Biological characteristics of methicillin resistant <em>Staphylococcus aureus</em> strains isolated from hospitals in Colombo

Abstract

This study was done to determine the antibiogram and biological characteristics of Methicillin resistant Staphylococcus aureus (MRSA) clinical isolates, to detect the existence of a multi-resistant strain conforming to an epidemic MRSA strain.Specimens received from some wards of the General Hospital Colombo, and other hospitals in Colombo and from a few out patients, during a fourteen month period, yielded sixty five MRSA strains. These strains were characterized by the following tests: Antibiotic susceptibility tests, coagulase production with human and rabbit plasma, urea hydrolysis at 24 and 48 hours, protein A levels, and pigment production.Forty five MRSA strains were resistant to the same seven antibiotics in addition to methicillin, and were arbitrarily named group A. This was the predominant strain in the surgical units (SU), plastic surgery unit (PSU) and burns unit (BU).Ninety seven percent of MRSA were resistant to at least one aminoglycoside tested. Resistance to fusidic acid (8%), clindamicin (8%) and rifampicin (4.6%) was rare in MRSA's. All MRSA strains tested were sensitive to vancomycin.The multi-resistant strain -group A, differed from the miscellaneous strains (group B) in the following way; they were marginally stronger in the coagulase test than group B, urea hydrolysis was greater at 24 and 48 hours (P=0.0125 and P=0.0165), protein A levels were marginally higher and the strains were more pigmented. Protein A levels were however low in all the MRSA's when compared to the Cowan strain of S. aureus. The multi-resistant, group A strain to some extent showed the biological characteristics of an epidemic strain of MRSA (EMRSA) described in the literature, which have spread among hospitalised patients and caused serious outbreaks of hospital infections. It remains to be seen if this strain too, will be the likely cause of outbreaks of serious hospital infections in Colombo, as has been described elsewhere in the world.