Microbes -Steinauer

Question 1

Your patient is a 30-year-old woman with non-bloody diarrhea for the past 14 hours. Which of the following organisms is LEAST likely to cause this illness?
A. Clostridium difficile
B. Streptococcus pyogenes
C. Shigella dysenteriae
D. Salmonella enteritidis

Answer 1

B. Streptococcus pyogenes

gram + coccus, catalase -, beta hemolytic, bacitracin sensitive

Question 2

Which of the following is most likely to cause bloody diarrhea?
A. Vibrio cholerae
B. Shigella flexneri
C. Giardia lamblia
D. Staphylococcus aureus

Answer 2

B. Shigella flexneri

low inoculum size

Question 3

Your patient is a 53-year-old woman who returned from Peru yesterday where there is an epidemic of cholera. Which is likely to be her chief complaint?
A. Fever and malaise
B. Dysentery
C. Watery diarrhea
D. Upper right quadrant pain

Answer 3

C. Watery diarrhea

cholera common in travelers

Question 4

What pathogen leads to “rice water stools”? What are the features of this? What are the enterotoxins associated with this?

Answer 4

V. cholerae (gram -, curves rods, oxidase +)

• CT: classic cholera toxin (A-B toxin that ribosylates G protein and over produces cAMP–> activate CFTR –> Cl- and HCO3- secretion –> water efflux)
• VCC –>makes anion permeable holes in cell surface–> Loss of Cl-
• ACE (accessory toxin) –> Decrease absorption of Na+

Question 5

What are the different types of E. coli and what are the features of each ?

Answer 5

• ETEC=enterotoxigenic
• Travellers
• Heat labile toxin (inc cAMP) (LT)
• Heat stabile toxin (ST): activates CFTR
• EPEC=enteropathogenic
• peds
• type III secretion, destroys microvilli
• A and E lesions
• EAEC=aggregate
• aggregate and from bricks (by pili)–> persistent and resistant to antibiotics (>14 days)
• biofilm
• EHEC=hemorrhagic
• shiga like toxin (verotoxin) –> binds to intestinal and kidney cells –>can cause HUS
• low inoculum
• food/cattle reservoir

Question 6

*Which form of E. coli should not be treated with antibiotics?

Answer 6

EHEC*

Question 7

Which E. coli can lead to hemorrhagic colitis (HUS)? Is this inflammatory?

Answer 7

EHEC

noninflammatory but bloody

Question 8

What are some key features of Shigella? How is it spread?

Answer 8

• Humans and primates
• Low inoculum (spreads easily)
• Invasive –>inflammatory
• spread cell to cell with actin tails
• day care center risk factor

Question 9

What are some key features of Salmonella? What can Salmonella cause? How is it spread?

Answer 9

gram - bacilli, lactose -, motile, H2S gas production

• Enteric disease
• Typhoid fever

-Animal reservoirs and food borne illness

Question 10

What is the major cause of bloody diarrhea in kids? How is it transmitted?

Answer 10

Campylobacter (gram -, motile, curved rods)

food (poultry, meat, milk)

Question 11

Several 4-year-old children who attend the same preschool are hospitalized for severe, bloody diarrhea. All of the children ate at the same fast-food restaurant during class field trip. In the second week of the illness, one of the children additionally develops thrombocytopenia, hemolytic anemia, and acute renal insufficiency. The most likely causative agent is:
A. EAEC
B. EHEC
C. EIEC
D. EPEC
E. ETEC
F. Campylobacter jejuni

Answer 11

B. EHEC

this kid got HUS

Question 12

Your patient is a 56-year-old woman who was treated with ampicillin for cellulitis caused by Streptococcus pyogenes. Several days later she developed bloody diarrhea and a colonoscopy indicated pseudomembranous plaques. Which of the following describes the most likely pathogen?
A. It is an anaerobic Gram-positive rod that produces exotoxins
B. It is a comma shaped Gram-negative rod that grows best at 41C
C. It is a facultative Gram-negative rod that forms spores
D. It is an obligate intracellular parasite that grows in cell culture but not blood agar
E. It is a parasite that produces cysts with four nuclei

Answer 12

A. It is an anaerobic Gram-positive rod that produces exotoxins

(c. diff)

Question 13

What color would Salmonella appear on MacConkey Agar? What color will EHEC appear?

