title: Effects of subinhibitory concentrations of antibiotics on virulence factor expression by community-acquired methicillin-resistant Staphylococcus aureus.
abstract: OBJECTIVE
  To examine the effect of subinhibitory concentrations (sub-MICs) of antistaphylococcal drugs on Panton-Valentine leucocidin (PVL), α-haemolysin (Hla) and protein A (SpA) expression by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA).
  
  
  METHODS
  Five clinical isolates representing the main worldwide CA-MRSA clones were grown with sub-MICs (1/8, 1/4 and 1/2 MIC) of five antibiotics (clindamycin, daptomycin, linezolid, tigecycline and vancomycin). After 4 and 6 h of incubation, culture pellets were used for relative quantitative RT-PCR with primers specific for pvl, hla, spa and gyrB. The PVL, Hla and SpA concentrations were measured in the supernatant (for PVL and Hla) and in the cell pellet (for SpA) using specific ELISAs.
  
  
  RESULTS
  For all strains tested, clindamycin and linezolid dramatically reduced mRNA levels of PVL and SpA. Tigecycline also decreased the PVL and SpA mRNA levels of 3/5 and 4/5 strains tested, respectively, whereas daptomycin and vancomycin had no significant effect. PVL and SpA quantification confirmed the concentration-dependent inhibition of PVL and SpA production by clindamycin and, to a lesser extent, by linezolid and tigecycline. Only clindamycin decreased Hla mRNA expression, whereas linezolid, tigecycline and daptomycin showed heterogeneous strain-dependent results, and vancomycin had no significant effect. Analysis of the Hla level revealed a stronger concentration-dependent inhibition of Hla release by clindamycin than by linezolid.
  
  
  CONCLUSIONS
  The effect of sub-MICs on virulence expression depended on the antibiotic and the virulence factor. Clindamycin and linezolid consistently suppressed the expression of different virulence factors by CA-MRSA, whereas tigecycline specifically suppressed PVL expression. Daptomycin and vancomycin seem to have no significant effects at these concentrations.
authors.affiliation: Centre National de Référence des Staphylocoques, Faculté de Médecine Lyon Est, Université de Lyon, Lyon F-69008, France.
authors.forename: Marie Pierre
authors.initials: MP
authors.lastname: Otto
authors.forename: Emilie
authors.initials: E
authors.lastname: Martin
authors.forename: Cedric
authors.initials: C
authors.lastname: Badiou
authors.forename: Segolene
authors.initials: S
authors.lastname: Lebrun
authors.forename: Michele
authors.initials: M
authors.lastname: Bes
authors.forename: François
authors.initials: F
authors.lastname: Vandenesch
authors.forename: Jerome
authors.initials: J
authors.lastname: Etienne
authors.forename: Gerard
authors.initials: G
authors.lastname: Lina
authors.forename: Oana
authors.initials: O
authors.lastname: Dumitrescu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000096:biosynthesis; D017714:Community-Acquired Infections / Q000382:microbiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005098:Exotoxins / Q000096:biosynthesis; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006460:Hemolysin Proteins / Q000096:biosynthesis; D006801:Humans; D007956:Leukocidins / Q000096:biosynthesis; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D060888:Real-Time Polymerase Chain Reaction; D013203:Staphylococcal Infections / Q000382:microbiology*; D013205:Staphylococcal Protein A / Q000096:biosynthesis; D037521:Virulence Factors / Q000096:biosynthesis*
chemical_list: D000900:Anti-Bacterial Agents; D001427:Bacterial Toxins; D005098:Exotoxins; D006460:Hemolysin Proteins; D007956:Leukocidins; C078284:Panton-Valentine leukocidin; D013205:Staphylococcal Protein A; D037521:Virulence Factors; C021091:staphylococcal alpha-toxin
keywords: PVL; leucocidin; protein A; α-haemolysin