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MHD 1 > L25 The Enterobacteriaceae I > Flashcards

L25 The Enterobacteriaceae I Flashcards

1
Q

Enterobacteriaceae are a diverse group of Gram ___ ___ (shape).

A

Negative; rods

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2
Q

Enterobacteriaceae are indigenous to the ___.

A

GI tract

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3
Q

Enterobacteriaceae colonize the ___ of hospitalized patients.

A

Respiratory tract

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4
Q

Enterobacteriaceae have ___ growth requirements.

A

Simple

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5
Q

Enterobacteriaceae are ___ (oxygen growth).

A

Facultative anaerobes

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6
Q

Describe the structure of Enterobacteriaceae.

A
  1. H-antigen: located in the peritrichous flagella (50+ serotypes)
  2. K-antigen: located in the capsule (80+ serotypes)
  3. LPS: endotoxin
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7
Q

What is the K-antigen important for?

A

Causing extraintestinal colonization, UTI, and invasive disease

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8
Q

What are the components of LPS?

A
  1. O-antigen: outer-most domain, polysaccharide that gives variability
  2. Core: attaches O to A
  3. Lipid A: innermost region; responsible for toxicity
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9
Q

How does Lipid A contribute to the toxicity of Enterobacteriaceae?

A

When bacterial cells are lysed, fragments of the membrane containing lipid A are released into the circulation, causing fever, diarrhea, and septic shock

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10
Q

What are some of the general virulence factors of Enterobacteriaceae?

A
  1. Endotoxins (LPS)
  2. Capsule
  3. Antigenic phase variation
  4. Type III secretion systems
  5. Sequestration of growth factors
  6. Resistance to serum killing (capsule)
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11
Q

What is antigenic phase variation?

A

Altered expression of K and H antigens protects from Ab-mediated cell death

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12
Q

What are the 4 common biochemical characteristics of Enterobacteriaceae?

A
  1. Facultative Gram-negative rods
  2. Ferment glucose
  3. Reduce nitrate to nitrite
  4. Oxidase negative
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13
Q

What are the non-lactose fermenting Enterobacteriaceae?

A
  1. Salmonella
  2. Shigella
  3. Proteus
  4. Yersinia
  5. Serratia
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14
Q

What are the lactose fermenting Enterobacteriaceae?

A
  1. E. coli
  2. Klebsiella
  3. Enterobacter
  4. Citrobacter
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15
Q

What is the major habitat of Escherichia?

A

Intestines of humans and animals

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16
Q

Why is the presence of E. coli in water considered an indicator of fecal contamination?

A

Because of its ubiquitous nature in human and animal feces

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17
Q

Most E. coli infections are ___.

A

Endogenous

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18
Q

E. coli is the most common gram negative rod to cause ___.

A

Gram negative sepsis

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19
Q

80% of community acquired ___ are caused by E. coli.

A

UTIs

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20
Q

In addition to gram negative sepsis and UTIs, what are 4 other clinical syndromes associated with E. coli?

A

Wound infections, pneumonia in immunocompromised hospitalized patients, meningitis in neonates, gastroenteritis

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21
Q

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

A
  1. ETEC
  2. EPEC
  3. EIEC
  4. EHEC/STEC
  5. EAggEC
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22
Q

How does ETEC (enterotoxigenic E. coli) cause gastroenteritis?

A

Elaboration of secretory toxins that do not damage the mucosal epithelium but that stimulate hypersecretion of fluid

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23
Q

What are the signs and symptoms of gastroenteritis caused by ETEC?

A

Profuse, watery, secretory diarrhea (traveler’s diarrhea); often accompanied by mild abdominal cramps, dehydration and vomiting occur in some cases.

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24
Q

How does EPEC (enteropathogenic E. coli) cause gastroenteritis?

A

Adhere to epithelial cells in localized microcolonies and cause attaching and effacing lesions

25
Q

What are the signs and symptoms of gastroenteritis caused by EPEC?

A

Low-grade fever, malaise, vomiting, diarrhea, with a prominent amount of mucus, but NO GROSS BLOOD; usually occurs in infants

26
Q

How does EIEC (enteroinvasive E. coli) cause gastroenteritis?

A

Invade epithelial cells

27
Q

What are the signs and symptoms of gastroenteritis caused by EIEC?

A

Inflammatory diarrhea (dysentery) similar to shigella; hallmarks are fever and colitis; symptoms include urgency and tenesmus; Blood, mucus, and many leukocytes are found in the stool.

28
Q

How does EHEC (enterohemorrhagic E. coli) cause gastroenteritis?

A

Elaboration of cytotoxins (Shiga toxins Stx1 and Stx2)

29
Q

What is the primary cause of EHEC?

