L25 The Enterobacteriaceae I Flashcards
Enterobacteriaceae are a diverse group of Gram ___ ___ (shape).
Negative; rods
Enterobacteriaceae are indigenous to the ___.
GI tract
Enterobacteriaceae colonize the ___ of hospitalized patients.
Respiratory tract
Enterobacteriaceae have ___ growth requirements.
Simple
Enterobacteriaceae are ___ (oxygen growth).
Facultative anaerobes
Describe the structure of Enterobacteriaceae.
- H-antigen: located in the peritrichous flagella (50+ serotypes)
- K-antigen: located in the capsule (80+ serotypes)
- LPS: endotoxin
What is the K-antigen important for?
Causing extraintestinal colonization, UTI, and invasive disease
What are the components of LPS?
- O-antigen: outer-most domain, polysaccharide that gives variability
- Core: attaches O to A
- Lipid A: innermost region; responsible for toxicity
How does Lipid A contribute to the toxicity of Enterobacteriaceae?
When bacterial cells are lysed, fragments of the membrane containing lipid A are released into the circulation, causing fever, diarrhea, and septic shock
What are some of the general virulence factors of Enterobacteriaceae?
- Endotoxins (LPS)
- Capsule
- Antigenic phase variation
- Type III secretion systems
- Sequestration of growth factors
- Resistance to serum killing (capsule)
What is antigenic phase variation?
Altered expression of K and H antigens protects from Ab-mediated cell death
What are the 4 common biochemical characteristics of Enterobacteriaceae?
- Facultative Gram-negative rods
- Ferment glucose
- Reduce nitrate to nitrite
- Oxidase negative
What are the non-lactose fermenting Enterobacteriaceae?
- Salmonella
- Shigella
- Proteus
- Yersinia
- Serratia
What are the lactose fermenting Enterobacteriaceae?
- E. coli
- Klebsiella
- Enterobacter
- Citrobacter
What is the major habitat of Escherichia?
Intestines of humans and animals
Why is the presence of E. coli in water considered an indicator of fecal contamination?
Because of its ubiquitous nature in human and animal feces
Most E. coli infections are ___.
Endogenous
E. coli is the most common gram negative rod to cause ___.
Gram negative sepsis
80% of community acquired ___ are caused by E. coli.
UTIs
In addition to gram negative sepsis and UTIs, what are 4 other clinical syndromes associated with E. coli?
Wound infections, pneumonia in immunocompromised hospitalized patients, meningitis in neonates, gastroenteritis
What are the 5 strains of E. coli that cause gastroenteritis?
- ETEC
- EPEC
- EIEC
- EHEC/STEC
- EAggEC
How does ETEC (enterotoxigenic E. coli) cause gastroenteritis?
Elaboration of secretory toxins that do not damage the mucosal epithelium but that stimulate hypersecretion of fluid
What are the signs and symptoms of gastroenteritis caused by ETEC?
Profuse, watery, secretory diarrhea (traveler’s diarrhea); often accompanied by mild abdominal cramps, dehydration and vomiting occur in some cases.
How does EPEC (enteropathogenic E. coli) cause gastroenteritis?
Adhere to epithelial cells in localized microcolonies and cause attaching and effacing lesions
What are the signs and symptoms of gastroenteritis caused by EPEC?
Low-grade fever, malaise, vomiting, diarrhea, with a prominent amount of mucus, but NO GROSS BLOOD; usually occurs in infants
How does EIEC (enteroinvasive E. coli) cause gastroenteritis?
Invade epithelial cells
What are the signs and symptoms of gastroenteritis caused by EIEC?
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.
How does EHEC (enterohemorrhagic E. coli) cause gastroenteritis?
Elaboration of cytotoxins (Shiga toxins Stx1 and Stx2)
What is the primary cause of EHEC?
E. coli O157:H7
What are the signs and symptoms of gastroenteritis caused by EHEC?
Bloody diarrhea without WBCs; often no fever; abdominal pain; may progress to hemolytic uremic syndrome (HUS)
How does EAggEC (Enteroaggregative E. coli) cause gastroenteritis?
Adheres to epithelial cells in a pattern resembling stacked bricks
What are the signs and symptoms of gastroenteritis caused by EAggEC?
Watery diarrhea with blood and mucus, vomiting, dehydration, and abdominal pain (less common); seen in infants and travelers
Compare the types of stool seen in the 5 strains of E. coli causing gastroenteritis.
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
What is the most commonly identified serotype of STEC?
E.coli O157
How is STEC identified?
Via the toxin (not the serotype)
Where STEC found?
Feces of cattle, sheep, deer
Human infection with E. coli O157 occurs via what two pathways?
- Contaminated food or water
2. Direct contact with an infected patient
Does E. coli O157 require a low or high inoculum?
Low
The CDC estimates that STEC causes ___ illnesses, ___ hospitalizations, and ___ deaths in the US each year.
265,000; 3,600; 30
Foodborne outbreaks of E. coli O157 are most commonly associated with ___.
Undercooked ground beef
Infections with E. coli O157 are associated with what three clinical manifestations?
- Bloody and non-bloody diarrhea
- Hemolytic uremic syndrome (HUS)
- Hemorrhagic colitis
What are the three (triad) symptoms of hemolytic uremic syndrome (HUS) and what precedes these symptoms?
- Acute renal failure
- Thrombocytopenia
- Hemolytic anemia
Bloody diarrhea
HUS is the leading cause of ___ in children.
Acute renal failure
HUS occurs in ___% of pediatric O157:H7 cases.
20
___% 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.
50; 14; 39; 3-5
HUS is usually diagnosed ___ (time) after onset of diarrhea.
1 week
What are schistocytes?
Destroyed RBCs
Why does HUS occur?
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.
HUS is most associated with which toxin?
Stx2
Shiga toxin stimulates cytokines - what do these do to help the bacteria?
Increase expression of the receptor
The vast majority of HUS cases are ___-related.
Diarrheal
Non-diarrheal HUS can occur in association with what three situations?
- Pneumococcal infection
- Chemotherapy
- Transplant immunosuppresion
Describe the symptoms of hemorrhagic colitis caused by E. coli O157.
Abdominal cramps, watery diarrhea, bloody discharge (vomiting in 50%), no significant fever, no WBC in stool
True or false - non-O157 STEC has emerged.
True
How can we identify E. coli O157?
Use sorbitol MacConkey agar - O157 does NOT ferment sorbitol (no pink colony)
How can antigen detection be used to diagnosed O157?
Shiga toxin or the O157 antigen can be detected
When using PCR to identify O157, what do we look for?
The genetic marker that codes for the toxin (not the toxin itself)
How is STEC diarrhea treated?
- Oral rehydration, supportive care, monitoring of kidney function
- NO antibiotics
- NO antimotility agents
Can E. coli O157 be treated with anti-microbial agents?
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.
