 2001 UI  530)

 

Key Code: M

The function of the sex pilus of bacterial cells involves

A) transport of nutrient
B) attachment of cells to inert surfaces
C) movement of cells in a type of twitching motion
D) transfer of DNA between bacteria during conjugation
E) organization and folding of the bacterial chromosome within the cytoplasm

Answer: D

(Year Posted: 2001 UI  531)

 

Key Code: M, Key Code: B

A S. typhimurium strain acquires a mutation which inactivates the protein responsible for inverting the DNA fragment which lies upstream of the H2 pilin gene. Which of the following statements best describes the expression of the H1 and H2 genes in the mutant strain?

A) The expression of the H1 and H2 genes will alternate
B) Neither the H1 nor the H2 gene will be expressed
C) Both the H1 and H2 genes will be expressed constitutively
D) Either the H1 or the H2 gene (but not both the H1 and H2 genes) will be expressed
E) Only the H2 gene will be expressed

Answer: D

(Year Posted: 2001 UI  532)

 

Key Code: B, Key Code: M

Transfer of antibiotic resistance genes is known to occur readily between all of the following pairs of organisms except one. Which pair is the exception?

A) N. meningitidis and N. gonorrhoeae
B) S. aureus and S. epidermidis
C) H. influenzae and H. parainfluenzae
D) E. coli and Shigella
E) E. coli and Salmonella

Answer: A

(Year Posted: 2001 UI  533)

 

Key Code: B, Key Code: V

A 12 month old child is seen in the Emergency Room. The child has been lethargic for the past two days and has refused to eat. Over the last six hours, the child has been vomiting. When the child's parent is questioned, she acknowledges that the child has not received well baby care since birth. Noteworthy findings on physical examination include neurological signs compatible with central nervous system disease. A spinal tap is performed. Which of the following findings would suggest an etiology OTHER THAN   H. influenza?

A) Coccobacilli on Gram stain
B) Photophobia
C) Fever
D) Prominent rash on the extremeties
E) Elevated protein in the CSF

Answer: D

(Year Posted: 2001 UI  534)

 

Key Code: B

Toxin mediated diseases from acute bacterial infections require different management strategies. For which of the following toxin mediated illnesses would antibiotic therapy be completely unjustified?

A) Group A streptococcal toxic shock syndrome
B) S. aureus food poisoning
C) Scalded skin syndrome
D) S. aureus toxic shock syndrome
E) Scarlet fever

Answer: B

(Year Posted: 2001 UI  535)

 

Key Code: F

It is July 1 and the first day of your internship. Your pager starts going "beep, beep, beep" and you are summoned to see a 22 year old female who is acutely ill with a fever of 104°F, sinus tenderness, and black, necrotic lesions on her oral palate. Laboratory exam reveals a high blood sugar and low pH, indicative of diabetic ketoacidosis. Which one of the following mycoses is the patient most likely to have?

A) Mucormycosis
B) Coccidiodomycosi
C) Cryptococcosis
D) Histoplasmosis
E) Aspergillosis

Answer: A

(Year Posted: 2001 UI  536)

 

Key Code: F

The pathology of invasive aspergillosis is best characterized by

A) Saprophytic colonization of a preexisting cavity
B) Invasive of blood vessels with hemorrhagic infarction
C) Eosinophilic infiltration
D) Mononuclear infiltrate with precipitans
E) Large numbers of non-septate hyphae with right angle branching

Answer: B

(Year Posted: 2001 UI  537)

 

Key Code: F

Most antifungal drugs target

A) chlorophyll
B) ergostero
C) DNA
D) Chitin
E) Golgi apparatus

Answer: B

(Year Posted: 2001 UI  538)

 

Key Code:V

A one-year-old child is brought to the emergency room by his mother because of severe diarrhea over the past two days. The child has a low grade temperature, and has vomited twice. The child has been in day care where a similar illness has been affecting other children. A pediatrician has ruled out bacterial and parasitic causes of illness in several other children in the day care center. The most likely cause for this infection is

A) Norwalk virus
B) Hantavirus
C) Influenza virus
D) Rotavirus
E) Enteric adenovirus

Answer: D

(Year Posted: 2001 UI  539)

 

Key Code: V

A major reason for the high prevalence of herpes simplex virus infections in the U.S. population is

A) The virus remains highly infective for many days on objects or surfaces where it is deposited by infected individuals
B) The very short incubation period (1-2 days between becoming infected and releasing infectious virus) facilitates rapid spread
C) Silent shedding of virus by infected individuals without symptoms facilitates spread of virus to unsuspecting contacts
D) Infection with the virus does not result in production of antibodies by the hos
E) The virus mutates frequently enough to escape immune resistance even in previously infected individuals

Answer: C

(Year Posted: 2001 UI  540)

 

Key Code: P

A camper who drank untreated water from a mountain stream developed diarrhea that persisted for more than one week. The patient had noted flatulence and foul-smelling bulky stools. The patient's geographical history and symptomatology are strongly suggestive of

A) Enterobiasis
B) Fish tapeworm infection
C) Giardiasis or lambliasis
D) Trichinelliasis
E) Toxoplasmosis

Answer: C

(Year Posted: 2001 UI  541)

 

Key Code: P

A two-year-old Ecuadorian child develops abdominal pain, projectile vomiting and a swollen abdomen. An x-ray shows dilated loops of bowel consistent with small bowel obstruction. Which of the following parasites is the most likely cause?

