The Quizzes about Bacteriology - Part 3

Bacteriology Quiz Part 3 (20 test)

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Question 1

A young man crashes his bicycle, injuring one leg. Bacteria from the wound and a subsequent blood culture are isolated and identified, and an acute hematogenous osteomyelitis is diagnosed. Which organism listed below most often causes this type of infection?

A	Escherichia coli
B	Proteus mirabilis
C	Staphylococcus aureus
D	Staphylococcus epidermidis
E	Streptococcus faecalis

Question 1 Explanation:

.) Staphylococcus aureus is implicated in the majority of cases of acute osteomyelitis, which affects children most often. A superficial staphylococcal lesion frequently precedes the development of bone infection. In the preantibiotic era, Streptococcus pneumoniae was a common cause of acute osteomyelitis. M. tuberculosis and gram-negative organisms are implicated less frequently in this infection.

Question 2

A 3-year-old girl, with no history of vaccination, is brought to the hospital with a sore throat, fever, malaise, and difficulty in breathing. Physical examination reveals a gray membrane covering the pharynx. Growth of the etiologic agent on cysteine-tellurite agar forms gray-to-black colonies with a brown halo. The major virulence factor of this organism is only produced by those strains that will most likely have which of th following characteristics?

A	Encapsulated
B	Endotoxin
C	Glucose fermenters
D	Lysogenic for β-prophage
E	Sucrose fermenters

Question 2 Explanation:

All toxigenic strains of C. diphtheriae are lysogenic for β-phage carrying the Tox gene, which codes for the toxin molecule. The expression of this gene is controlled by the metabolism of the host bacteria. The greatest amount of toxin is produced by bacteria grown on media containing very low amounts of iron. Fragment B of the toxin is required for cell entry, while Fragment A stops protein production by inhibiting elongation factor 2 (EF-2). Corynebacterium diphtheriae does not possess a capsule, which is normally used to impede phagocytosis by WBCs. Glucose and/or sucrose fermentation is not a virulence factor. Endotoxin comes from gram-negative bacteria while corynebacteria are gram positive.

Question 3

A 28-year-old menstruating woman appears in the emergency room with the following signs and symptoms: fever, 104°F (40°C); WBC, 16,000/μL; blood pressure, 90/65 mm Hg; a scarlatiniform rash on her trunk, palms, and soles; extreme fatigue; vomiting; and diarrhea. Which of the following is the most likely diagnosis?

A	Chicken pox
B	Guillain–Barré syndrome
C	Scalded skin syndrome
D	Staphylococcal food poisoning
E	Toxic shock syndrome (TSS)

Question 4

Culture of the menstrual fluid in this case cited would most likely reveal a predominance of which of the following?

A	Clostridium difficile
B	Clostridium perfringens
C	Gardnerella vaginalis
D	Staphylococcus aureus
E	No organisms isolated

Question 5

Which of the following is the most likely source and characteristic finding not yet revealed in the case just presented?

A	A meal of chicken in a fast-food restaurant
B	A retained tampon
C	Heavy menstrual flow
D	Recent exposure to rubella
E	Travel to Vermont

Question 6

A severe URT outbreak occurs in the residence of students of a private school, resulting in several cases of otitis media and acute sinusitis. Some students do not have any clinical evidence of infection. The state public health laboratory receives and evaluates a new LA reagent for H. influenzae polysaccharide capsular antigen in urine (intact antigen elimination). The results, shown below, are compared with the isolation of H. influenzae from pharyngeal swabs. LA POS, CULT POS: 25 LA POS, CULT NEG: 5 LA NEG, CULT POS: 5 LA NEG, CULT NEG: 95

Which of the following best indicates the sensitivity of LA?

A	0%
B	30%
C	85%
D	95%
E	100%

Question 7

Which of the following best indicates the specificity of LA?

A	0%
B	30%
C	85%
D	95%
E	100%

Question 8

A severely burned firefighter develops a rapidly disseminating bacterial infection while hospitalized. “Green pus” is noted in the burned tissue, and cultures of both the tissue and blood yield small, oxidase-positive, gram-negative rods. Which of the following statements best describes this organism?

