Microb Review New

Question 1

52-year-old man leaves work shortly after lunch with nausea, abdominal cramps, and vomiting. Early that morning he had consumed several cream-chocolate éclairs in office breakfast. Several of his coworkers are also experiencing similar symptoms.
By the next morning he is feeling fairly well and is able to return to work. Which of the following is the most likely causative agent?

A. Anaerobic gram-positive rods with spores
B. Aerobic gram-positive rods with spores
C. Microaerophilic curved gram-negative rods
D.Aerobic gram-positive cocci in clusters
E.
Aerobic gram-negative rods.

Answer 1

Aerobic gram-positive cocci in clusters

Question 2

A 52-year-old man leaves work shortly after lunch with nausea, abdominal cramps, and vomiting. Early that morning he had consumed several cream-chocolate éclairs in office breakfast. Several of his coworkers are also experiencing similar symptoms.
By the next morning he is feeling fairly well and is able to return to work. Which one of the following factors is most likely medlating this infection?

A. Coagulase
Be Hvalaroniosse
C. Protein A
D. Superantigen
E. Exfoliative tosir

Answer 2

Superantigen

Question 3

A 46-year-old man suddenly feels ill and starts vomiting at 1:00 a.m. He continues vomiting approximately 2 to 3 times per hour for the next 4 hours.
The man had leftover Chinese takeout for dinner the previous evening and consumed vegetable fried rice and beef lo mein. By the next afternoon he is feeling better. Which of the following is the most likely causative agent of this infection?
A. Aerobic gram-positive rod
B. Aerobic gram-positive cocci
C Anaerobic gram-positive rod
D. Flagellated protozoan parasite
E. Single-stranded RNA virüs

Answer 3

Anaerobic gram-positive rod

Question 4

A 19-year-old young man presents with a history of diarrhea, abdominal cramps, and fever a few days after acquiring a pet turtle.
Which of the following is the likely cause of his diarrhea?
A. Campylobacter jejuni
B. E. coli 0157:H7
C. salmonella spp
D. Shigella spp
E. Yersinia enterocolitica

Answer 4

salmonella spp

Question 5

Regarding Vibrio vulnificus, which of the following best describes this organism?
a. Cause of gastroenteritis; reservoir in birds and mammals , optimal growth at 107.6°F (42°C)
b. Human pathogen, halophilic, lactose-negative, sucrose-negative; causes
GI diseases primarily from ingestion of under-cooked sea food
c. Human pathogen, halophilic, lactose-positive; produces heat-labile, extra cellular toxin, wound infections
d. Organisms susceptible to acids; not an invasive organism
e. Urease-positive; cause of fetal distress in cattle

Answer 5

Human pathogen, halophilic, lactose-negative, sucrose-negative; causes
GI diseases primarily from ingestion of under-cooked sea food

Question 6

Which of the following is the mechanism of action of the cholera toxin?
ADP ribosylation of Elongation Factor 2
Depolymerization of actin.
Hydrolysis of lecithin
Interaction with G proteins causing increased intracellular cAMP
Formation of cation-selective pores in cell membranes

Answer 6

Interaction with G proteins causing increased intracellular cAMP

Question 7

A 60-year-old male in the intensive care unit recovering from back surgery required intubation for respiratory support. Forty-eight hours after intubation, he developed ventilator-associated pneumonia. The microorganism isolated from tracheal secretions aspirated from the patient is a gram-negative, oxidase positive, obligate aerobe that produces a multitude of virulence factors including proteases, toxins, and adhesins.
Which is the most likely causative agent of this patient’s infection?
Escherichia coli
Haemophilus influenzae
Klebsiella pneumoniae
Stenotrophomonas maltophilia
Pseudomonas aeruginosa

Answer 7

Pseudomonas aeruginosa

Question 8

A 54-year-old man presents with diarrhea of 3-day duration. He has had 8 to 9 bowel movements per day and has been periodically vomiting. The man returned 4 days ago from vacation in several South Asian countries. His temperature is
37.2°C (98.9°F) and his blood pressure is 92/63 mm Hg. On examination the man seems lethargic, his eyes are sunken, his skin feels cold and clammy, and his skin turgor is poor. Stool for culture is collected and an organism grows on selective media. A Gram stain from the colonies growing on this media is shown here:
Thich of the followins is most likely to be observed from this patient?
A. Blood in the stool
P. Clov-colored 34901
C. Greasy stool
D. Macous in the stool
E. White cells in the stool

