Enterobacteria I

Question 1

What are the 4 characteristics of Enterobacteria?

Answer 1

􏰀Facultative Gram-Neg rods
􏰀Ferment glucose
􏰀Reduce nitrate to nitrite 􏰀
Oxidase negative

Question 2

What are the 5 enterobacteria genera that cause GI disease?

Answer 2

E. coli
Shigella spp.
Salmonella spp. 
Edwardsiella spp.
Y. enterocolitica

Question 3

What are the 5 groups of E. coli that cause gastroenteritis?

Answer 3

ETEC
EPEC
EIEC
EHEC and STEC
EAggEC

Question 4

What is ETEC and what does it cause?

Answer 4

Enterotoxigenic

Traveler’s Diarrhea. Profuse watery diarrhea is predominant symptom.

Toxins that do not damage the mucosal epithelium.

Question 5

What is EPEC and what does it cause?

Answer 5

Enteropathogenic

Usually occurs in infants. Characterized by low-grade fever, malaise, vomiting, and diarrhea, with a prominent amount of mucus, but with NO gross blood.

Question 6

What is EIEC and what does it cause?

Answer 6

Enteroinvasive

Epithelial cells invaded.

Hallmarks are fever and colitis. Symptoms are urgency and tenesmus; blood, mucus, and many leukocytes in stool.

Question 7

What is EHEC and STEC and what does it cause?

Answer 7

Enterohemorrhagic
Shiga Toxin Producing

Release of Shiga toxins and is often caused by E. coli O157 and it causes bloody diarrhea without WBCs.

Question 8

What is EAggEC and what does it cause?

Answer 8

Enteroaggregative

Adhere to epithelial cells in a pattern resembling a pile of stacked bricks. Symptoms include watery diarrhea with blood and mucus.

Question 9

What is the triad of symptoms with hemolytic uremic syndrome?

Answer 9

• acute renal failure
• thrombocytopenia
• hemolytic anemia

Question 10

What is the reservoir of STEC?

Answer 10

Healthy dairy cattle - shed in feces

Question 11

How is STEC acquired in humans?

Answer 11

Eating undercooked ground beef mainly.

Others include: unpasteurized milk, apple cider, lettuce and other produce, petting zoos, state fair show barns, contaminated water

Question 12

What are the clinical manifestations of STEC infection?

Answer 12

Hemorrhagic Colitis

Hemolytic Uremic Syndrome

Question 13

What are the 5 clinical manifestations of Salmonella?

Answer 13

A. Carrier

B. GI-itis = typical abd pain & diarrhea

C. Enteric (“Typhoid”) fever - Transmission = S. Typhi in GI (reservoir is humans only - exception)

• Manifestations = rose spots w/ fever & septicemia for first 2 weeks –> diarrhea for last 2 weeks
• Mechanism = mucosa –> macrophages –> Peyer’s patches –> blood

D. Septicemia = w/o GI symptoms, found in immunosuppressed pts

E. Focal Infections = brain, bone, heart

Question 14

What are the main virulence factors of Enterobacteria?

Answer 14

􏰀Endotoxins
􏰉􏰀Capsule
Antigenic Phase Variation

Question 15

What color do lactose fermenters stain on MacConkey agar?

Answer 15

Purple

Question 16

What color do non-lactose fermenters stain on MacConkey agar?

Answer 16

White/Colorless

Question 17

What are the 7 tribes of Enterobacteria?

Answer 17

Tribe I – Escherichieae 􏰉
􏰀Tribe II – Edwardsielleae 􏰉
􏰀Tribe III – Salmonelleae 
􏰀Tribe IV – Citrobactereae 􏰉 
􏰀Tribe V – Klebsielleae 􏰉 Genus Klebsiella
􏰀Tribe VI – Proteeae
􏰀Tribe VII – Yersinieae

Question 18

What is the reservoir of E. coli?

Answer 18

Intestines of humans and animals

Question 19

What is the presence of E. coli in water indicative of?

Answer 19

Fecal contamination

Question 20

What is the most common cause of UTIs?

Answer 20

E. coli

Question 21

A college student returning from a Spring vacation in Puerto Vallarta, Mexico developed a profuse watery diarrhea accompanied by mild abdominal cramps. His diarrhea is so profuse that he is experiencing symptoms of dehydration. While on vacation he was careful not to purchase food from street vendors but did frequent the local bars and had drinks served with ice. Stool exam revealed no blood or WBC’s. What type of diarrheagenic E. coli is most likely to cause the symptoms experienced by this student?

A. E. coli O157
B. Enterotoxigenic E.coli (ETEC)
C. Enteroinvasive E.coli (EIEC)
D. Enteropathogenic E. coli (EPEC)
E. Enterohemorrhagic E. coli (EHEC)

Answer 21

B. Enterotoxigenic E.coli (ETEC)

Question 22

What is the most common Shiga Toxin producing E. coli?

Answer 22

E. coli O157

Question 23

What are the symptoms of hemorrhagic colitis - related to E. coli O157?

Answer 23

􏰀Abdominal cramps, watery diarrhea, bloody discharge
􏰀No significant fever
􏰀Absence of WBC in stool

Question 24

How is hemolytic uremic syndrome caused by E. coli O157 (STEC also known as EHEC)?

Answer 24

E. coli 0157 does not invade plasma but Shiga toxin does
and it attaches to receptors in renal epithelial cell wall and damages the blood vessel walls - fibrin deposits are rough
-> Cause RBCs to start tearing and O2 supply to kidney is
affected leading to acute renal failure.

This leads to hemolytic anemia, renal failure and thrombocytopenia.

Question 25

What is multiplex PCR used for?

Answer 25

Allows for a single test that can look for MANY targets ranging from EHEC to V. cholera

Question 26

What is the treatment for STEC?

Answer 26

Oral rehydration (Gatorade, Pedialyte), supportive care, and careful monitoring of kidney function.

Question 27

Why are antibiotics not given for STEC?

Answer 27

Antibiotics will cause the massive destruction of
E. coli and lead to the singular release of the
endotoxin AND Shiga toxin -> shock and death

Question 28

A healthy 3-year-old child develops diarrhea that lasts about a week, and that is bloody for a few days. His diarrhea resolves, but he remains lethargic, and passes only a little urine. A blood smear shows fragmented red blood cells and no platelets. What etiologic agent of infection would most likely produce the signs and symptoms displayed in this case?

A. E. coli 0157
B. Campylo bacter jejuni
C. Salmonella typhi
D. Shigella flexneri
E. Yersinia enterocolitica

Answer 28

A. E. coli 0157