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Antimicrob. Agents Chemother. doi:10.1128/AAC.01127-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Promoter and Transcription Analysis of Penicillin-Binding Protein Genes in Streptococcus gordonii

Department of Fundamental Microbiology, University of Lausanne, Switzerland

^* To whom correspondence should be addressed. Email: philippe.moreillon{at}unil.ch.

	Abstract

An optimally crosslinked peptidoglycan requires both transglycosylation and transpeptidation, provided by class A and class B penicillin-binding proteins (PBPs). Streptococcus gordonii possesses three class A (PBP 1A, 1B and 2A) and two class B PBPs (PBP 2B and 2X), that were important for penicillin-resistance. High-level resistance (MIC, 2 µg/ml) required mutations in class B PBPs. However, although unmutated, class A PBPs were critical to facilitate resistance development (Haenni, M., and P. Moreillon. 2006. Antimicrob Agents Chemother 50:4053-4061). Thus, their over-expression might be important to sustain the drug. Here, we determined the promoter regions of the S. gordonii PBPs and compared them to those of other streptococci. The extended -10 box was highly conserved and complied with a ^A-type promoter consensus sequence. In contrast, the -35 box was poorly conserved, leaving the possibility of differential PBP regulation. Gene expression was monitored in a penicillin-susceptible parent (MIC, 0.008 µg/ml) and a high-level resistant mutant (MIC, 2 µg/ml) using luciferase fusions. In the absence of penicillin, all PBPs were constitutively expressed, but their expression was globally increased (1.5-2x) in the resistant mutant. In the presence of penicillin, class A PBPs were specifically over-expressed both in the parent (PBP 2A) and in the resistant mutant (PBP 1A and 2A). By increasing transglycosylation, class A PBPs could promote peptidoglycan stability when transpeptidase is inhibited by penicillin. Since penicillin-related induction of class A PBPs occurred in both susceptible and resistant cells, such mutation-independent facilitating mechanism could be operative at each step of resistance development.

This article has been cited by other articles:

• Haenni, M., Moreillon, P. (2008). Fitness Cost and Impaired Survival in Penicillin-Resistant Streptococcus gordonii Isolates Selected in the Laboratory. Antimicrob. Agents Chemother. 52: 337-339 [Abstract] [Full Text]