Answer 8

Macous in the stool

Question 9

Which one of the following bacteria has the lowest 50% infectious dose (ID50)?
• Shigella sonnei
• Vibrio cholerae
• Salmonella Typhi
• Campylobacter jejuni
• Salmonella Typhimurium

Answer 9

Shigella sonnei

Question 10

An 18-year-old student has abdominal cramps and diarrhea.
A selective agar plate is inoculated and grows suspicious Gram negative rods. Triple sugar iron agar is used to identify the isolates as salmonellae or shigellae. A result suggesting one of these two pathogens would be
(A) Production of urease
(B) Motility in the medium
(C) Inability to ferment lactose and sucrose
(D) Fermentation of glucose
(E) Production of gas in the medium

Answer 10

Inability to ferment lactose and sucrose

Question 11

• Five hours after eating reheated rice at a restaurant, a 24-year-old woman and her husband both developed nausea, vomiting, and diarrhea. Which one of the following organisms is the MOST likely to be involved?
• (A) Clostridium perfringens
• (B) Enterotoxigenic Escherichia coli
(C) Bacillus cereus
• (D) Salmonella typhi

Answer 11

(C) Bacillus cereus

Question 12

Two hours after a delicious Thanksgiving dinner of barley soup, roast turkey, stuffing, sweet potato, green beans, cranberry sauce, and pumpkin pie topped with whipped cream, the Smith family of four experience vomiting and diarrhea. Which one of the following organisms is MOST likely to cause these symptoms?
A. Shigella flexneri
B. Campylobacter jejuni
C. Staphylococcus aureus
D. Salmonella enteritidis
E. Shigella sonnei

Answer 12

Staphylococcus aureus

Question 13

A 5 year-old child has had abdominal pain and diarrhea for 2 days. A stained preparation of the stool demonstrates polymorphonuclear leukocytes. Which of the following is least likely to produce these findings?
A. Vibrio cholerae
B. Shigella sonnei
C. Shigella dysenteriae
D. Salmonella serotype Typhimurium
E. Campylobacter jejuni

Answer 13

Vibrio cholerae

Question 14

Each of the following statements concerning exotoxins is correct
EXCEPT:
(A) some strplins of Escherichia col/produce an enterotoxin that causes
(B) Cholera toxin acts by stimulating adenylate cyclase.
(C) Diphtheria is caused by an exotoxin that inhibits protein synthesis by inactivating an elongation factor.
(D) Botulism is caused by a toxin that hydrolyzes lecithin (lecithinase), thereby destroying nerve cells.

Answer 14

some strplins of Escherichia col/produce an enterotoxin that causes diarrhoea

Question 15

Five children (age range 2-3 years old) are sent home from a day care center with diarrhea and fever within a 2-day period. All of the children had more than 4 to 5 loose stools the day they were sent home. The next day, two of the day care workers call in sick with similar symptoms. One of the workers visits the urgent care clinic when she notices blood in her stool. Which of the following is the most likely causative agent?
A. Enteropathogenic Escherichia coli (EPEC)
B. Rotavirus
C. Salmonella typhi
D. Shigella sonnel
E. Vibrio cholerae

Answer 15

Salmonella typhi

Question 16

A5-year-old boy presents with a 2-day history of pronounced abdominal pain, bloody diarrhea, fever, and a sore throat. The family lives on a farm and drinks unpasteurized milk. The boy’s temperature is 38.7°C (101.
8°F). The boy’s throat is erythematous and
his tonsils are edematous. An abdominal examination reveals tenderness of the right lower quadrant and rebound with guarding. A CBC demonstrates elevated peripheral leukocytes. Fecal leukocytes are present and fecal occult blood is positive.
• The causative agent of this infection is most likely to infect the:
• A. Duodenum
• B. Gallbladder
• C. Liver
• D. Mesenteric lymph nodes
• E. Stomach

Answer 16

Mesenteric lymph nodes

Question 17

For which one of the following enteric illnesses is a chronic carrier state MOST likely to develop?
(A) Campylobacter enterocolitis
(B) Shigella enterocolitis
(C) Cholera
(D) Typhoid fever
(E) ETEC