A) Pinworm (Enterobius vermicularis)
B) Whipworm (Trichuris trichiura)
C) Hookworm
D) Ascaris lumbricoides
E) Strongyloides stercoralis

Answer: D

(Year Posted: 2001 UI  542)

 

Key Code: P

You are evaluating an immigrant from Southeast Asia for a kidney transplant. She complains of peptic ulcer-like pain and has an increased number of eosinophils on her blood smear. Before transplantation and treatment with immunosuppressive drugs you should rule out infection with

A) Enterobius vermicularis (pinworm)
B) schistosomes
C) Taenia saginata (beef tapeworm)
D) Ancyclostoma caninum (dog hookworm)
E) Strongyloides stercoralis

Answer: E

(Year Posted: 2001 UI  543)

 

Key Code: B

A 17-year-old man with a history of cystic fibrosis is admitted with a brief history of fever, cough and shortness of breath. A chest X-ray shows changes consistent with chronic infection and sputum Gram-stain reveals PMNs and many Gram-negative bacilli. The most likely cause of his infection is

A) Streptococcus pneumoniae
B) Haemophilus pneumoniae
C) Pseudomonas aeruginosa
D) Klebsiella pneumoniae
E) Mycoplasma pneumoniae

Answer: C

(Year Posted: 2001 UI  544)

 

Key Code: B

A 20-year-old woman with cystic fibrosis suffers from chronic lung infections that are resistant to anti-staphylococcal drugs. Which of the following factors renders this woman more susceptible to bacterial colonization of her lungs?

A) A defect in glycolipid sialylation
B) Increased ICAM receptor expression
C) Susceptibility to encapsulated pathogens
D) A high density of Duffy red blood cell antigen
E) Loss of sensitivity to the tuberculin antigen

Answer: A

(Year Posted: 2001 UI  545)

 

Key Code: B

A 12-year-old girl complains of severe pain in her right knee. The child claims that the pain is far worse when she stands or walks than when she is sitting or lying down. Examination of the knee reveals no swelling, discoloration, or unusual warmth. Discussion with the girl reveals that she had had a pyogenic infection on her foot in the recent past. Your tentative diagnosis would be

A) Septic arthritis
B) Osteomyelitis
C) Reactive arthritis
D) Reiter's syndrome
E) Not enough information for a diagnosis

Answer: B

(Year Posted: 2001 UI  546)

 

Key Code: B

A 37-year-old tree surgeon suffered a penetrating injury to his eye. Which of the following infectious processes is most likely to result from his injury?

A) Histoplasma capsulatum chorioretinitis
B) Toxoplasma gondii chorioretinitis
C) Staphylococcus aureus endophthalmitis
D) Haemophilus influenzae conjunctivitis
E) Chlamydia trachomatis chronic follicular conjunctivitis

Answer: C

(Year Posted: 2001 UI  547)

 

Key Code: B

A 38-year-old homeless man presents with a history of cough of long duration productive of yellowish sputum and 15-pound weight loss over a 2-month period. He is a known alcoholic and spends nights sleeping in a homeless shelter. On exam he appears to be chronically ill. He has a low-grade fever, his teeth are in very poor condition and his chest exam findings are consistent with disease in the right upper lobe. His chest X-ray shows an infiltrate, but his sputum Gram-stain reveals PMNs but no organisms. The most likely cause of his illness is

A) Streptococcus pneumoniae
B) Mixed anaerobic organisms
C) Mycobacterium tuberculosis
D) Mycoplasma pneumoniae
E) Adenovirus

Answer: C

(Year Posted: 2001 UI  548)

 

Key Code: B

A Gram stain of pus from the oral abscess of a 62-year-old man with periodontitis shows that the patient's infection is polymicrobic. What is the most likely source of this man's infection?