A

E. coli O157:H7

30
Q

What are the signs and symptoms of gastroenteritis caused by EHEC?

A

Bloody diarrhea without WBCs; often no fever; abdominal pain; may progress to hemolytic uremic syndrome (HUS)

31
Q

How does EAggEC (Enteroaggregative E. coli) cause gastroenteritis?

A

Adheres to epithelial cells in a pattern resembling stacked bricks

32
Q

What are the signs and symptoms of gastroenteritis caused by EAggEC?

A

Watery diarrhea with blood and mucus, vomiting, dehydration, and abdominal pain (less common); seen in infants and travelers

33
Q

Compare the types of stool seen in the 5 strains of E. coli causing gastroenteritis.

A

ETEC: profuse, watery secretory diarrhea (traveler’s)

EPEC: diarrhea with lots of mucus, but no gross blood

EIEC: inflammatory diarrhea with blood, mucus, and many leukocytes

EHEC: bloody diarrhea without WBCs

EAggEC: watery diarrhea with blood and mucus

34
Q

What is the most commonly identified serotype of STEC?

A

E.coli O157

35
Q

How is STEC identified?

A

Via the toxin (not the serotype)

36
Q

Where STEC found?

A

Feces of cattle, sheep, deer

37
Q

Human infection with E. coli O157 occurs via what two pathways?

A
  1. Contaminated food or water

2. Direct contact with an infected patient

38
Q

Does E. coli O157 require a low or high inoculum?

A

Low

39
Q

The CDC estimates that STEC causes ___ illnesses, ___ hospitalizations, and ___ deaths in the US each year.

A

265,000; 3,600; 30

40
Q

Foodborne outbreaks of E. coli O157 are most commonly associated with ___.

A

Undercooked ground beef

41
Q

Infections with E. coli O157 are associated with what three clinical manifestations?

A
  1. Bloody and non-bloody diarrhea
  2. Hemolytic uremic syndrome (HUS)
  3. Hemorrhagic colitis
42
Q

What are the three (triad) symptoms of hemolytic uremic syndrome (HUS) and what precedes these symptoms?

A
  1. Acute renal failure
  2. Thrombocytopenia
  3. Hemolytic anemia

Bloody diarrhea

43
Q

HUS is the leading cause of ___ in children.

A

Acute renal failure

44
Q

HUS occurs in ___% of pediatric O157:H7 cases.

A

20

45
Q

___% of patients with HUS require dialysis. ___% develop severe in-hospital complications such as stroke, blindness, and bowel resection. ___% develop chronic kidney abnormalities years later. ___% die.

A

50; 14; 39; 3-5

46
Q

HUS is usually diagnosed ___ (time) after onset of diarrhea.

A

1 week

47
Q

What are schistocytes?

A

Destroyed RBCs

48
Q

Why does HUS occur?

A

There is a high concentration of receptors for toxin in the intestinal villi and renal endothelial cells. Glomerular endothelial cells are destroyed, which leads to platelet activation and thrombin deposition. Decreased GFR leads to acute renal failure.

49
Q

HUS is most associated with which toxin?

A

Stx2

50
Q

Shiga toxin stimulates cytokines - what do these do to help the bacteria?

A

Increase expression of the receptor

51
Q

The vast majority of HUS cases are ___-related.

A

Diarrheal

52
Q

Non-diarrheal HUS can occur in association with what three situations?

A
  1. Pneumococcal infection
  2. Chemotherapy
  3. Transplant immunosuppresion
53
Q

Describe the symptoms of hemorrhagic colitis caused by E. coli O157.

A

Abdominal cramps, watery diarrhea, bloody discharge (vomiting in 50%), no significant fever, no WBC in stool

54
Q

True or false - non-O157 STEC has emerged.

A

True

55
Q

How can we identify E. coli O157?

A

Use sorbitol MacConkey agar - O157 does NOT ferment sorbitol (no pink colony)

56
Q

How can antigen detection be used to diagnosed O157?

A

Shiga toxin or the O157 antigen can be detected

57
Q

When using PCR to identify O157, what do we look for?

A

The genetic marker that codes for the toxin (not the toxin itself)

58
Q

How is STEC diarrhea treated?

A
  1. Oral rehydration, supportive care, monitoring of kidney function
  2. NO antibiotics
  3. NO antimotility agents
59
Q

Can E. coli O157 be treated with anti-microbial agents?

A

Most strains are susceptible; however, treatment with antimicrobials has not been shown to shorten the duration or severity of the disease. Treatment possibly increases the risk of developing HUS.

MHD 1 (58 decks)

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