Answer 17

Typhoid fever

Question 18

The pathogenesis of which one of the following organisms is MOST likely to involve invasion of the intestinal mucosa?
(A) Vibrio cholerae
(B) Shigella sonnei
(C) Enterotoxigenic Escherichia coli
(D) Clostridium botulinum
(E) Staphylococcus aureus

Answer 18

Shigella sonnei

Question 19

An outbreak of gastroenteritis occurred in a youth group camp. Water at the camp, which was not chlorinated or filtered, was obtal ned from a spring on the premises. The farmland near the camp was grazed by cattle and sheep. Run-off from the pasture entered the camp spring. The isolated microorganism required an atmosphere containing reduced oxygen and
increased carbon dioxide for its growth.
• In most cases, the gastroenteritis Which was likely agent
a. Campylobacter jejuni
b. Enteroinvasive Escherichia coli (EIEC)
c. Enteropathogenic Escherichia coli (EPEC)
d. Vibrio cholerae
e. Vibrio parahaemolyticus

Answer 19

Campylobacter jejuni

Question 20

2 years old infant is brought to the emergency department with a history of
2 days diarrhea. His mother notices that he has been less active than normal. On examination, the child is restless and irritable. He is afebrile, his eyes appear slightly sunken, and skin turgor is poor. Stool from the boy grows a lactose positive (fermenter), sorbitol positive (fermenter) organism on MacConkey agar that grows best at 37°C.9. Which of the following is the most likely causative agent?
• A. Campylobacter jejuni
• B. Enterohemorrhagic Escherichia coli (EHEC)
• C. Enteropathogenic Escherichia coli (EPECL
• D. Rotavirus
• E. Shigella sonnei

Answer 20

Enteropathogenic Escherichia coli (EPECL

Question 21

A 27-year-old woman is admitted to the hospital because of fever, with increasing anorexia, headache, weakness, and altered mental status of 2 davs’ duration. She works for
an airline as a
cabin attendant, flying between the Indian subcontinent and other places in Southeast Asia and the West Coast of the United States. Ten days before admission, she had a diarrheal illness that lasted for about 36 hours. She has been constipated for the past 3 days. Her temperature is 39°C, heart rate is 68 beats/min, blood pressure is 120/80 mm Hg.
and respirations are 18 breaths/min.
She knows who she is and where she is but does not know the date. She is picking at the bedclothes. Rose spots are seen on her trunk.
The remainder of the physical examination is
normal. Blood cultures are done, and an intravenous line is placed. The most likely cause of her illness is
(A) Enterotoxigenic E. coli (ETEC)
(B) S. sonnei
(C) S. enterica subspecies enterica serotype Typhimurium (Salmonella Typhimurium)
(D) S. enterica subspecies enterica serotype Typhi (Salmonella Typhi)

Answer 21

D) S. enterica subspecies enterica serotype Typhi (Salmonella Typhi)

Question 22

A woman with colon cancer has been in the hospital. Five days into a course of antibiotic for suspected pneumonia she developed diarrhea. Colonoscopy revealed multiple plaques on the mucosa which are composed of fibrin and white blood cells. Stool examinations for Salmonella, Shigella, Campylobacter, and amoebas are negative. The diarrhea and plaques are most likely produced by which of the following?
A. Endotoxin from clostridial spores
B. Exotoxin from clostridial spores
C. Exotoxin from clostridial cells
D. Exotoxin from E coli cells
E. Endotoxin from E coli cells

Answer 22

C. Exotoxin from clostridial cells

Question 23

Your patient is a 40-year-old woman with a severe attack of diarrhea that began on the airplane while she was returning from a vacation. She had had multiple episodes of watery, nonbloody diarrhea and little vomiting.
She is afebrile. A stool culture reveals only lactose-fermenting colonies on (Eosin-metyhlene-blue) EMB agar. Which of the following is the most likely cause?
• Shigella sonnei
• Escherichia coli
• Pseudomonas aeruginosa
• Salmonella enteritidis
• Campylobacter jejuni

Answer 23

Escherichia coli

Question 24

Which of the following is correct regarding Enterobacteriaceae?
All ferment glucose, and lactose
All are oxidase positive, catalase negative
All can grow only anaerobical conditions
All have core polysaccharide
All K antigens are heat-labile flagellin proteins.

Answer 24

All have core polysaccharide