A) Autoinfection with oral anaerobes
B) Autoinfection with oral Staphylococcus spp.
C) Actinomyces israelii following tooth extraction
D) Pseudomonas aeruginosa following primary viral infection
E) Periodontitis is not an infectious process

Answer: A

(Year Posted:UI  549)

 

Key Code: B

A 51-year-old woman is admitted to hospital with a 2-week history of progressive cough, productive of slightly blood-tinged sputum, all of which began shortly after she had an alcohol withdrawal seizure. Her friends complain that the patient's breath smells foul. The most likely cause of her infection is

A) Streptococcus pneumoniae
B) Streptococcus pyogenes
C) Haemophilus influenzae
D) Fusobacterium spp., Peptostreptococcus, Prevotella spp. and other anaerobic bacteria
E) Klebsiella pneumoniae, Staphylococcus aureus and other Gram-negative bacteria

Answer: D

(Year Posted:UI  550)

Key Code: B

An 87-year-old man who had never received any immunizations developed diphtheria and died following a lengthy illness. Strains of Corynebacterium diphtheria isolated from the man's contacts were screened for the presence of the toxin-converting bacteriophage v.Which of the following mechanisms most likely prevented some of the isolated strains from being converted to toxin production by v.

A) Host modification systems
B) Host restriction barriers
C) Defective uvr genes
D) Loss of sex pili
E) Periplasmic DNAase

Answer: B

(Year Posted:UI  551)

 

Key Code: B

A 45-year-old man reports to his physician's office with a pus-filled sinus in his mouth. The man had an impacted wisdom tooth extracted 3 weeks prior to this infection. Microscopic examination of aspirated pus would most likely reveal which of the following?

A) Large oval shaped cells with germ tubes
B) Spherules
C) Gram-positive filamentous rods
D) Extracellular trophozoites
E) Conidia

Answer: C

(Year Posted:UI  552)

 

Key Code: B

A 15-year old boy develops pneumonia that is not cured by penicillin. Gram stain and culture of his sputum are both negative. An ELISA to measure IgM levels is used for diagnosis. The most likely infecting pathogen causes direct damage to tissue by which of the following mechanisms?

A) Coagulase-mediated fibrin polymerization
B) Pneumolysin-mediated cell death
C) Granuloma formation
D) Capsule-induced cytokine production
E) Superoxide radical secretion

Answer: E

(Year Posted: 2001 UI  553)

 

Key Code: B

Gram positive, ß-hemolytic cocci are isolated from a patient with pharyngitis. The attending physician failed to prescribe antibiotics and the patient developed a rash over his trunk 3 weeks later. This patient is at risk for life-threatening sequelae due to which of the following processes?

A) Induction of anergy
B) Antigenic variation
C) Secretion of Fc receptor molecules
D) Superantigen synthesis
E) Molecular mimicry

Answer: E

(Year Posted: 2001 UI  554)

 

Key Code: B

A 73-year-old woman who has been hospitalized for 3 weeks following a stroke develops pneumonia. A sputum sample reveals Gram-positive diplococci. Which of the following virulence attributes of this pathogen is responsible for killing pulmonary endothelial cells?

A) Capsule
B) Teichoic acid
C) Pneumolysin
D) Streptolysin O
E) Metalloprotease

Answer: C

(Year Posted: 2001 UI  555)

 

Key Code: B

A 37-year-old woman with a history of mitral valve prolapse and a murmur has been complaining of low grade fevers, fatigue, weight loss and generalized weakness for several weeks. The most important test to make the diagnosis is

A) Transthoracic echocardiogram (2D)
B) Transesophageal echocardiogram (TEE)
C) Chest X-ray
D) Blood culture
E) Complete blood count, including white blood count

Answer: D

(Year Posted: 2001 UI  556)

 

Key Code: B

A 1-year-old girl suffers from recurrent episodes of otitis media. Due to concern that one of the girl's immunizations failed, her physician decides to take a blood specimen to test for the presence of specific immunoglobulins. Antibody levels to which of the following bacterial components would be of primary concern?

A) Phospholipid
B) Pili
C) Mycolic acid
D) Polyribitol phosphate
E) Peptidoglycan

Answer: D

(Year Posted: 2001 UI  557)

 

Key Code: B

Bacterial cytotoxins have several structural and functional properties in common. One well-studied toxin binds to a ganglioside receptor and stimulates the production of cAMP by activating adenylate cyclase. Identify the bacterial pathogen that produces this toxin

A) Corynebacterium diphtheriae
B) Clostridium tetani
C) Clostridium botulinum
D) Staphylococcus aureus
E) Vibrio cholerae

Answer: E

(Year Posted: 2001 UI  558)

 

Key Code: B

Researchers introduced mutations in the bvgS (sensor) gene in an attempt to construct a safe whooping cough vaccine strain. However, the mutated strain failed to elicit adequate protection from an initial infection during vaccine trials. The most likely explanation for the failure of this vaccine strain was because it lost the capacity to express

A) Pertussis toxin
B) Filamentous hemagglutinin
C) Invasive adenylate cyclase toxin
D) Polyribitol phosphate
E) Diphtheria toxin

Answer: B

(Year Posted: 2001 UI  559)

 

