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factor in selecting resistant microorganisms. The microorganisms are responding to
the normal pressures but these pressures have increased with the misuse of
antibiotics (Johnson, 2001).
4.3 DESCRIPTION OF MICROORGANISMS
4.3.1 Bacillus subtilis
Bacillus subtilis, which is one of the food-poisoning bacteria, is a Gram-positive,
facultative, aerobic, sporulating bacillus normally found in soil. One of the earliest
bacteria to be described was Vibrio subtilis. In 1872 the organism was renamed
Bacillus subtilis by Gordon. This organism is a charter member of a large and
diverse genus which is part of the family Bacillaceae. This family’s distinguishing
feature is the production of endospores, which are round, oval or cylindrical, highly
refractile structures formed within bacterial cells. The spores were first described by
Cohn in Bacillus subtilis and later by Koch in the pathogens. Bacteriophages that
infect bacillus are common in soil. The most extensively studied Bacillus phages are
those associated with Bacillus subtilis and can grow in minimal-salt-bacterial media
with glucose as a carbon source (Aymerich et al., 1986). Bacillus subtilis is normally
considered as being non-pathogenic; but it has been linked to food-borne illnesses,
causing diarrhoea, nausea, vomiting, and associated with rice dishes served in
oriental restaurants, infection is self-limiting (Willey et al. 2008). Bacillus subtilis
produces proteolitic enzyme, subtilism, which is an extracellularenzyme that
catalyzes the breakdown of proteins into polypeptides, resembles trypsin in its
action, and has been shown to be a potent occupational allergen (Willey et al.,
2008).
4.3.2 Escherichia coli
Escherichia coli are Gram-negative, non-sporulating, rodlike, facultative, aerobes
which are usually found in the gastro-intestinal tracts of warm blooded organisms.
Escherichia coli contain different types of pilus and are found in virtually every genus
of Gram-negative bacteria. No matter where pili are encountered, they are usually
assumed to confer some form of attachment capability upon the bacteria possessing
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