Gene transfer and the evolution of penicillin resistance: PBPs and non-PBP genes in laboratory mutants and clinical isolates in Streptococcus pneumoniae

• Applicant: Professorin Dr. Regine Hakenbeck
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
• Term: from 2008 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 73111189

Multiple players are involved in the development of beta-lactam resistance in Streptococcus pneumoniae. Most importanta are the target enzymes of these antibiotics, the penicillin-binding proteins (PBPs). Alterations in at least three PBPs are required to achieve high resistance level. In particular clinical isolates MurM is also altered, conferring resistance in the presence of PBPs. PBPs are the main transpeptidases responsible for crosslinkage of the peptidoglycan subunits, and MurM modifies these subunits and contributes to the synthesis of interpeptide bridges. In resistant laboratory mutants, the two component system CiaRH is activated via mutations in the histidine protein kinase CiaH. We have recently shown that the cell wall associated serine protease/chaperone HtrA which is part of the Cia regulon targets GFP-BP2x derivatives. Moreover, the biosynthesis of the major glycolipid in pneumococci is affected by mutations in the glycosyltransferase CpoA. All these components are important for cell growth and division, and several of them have been shown to localize to septal sites such as PBP2x, PBP1a, HtrA and as will be shown here also CiaH.The current proposal is related to the interplay of these components during the development of beta-lactam resistance. One part concerns mutations that occurred during transformation of S. pneumoniae using DNA of high level resistant commensal species. In a second series of experiments, the contribution of genes known to be involved in the resistance phenotype is analyzed in one partFP-icular resistant clone of S. pneumoniae Hungary19A-6. In this clone, murM and ciaH are altered in addition to three PBPs. Finally experiments concerning the localization of PBP2x using GFP-fusion proteins are described, including quality control of PBP2x mutants by the cell wall protease HtrA.

• DFG Programme: Research Grants