Inactivation of mrcA gene derepresses the basal-level expression of L1 and L2 beta-lactamases in Stenotrophomonas maltophilia.

摘要

OBJECTIVES: To characterize the relationship between inactivation of the mrcA gene and beta-lactamase expression and beta-lactams resistance in Stenotrophomonas maltophilia KJ and to investigate the involvement of ampR, ampN-ampG, ampD(I) and creBC in this. METHODS: The mrcA deletion mutant KJDeltamrcA was constructed to investigate the role of this putative penicillin-binding protein 1a (PBP1a) in beta-lactamase expression and beta-lactam resistance. The DeltaampR, DeltaampNG, DeltaampDI and DeltacreBC alleles were introduced into KJDeltamrcA, and KJDeltaDIDeltaBC and KJDeltaDIDeltamrcADeltaBC were also constructed for comparison. All the mutants and their corresponding parent strains were assayed for beta-lactamase activities and MICs of beta-lactams. RESULTS: Inactivation of mrcA caused basal L1/L2 beta-lactamase production to increase by approximately 100-fold, but made little difference to cefuroxime-induced beta-lactamase activity and the MICs of beta-lactams. The DeltamrcA-derived basal beta-lactamase hyperproduction was ampR and ampN-ampG dependent. Simultaneous inactivation of ampD(I) and mrcA did not augment beta-lactamase production over and above that seen in an ampD(I) mutant alone. Furthermore, we could find no evidence for a role of the creBC two-component regulatory system in beta-lactamase hyperproduction in a DeltaampD(I) or DeltamrcA background. CONCLUSIONS: Inactivation of mrcA, predicted to encode PBP1a, causes basal L1/L2 beta-lactamase hyperproduction in S. maltophilia.