Colibacillinum Anhang = Escherichia coli
Escherichia coli, while part of the normal gastro-intestinal tract
flora, may become a major cause of watery, inflammatory, or bloody diarrhoea.
Urinary tract, hepatobiliary, peritoneal, cutaneous,
and pulmonary infections also occur. This organism is also an
opportunistic pathogen, causing disease in patients who have defects in host
resistance because of other disease or who have received
treatment with corticosteroids, radiation, antineoplastic drugs or
antibiotics. (Beers et al., 1999: 1158.)
[Jonathan Reuben Rai Invernizzi]
2.4.1.1 Classification
l.~.coli falls under the family Enterobacteriaceae, which form a large
group of Gramnegative rods whose natural habitat is the intestinal tract of
humans and animals (Jawetz, el aI., 1991:204).
In the genus Escherichia to which it belongs, it is the only species of
medical importance (Mims, el al., 1998: 523).
2.4.1.2 Morphology and identification
E. coli are short, motile, Gram-negative, non-spare-forming bacilli that
can grow both aerobically and anaerobically on laboratory media (Mackie and
Mcf'artney, ]996:361).
E. coli grows well on non-selective media, fanning smooth, colourless,
circular colonies 2-3mm in diameter after 18 hours incubation on nutrient agar,
and larger red colonies when grown on MacConkey agar. They are able to grow
over a large temperature range (15 - 45°C), with some strains being able to
survive temperatures of up to 60° C for] 5 minutes, or 55°C for 60 minutes.
(Greenwood, Slack and Peutherer, 1992:323.) Optimal growth temperature for E.
coli is 36 - 37°C (Mackie and McCartney, 1996:36]).
2.4.1.3 Epidemiology
E. coli is a member of the normal intestinal flora generally not causing
disease, and often contributing to the normal function and nutrition of the
intestine (Jawetz, el al., 1991:215).
2.4.1.4 E. coli infections
E. coli usually only becomes pathogenic when it reaches areas outside of
the intestines, such as the urinary tract, billiary tract, lungs, meninges,
blood stream, bone or other anatomical sites.
This bacteria is most often an opportunistic pathogen with infections
most often arising in infancy, old age, during terminal stages of other
disease, or during periods of immunosuppression.
With severe infections, it may reach the blood stream causing sepsis.
f,;. coli may possess lipopolysaccharidal endotoxins in their cell
walls. They may also sometimes produce exotoxins of clinical importance.
(Jawetz, et aI., 1991 :215-216.)
Four pathogenic groups of E. coli are known to be responsible for
diarrhoeal disease:
• Enterotoxigenic E. coli (ETEC). Known to produce acute watery
diarrhoea, which may lead to severe and possibly fatal dehydration (infants and
small children). This type also is responsible
for what is known as travellers diarrhoea (turista).
e Enteroinvasive E. coli (EIEC). This type produces dysentery that is
clinically indistinguishable from shigellosis. Blood, pus and mucous are often
present in the faeces of infected individuals.
e Enteropathogenic E. coli (EPEC).
This type is mainly associated
with outbreaks of infantile diarrhoea.
o Vero cytotoxin-producing E. coli (VTEC). This type is also termed
"enterohaemorrhagic" E. coli. This type is characterised by a mild to
bloody diarrhoea that may precede a severe haemorrhagic colitis or
haemolyticuraemic syndrome. Two different types of Vero cytotoxins produced by
the bacteria are responsible for the condition. (Mackie and McCartney,
1996:366.)
2.4.1.5 Anti-microbial sensitivity
Anti-microbials used to treat E. coli infections include all those that
have action against Gram-negative organisms. These include
pthalysulphathiazole, neomycin, doxycycline, trimethoprim, norf1oxacin, and
other fluoroquinolones. (Greenwood, Slack and Peutherer, 1992:333.) The two
antibiotics most commonly used against E. coli infections are gentamyein and
ciproflocin (Gladwin and Trattler, 2000: 133).
Escherichia coli is a member of the Enterobacteriaceae. It is a
Gram-negative facultative anaerobe. It is found as a member of normal flora in
the gut of humans and it is highly motile.
Morphology and Identification
E. coli are facultative anaerobic, short, straight, gram-negative
bacilli that are non-sporing, usually motile with flagella and occur singly or
in pairs in rapidly growing
liquid cultures (Williams et al., 2004).
E. coli grows well on non-selective media forming circular, convex,
smooth colonies with distinct edges (Jawetz et al., 1991).
E. coli readily ferments glucose, lactose and certain other sugars producing
both acid and gas, a property used in preliminary identification (Pattison et
al., 1995)
E. coli can be easily recovered from samples such as urine, stools,
blood and pus on lactose containing media e.g. MacKonkey agar plate. Colonies
become visible within a day.
Lactose fermentation together with other biochemical tests helps to
differentiate E. coli from other highly gram-negative rods (Howes, 2002).
