Evaluation of a new selective medium for methicillin-resistant Staphyloccocus aureus

The aims of this study were to evaluate the performance of anew medium, des ferrioxamine oxacillin tellurite egg-yolk mannitol salt agar (DOTEMSA) in d etecting methicillin-resistant Staphylococcus aureus (MRSA) and then to com pare this medium against the Public Health Laboratory Service (PHLS) recomm endation of mannitol salt agar (Oxoid) with oxacillin (OMSA) and Baird-Park er medium with ciprofloxacin (BPC) for the isolation of MRSA, The individua l selective agents contained in DOTEMSA were tested against isolates of coa gulase-negative staphylococci (CNS) and the medium with all constituents wa s challenged with various bacteria. Routine screening specimens were plated out on OMSA, BPC and DOTEMSA and the plates were incubated and examined at 24 and 48 h, Tellurite, desferrioxamine and oxacillin each inhibited the m ajority of CNS isolates; only three (of 103) grew in the presence of all th ree agents. Sixty-two of 63 isolates of MRSA grew on DOTEMSA and 59 produce d lipase, Most other bacteria mere inhibited, In all, 184 MRSA isolates wer e isolated from 540 screening specimens. The sensitivity of OMSA, BPC and D OTEMSA was 42%, 81% and 51% at 24 h, and 60%, 89% and 89% at 48 h, At 48 h, the combination of BPC and DOTEMSA detected 99% of MRSA isolates. Seventy, 49 and one non-MRSA isolates needed investigation for each of the three me dia respectively, A proposed strategy for MRSA screening would use BPC and DOTEMSA, examining BPC at 24 h and both media at 48 h, Provisional reports could then be issued at 24 h on the basis of rapid agglutination tests to c onfirm isolates as S, aureus from BPC and at 48 h on the basis of typical c olonies from DOTEMSA.