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anging from asymptomatic colonization of the intestinal, urinary or respiratory tract
to fatal septicemia and are widely recognized as important opportunistic pathogens
in humans, especially hospital patients. Infections with Klebsiella are caused mainly
by Klebsiella pneumoniae and Klebsiella oxytoca in a proportion of about two to one.
Capsular types found to be endemic in hospitals are diverse and include K2 and
other K-antigen types above K-6. Features predisposing to nosocomial infection by
Klebsiella pneumoniae or Klebsiella oxytoca are the same as those which dispose
the Enterobacter infections. These include extremes of age, chronic alcoholism,
diabetes mellitus or chronic cardiac, renal, pulmonary or neoplastic disease (Willey
et al. 2008).
Strains of Klebsiella pneumonia and Klebsiella oxytoca which have not acquired any
resistance are determined as naturally resistant to ampicillin and carboxypenicillin
but susceptible to other beta-lactam antibiotics. This is due to the production of a
chromosomal penicillinase which is inhibited by clavulanic acid (Cohen and
Powderly, 2004).
4.3.4 Staphylococcus aureus
Staphylococcus aureus is a Gram-positive, non-sporulating, non-motile, usually non-
capsulate, facultative, aerobic cocci. Staphylococci are widespread in nature
although they are found more consistently in denser populations on the skin, skin
glands and mucous membranes of mammals and birds. These microorganisms are
sometimes found in the pharynx, mouth, blood, mammary glands, intestines, and
upper respiratory tracts of these hosts. The largest populations are found in the
region of the skin supplied with large numbers of sweat glands, and on the skin and
mucous membranes surrounding openings on the body surface.
Staphylococcus is coagulase-positive and is regarded as a potentially serious
pathogen. It is a major cause of mortality and is also responsible for a variety of
infections. The mechanism of staphylococcal pathogenicity is extensively in the
species Staphylococcus aureus. This aggressive and invasive species has at it
disposal a variety of extra-cellular enzymes, toxins and antiphagocytic components
of the cell wall to use against the host. Some principal toxins include the alpha
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