Regine R. Hakenbeck, Germany
University of Kaiserslautern Department of MicrobiologyAuthor Of 1 Presentation
DIFFERENT VIEW ON BETA-LACTAM RESISTANCE IN STREPTOCOCCUS PNEUMONIAE: SERINE PROTEASE HTRA DEGRADES ALTERED PENICILLIN-BINDING PROTEIN 2X (ID 368)
Abstract
Background
Reduced amounts of the essential penicillin-binding protein 2x (PBP2x) were noted in two cefotaxime resistant S. pneumoniae laboratory mutants C405 and C606 derived independently from the sensitive strain R6. These mutants contain two or four mutations, respectively, in the transpeptidase domain of PBP2x. Furthermore, they carry a mutation in ciaH encoding the histidine protein kinase of the two-component system CiaRH, resulting in enhanced CiaR-mediated gene expression.
Methods
To characterize the effect of each of these mutations, beta-galactosidase assays, fluorescence microscopy and depletion studies were performed on mutants and derivatives thereof. Susceptibility to beta-lactam antibiotics was determined by agar dilution method.
Results
The transcription of pbp2x in both mutants is not affected, thus the reduced amount of PBP2x is likely to be due to degradation of the protein. We tested the cell wall associated serine protease HtrA, which is part of the CiaRH regulon, as a potential candidate. Deletion of htrA or introduction of a mutation in the active site of HtrA in C405 and C606 lead to wild type amounts of PBP2x. Depletion studies of the PBP2xC405 variant and localization studies of GFP-PBP2xC405 fusion-protein confirmed that HtrA degrades PBP2x in C405 and C606.
Conclusions
Our results show that HtrA targets altered PBP2x.