Key Code: B

Several cases of keratoconjunctivitis, some with corneal perforation, are traced to the same ophthalmologist. Specimens cultured from the physician's examination equipment are Gram negative, oxidase positive rods. A virulence factor that most likely contributed to the corneal perforation was

A) Coagulase
B) Exotoxin A
C) Capsule
D) Elastase
E) Staphylokinase

Answer: D

(Year Posted: 2001 UI  560)

 

Key Code: B

A previously healthy injection drug user is admitted with sudden onset of fever, shortness of breath, chest pain, and hemoptysis (coughing up blood). His disease is most likely due to infection with

A) Streptococcus viridans
B) Streptococcus pyogenes
C) Pseudomonas aeruginosa
D) Staphylococcus epidermidis
E) Staphylococcus aureus

Answer: E

(Year Posted: 2001 UI  561)

 

Key Code: B

A 26-year old woman presents with severe pain in her right knee, lower back pain, and mild conjunctivitis. A patient history reveals no recent gastrointestinal or urogenital infections and no unusual respiratory infections. Onset of the joint and lower back pain was about 4 days prior to your examination and interview. Examination of the knee reveals slight swelling but no discoloration; the knee is painful when touched. Laboratory analysis of a synovial fluid sample is negative. The most probable correct diagnosis for this patient would be

A) Reiter's syndrome due to Chlamydia trachomatis infection
B) Reactive arthritis due to Salmonella enteritidis infection
C) Septic arthritis due to Staphylococcus aureus
D) Undifferentiated monoarthritis due to Chlamydia trachomatis
E) Reactive arthritis due to Chlamydia pneumoniae

Answer: D

(Year Posted: 2001 UI  562)

 

Key Code: B

A 7-year-old child is seen in the Pediatric Clinic suffering from a low-grade fever, swelling around the face, and blood while passing urine. The child's history includes treatment for an infected knee wound 3 weeks earlier. What is the most likely cause of the child's current condition?

A) Streptococcal pyrogenic exotoxins
B) Staphylococcal alpha toxin
C) Tetanus toxin
D) Post-streptococcal sequelae
E) A current Gram-negative infection

Answer: D

(Year Posted: 2001 UI  563)

 

Key Code: B

A 22-year-old man comes to your office complaining of a urethral discharge of several days duration. He admits to recent sexual contact with a prostitute. The causative agent could be isolated from his urethra. The infection of his urethra is an example of

A) Opsonization
B) Tropism
C) Immune response
D) Immunosuppression
E) Treatment failure

Answer: B

(Year Posted: 2001 UI  564)

 

Key Code: B

A 30-year-old man was in good health until he developed headache, high fever, abdominal cramps and diarrhea containing blood and mucous. Examination of the stool revealed sheets of leukocytes. Antibiotics and fluid were given and he improved over 3 days. Ten days later he was brought back to the hospital. His diarrhea was gone, but he had new and worsening bilateral leg and arm weakness. A tentative diagnosis of Guillain-Barré is made. Which of the following characterizes the organism responsible for the man's illness?

A) Diagnosis can be made using a microaerophilic atmosphere and 42°C incubation of stool culture
B) The organism causes diarrhea primarily by enterotoxin production and can be isolated using bile-salt agar
C) The organism causes this disease complex by penetrating bowel mucosa and entering the blood stream. Blood culture will be positive in most cases
D) The organism cannot be isolated on culture, but can be identified using enzyme immunoassay (EIA) of a stool sample

Answer: A

(Year Posted: 2001 UI  565)

 

Key Code: B

An aspirate from a peritoneal abscess grows two organisms. One is an Escherichia coli while the other has the following characteristics: Gram-negative bacillus, obligate anaerobe, resistant to bile salts, and a polysaccharide capsule. This organism is most likely

A) Proteus mirabilis
B) Pseudomonas aeruginosa
C) Bacteroides fragilis
D) Salmonella typhi
E) Enterococcus faecalis

Answer: C

(Year Posted: 2001 UI  566)

 

Key Code: B

A patient presents with dysentery but repeated stool cultures for bacterial pathogens are negative. The patient is treated empirically with antibiotics for bacillary dysentery but shows no improvement. A colonoscopy is performed and numerous ulcers are observed. A sample is removed and submitted to the microbiology laboratory for microscopic examination. The etiological agent is observed and is best described as

A) Motile, curved Gram-negative bacilli
B) Curved bacilli which produce a positive CLO test
C) Cyst structures with four nuclei
D) Cyst structures with eight nuclei
E) Microscopic worms with whip-like structure

Answer: C

(Year Posted: 2001 UI  567)

 

Key Code: B

A 43-year-old woman is admitted to the hospital because of right lower lobe pneumonia. Her teeth are badly decayed and she has a history of poorly controlled seizures. Antibiotic treatment is prescribed for the pneumonia. Within 3 days she is much improved. However, on the seventh hospital day she has a recurrence of fever and new onset of diarrhea and abdominal tenderness. The best course of action is to