A	Endotoxin is the only virulence factor known to be produced by these bacteria
B	Humans are the only known reservoir hosts for these bacteria
C	The bacteria are difficult to culture because they have numerous growth requirements
D	These are among the most antibiotic resistant of all clinically relevant bacteria
E	These highly motile bacteria can “swarm” over the surface of culture media

Question 8 Explanation:

Pseudomonads occur widely in soil, water, plants, and animals. They are gram-negative, motile, aerobic rods that produce water-soluble pigments (blue and green). They are very opportunistic when abnormal host defenses are encountered. While motile, they do not “swarm” over the surface of an agar plate, as Proteus does. Being gramnegative, as many enteric and environmental organisms are, their cell walls contain endotoxin (LPS). Many of the pseudomonads are resistant to a wide range of antimicrobials, enhancing their opportunistic characteristics.

Question 9

Several hours after dining on sweet and sour chicken and pork fried rice at the home of an Asian friend, a 34-year-old car salesman exhibits abdominal discomfort, nausea, and vomiting. In the middle of the night he awakens with watery diarrhea. Which of the following pairs of organisms is routinely responsible for food poisoning?

A	Clostridium botulinum and Bacillus anthracis
B	Clostridium difficile and C. botulinum
C	Clostridium perfringens and B. cereus
D	Clostridium tetani and B. anthracis
E	Clostridium tetani and B. cereus

Question 9 Explanation:

Clostridium and Bacillus organisms exist widely in nature. While many Clostridium are pathogenic due to exotoxin production (C. tetani, C. botulism), and anthrax has multiple virulence factors (capsule, LF, EF, and PA), C. perfringens and B. cereus are found routinely in gastroenteritis outbreaks. Since both are spore formers, the usual epidemiological investigation finds that heating foods kills vegetative bacteria but not spores. If food is inappropriately stored (>40-140°F), spores may germinate into vegetative bacteria and be ingested, causing the disease. Most episodes are self-limited. Both produce enterotoxins that account for similar disease presentations.

Question 10

MRSA is isolated from seven patients in a 14-bed intensive care unit. All patients are isolated and the unit closed to any more admissions. Which of the following best explains these rigorous methods to control MRSA?

A	MRSA causes TSS
B	MRSA is inherently more virulent than other staphylococci
C	MRSA is resistant to penicillin
D	MRSA spreads more rapidly from patient to patient than antibiotic-susceptible staphylococci do
E	The alternative for treatment of MRSA is vancomycin, an expensive and potentially toxic antibiotic

Question 10 Explanation:

The incidence of oxacillin and MRSA has been rapidly increasing. MRSA and methicillin-sensitive S. aureus (MSSA) coexist in heterologous populations. Treatment of a patient harboring this heterologous population may provide a selective environment for the MRSA. Prior to changing therapy, the susceptibility of the isolate should be determined. Vancomycin has often been used effectively for MRSA, but it is expensive and nephrotoxic. There is no evidence that MRSA is any more virulent or invasive than susceptible strains. See the table below for a listing of medically important staphylococci.

Question 11

A 2-year-old infant is brought to the emergency room with hematuria, fever, and thrombocytopenia. Which one of the following bacteria would most likely be isolated from a stool specimen?

A	Aeromonas species
B	Enterobacter aerogenes
C	Escherichia coli 0157/H7
D	Salmonella enteritidis
E	Shigella flexneri

Question 11 Explanation:

Food poisoning with E. coli 0157/H7 causes hemorrhagic colitis; it is often seen in people who have eaten beef hamburgers. The same organism also causes a hemorrhagic uremic syndrome. The toxin, called Shiga-like toxin, can be demonstrated in Vero cells, but the cytotoxicity must be neutralized with specific antiserum. With the exception of sorbitol fermentation, there is nothing biochemically distinctive about these organisms.

Question 12

A 65-year-old healthy, retired female executive goes to Mexico on her yearly vacation. Unlike her previous trips, she decides to use the local water to make her favorite punch. Thirty-six hours later, she develops profuse watery diarrhea, severe cramping, and abdominal pain. She is diagnosed with Escherichia coli-related diarrhea. Which of the following E. coli types is characterized by the presence of heat-labile (LT) and heatstable (ST) toxin proteins?

