Enterobacteriaceae (E.Coli-Specific) Flashcards
Describe the general structure of Enterobacteriaceae:
Gram negative rods
Many have flagella and a capsule
H and K Antigens
LPS
What are the locations of H and K Antigens in Enterobacteriaceae?
H-antigen: located in peritrichous flagella
K-antigen: located in capsule
Function of the capsule in Enterobacteriaceae?
Important in causing extraintestinal colonization, UTI, and invasive disease
Describe the composition of LPS in the membrane of Enterobacteriaceae.
O-antigen: located on outer most domain
Core oligosaccharide
Lipid A: inner most region of LPS
What is significant about of O-antigen?
Targeted antigen for detection in laboratory
What is the pathogenesis of lipid A?
Causes toxicity: fever, diarrhea, and possible fatal endotoxic shock
Name the 6 virulence factors of Enterobacteriaceae:
Endotoxin (LPS) Capsule Antigenic Phase Variation Type III secretion systems Sequestration of growth factors
What is the significance of antigenic phase variation in Enterobacteriaceae?
Alte expression of H and K antigens to protect organisms from Ab mediated cell death
What is the significance of Type III secretion systems in Enterobacteriaceae?
Facilitates secretion of virulence factors into host cells
Morphology of Enterobacteriaceae
Gram-negative rods that stain red
Culture Characteristics of Enterobacteriaceae
Grow on standard media (i.e. blood agar)
5 Biochemical characteristics of Enterobacteriaceae
Facultative (aerobic & anaerobic)
Ferment glucose
Reduce nitrate to nitrite
Oxidase negative
Grow on MacConkey Agar (salt)
What differentiates Enterobacteriaceae from other gram-negative rods?
Enterobacteriaceae is Oxidase negative
Non-lactose fermenting Enterobacteriaceae
Salmonella Shigella Proteus Yersinia Serratia
Lactose fermenting Enterobacteriaceae
E. coli
Klebsiella
Enterobacter
Citrobacter
6 Escherichia Coli Clinical Syndromes:
Gram negative bacteremia and sepsis
Most common contributor to community-acquired UTIs
Wound infections
Pneumonia in immunocompromised hospitalized patients
Meningitis in neonates
Gastroenteritis
Pathogenic Phenotype of Enterotoxigenic
E. coli (ETEC)
Elaboration of secretory toxins (LT, ST) that do not damage the mucosal epithelium but stimulate hypersecretion of fluids
Signs and Symptoms of Enterotoxigenic
E. coli (ETEC)
Profuse, watery, secretory diarrhea is predominant symptom. Often accompanied by mild abdominal cramps. Dehydration and vomiting occur in some cases.
Pathogenic Phenotype of Enteropathogenic E. coli (EPEC)
Adheres to epithelial cells in localized micro-colonies and causes attaching/ effacing lesions
Signs and Symptoms of Enteropathogenic E. coli (EPEC)
Usually occurs in infants.
Characterized by low-grade fever, malaise, vomiting, and diarrhea, with a prominent amount of mucus, but with no gross blood
Pathogenic Phenotype of Enteroinvasive E. coli (EIEC)
Invasion of epithelial cells
Signs and Symptoms of Enteroinvasive E. coli (EIEC)
Inflammatory diarrhea (Dysentery) similar to Shigella. Hallmarks are fever and colitis. Symptoms are urgency and tenesmus; blood, mucus, and many leukocytes in stool
Pathogenic Phenotype of Enterohemorrhagic E. coli (EHEC)
Shiga Toxin producing E. coli (STEC) -Carry cytotoxins (Shiga toxins, Stx1 and Stx2). Primarily caused by E.coli O157:H7
Signs and Symptoms of Enterohemorrhagic E. coli (EHEC)
Bloody diarrhea without WBCs. Often no fever. Abdominal pain is common. May progress to hemolytic uremic syndrome (HUS) or hemorrhagic colitis.
Pathogenic Phenotype of Enteroaggregative E. coli (EAggEC)
Adhere to epithelial cells in a pattern resembling a pile of stacked bricks
Signs and Symptoms of Enteroaggregative E. coli (EAggEC)
Infants and travelers. Symptoms include watery diarrhea with blood and mucus, vomiting, dehydration and less commonly, abdominal pain.
Two other names for Shiga Toxin Producing E. coli (STEC).
EHEC and E.coli O157:H7
How is E.coli O157:H7 transmitted?
contaminated food or water
direct contact with an infected patient
E. coli O157 Reservoir
Reservoir in healthy dairy cattle
Foodborne outbreaks of E. coli O157 are most commonly associated with ______________.
Foodborne outbreaks of E. coli O157 are most commonly associated with undercooked ground beef.
Infections caused by E. coli O157:
Hemolytic Uremic Syndrome (HUS)
Hemorrhagic Colitis
Hemolytic Uremic Syndrome triad of symptoms:
acute renal failure
thrombocytopenia - low platelet count
Microangipathic hemolytic anemia - the destruction of RBCs prior to their natural death cycle (shistocytes)
Hemolytic Uremic Syndrome is usually preceded by:
bloody diarrhea
HUS is the leading cause of ________________ in children.
HUS is the leading cause of acute renal failure in children.
Treatment of HUS:
Mainly supportive
Dialysis
No antibiotics
Plasmapharesis/IVIG
Mechanism of Hemolytic Uremic Syndrome (HUS) - 3 steps
- Toxin (STX2) binds to receptors in the intestinal villi and renal endothelial cells
- The toxin causes damage to endothelial cells, which leads to platelet activation and thrombin deposition forming a clot at the region of endothelial destruction
- Leads to decreased glomerular filtration and acute renal failure
Describe the 2 Types of HUS:
Diarrheal-related: majority of cases
Non-diarrheal HUS: occurs in association with pneumococcal infection, chemotherapy, or transplant immunosuppression
Clinical Presentation of E. coli O157 Hemorrhagic Colitis
Abdominal cramps, watery diarrhea, bloody discharge (vomiting in 50%)
Patients progress to bloody diarrhea within 2 days of onset of clinical symptoms of abdominal cramps
No significant fever
Absence of WBC in stool
Symptoms resolve in 4-10 days
How would you isolate E. coli O157 from other strains on agar?
Sorbitol MacConkey Agar is used because these organisms do not ferment sorbitol
How would you detect E. coli O157 from other strains using surface antigens? Describe the process.
ProSpecT™ Shiga Toxin E. coli (STEC) Microplate - Remel
- Direct fecal specimen detection by placing stool in sample well
- If Shiga toxin and/or the O157 antigen are present, the lines will show
- LPS antigen is used as a control
- Enriched broth culture detection done overnight (more sensitive)
How would you isolate E. coli O157 from other strains via toxin/antigen detection method?
BioFire FilmArray – Multiplex PCR
Integrated Sample Preparation, Amplification, and Detection for 22 Enteric Pathogens
Detects Shiga-toxin producing E. coli (STEC) stx1/stx2 and/or E. coli O157
Treatment of STEC:
Oral rehydration (Gatorade, Pedialyte), supportive care, and careful monitoring of kidney function.
HUS and renal failure: managed by dialysis
What treatments should be avoided for STEC Diarrhea? Why?
Antibiotics and Anti-motility agents NOT given in STEC diarrhea because they will push patients toward HUS
Is Treatment of E. coli O157 with Antimicrobial Agents useful?
Most strains are very susceptible, but Abx treatment has not been shown to shorten the duration or severity of disease.
Treatment possibly increases the risk of developing HUS
