Enterobacteriaceae I Flashcards
Characteristics of Enterobacteriaceae
Facultative Gram Neg Rods Ferment Glucose No Oxidase simple growth requirements- blood agar LPS Endotoxin Reduce nitrate to nitrite
What are the components of LPS?
O Antigen: outer most element-> gives many serotypes; Antibodies are against O polysaccharides
Lipid A: Innermost region of LPS leading to toxicity and septic shock when released into blood
Where are H and K antigens located?
H Antigen: In the peritrichous flagella
K Antigen: Capsule
Which Enterobacteriaceae do NOT ferment lactose?
Salmonella
Shigella
Proteus
Yersinia
Which Enterobacteriaceae ferments lactose?
E.Coli Klebsiella Enterobacter Citrobacter Serratia
What is MacConkey Agar good for?
Selective fro gram negative growth and doesn’t allow gram positive growth
Can make diffferential as well by putting latose and checking for lactose fermenting ability
Purple: lactose fermenter
Colorless: non lactose fermenter
What are the main genera of Enterobacteriaceae?
E.coli Shigella Edwardsiella Salmonella Citrobacter Klebsiella Enterobacter Serratia Proteus Yersinia
Where is E.coli normally found?
Instestines of humans and animals
How does Ecoli grow on Macconkey Agar?
purple: Lactose fermenter
Flat
What is Ecoli most know for clinically?
Common cause of UTI
Number 1 cause of meningitis in neonates
What are clinical sx of E.coli infection?
Gram Neg Sepsis UTI Wound infections Pneumonia Neonatal meningitis Gastroenteritis
What are the different strains of Ecoli causing gastroenteritis?
ETEC: enterotoxigenic EPEC: enteropathogenic EIEC: Enteroinvasive EHEC: hemorrhagic STEC: Shiga Toxin producing EAggEC: Enteroaggregative
What is characteristic of ETEC?
Enterotoxigenic E.Coli
Due to secretory toxins that do not damage mucosal
Secretory diarrhea -> profuse and watery
AKA Traveler’s Diarrhea
What is characteristic of EPEC?
Enteropathogenic
Adheres to epithelial cells -> attaching and effacing lesions
Occurs in infants -> infantile diarrhea with mucous but no blood
what is characteristic of EIEC?
Enteroinvasive
invades epithelial cells -> inflammatory diarrhea (like dysentery in shigella) with blood mucus and leukocytes
Hallmarks: Fever and colitis
What are the characteristics of EHEC/STEC?
Enterohemorrhagic/Shiga Toxin Producing
Genes to produce shiga toxins -> E.Coli O157:H7 mainly -> bloody diarrhea without WBCS
No fever
Can lead to Hemolytic Uremic Syndrome
What are the characteristics of EAggEC?
Enteroaggregative
Adhere to epithelial cells -> watery diarrhea with blood and mucus
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)
B
Which strain of E.coli is most identified wiht producing Shiga Toxi?n
E.Coli O157/STEC
How is E.coli O157 transmitted?
Shed in feces of animasl -> contaminated food or water
Also direct contact with infected patietn
Where is the reservoir of E.coli O157?
Healthy dairy cattle -> Ground beef in hamburgers
What is HUS?
Hemolytic Uremic Syndrome:
Acute Renal Failure
Thrombocytopenia
Hemolytic Anemia
Precedes bloody diarrhea -> only about 20% with infection get HUS
What is the clinical sequence of sx for EHEC?
3-4 days nonbloody diarrhea with abd pain => onset of bloody diarrhea with severe abd pain => resolution in 4-10 days
OR
HUS => death or long term sequelae (renal impairment, HTN, CNS)
Do the E.coli O157 organisms cause infections by invading bloodstream?
NO
Stay in intestines-> secrete Shiga toxins into blood -> bind to receptors on endothelial cells (renal endothelial area have large conc of receptors) => RENAL FAILURE
How do the shiga toxins work?
Inhibit protein synthesis in commensal bacteria and host cells
Damage microcircultion -> vasculitis -> mucosal damage-> blood diarrhea
Induce cytokines and apoptosis
What are the risk factors for developing HUS after EO157 infection?
Very young/old age
P Antigen on RBCs
How is EO157 detected?
Anigens: Shiga Toxin or O157 LPS antigen
Direct fecal specimen detection
Enriched broth culture detection
How is STEC diarrhea treated?
Oral rehydration
Dialysis for HUS/Renal Failure
NO ABX!!! => destroy Ecoli cells -> massive release of ST and endotoxin all at once-> potentiation -> bad for patient
Let it play out and manage sx
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. Campylobacter jejuni C. Salmonella typhi D. Shigella flexneri E. Yersinia enterocolitica
A