A) Draw blood cultures and increase intravenous fluids
B) Evaluate the stool for toxin using enzyme immunoassay (EIA) and change antibiotics to metronidazole
C) Send a stool sample for culture and change antibiotics to a quinolone
D) Send a stool sample for fecal leukocytes; treat with a different antibiotic only if it is positive

Answer: B

(Year Posted: 2001 UI  568)

 

Key Code: B

Gram-positive cocci were grown on a blood agar plate inoculated with the urine of a sexually active 16-year old female diagnosed with pyelonephritis. The patient's symptoms failed to improve after she was given a 10-day regimen of double-strength trimethoprim-sulfamethoxazole. What rapid test can presumptively identify the organism responsible for her infection?

A) Red blood cell agglutination test for P fimbriae
B) Coagulation of rabbit serum
C) Catalase test
D) Hemolysis of red blood cells
E) Swarming motility in a wet mount

Answer: C

(Year Posted: 2001 UI  569)

 

Key Code: B

A 24-year-old man is admitted to the emergency department after suffering multiple gunshot wounds to the abdomen. Which of the following lists of organisms is likely to cause infection in this patient's wound?

A) Enterobacter aerogenes, Pseudomonas aeruginosa, Haemophilus influenza
B) Escherichia coli, Bacteroides fragilis, Streptococcus pneumoniae
C) Enterococcus faecalis, Bacteroides fragilis, Escherichia coli
D) Klebsiella pneumoniae, Corynebacterium diphtheriae, Enterococcus faecium
E) Escherichia coli, Proteus mirabilis, Neisseria meningitidis

Answer: C

(Year Posted: 2001 UI  570)

 

Key Code: B

A 32-year-old pregnant woman presents with flu-like symptoms. She suspects that she ate hot dogs contaminated with Listeria monocytogenes. Her fetus is

A) Not at risk since L. monocytogenes is not capable of crossing the placenta
B) At risk only if the mother becomes vaginally colonized with L. monocytogenes
C) Not at risk since this is the mother's first pregnancy
D) Not at risk because the hot dogs were refrigerated before consumption
E) Is at risk and the mother should receive antibiotic treatment

Answer: E

(Year Posted: 2001 UI  571)

 

Key Code: B

In an attempt to construct a vaccine against the bubonic plague, a fusion protein of Yersinia pestis adhesins was constructed. Which antigens would be used to create this fusion protein?

A) V antigen and fraction 1
B) PsaA and YadA
C) YopH and YopM
D) Plasminogen activator and YopE
E) P and S fimbriae

Answer: B

(Year Posted: 2001 UI  572)

 

Key Code: B

A 76-year-old man with prostate cancer was having difficulty urinating for 3 weeks. Before cancer treatment was started, he noted high fever and shaking chills. What is the best course of action?

A) Initiate treatment for cancer immediately
B) Check urine for cancer cells
C) Initiate antibiotic therapy effective against Gram-negative bacteria
D) Initiate antibiotic therapy effective against Gram-negative bacteria and anaerobic bacteria

Answer: C

(Year Posted: 2001 UI  573)

 

Key Code: M

A strain of Proteus mirabilis altered its 30S ribosomal subunit in response to treatment with sub-lethal concentrations of an antibiotic. Which antibiotic would induce such a mutation in this strain?

A) Streptomycin
B) Erythromycin
C) Chloramphenicol
D) Penicillin
E) Vancomycin

Answer: A

(Year Posted:UI  574)

 

Key Code: M

E. coli was cultivated in culture media containing glucose and lactose as the sole carbon sources. Growth in this medium is depicted by the graph shown below. The observed growth pattern is most 
likely the result of?

 

A) High concentrations of ß-galactosidase during the first 4 hour
B) Depletion of lactose followed by utilization of glucose
C) Depletion of glucose followed by induction of the lac operon
D) Increased cAMP synthesis in the first 4 hours of growth
E) Decreased CAP-cAMP binding during the last 4 hours of growth

Answer: C

(Year Posted:UI  575)

Key Code: M

A 4-year old girl from a country with poor vaccination practices is diagnosed with whooping cough. Which of the following enzymes directly controls expression of a key virulence factor by the pathogen causing this girl's disease?

A) Recombinase
B) RNA polymerase
C) DNA polymerase
D) Protein kinase
E) Invertase

Answer: D

(Year Posted: 2001 UI  576)

 

Key Code: M

Some antibiotics promote the release of outer membrane vesicles from dead or dying Gram-negative bacteria. A new treatment was developed to neutralize the toxic effects of these vesicles. Which component of the outer membrane would this new treatment target to prevent the effects of septic shock?

