LACK OF MECA TRANSCRIPTION IN SLIME-NEGATIVE PHASE VARIANTS OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-EPIDERMIDIS

Five phase variants (PV1 to PV5) of the well-characterized, slime prod ucing, methicillin-resistant, pathogenic strain of Staphylococcus epid ermidis sensu strictu RP62A (ATCC 35984) were isolated by the Congo re d agar method. In comparison with the parent strain, the phase variant s showed a different colonial morphology on Congo red agar, a strongly reduced adherence capacity, and decreased levels of resistance to met hicillin, oxcillin, and penicillin. All phase variants yielded biochem ical reaction patterns and profiles in pulsed-field gel electrophoresi s identical to those of parent strain RP62A, indicating a common origi n. All phase variants proved to have the capacity to shift back to the original phenotype of parent strain RP62A. A search for the resistanc e mechanisms of strain RP62A revealed beta-lactamase production and th e presence of mecA in PV1 to PV5 as well as parent strain RP62A. In No rthern blots of total staphylococcal RNA, the phase variants showed no detectable mecA-specific transcription product, whereas parent strain RP62A revealed a strong signal, indicating that mecA transcription is not the mechanism responsible for the decreased methicillin resistanc e phenotype of phase variants PV1 to PVS.