A	Enteroinvasive (EIEC)
B	Enterotoxigenic (ETEC)
C	Enterohemorrhagic (EHEC)
D	Enteropathogenic (EPEC)

Question 12 Explanation:

ETEC is an important cause of traveler’s diarrhea, producing a heat-labile exotoxin (LT) and a heat-stable enterotoxin (ST). To cause diarrhea, E. coli must produce not only LT and ST toxins but also adhere to the lining of the small intestine. Fimbrial antigens are involved in adherence. O657/H7 stain is called EHEC, while EPEC is also an important cause of diarrhea in infants. EIEC produces a shigellosis-type disease.

Question 13

A 48-year-old farmer in New Mexico is bitten by a flea and, 5 days later, develops a sudden onset of fever, chills, weakness, and headache. A few hours later he develops swollen, necrotic lymph nodes (buboes) in the right axilla and groin, which are intensely painful. This patient is subsequently diagnosed with bubonic plague and does not develop any pneumonic features of the disease. Human plague can be bubonic or pneumonic. Which of the following is the primary epidemiologic difference between the two clinical forms of plague?

A	Age of the patient
B	Geographic location of the animal vector
C	Health of the animal vector
D	Route of infection
E	Season of the year

Question 13 Explanation:

Bubonic plague and pneumonic plague differ clinically. Bubonic plague, characterized by swollen lymph nodes and fever, is usually transmitted through a flea bite. Pneumonic plague, which is characterized by sepsis and pneumonia, is transmitted by the droplet route, usually after contact with an infected human or animal. Age of the patient, geographic location and/or health of the animal vector, and season of the year would all be insignificant in considering epidemiological differences between the clinical presentations of the two plagues.

Question 14

A 9-year-old child is brought to the emergency room with the chief complaint of enlarged, painful axillary lymph nodes. The resident physician also notes a small, inflamed, dime-sized lesion surrounding what appears to be a small scratch on the forearm. The lymph node is aspirated and some pus is sent to the laboratory for examination. A Warthin-Starry silver impregnation stain reveals many highly pleomorphic, rod-shaped bacteria. Which of the following is the most likely cause of this infection?

A	Bartonella henselae
B	Brucella canis
C	Mycobacterium scrofulaceum
D	Yersinia enterocolitica
E	Yersinia pestis

Question 14 Explanation:

While the essential information (ie, the evidence that the child in question was scratched by a cat) is missing, the clinical presentation points to a number of diseases, including cat scratch disease (CSD). Until recently, the etiologic agent of CSD was unknown. Evidence indicated that it was a pleomorphic, rod-shaped bacterium that had been named Afipia. It was best demonstrated in the affected lymph node by a silver impregnation stain. However, it now appears that Afipia causes relatively few cases of CSD and that the small, pleomorphic, gram-negative rods present mainly in the walls of capillaries primarily responsible are Rochalimaea henselae, which has recently been renamed B. henselae. Brucella, Mycobacterium, and Yersinia species have not been shown to have any association with CSD.

Question 15

A sixth-grade boy returns from a summer camp with several minor cuts and abrasions. Within a week, extensive cellulitis develops, and it is apparent that subcutaneous tissue is involved, requiring surgical removal of nonviable tissue. Antibiotics are used aggressively. Cellulitis is usually caused by which of the following?

A	Bacillus cereus
B	Clostridium tetani
C	Group A streptococci
D	Micrococcus species
E	Staphylococcus aureus

Question 15 Explanation:

There has been a marked increase in fatal streptococcal infections, including those that are described as “necrotizing fasciitis.” The strains of group A streptococci isolated have a pyrogenic exotoxin with properties not unlike those of the toxic shock toxin of S. aureus. Mortality is high (30%) in spite of aggressive antibiotic therapy.

Question 16

A 40-year-old female reports chronic gastritis. She tests positive for H. pylori. After a course of the appropriate antibiotic therapy, her symptoms subside. Which of the following is the most effective noninvasive test for the diagnosis of Helicobacter-associated gastric ulcers?

