title: Fate of mutation rate depends on agr locus expression during oxacillin-mediated heterogeneous-homogeneous selection in methicillin-resistant Staphylococcus aureus clinical strains.
abstract: Methicillin-resistant Staphylococcus aureus (MRSA) strains are characterized by a heterogeneous expression of resistance. We have previously shown in clinical oxacillin-susceptible, mecA-positive MRSA strains that selection from a very heterogeneous (HeR) to highly homogeneous (HoR) resistant phenotype was mediated by acquisition of mutations through an oxacillin-induced SOS response. In the present study, we used a spotted DNA microarray to evaluate differential gene expression during HeR-HoR selection and found increased expression of the agr two-component regulatory system. We hypothesized that increased expression of agr represents a mechanistically relevant component of this process. We demonstrated that inactivation of agr during the HeR-HoR selection process results in a significant increase in mutation rate; these effects were reversed by complementing the agr mutant. Furthermore, we found that extemporal ectopic expression of agr and, more specifically, RNAII in agr-null mutant HeR cells suppressed mutation frequency and the capacity of these cells to undergo the HeR-HoR selection. These findings sustain the concept that increased expression of agr during HeR-HoR selection plays a critical role in regulating the β-lactam-induced increased mutation rate in very heterogeneous MRSA strains. Moreover, they indicate that a temporally controlled increase in agr expression is required to tightly modulate SOS-mediated mutation rates, which then allows for full expression of oxacillin homogeneous resistance in very heterogeneous clinical MRSA strains.
authors.affiliation: Center for Molecular and Translational Human Infectious Diseases Research, The Methodist Hospital Research Institute, Houston, Texas 77030, USA.
authors.forename: Konrad B
authors.initials: KB
authors.lastname: Plata
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Rosato
authors.forename: Adriana E
authors.initials: AE
authors.lastname: Rosato
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D005816:Genetic Complementation Test; D005838:Genotype; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D010068:Oxacillin / Q000494:pharmacology*; D010957:Plasmids; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D010068:Oxacillin