A) Porins
B) Phospholipids
C) O antigens
D) Lipoprotein anchors
E) Lipid A

Answer: E

(Year Posted: 2001 UI  577)

 

Key Code: M

The rpoD gene of E. coli, which encodes the sigma factor of RNA polymerase, was experimentally altered by site-specific mutagenesis. This alteration could be indirectly suppressed by introducing it into a strain of E. coli with a mutated

A) Operator
B) Attenuator
C) Terminator
D) Catabolite-activator protein (CAP) binding site
E) Promoter

Answer: E

(Year Posted: 2001 UI  578)

 

Key Code: V

A 6-year old child becomes ill with fever, chills, and muscular pain. These symptoms persist for several days and then discontinue. Several days later, she develops an erythematous rash on her face and upper limbs. She also experiences arthritic pains in several joints. These symptoms persist for several days and then discontinue. She was most likely suffering from an infection with which of the following viruses?

A) Parvovirus B19
B) Measles
C) Mumps
D) Herpes Simplex Virus Type 1
E) Varicella-Zoster Virus

Answer: A

(Year Posted: 2001 UI  579)

 

Key Code: V

A group of Virologists investigating the infectious dose (ID50) for rhinovirus found that the ID50 for the virus inoculated into the nasal cavity was 1 while the ID50 for the pharynx was 200. The observed difference in ID50 was most likely related to the

A) Replication rate
B) Competing microflora
C) Environmental stability of the virus
D) Density of ICAM-type receptors
E) Mucosal immunity

Answer: D

(Year Posted: 2001 UI  580)

 

Key Code: V

A 60-year old woman presents to the clinic with a painful outbreak of vesicular and ulcerative lesions confined to sharply bordered region on her lower back. Which of the following is the most likely diagnosis?

A) Zoster
B) Human Papillomavirus 16 infection
C) Herpes simplex Virus Type 2 infection
D) Varicella
E) Herpangina

Answer: A

(Year Posted: 2001 UI  581)

 

Key Code: V

A child who was complaining of sore throat and breathing problems was tested for the presence of antibodies to several of the common respiratory viral pathogens. Laboratory tests of the patient's serum revealed the presence of anti-G and anti-F antibodies. Which virus do you suspect as the etiologic agent of this child's illness?

A) Adenovirus
B) Influenza virus
C) Herpesvirus
D) RSV
E) Parainfluenza virus

Answer: D

(Year Posted: 2001 UI  582)

 

Key Code: V

A 55-year-old man presented to the emergency room, hypotensive and vomiting blood. Abnormal findings on his exam support the diagnosis of cirrhosis. The patient and his family are surprised because he used alcohol only occasionally and to their knowledge never had hepatitis. What is the most likely explanation for his cirrhosis?

A) He acquired hepatitis A while he was serving in Vietnam 30 years ago, but was never jaundiced from that infection
B) His extensive travels exposed him to Hepatitis B
C) He acquired cytomegalovirus (CMV) during a blood transfusion 20 years ago
D) He experimented with injecting drugs 30 years ago

Answer: D

(Year Posted: 2001 UI  583)

 

Key Code: V

A 2-month-old child presented to her pediatrician in July with a 7-day history of diarrhea and a temperature of 39(C. She was irritable and vomited in the pediatrician's office. It was discovered that her anterior fontanel was full on physical exam. The mother was directed to take the infant to the emergency department where a spinal tap was performed. Analysis of the CSF revealed elevated mononuclear cells and normal glucose levels. A Gram stain and bacterial antigen test of the CSF were both negative. The most likely etiologic agent for this case

A) Possesses a lipooligosaccharide outer membrane
B) Possesses a polysaccharide capsule
C) Characteristically causes outbreaks in the winter
D) Is prevented by an attenuated vaccine first administered at 2 months of age
E) Is transmitted by the fecal-oral route

Answer: E

(Year Posted: 2001 UI  584)

 

Key Code: V

A leukemia patient develops a progressive degenerative neurological disorder that is subsequently diagnosed as progressive multifocal leukoencephalopathy (PML). Should persons having close contact with this patient, such as his immunocompetent wife, be tested for the presence of JC Virus-specific antibodies?

A) No, because immunocompetent persons are not at risk of developing PML
B) Yes, because antiviral drugs are useful against JC virus if administered early enough
C) No, because JC Virus is not transmitted from person to person
D) Yes, because if she has no JC virus-specific antibodies, she can be treated with immunoglobulin

Answer: A

(Year Posted: 2001 UI  585)

 

Key Code: V

A homeless person is hospitalized with apparent encephalitis. It is not possible to obtain a medical history due to his condition. However, lab tests rule out the possibility of a bacterial infection. Which of the following viruses would be the least likely etiologic agent of encephalitis in this case?