A	Culture of stomach contents for H. pylori
B	Detection of H. pylori antigen in stool
C	Growth of H. pylori from a stomach biopsy
D	Growth of H. pylori in the stool
E	IgM antibodies to H. pylori

Question 16 Explanation:

Helicobacter pylori antigen tests from a stool sample using an ELISA format and a monoclonal antibody to H. pylori are as sensitive as culture of the control portion of the stomach. Urea breath tests are also widely used. Helicobacter pylori has an active enzyme (urease) that breaks down radioactive urea. The patient releases radioactive CO 2 if H. pylori are present. Helicobacter pylori antibody tests, IgG and IgA, indicate the presence of H. pylori and usually decline after effective treatment. Culture of stomach contents is insensitive and not appropriate as a diagnostic procedure for H. pylori. Direct tests, such as antigen or culture of gastric mucosa, are preferred because they are the most sensitive indication of a cure.

Question 17

The following examination and test results are observed in a woman tested in November who reports being in the woods in Pennsylvania during the last summer. While there, she was bitten by a tick, and now has a flattened red area near the bite with central clearing. She also has flu-like illness with fever, myalgia, and headache. Which of the following is the most appropriate course of action?

A	Ask the patient if she has a severe headache
B	Do a spinal tap for CSF
C	Observe the lesion
D	Order a Lyme disease antibody titer
E	Start treatment with tetracycline

Question 17 Explanation:

At present, Lyme disease may be diagnosed clinically and serologically. Patients who are from endemic areas such as eastern Pennsylvania and report joint pain and swelling months subsequent to exposure to ticks must be evaluated for Lyme disease and treated if the test is positive. Patients may also report a variety of neurologic problems such as tingling of the extremities, Bell palsy, and headache. IgM antibody appears soon after the tick bite (10 days-3 weeks) and persists for 2 months; IgG appears later in the disease but remains elevated for 1 to 2 years, especially in untreated patients. A significant IgG titer is at least 1:320. Most investigators feel that IgM titers of 1:100 are significant; some investigators say that any IgM titer is significant. Management of this patient would best be done by immediately starting treatment with tetracycline, effective against B. burgdorferi.

Question 18

Several white male patients, over 50 years of age and suffering from cavitary pulmonary disease, being followed and treated at a university AIDS clinic are found to be infected by Mycobacterium avium, a major opportunist pathogen. M. avium from these patients is best characterized by which one of the following statements?

A	Few isolates from AIDS patients are acid-fast.
B	Most isolates from AIDS patients are sensitive to isoniazid and streptomycin
C	M. avium can be isolated from the blood of many AIDS patients
D	M. avium isolates from AIDS patients are of multiple serovars
E	The majority of M. avium isolates from AIDS patients are nonpigmented

Question 18 Explanation:

There are some interesting characteristics of M. avium from AIDS patients. According to data from the National Jewish Hospital and Research Center in Denver and the CDC, 75% of the isolates were serovar 4, and 76% produced a deep-yellow pigment. Yellow pigment is not a characteristic of most isolates of M. avium. The significance of these findings is unknown. Most M. avium isolates are resistant to isoniazid and streptomycin but susceptible to clofazimine and ansamycin. In vitro susceptibility testing, however, may not be reliable for M. avium. A blood culture is often the most reliable way to diagnose the disease. Finally, all isolates of M. avium are acid-fast, by definition.

Question 19

A 12-year-old girl experiences a group A streptococcus pharyngitis and, within 3 weeks, has chest pain and develops new murmurs of mitral regurgitation. Which of the following statements best typifies the disease she is suffering from?

A	It is a complication of group A streptococcal skin disease but usually not of pharyngitis
B	It is characterized by inflammatory lesions that may involve the heart, joints, subcutaneous tissues, and CNS
C	It is very common in developing countries but extremely rare and decreasing in incidence in the United States
D	Prophylaxis with benzathine penicillin is of little value
E	The pathogenesis is related to the similarity between a staphylococcal antigen and a human cardiac antigen

Question 19 Explanation:

