ROSATO AE; Interscience Conference on Antimicrobial Agents and Chemotherapy.
Abstr Intersci Conf Antimicrob Agents Chemother Intersci Conf Antimicrob Agents Chemother. 1999 Sep 26-29; 39: 125 (abstract no. 1438).
Med. Coll. of Virginia, VCU, Richmond, VA.
Methicillin resistance in staphylococci is mediated by mecA which codes for the low affinity penicillin binding protein 2a (PBP2a) with low affinity for beta-lactam antibiotics. mecA transcription its regulated by its repressor and signal transducer, mecI and mecRI, respectively. Expression of mec encoded methicillin resistant is often heterogeneous. In these isolates the majority of the bacterial population expresses resistance at a low level upon exposure to beta-lactam antibiotics, a highly resistant population is selected. We grew S. aureus and S. epidermidis isolates with heterotypic resistance expression in broth containing oxacillin. Conversion to homotypic resistance occurred 6-12 hs following exposure to concentrations of oxacillin (0.4-1.0microg/ml) that induce a lag in growth. No other antibacterial agent and no change in growth conditions caused the conversion to homotypic resistance; it was beta-lactam specific. We also confirmed previous observations that conversion to homotypic expression did not require on increase in mecA transcription and that the conversion was due to selection of mutation(s) rather than induction of regulatory pathways. Finally, we looked for changes in the transcription of some genes involved in peptidoglycan synthesis or stress response by Northern Blot analysis. There was an increase in femAB and femC, but not change in femD, PBP1, 2 and 4 or SigB transcription. The increase in femAB expression following the heterotypic to homotypic conversion was not associated with mutations in DNA sequence suggesting involvement of regulator(s).
Publication Types:
Keywords:
- Anti-Bacterial Agents
- Methicillin Resistance
- Oxacillin
- Penicillin-Binding Proteins
- Phenotype
- Staphylococcus
- Transcription, Genetic
- genetics
Other ID:
UI: 102244889
From Meeting Abstracts