Clinical Manifestations
Despite the fact that E. coli is a member of the normal flora and is not
highly pathogenic, it is of great medical importance due to the frequency and
sacrity of
infections it causes. The organism is a commensal in the small
intestines, however, because of its presence in stools, it often reaches and
incites disease in other parts
of the body, especially the urinary tract and peritoneum (Myrvik and
Weiser, 1989)
E. coli produce two types of toxins, viz. heat-labile enterotoxin and
heat-stable enterotoxin (Howard et al., 1995), thus causing different types of
clinical symptoms.
Urinary Tract Infection
The normal urinary tract is sterile and resistant to bacterial
colonisation. However, urinary tract infections are the most common bacterial
infection in all age groups (Simon, 2002).
E. coli is the most common cause of urinary tract infections and
accounts for 90% of first urinary tract infections in young women. In
hospitalised patients, E. coli
accounts for 50% of cases (Howes, 2004).
E. coli enters the urinary tract by natural means or may be introduced
via catheters or other instruments. Their persistence in the urinary tract is
favoured by anesthesia,
paralysis by any other agent that interrupts the normal voiding reflex,
or by anatomical abnormalities that permit retention of urine. Although
obstruction alone
does not cause urinary tract infection, its presence does predispose to
infection and makes infection more difficult to eradicate with medical therapy.
Urine is an
excellent culture medium and readily supports the growth of E. coli
(Berkow and Beers, 1999).
Diarrhoeal Diseases
Diarrhoea-causing E. coliare classified into different categories based
on their virulence properties. The
major categories are enteropathogenic (EPEC),
Enterotoxigenic (ETEC), enteroinvasive (EIEC), enteroaggeregative
(EaggEC) (Parry et al., 2002) and enterohaemorragic (EHEC) (Mackie and
McCartney, 1996).
Enteropathogenic (EPEC) is associated with acute outbreaks of diarrhoea
in young children (Parry et al., 2002). Illness results from the bacteria
adhering to the
intestinal wall and subsequent destruction of the microvilli (Centre for
Food Safety and Applied Nutrition, 2003).
Enterotoxigenic (ETEC) is associated with infant diarrhoea in developing
countries and traveller’s diarrhoea. Acute watery diarrhoea, similar to
cholera, is produced by
heat stable or heat labile toxins. It is acquired by consuming
contaminated water or food (Howard et al., 1993).
Enteroinvasive (EIEC) is associated with dysentery-type illness caused
by the invasion of the gut epithelial cells (Parry et al., 2002). Clinically
the illness characterised
by fever, abdominal cramps, malaise, toxaemia and watery diarrhoea
consisting of blood and mucous (Centre for Food Safety and Applied Nutrition,
2003).
Enteroaggregative (EaggEC) is associated with persistent diarrhoea in
people in developing countries (Parry et al., 2002). These bacteria are
emerging as a potential
cause of diarrhoea in patients with AIDS (Berkow and Beers, 1999).
Enterohaemorrhagic (EHEC) is associated with haemorrhagic colitis and haemolytic
uraemic syndrome. It affects the cells lining the gastrointestinal tract and
kidneys
(Parry et al., 2002)
Neonatal Sepsis
Neonatal sepsis can be described as an invasive bacterial infection of
the bloodstream occurring in the first four weeks of life (Berkow and Beers,
2000).
Newborns may be highly susceptible to E. coli sepsis because they lack
IgM antibodies (Jawetz et al., 1989). A newborn may be predisposed to neonatal
sepsis by
obstetric complications, maternal bleeding, toxaemia, precipitous
delivery or maternal infection particularly of the urinary tract or endometrium
(Myrvik and
Weiser, 1989). The symptoms of sepsis are not specific and they vary
from one child to another.
Neonatal Meningitis
Neonatal meningitis is defined as the inflammation of the meninges due
to bacterial invasion in the first four weeks of life (Berkow and Beers, 2000).
Neonatal meningitis most frequently results from pre-existing
bacteraemia associated with neonatal sepsis. Meningitis may also result from
skin lesions of the scalp that,
along with developmental defects, lead to communication of the skin
surface with the subarachnoid space.
Direct extension to the central nervous system from the ear rarely
occurs (Berkow and Beers, 2002). Symptoms of the infection in the newborns are
not very specific
and may include crying, irritability, sleeping more than usual,
lethargy, refusing to take breast milk or bottle milk, low or unstable body
temperature,
jaundice, pallor, breathing problems, rash, vomiting and diarrhoea.
There may also be bulging of the fontanelle. Cranial nerve abnormalities
may also be present (Berkow and Beers, 2000).
Antimicrobial sensitivity
Antimicrobials used to treat E. coli infections include all those that
have action against gram negative organisms. These include
pthalysulphathiazole, neomycin,
doxycycline, trimethoprim, norfloxacin, chloramphenicol and other
fluoroquinolones (Singh, 2004b).
Some strains of E. coli are developed resistance to these antibiotic
agents (Singh, 2004b).