Rheumatic fever (RF) is a disease that causes polyarthritis, carditis, chorea, and erythema marginatum. The mechanism of damage appears to be autoimmune; that is, antibodies are synthesized to a closely related streptococcal antigen such as M-protein, but these same antibodies cross react with certain cardiac antigens such as myosin. Until recently, RF was very rare in the United States. In 1986, there were at least 135 cases of RF in Utah. Subsequently, scattered cases of RF have occurred in other states. Epidemiologists do not have a reason for this increase in RF. Some evidence suggests that there may be a genetic predisposition to the disease. Intramuscular injection of benzathine penicillin is effective treatment for and prophylaxis against group A streptococcal infection. While it appears that certain strains of streptococci contain cell membrane antigens that are identical to human heart tissue antigens, the strains can infect skin and cause pharyngitis. The first attack of RF (rheumatic fever) usually produces only slight cardiac damage. It is important to protect such patients from recurrent S. pyogenes infections by prophylactic penicillin use to prevent increased damage from multiple future bacterial attacks. Answer option (e) refers to a staphylococcal antigen as similar, but the correct comparison would be with streptococcal antigen and cardiac antigen.

Question 20

After extraction of a wisdom tooth, an 18-year-old male student is diagnosed with subacute bacterial endocarditis (SBE). He has a congenital heart disease that has been under control. Which of the following is the most likely organism causing the infection?

A	Staphylococcus aureus
B	Staphylococcus epidermidis
C	Streptococcus pneumoniae
D	Streptococcus viridans
E	Enterococcus faecalis

Question 20 Explanation:

In the healthy oral cavity, gram-positive, α-hemolytic streptococci make up the predominant flora. Any dental manipulation causes bleeding, allowing the oral flora to get into the blood (bacteremia). Phagocytic activity by WBCs usually clears this in a few minutes. However, these same organisms are quite efficient at attaching to and colonizing heart valve defects. Streptococcus viridans is a typical member of this α-hemolytic group and is commonly found in SBE. Staphylococcus aureus and S. epidermidis are present in the oral flora in very small numbers, as is S. pneumoniae. If E. faecalis gets into the bloodstream from the GI tract, it could potentially also cause heart valve problems. The α-hemolytic viridans streptococci are reported as being isolated from SBE most often.

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1. A young man crashes his bicycle, injuring one leg. Bacteria from the wound and a subsequent blood culture are isolated and identified, and an acute hematogenous osteomyelitis is diagnosed. Which organism listed below most often causes this type of infection?
a. Escherichia coli
b. Proteus mirabilis
c. Staphylococcus aureus
d. Staphylococcus epidermidis
e. Streptococcus faecalis

2. A 3-year-old girl, with no history of vaccination, is brought to the hospital with a sore throat, fever, malaise, and difficulty in breathing. Physical examination reveals a gray membrane covering the pharynx. Growth of the etiologic agent on cysteine-tellurite agar forms gray-to-black colonies with a brown halo. The major virulence factor of this organism is only produced by those strains that will most likely have which of the following characteristics?
a. Encapsulated
b. Endotoxin
c. Glucose fermenters
d. Lysogenic for β-prophage
e. Sucrose fermenters

3. A 28-year-old menstruating woman appears in the emergency room with the following signs and symptoms: fever, 104°F (40°C); WBC, 16,000/μL; blood pressure, 90/65 mm Hg; a scarlatiniform rash on her trunk, palms, and soles; extreme fatigue; vomiting; and diarrhea.
Which of the following is the most likely diagnosis?
a. Chicken pox
b. Guillain–Barré syndrome
c. Scalded skin syndrome
d. Staphylococcal food poisoning
e. Toxic shock syndrome (TSS)

4 28-year-old menstruating woman appears in the emergency room with the following signs and symptoms: fever, 104°F (40°C); WBC, 16,000/μL; blood pressure, 90/65 mm Hg; a scarlatiniform rash on her trunk, palms, and soles; extreme fatigue; vomiting; and diarrhea.

Culture of the menstrual fluid in this case cited would most likely reveal a predominance of which of the following?
a. Clostridium difficile
b. Clostridium perfringens
c. Gardnerella vaginalis
d. Staphylococcus aureus
e. No organisms isolated

5. A 28-year-old menstruating woman appears in the emergency room with the following signs and symptoms: fever, 104°F (40°C); WBC, 16,000/μL; blood pressure, 90/65 mm Hg; a scarlatiniform rash on her trunk, palms, and soles; extreme fatigue; vomiting; and diarrhea.