A) Herpes Simplex Virus Type 1
B) West Nile Virus
C) Rabies Virus
D) Varicella-Zoster Virus
E) Parvovirus B19

Answer: E

(Year Posted: 2001 UI  586)

 

Key Code: P

A pregnant woman is concerned about the risk of transmitting Toxoplasma gondii to her developing fetus. This is her first pregnancy. The best course of immediate action is to

A) Request laboratory culture of the parasite
B) Begin prophylactic antibiotic treatment at once
C) Do nothing if the woman shows no overt disease symptoms from the infection
D) Take a blood sample to test for IgG titers against T. gondii
E) Assume that the woman is immune and take no action

Answer: D

(Year Posted: 2001 UI  587)

 

Key Code: P

J.B. is an eleven-year-old boy who spends summers at his grandparents' farm in Georgia. He enjoys the freedom of only wearing shorts with no shirt or shoes. J.B.s parents would not allow the trip this summer because of his general poor health that developed over the last eight months. He has abdominal pain, diarrhea, and weight loss. The parents bring him to their family physician who detects low hemoglobin and iron deficiency anemia. What is the most likely cause of the boy's condition?

A) Enterobius vermicularis
B) Chronic Salmonella infection
C) Campylobacter jejuni
D) Hookworm infestation
E) Giardia lamblia infestation

Answer: D

(Year Posted: 2001 UI  588)

 

Key Code: P

A 41-year-old AIDS patient developed headaches, weakness, and slurred speech. A cryptococcal antigen test of the patient's CNS was negative. A brain scan revealed multiple ring-enhancing lesions. The infectious agent causing the neurologic symptoms in this patient was most likely transmitted by

A) Sexual contact
B) Ingestion of oocysts
C) Inhalation of infective arthroconidia
D) Transplacental passage
E) Ticks

Answer: B

(Year Posted: 2001 UI  589)

 

Key Code: F

A 22-year-old woman reports to the clinic suffering from shortness of breath and a nonproductive cough. A personal history reveals that the woman is in the high-risk category for HIV infection. Extracellular cysts are seen in the aspirate fluid from a bronchoalveolar lavage. This most likely diagnosis for this woman is

A) Coccidiomycosis
B) Blastomycosis
C) Histoplasmosis
D) Pneumocystosis
E) Aspergillosis

Answer: D

(Year Posted: 2001 UI  590)

 

Key Code: N

An AIDS patient developed an oral Candida infection. An antibiotic that would be effective in treating this patient would inhibit which of the following functions?

A) A transpeptidase essential for peptidoglycan synthesis
B) The 30S ribosome
C) The 50S ribosome
D) A methylase essential for ergosterol synthesis
E) DNA gyrase

Answer: D

(Year Posted: 2001 UI  591)

 

Key Code: N

A tuberculosis patient undergoing antibiotic therapy with Rifamateâ, which is a combination of isoniazid and rifampin. This patient has non-insulin-dependent diabetes and is prescribed a sulfonylurea hypoglycemic. However, the diabetes treatment is not effective. Which of the following is a reasonable explanation for the ineffectiveness of the hypoglycemic drug?

A) Isoniazid combines with pyridoxal resulting in a vitamin-B6 deficiency
B) Rifampin combines with pyridoxal resulting in a vitamin-B6 deficiency
C) Rifampin induces hepatic metabolism of sulfonylureas
D) Isoniazid induces hepatic metabolism of sulfonylureas

Answer: C

(Year Posted: 2001 UI  592)

 

Key Code: N

A 28-year-old man undergoes surgery to repair intestinal wounds following multiple penetrating gunshots in the abdomen. During surgery, fecal contents from the colon are found in the peritoneal cavity. In addition to physical cleansing by irrigation and repair of the bowel, empiric antibiotic therapy would include all but which one of the following regimens?

A) Piperacillin and tobramycin
B) Imipenem
C) Cefoxitin
D) Ampicillin/sulbactam (Unasyn)
E) Metronidazole and ceftriaxone

Answer: A

(Year Posted: 2001 UI  593)

 

Key Code: N

An 87-year-old man who underwent prostatectomy develops a urinary tract infection with Pseudomonas aeruginosa growing in cultures of urine and blood. The isolate was susceptible to all agents that one might expect to be active. Although his symptoms improve while he is being treated with piperacillin, several days later he develops high fever and chills, and he again has Gram-negative bacilli in a Gram-stained smear of his urine. Which of the following treatment regimens would be preferable?

