title: Identification and phenotypic characterization of a beta-lactam-dependent, methicillin-resistant Staphylococcus aureus strain.
abstract: Methicillin resistance in Staphylococcus aureus is primarily mediated by the acquired penicillin-binding protein PBP 2a, which is encoded by mecA. PBP 2a acts together with native PBP 2 to mediate oxacillin resistance by contributing complementary transpeptidase and transglycosylase activities, respectively. In this study, we have investigated a phenotype of beta-lactam dependence in a clinical methicillin-resistant S. aureus strain (strain 2884D) obtained by in vitro selection with ceftobiprole. 28884D, which grew very poorly in blood agar, required the presence of the beta-lactam antibiotics to grow. On the basis of this observation, we hypothesized that a gene or genes essential for growth were dependent on oxacillin induction. Identification and analysis of genes regulated by oxacillin were performed by both real-time reverse transcription-PCR and spotted microarray analysis. We found that mecA was constitutively expressed in strain 2884D and that the constitutive expression resulted from perturbations in the two systems involved in its regulation, i.e., MecI/MecR1 (staphylococcal chromosome cassette mec type I) and BlaI/BlaR1 (nonfunctional penicillinase operon). PBP 2 appeared to be poorly induced by oxacillin in 2884D. Further analysis of the PBP 2 two-component VraSR regulatory system showed that it was nonfunctional, accounting for the lack of response to oxacillin. Together, these results support the notion that limited PBP 2 availability may have led 2884D to become dependent on oxacillin-mediated mecA induction as a required survival mechanism.
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors.forename: Fred
authors.initials: F
authors.lastname: Goldstein
authors.forename: Jiri
authors.initials: J
authors.lastname: Perutka
authors.forename: Arabela
authors.initials: A
authors.lastname: Cuirolo
authors.forename: Konrad
authors.initials: K
authors.lastname: Plata
authors.forename: Diego
authors.initials: D
authors.lastname: Faccone
authors.forename: Joanne
authors.initials: J
authors.lastname: Morris
authors.forename: Aude
authors.initials: A
authors.lastname: Sournia
authors.forename: Marie Dominique
authors.initials: MD
authors.lastname: Kitzis
authors.forename: Aicha
authors.initials: A
authors.lastname: Ly
authors.forename: Gordon
authors.initials: G
authors.lastname: Archer
authors.forename: Adriana E
authors.initials: AE
authors.lastname: Rosato
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D002511:Cephalosporins / Q000494:pharmacology; D002876:Chromosomes, Bacterial; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D004268:DNA-Binding Proteins; D016521:Electrophoresis, Gel, Pulsed-Field; D015964:Gene Expression Regulation, Bacterial; D016106:Methicillin Resistance / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D014158:Transcription, Genetic; D047090:beta-Lactams / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C478170:VraR protein, Staphylococcus aureus; C478169:VraS protein, Staphylococcus aureus; D047090:beta-Lactams; C443755:ceftobiprole