Which of the following is the most likely source and characteristic finding not yet revealed in the case just presented?
a. A meal of chicken in a fast-food restaurant
b. A retained tampon
c. Heavy menstrual flow
d. Recent exposure to rubella
e. Travel to Vermont

6. A severe URT outbreak occurs in the residence of students of a private school, resulting in several cases of otitis media and acute sinusitis. Some students do not have any clinical evidence of infection. The state public health laboratory receives and evaluates a new LA reagent for H. influenzae polysaccharide capsular antigen in urine (intact antigen elimination). The results, shown below, are compared with the isolation of H. influenzae from pharyngeal swabs.
LA POS, CULT POS: 25
LA POS, CULT NEG: 5
LA NEG, CULT POS: 5
LA NEG, CULT NEG: 95
Which of the following best indicates the sensitivity of LA?
a. 0%
b. 30%
c. 85%
d. 95%
e. 100%

7. A severe URT outbreak occurs in the residence of students of a private school, resulting in several cases of otitis media and acute sinusitis. Some students do not have any clinical evidence of infection. The state public health laboratory receives and evaluates a new LA reagent for H. influenzae polysaccharide capsular antigen in urine (intact antigen elimination). The results, shown below, are compared with the isolation of H. influenzae from pharyngeal swabs.
LA POS, CULT POS: 25
LA POS, CULT NEG: 5
LA NEG, CULT POS: 5
LA NEG, CULT NEG: 95Which of the following best indicates the specificity of LA?
a. 0%
b. 30%
c. 80%
d. 95%
e. 100%

8. A severely burned firefighter develops a rapidly disseminating bacterial infection while hospitalized. “Green pus” is noted in the burned tissue, and cultures of both the tissue and blood yield small, oxidase-positive, gram-negative rods. Which of the following statements best describes this organism?
a. Endotoxin is the only virulence factor known to be produced by these bacteria
b. Humans are the only known reservoir hosts for these bacteria
c. The bacteria are difficult to culture because they have numerous growth requirements
d. These are among the most antibiotic resistant of all clinically relevant bacteria
e. These highly motile bacteria can “swarm” over the surface of culture media

9. Several hours after dining on sweet and sour chicken and pork fried rice at the home of an Asian friend, a 34-year-old car salesman exhibits abdominal discomfort, nausea, and vomiting. In the middle of the night he awakens with watery diarrhea. Which of the following pairs of organisms is routinely responsible for food poisoning?
a. Clostridium botulinum and Bacillus anthracis
b. Clostridium difficile and C. botulinum
c. Clostridium perfringens and B. cereus
d. Clostridium tetani and B. anthracis
e. Clostridium tetani and B. cereus

10. MRSA is isolated from seven patients in a 14-bed intensive care unit. All patients are isolated and the unit closed to any more admissions.
Which of the following best explains these rigorous methods to control MRSA?
a. MRSA causes TSS
b. MRSA is inherently more virulent than other staphylococci
c. MRSA is resistant to penicillin
d. MRSA spreads more rapidly from patient to patient than antibiotic-susceptible staphylococci do
e. The alternative for treatment of MRSA is vancomycin, an expensive and potentially toxic antibiotic

11. A 2-year-old infant is brought to the emergency room with hematuria, fever, and thrombocytopenia. Which one of the following bacteria would most likely be isolated from a stool specimen?
a. Aeromonas species
b. Enterobacter aerogenes
c. Escherichia coli 0157/H7
d. Salmonella enteritidis
e. Shigella flexneri

12. A 65-year-old healthy, retired female executive goes to Mexico on her yearly vacation. Unlike her previous trips, she decides to use the local water to make her favorite punch. Thirty-six hours later, she develops profuse watery diarrhea, severe cramping, and abdominal pain. She is diagnosed with Escherichia coli-related diarrhea. Which of the following E. coli types is characterized by the presence of heat-labile (LT) and heatstable (ST) toxin proteins?
a. Enteroinvasive (EIEC)
b. Enterotoxigenic (ETEC)
c. Enterohemorrhagic (EHEC)
d. Enteropathogenic (EPEC)

