Promoter and transcription analysis of penicillin-binding protein genes in Streptococcus gordonii.
An optimally cross-linked peptidoglycan requires both transglycosylation and transpeptidation, provided by class A and class B penicillin-binding proteins (PBPs). Streptococcus gordonii possesses three class A PBPs (PBPs 1A, 1B, and 2A) and two class B PBPs (PBPs 2B and 2X) that are important for penicillin resistance. High-level resistance (MIC, > or =2 microg/ml) requires mutations in class B PBPs. However, although unmutated, class A PBPs are critical to facilitate resistance development (M. Haenni and P. Moreillon, Antimicrob. Agents Chemother. 50:4053-4061, 2006). Thus, their overexpression 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 sigma(A)-type promoter consensus sequence. In contrast, the -35 box was poorly conserved, leaving the possibility of differential PBP regulation. Gene expression in a penicillin-susceptible parent (MIC, 0.008 microg/ml) and a high-level-resistant mutant (MIC, 2 microg/ml) was monitored using luciferase fusions. In the absence of penicillin, all PBPs were constitutively expressed, but their expression was globally increased (1.5 to 2 times) in the resistant mutant. In the presence of penicillin, class A PBPs were specifically overexpressed both in the parent (PBP 2A) and in the resistant mutant (PBPs 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 a mutation-independent facilitating mechanism could be operative at each step of resistance development.
Haenni
Marisa
M
Department of Fundamental Microbiology, Quartier UNIL-Sorge, Biophore Building, Lausanne, Switzerland.
Moreillon
Philippe
P
Lazarevic
Vladimir
V
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D046915:Penicillin-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010406:Penicillins / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D013291:Streptococcus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D000900:Anti-Bacterial Agents; D046915:Penicillin-Binding Proteins; D010406:Penicillins