EVALUATION OF THE ENRICHMENT BROTH CULTURES IN THE ISOLATION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS

The detection of the methicillin-resistant Staphylococcus aureus (MRSA) carriers and the establishment of isolation precautions are of crucial importance to prevent the development of nosocomial infections due to MRSA. Previous studies have demonstrated that the use of enrichment broths increased the rate of MRSA isolation both in clinical samples and surveillance cultures. The aim of this study was to evaluate the MRSA isolation results obtained by inoculation of surveillance cultures in enrichment broth, for the patients staying in intensive care unit of our hospital during September 2006-January 2007 period. A total of 1536 samples (deep tracheal aspirate, nose, throat, pus, inguinal and axial swabs) from 250 patients were inoculated on routine primary media including sheep blood agar, EMB agar and 6 mu g/ml oxacillin containing Mueller-Hinton agar (Ox-MH Agar) and also in an enrichment broth (EB) containing 6.5% NaCl in brain-heart infusion. After incubation for 24 and 48 hours, primary plates were examined for MRSA growth and enrichment broths were examined for turbidity. Turbid tubes were subcultured on Ox-MH agar. Tubes with no turbidity after 48 hours were discarded as negative; MRSA growth in both primary plates and in EBs were evaluated as "parallel growth". Parallel MRSA growth was detected in 15.2% (234/1536), MRSA growth only in EB was detected in 5.9% (91/1536) and MRSA growth only on primary plates was detected in 0.26% (4/1536) of the samples. Among the 71 patients in whom the first MRSA isolation was detected, 19 (27%) yielded MRSA only in EB, 44 (62%) exhibited parallel growth and 8 (11%) yielded MRSA either in EB or as parallel growth of different samples of the same patient. The use of the EB increased MRSA isolation 5.9% (91/1536) on specimen basis and 7.6% (19/250) on patient basis. It can be concluded that, inoculation of surveillance culture samples into an enrichment broth in addition to primary plate media aids to the early isolation of MRSA from colonized patients.