Tuesday, August 23, 2011

Escherichia coli

E. coli as a typical member of Enterobacteriacae from rod-shaped cell 2-6 µ in length and 1.1 – 1.5 µ in width with rounded ends (Castellani and Chalmers, 1919).

E. coli, the most common member of the family Enterobacteriaceae implicated in human infectious diseases, has not been spared acquisition of antibiotic resistance causing a complex therapeutic problem (Chaibi et al., 1999).

Most strains of E. coli can grow on simple laboratory media containing glucose as asole source of carbon. The optimum growth temperature range is 18-44°C. Most strains recovered in the lab, ferment lactose thus grow as smooth pink colonies on MacConkey,s agar. They grow as yellow colonies on cystine-lactose electrolyte-deficient agar (CLED), and xylose-lysine deoxycholate (XLD) which are useful media for routine culture of urine and feces respectively (Crichton, 1996).

Escherichia coli is the most common organism present (80%) in UTI, although other enteric organisms such as Klebsiella sp. and enterococci, as well as staphylococci, have been identified Lerner, (1994). This organism is pathogen causing urinary tract infections, pneumonia, meningitis and
septicemia. Recent studies have demonstrated that certain strains of E. coli the major facultative inhabitant of the large intestine and are unique among normal flora organisms in that, it is also the most commonly isolated human
are also important intestinal pathogens causing a wide variety of gastrointestinal disease (Joklik et al., 1988).

High precentage of nosocomially isolated E.coli are rasistant to antibiotics, which is due to production of ESBLs Hanberger et al. (2001).
An increasing prevalence of extended-spectrum β-lactam-resistant E. coli, from 2.5% in 1993 to 6.7% in 1997, was also observed. Compared with the
average data from a hospital wide surveillance, the frequencies of extended-
spectrum beta-lactam resistant K. pneumoniae and E. coli isolates in a pediatric ward were found to be three to five times higher than other wards (Siu et al., 1999).

Escherichia coli is among the common bacterial enteric pathogens capable of causing intestinal disease. Several classes of diarrhea-causing E. coli are now recognized on the basis of production of virulence factors Echeverria et al. (1989). These bacteria include strains of Entero-aggregative E.coli (EaggEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC) also referred to as shiga toxin producing E. coli (STEC) and entero-adherent E. coli (Pollard et al., 1990).
Entero-aggregative E.coli (EaggEC), characteristically enhance mucus secretions by the mucosa, with trapping of the bacteria in a bacterium- mucus biofilm Tzipori et al. (1992), and volunteers fed EAEC develop a diarrhea predominately mucoid in character (Nataro, 2001).

Enteroinvasive strains of E.coli (EIEC) are strains produce dysentry with direct penetration, invasion, and destruction of the intestinal mucosa. This diarrheal illness is very similar to that produced by Shigella. The EIEC infections seem to occur in adults and children alike (Mahon and Manuselis 2000).

Enteropathogenic E. coli (EPEC) is a major cause of infants' diarrhea in developing countries. Numerous studies have been founds EPEC to be more frequently isolated from infants with diarrhea than from matched healthy controls (Donnenberg 1995).

Several studies have shown that breast feeding is protective against diarrhea due to EPEC (Camara et al., 1994).

Enterohemorrhagic E. coli (EHEC) typically cause an afehrile bloody colitis and in about 10% of patients this infection may be follwed by haemoltic uraemic syndrome (HUS) (Pradel et al., 2000).

E. coli O157:H7 rapidly ferments lactose and is indistinguishable from most other E. coli on traditional lactose-containing media. However, unlike
approximately 80% of other E. coli, nearly all isolates of E. coli O157:H7 ferment D-sorbitol slowly, or not at all. Sorbitol-Mac Conkey (SMAC) agar was developed to take advantage of this characteristic by substituting the carbohydrate sorbitol for lactose in MacConkey agar and is the medium of choice for isolation of E. coli O157:H7

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