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Escherichia coli

Escherichia coli

Four different strains of Escherichia coli on Endo agar with biochemical slope (see here). Glucose fermentation with gas production, urea and H2S negative, lactose positive (with exception of strain D - "late lactose fermenter"; on Endo agar it looks like lactose negative). All four strains are mannitol positive (best seen in fig. D), cellobiose negative (strains A, B). Approximately 50% of E.coli strains are sucrose negative (fig.A, D). Colonies of some strains have typical greenish metallic sheen (fig.E) but many of them grow without it (fig.F).

E.coli

Escherichia coli (commonly abbreviated E. coli) is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K2, and by preventing the establishment of pathogenic bacteria within the intestine. E. coli and related bacteria constitute about 0.1% of gut flora, and fecal-oral transmission is the major route through which pathogenic strains of the bacterium cause disease.


Gastrointestinal infection

Certain strains of E. coli, such as O157:H7, O104:H4, O121, O26, O103, O111, O145,and O104:H21, produce potentially lethal toxins. Food poisoning caused by E. coli can result from eating unwashed vegetables or undercooked meat. O157:H7 is also notorious for causing serious and even life-threatening complications such as hemolytic-uremic syndrome. The O104:H4 strain is equally virulent. It is the strain behind the ongoing and deadly June 2011 E. coli outbreak in Europe.

Enteric E. coli (EC) are classified on the basis of serological characteristics and virulence properties:
  • Enterotoxigenic E. coli (ETEC)
  • Enteropathogenic E. coli (EPEC)
  • Enteroinvasive E. coli (EIEC)
  • Enterohemorrhagic E. coli (EHEC)
  • Enteroaggregative E. coli (EAEC)

Urinary tract infection

Uropathogenic E. coli (UPEC) is responsible for approximately 90% of urinary tract infections (UTI) seen in individuals with ordinary anatomy. In ascending infections, fecal bacteria colonize the urethra and spread up the urinary tract to the bladder as well as to the kidneys (causing pyelonephritis), or the prostate in males. Because women have a shorter urethra than men, they are 14 times more likely to suffer from an ascending UTI. Uropathogenic E. coli use P fimbriae (pyelonephritis-associated pili) to bind urinary tract endothelial cells and colonize the bladder. Uropathogenic E. coli produce alpha- and beta-hemolysins, which cause lysis of urinary tract cells.

Neonatal meningitis

It is produced by a serotype of Escherichia coli that contains a capsular antigen called K1. The colonisation of the newborn's intestines with these stems, that are present in the mother's vagina, lead to bacteraemia, which leads to meningitis. And because of the absence of the IgM antibodies from the mother (these do not cross the placenta because FcRn only mediates the transfer of IgG), plus the fact that the body recognises as self the K1 antigen, as it resembles the cerebral glicopeptides, this leads to a severe meningitis in the neonates.

COLONY MORPHOLOGY

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GRAM-NEGATIVE RODS
MOTILE
NONSPOREFORMING
CATALASE: POSITIVE
OXIDASE: NEGATIVE
FACULTATIVELY ANAEROBIC

BASIC TESTS FOR IDENTIFICATION

MacConkey growth+
Indole production+
Methyl red+
Voges-Proskauer-
Citrate(Simmons)-
Hydrogen sulfide(TSI)-
Urea hydrolysis-
Lysine decarboxylase+
Arginine dihydrolased
Ornithine decarboxylaseD
Motility (36 °C)+
D-glucose acid/gas+/+
D-mannitol fermentation+
Sucrose fermentationD
Lactose fermentation+
D-sorbitol fermentation+
Cellobiose-
Esculin hydrolisis-
Acetate utilizationD
ONPG test+
 
+ positive ( > 90% of strains are positive)
D most positive (51 - 89%)
d most negative (11 - 50%)
- negative (0 - 10%)
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Should be always guided by
in vitro susceptibility
tests!!

Selection of appropriate antibiotics depends on diagnosis!!

IF SUSCEPTIBLE:

Cephalosporins I, II, III (e.g., ceftriaxone)
Ampicillin(AMP)
Aminoglycosides
Nitrofurantoin
Trimethoprim-sulfamethoxazole
Doxycycline

ALTERNATIVES:

Quinolones (e.g., norfloxacin, ofloxacin, ciprofloxacin)
Imipenem
Meropenem
AMP + GEN

list of anntibiotics escherichia coli
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