A) Erythromycin
B) Ceftriaxone
C) Piperacillin/tazobactam (Zosyn) and tobramycin
D) Imipenem and tobramycin
E) Trimethoprim/sulfamethoxazole (TMP/SMX)

Answer: D

(Year Posted: 2001 UI  594)

 

Key Code: N

An 80-year-old woman is admitted from a nursing home with acute pyelonephritis. Since she recently came to the nursing home following a stormy three-week hospitalization for pneumonia, treatment is initiated with ceftazidime and tobramycin. Two days later, cultures of urine and blood yield Klebsiella pneumoniae. Susceptibility results the next day reveal resistance to ceftazidime and susceptibility to imipenem, ampicillin/sulbactam, and piperacillin/tazobactam. The observed resistance to ceftazidime is most likely due to

A) Genetic derepression of a class C beta-lactamase
B) A mutant derivative of a plasmid-encoded TEM beta-lactamase
C) Selection of a mutation in a chromosomal gene that encodes a PBP
D) Expression of an efflux pump
E) Acquisition of a plasmid that alters a porin protein in the outer membrane

Answer: B

(Year Posted: 2001 UI  595)

 

Key Code: N

A 42-year-old alcoholic man presents with fever, chills, cough, and chest X-ray suggestive of pneumonia. The Gram-stained smear of sputum shows many PMNs and Gram-positive cocci in pairs and chains. The penicillin resistance of the strain of Streptococcus pneumoniae that grew in blood and sputum cultures

A) Can be overcome by high concentrations of penicillin G or ampicillin
B) Is of special concern because of potential dissemination via a plasmid to other strains
C) Can be reversed by clavulanic acid or sulbactam
D) May be due in part to reduced penetration of beta-lactams into the cell
E) May be due in part to acquisition of a novel plasmid-encoded PBP to which penicillins bind less avidly than to endogenous PBPs

Answer: A

(Year Posted: 2001 UI  596)

 

Key Code: N

A strain of Mycobacterium tuberculosis that grew from the sputum of a patient with an HIV infection is found to exhibit multi-drug resistance (resistance to isoniazid, rifampin, and pyrazinamide). The most likely explanation of this multiple resistance is

A) Alteration of the cell wall to reduce entry of the drugs in question
B) Acquisition of a plasmid with a gene that confers multi-drug resistance
C) Acquisition of a plasmid bearing individual genes conferring resistance to isoniazid, rifampin, and pyrazinamide
D) Sequential selection of resistance to these drugs individually by mutations in three separate genes
E) Efflux of the three drugs from the cell

Answer: D

(Year Posted: 2001 UI  597)

 

Key Code: N

A 54-year-old man with a post-surgical wound infection has PMNs and Gram-negative bacilli in a Gram-stained smear of pus from the wound. His fever resolves after 24-36 hours of treatment with ceftriaxone (a third-generation cephalosporin). The culture of pus yields Enterobacter cloacae that are susceptible to third-generation cephalosporins, piperacillin, aztreonam, imipenem, and gentamicin. After five days of therapy, fever returns and pus that re-emerges from the wound again yields E. cloacae, but it is now resistant to cephalosporins, piperacillin, piperacillin/tazobactam, and aztreonam, but not to imipenem or gentamicin. The new pattern of resistance is most likely due to

A) Acquisition of a plasmid that encodes a beta-lactamase
B) Acquisition of a plasmid that encodes individual resistance mechanisms for cephalosporins, piperacillin, and aztreonam
C) Selection of a mutation in a chromosomal gene that results in permanently de-repressed production of a broad-spectrum beta-lactamase
D) Selection of a mutation in a chromosomal gene that encodes a PBP
E) Mutational alteration of a porin protein in the outer membrane

Answer: C

(Year Posted: 2001 UI  598)

 

Key Code: N

An 18-year-old college student presents with a 5-day history of dry cough and fever. Chest X-ray shows diffuse infiltrates. A small amount of sputum is obtained with considerable effort, and the smear shows rare PMNs and rare mixed organisms. A radiologist hearing the history and viewing the chest X-ray suggests that the clinicians consider an "atypical pneumonia." An appropriate oral antibiotic for therapy would be

A) Amoxicillin
B) Amoxicillin/clavulanic acid (Augmentin)
C) Norfloxacin
D) Azithromycin
E) Trimethoprim/sulfamethoxazole (TMP/SMX)

Answer: D

(Year Posted:UI  599)

 

Key Code: N

A 22-year-old motorcyclist is thrown from his vehicle when it collides with a tree. He lands in a gravel pit and suffers a compound fracture of his right tibia and fibula. The bones are set with metal rods, and the soft tissue heals over by a month later. Four months after that, a sinus draining thin pus opens up on the wound. X-ray of the leg suggests that the tibia is infected. A bone biopsy shows PMNs and Gram-negative bacilli in the smear that emerge as Pseudomonas aeruginosa in culture. While awaiting susceptibility results, it would be preferable to begin treatment with which one of the following drug regimens?

A) Ceftazidime
B) Piperacillin and tobramycin
C) Vancomycin and gentamicin
D) Trimethoprim/sulfamethoxazole (TMP/SMX)
E) Metronidazole and tobramycin

Answer: B

(Year Posted:UI  600)