13. A 48-year-old farmer in New Mexico is bitten by a flea and, 5 days later, develops a sudden onset of fever, chills, weakness, and headache. A few hours later he develops swollen, necrotic lymph nodes (buboes) in the right axilla and groin, which are intensely painful. This patient is subsequently diagnosed with bubonic plague and does not develop any pneumonic features of the disease. Human plague can be bubonic or pneumonic. Which of the following is the primary epidemiologic difference between the two clinical forms of plague?
a. Age of the patient
b. Geographic location of the animal vector
c. Health of the animal vector
d. Route of infection
e. Season of the year

14. A 9-year-old child is brought to the emergency room with the chief complaint of enlarged, painful axillary lymph nodes. The resident physician also notes a small, inflamed, dime-sized lesion surrounding what appears to be a small scratch on the forearm. The lymph node is aspirated and some pus is sent to the laboratory for examination. A Warthin-Starry silver impregnation stain reveals many highly pleomorphic, rod-shaped bacteria. Which of the following is the most likely cause of this infection?
a. Bartonella henselae
b. Brucella canis
c. Mycobacterium scrofulaceum
d. Yersinia enterocolitica
e. Yersinia pestis

15. A sixth-grade boy returns from a summer camp with several minor cuts and abrasions. Within a week, extensive cellulitis develops, and it is apparent that subcutaneous tissue is involved, requiring surgical removal of nonviable tissue. Antibiotics are used aggressively. Cellulitis is usually caused by which of the following?
a. Bacillus cereus
b. Clostridium tetani
c. Group A streptococci
d. Micrococcus species
e. Staphylococcus aureus

16. A 40-year-old female reports chronic gastritis. She tests positive for H. pylori. After a course of the appropriate antibiotic therapy, her symptoms subside. Which of the following is the most effective noninvasive test for the diagnosis of Helicobacter-associated gastric ulcers?
a. Culture of stomach contents for H. pylori
b. Detection of H. pylori antigen in stool
c. Growth of H. pylori from a stomach biopsy
d. Growth of H. pylori in the stool
e. IgM antibodies to H. pylori

17. The following examination and test results are observed in a woman tested in November who reports being in the woods in Pennsylvania during the last summer. While there, she was bitten by a tick, and now has a flattened red area near the bite with central clearing. She also has flu-like illness with fever, myalgia, and headache. Which of the following is the most appropriate course of action?
a. Ask the patient if she has a severe headache
b. Do a spinal tap for CSF
c. Observe the lesion
d. Order a Lyme disease antibody titer
e. Start treatment with tetracycline

18. Several white male patients, over 50 years of age and suffering from cavitary pulmonary disease, being followed and treated at a university AIDS clinic are found to be infected by Mycobacterium avium, a major opportunist pathogen. M. avium from these patients is best characterized by which one of the following statements?
a. Few isolates from AIDS patients are acid-fast.
b. Most isolates from AIDS patients are sensitive to isoniazid and streptomycin
c. M. avium can be isolated from the blood of many AIDS patients
d. M. avium isolates from AIDS patients are of multiple serovars
e. The majority of M. avium isolates from AIDS patients are nonpigmented

19. A 12-year-old girl experiences a group A streptococcus pharyngitis and, within 3 weeks, has chest pain and develops new murmurs of mitral regurgitation. Which of the following statements best typifies the disease she is suffering from?
a. It is a complication of group A streptococcal skin disease but usually not of pharyngitis
b. It is characterized by inflammatory lesions that may involve the heart, joints, subcutaneous tissues, and CNS
c. It is very common in developing countries but extremely rare and decreasing in incidence in the United States
d. Prophylaxis with benzathine penicillin is of little value
e. The pathogenesis is related to the similarity between a staphylococcal antigen and a human cardiac antigen

20. After extraction of a wisdom tooth, an 18-year-old male student is diagnosed with subacute bacterial endocarditis (SBE). He has a congenital heart disease that has been under control. Which of the following is the most likely organism causing the infection?
a. Staphylococcus aureus
b. Staphylococcus epidermidis
c. Streptococcus pneumoniae
d. Streptococcus viridans
e. Enterococcus faecalis

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The Quizzes about Bacteriology – Part 3

Bacteriology Quiz Part 3 (20 test)

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