The incidence of methicillin resistant S. aureus strains in clinical specimens in relation to their beta-lactamase producing and multiple-drug resistance properties in Addis Abeba.

From December 1987 to July 1988, a total of 17,142 clinical specimens were examined at the National Research Institute of Health (NRIH), Addis Abeba, to determine the incidence of methicillin resistant S. aureus (MRSA) strains. Coagulase positive Staphylococcus spp. were isolated from 355 specimens. Two hundred and forty-nine 249 (70%) isolates were tested for methicillin resistance by minimum inhibition concentration method (MIC) of which 76 (30.5%) were found to be MRSA and 173 (69.5%) were methicillin sensitive S. aureus (MSSA) strains. The presence of beta-lactamase production was determined in the 355 S. aureus isolates using the rapid Iodometric and Nitrocefin methods and 252 (71%) isolates were found to be beta-lactamase procedures. Furthermore, 47 (62%) of the 76 MRSA isolates and 140 (81%) of the 173 MSSA isolates were beta-lactamase positive strains. The sensitivity pattern of all the S. aureus isolates against 11 common drugs indicated that the majority (80%) of the MRSA strains were multipledrug resistant while 4 (8%) were not resistant to any of the drugs tested. Among the antibiotics, vancomysin and clindamycin were effective against all S. aureus isolates. It was also found that 41 (54%) of the MRSA strains were both betalactamase producers and multiple-drug resistant isolates; of the latter, 36 (87.8%), strains were isolated from pus specimens of patients with post-operative wound infections. The results of this study show that MRSA strains are quite prevalent among specimens referred to the NRIH.