CLONING AND CHARACTERIZATION OF THE FMT GENE WHICH AFFECTS THE METHICILLIN RESISTANCE LEVEL AND AUTOLYSIS IN THE PRESENCE OF TRITON X-100 IN METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

In methicillin-resistant Staphylococcus aureus (MRSA) strains, Triton X-100 reduced the oxacillin resistance level, although the degree of r eduction varied from strain to strain. To study the responses of MRSA strains to Triton X-100, we isolated a Tn551 insertion mutant of the C OL strain that became more susceptible to oxacillin in the presence of 0.02% Triton X-100. The Tn551 insertion of the mutant was transduced back to the parent strain, other MRSA strains (strains KSA8 and NCTC 1 0443), and methicillin-susceptible strain RN450. All transductants of MRSA strains had reduced levels of resistance to oxacillin in the pres ence of 0.02% Triton X-100, while those of RN450 did not. Tn551 mutant s of KSA8 and NCTC 10443 also had reduced levels of resistance in the absence of 0.02% Triton X-100. The autolysis rates of the transductant s in the presence of 0.02% Triton X-100 were significantly increased. Amino acid analysis of peptidoglycan and testing of heat-inactivated c ells for their susceptibilities to several bacteriolytic enzymes showe d that there were no significant differences between the parents and t he respective Tn551 mutants. The Tn551 insertion site mapped at a loca tion different from the previously identified fem and llm sites. Cloni ng and sequencing showed that Tn551 had inserted at the C-terminal reg ion of a novel gene designated fmt. The putative Fmt protein showed a hydropathy pattern similar to that of S. aureus penicillin-binding pro teins and contained two of the three conserved motifs shared by penici llin-binding proteins and beta-lactamases, suggesting that fmt may be involved in cell wall synthesis.