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them. It should be noted, however, that while this assumption is useful in certain
circumstances, it is not strictly valid. Many bacteria which possess medical
importance have been examined for the presence of pili; but only in relatively few
cases has the importance of these structures in pathogenesis been rigorously
established. Pili associated with Escherichia coli are classified by their morphology
under electron microscopic examination and by their binding properties, e.g., type 1
pili of Escherichia coli are rigid-appearing organelles which are seven nanometers
wide and one to two micrometers long.
Certain types of pili have long been associated with the utero-toxigenic strain of
Escherichia coli which causes diarrhoea in humans. The most common cause of
urinary tract infection in humans is Escherichia coli. The isolates are nearly always
type-1, piliated and most often, pap-piliated. Escherichia coli causes at least five
types of gastro-intestinal diseases in humans. Pathogenicity is generally due to the
presence of one or more virulence factors, including invasiveness factors, heat-lable
and heat-stable enterotoxins, verotoxins and colonization factors or adhesins.
Pathogenic strains are usually identified by detection of specific virulence factors or
of a serotype associated with a virulence factor (Willey et al. 2008).
The most recently identified Escherichia coli disease is hemorrhagic colitis, caused
by strains of serotype 0157:H7 and a few other serotypes. This disease,
characterized by painful abdominal cramping and bloody diarrhoea, is caused by
strains that produce verotoxin and some strains associated with haemolytic uremic
syndrome. Escherichia coli is an emerging cause of a food-borne infection which
leads to bloody diarrhoea and occasionally to kidney failure. Most cases of the
illness have been associated with eating under-cooked, contaminated, ground beef.
Person-to-person contact in families and childcare centers is also an important mode
of transmission if hygiene is inadequate.
Escherichia coli infection can also occur after drinking raw milk and after swimming
in or drinking contaminated water. The organisms live in the intestines of healthy
cattle, so preventive measures on cattle farms and during meat processing are
necessary. Meat can be contaminated during slaughter; but the microorganism can
also be thoroughly mixed into beef when it is being ground, while the bacteria
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