Answer 13

Salmonella =clear
(does not ferment lactose)

EHEC=pink

Question 14

What color will EHEC appear on a Macconkey sorbitol agar?

Answer 14

Clear

Question 15

What is Hektoen’s agar used to differentiate? What colors will these turn?

Answer 15

Shigella (blue/green)

Salmonella =black (produces H2S)

Question 16

How should Vibrio cholera be tested for?

Answer 16

culture is the gold standard (TCBS agar)

Question 17

A 20-year-old man presents with watery diarrhea that has lasted 3 days. He just returned from a trip to Kenya 2 days ago. He has no fever and no fecal leukocytes are detected in a stool sample. The pathogen is an oxidase negative, Gram-negative rod that grows pink colonies on Mac Conkey Agar. Which of the following is most likely?
A. Vibrio cholerae
B. Shigella sonnei
C. Campylobacter jejuni
D. ETEC
E. EHEC
F. EPEC

Answer 17

D. ETEC

Question 18

What complications can Entamoeba histolytic produce?

Answer 18

Liver abscess

eyes, genital problems

Question 19

A 43-year-old man with history of polysubstance abuse and bipolar disorder is involuntarily admitted to the hospital because of persistent bloody diarrhea for the past 1 week. Quantitative analysis of stool shows spherical, quadrinucleate, thin walled cysts measuring 10-20um in diameter. Which is the most likely pathogen?
A. Cryptosporidium parvum
B. Dientamoeba fragilis
C. Entamoeba histolytica
D. Giardia lamblia
E. Shigella sonnei

Answer 19

C. Entamoeba histolytica

Question 20

A 24-year-old man comes to the physician because of prolonged diarrhea. He undergoes esophagogastroduodenoscopy with biopsy of the small intestine. Microscopic examination of the biopsy specimen shows numerous crescent-shaped protozoa adjacent to the epithelial brush border. Which is the most likely etiologic agent?
A. Cryptosporidium parvum
B. Dientamoeba fragilis
C. Entamoeba histolytica
D. Giardia lamblia
E. Shigella sonnei

Answer 20

D. Giardia lamblia

Question 21

Which of the following host defense mechanisms is the MOST important for preventing dysentery caused by Salmonella?
A. Gastric acid
B. Salivary enzymes
C. Normal flora of the mouth
D. Alpha interferon

Answer 21

A. Gastric acid

Question 22

Which one of the following pathogens has the LOWEST 50% infectious dose (ID50)?
A. Shigella sonnei
B. Vibrio cholerae
C. Salmonella typhi
D. Campylobacter jejuni

Answer 22

A. Shigella sonnei

Question 23

Which one of the following pathogens that infects the GI tract is most likely to cause bacteremia?
A. Shigella sonnei
B. Vibrio cholerae
C. Salmonella typhi
D. Campylobacter jejuni

Answer 23

C. Salmonella typhi

Question 24

A 3-year-old boy who attends a large daycare facility suddenly develops a fever, vomiting, diarrhea, and abdominal pain. When he is brought to the ED three days later, he has more than 10 bowel movements in a day, and mucus, blood, and pus are seen in the stool. He has developed weight loss and severe dehydration. His temperature is 38C, blood pressure is 90/60 mm Hg, pulse is 130 min, and respirations are 20/min. O2 saturation is 98%. No rash is observed. Which is most likely?

A. Norovirus
B. Rotavirus
C. Salmonella enterica typhi
D. Shigella sonnei
E. Vibrio cholerae

Answer 24

D. Shigella sonnei

Question 25

The pathogenesis of which of the following organisms is MOST likely to invade the intestinal mucosa?
A. V. cholerae 
B. Entamoeba histolytica 
C. Giardia Lamblia 
D. ETEC
E. EPEC

Answer 25

B. Entamoeba histolytica

Question 26

A 10-year-old male has become pale and seems to have lost his normal energy. On examination, the child’s skin is somewhat pale and clammy, and a complete blood count detects a microcytic, hypochromic anemia. A fecal sample from this child will most likely show:

A. Brown, rough shelled ova 
B. Golden, football shaped ova with bipolar plugs 
C. Living larvae 
D. Oval, golden, clear, shelled ova 
E. Spined eggs

Answer 26

D. Oval, golden, clear, shelled ova