Escherichia coli and the associated intestinal and extraintestinal infections Flashcards
General Features and habitat of Escherichia Coli
Gram –
Rod shape
Habitat- normal intestinal flora (Enterobacteriaceae)
Motile with peritrichous flagella-
H antigen (55 types, used for serotyping)
Biochemical Properties of Escherichia Coli
Lactose fermenter (+)
Glucose +, Indole + (urease, oxidase and H2S are all negative)
Catalase +
Capsule- K antigen (100 types, important for serotyping)
Fimbriae (pili)- help E. coli adhere to the urinary tract
Outer membrane (Gram negative)- O antigen (174 types, used for serotyping)
Pathogenesis of Escherichia Coli
Endogenous or exogenous feces may contaminate food or directly into body
Pathogenic types (e.g. K1 and K100 antigens) cause serious infection
Clinical Features of Escherichia Coli
Extra-intestinal diseases: (caused by normal, “apathogenic” types of E. coli when leave outside the intestine)
Urinary Tract Infection (UTI)- #1 cause of UTI
Endogenous fecal flora contaminates and ascend into urethra causing cystitis
Can ascend further causing pyelonephritis
Neonatal meningitis- #2 most common cause (after S. agalactiae)
Only if it has K1 capsular Ag (when maternal fecal flora contaminates during delivery)
Sepsis- due to LPS endotoxin
Gastroenteritis- in case of ETEC, EHEC, EIEC, EPEC and EAEC
Diagnosis of Escherichia Coli
Specimens- urine, pus, blood (hemoculture) and CSF
MacConkey agar- show pink colonies
EMB agar (Eosin, Methylene Blue + Lactose)- show green / dark blue colonies
Indole test- positive, convert tryptophan into indole (by tryptophanase enzyme)
Treatment of Escherichia Coli
Often resistant- ESBL in plasmid (easy transferring) or in chromosome
− Resistant to Penicillin and Cephalosporin
− Antibiogram (disc diffusion) is essential
Supportive treatment (i.e. hydration when severe diarrhea)
In complicated cases: beta-lactam + enzyme inhibitor, Carbapenem, Fluoroquinolones, Aminoglycosides, 3rd generation Cephalosporin
General features of Intestinal E. coli Pathogens
Certain E. coli strains became entero-pathogenic.
All of them are Gram negative rods.
Virulence factor are on plasmid, phages from other obligate enteral pathogens.
Common clinical feature: severe diarrhea.
Enterotoxigenic E. Coli (ETEC):
Endemic in developing countries
Transmitted via water (truck carrying water)
Enterotoxin Heat-Labile Toxin (LT)- activating adenylyl cyclase, increasing cAMP
Enterotoxin Heat-Stable Toxin (ST)- activating guanylate cyclase, increasing cGMP
Both toxins cause water and ions secretion
Major cause of Traveler’s diarrhea - severe watery diarrhea
Therapy: antibiotics, fluid and electrolytes replacement
Enterohemorrhagic E. Coli (EHEC):
Distinguish feature: does not ferment sorbitol (‘sorbitol free’ cola bottle), unlike all other pathogenic E. coli
Associated with O157:H7 antigen (only $1.57 burger sign)
Transmitted by eating undercooked meat, especially beef (hamburger) or milk
Shiga-like toxin A.K.A Verotoxin from shigella plasmid (she-gorilla toy on boy’s legs)- inhibiting 60S ribosomal subunits, causing cell death
Hemorrhagic colitis- severe, bloody diarrhea (red ketchup spilled) without fever, might cause hemolytic-uremic syndrome (HUS)
Therapy: antibiotics, fluid and electrolytes replacement
Enteroinvasive E. Coli (EIEC):
Transmitted by contact spread (less easily spread than shigella)
Full invasion of plasmid from shigella
Act on large intestine by invasion and destruction of the epithelial cells
Dysentery disease- severe watery diarrhea with mucus and fever can also occur (in adults and children)
Enteropathogenic E. Coli (EPEC):
Outbreak in nursing homes
Attachment to epithelial cells of the small intestine by Intimin/Tir complex
Causing watery diarrhea in newborns (children < 1 year)
Enteroaggregative E. Coli (EAEC):
Attachment to small intestine’s epithelial cells using fimbriae (pili)- causing bacterial aggregation, then release cytotoxins that damage the cells
Severe, watery diarrhea often chronic (> 14 days)- relatively high mortality
Mainly in children and in developing countries
