Contributions of sigB and sarA to distinct multiple antimicrobial resistance mechanisms of Staphylococcus aureus

Abstract

Multiple antimicrobial resistance in Staphylococcus aureus can result from mutations leading to reduced susceptibility to Pine oil-based cleaners (PS(RS)) as well as following growth with the non-steroidal anti-inflammatory salicylate. We now define the contributions of the alternative sigma factor (sigB) and staphylococcal accessory regulator (sarA) to these mechanisms. We conclude that sarA plays a more prominent role than sigB in overall intrinsic multiple antimicrobial resistance. Both genes have similar effects on intrinsic vancomycin resistance, and the salicylate-inducible mechanism is not sigB- or sarA-dependent. Furthermore, analyses determined that altered expression of sigB and sarA is not responsible for the salicylate-inducible mechanism, and sarA upregulation is associated with the PS(RS) phenotype.

Response of Staphylococcus aureus to Salicylate Challenge

“…This suggests that sarA is upregulated by salicylate induction, which was demonstrated by real-time PCR analysis in our previous study using SH1000 (46). We also demonstrated that sarA is required for the full expression of intrinsic multiple antimicrobial resistance (36) and salicylate-induced reduced susceptibility to multiple anti- a Cip, ciprofloxacin; Sal, 2 mM salicylate; Fus, fusidic acid; PS, Pine-Sol; FI, increase (n-fold) in resistance expression of mgr::cat mutant compared to parent or salicylate-induced increase in resistance level compared to uninduced; FD, salicylate-induced decrease (n-fold) in resistance level compared to uninduced, or decrease in resistance expression of mgr::cat mutant compared to parent; ND, not determined.…”

“…It is therefore of interest that the overexpression of norB leads to increased ethidium resistance (52) and that growth in the presence of salicylate induces ethidium efflux and resistance (43). Since growth of S. aureus in the presence of salicylate reduces susceptibility to fusidic acid (42) and common house cleaners (46) and reduces mgrA expression (this study), we hypothesized that mgrA mutants should demonstrate reduced susceptibility to fusidic acid and a common house cleaner. mgrA::cat mutants of strains Becker (CYL1040) and Newman (CYL1050) demonstrated reduced susceptibility to ciprofloxacin, as expected (53), and to a common house cleaner but increased susceptibility to fusidic acid (Table 4).…”

“…S. aureus chromosomal DNA was extracted as described previously (46), and plasmid DNA was purified from E. coli using the Plasmid Midi kit (QIAGEN Inc., Valencia, CA) following the manufacturer's instructions. RNA for selective capture of transcribed sequences (SCOTS) (13) and real-time PCR was isolated using a bead mill homogenization procedure (28).…”

“…It was later reported that nonsteroidal anti-inflammatories induce expression of the E. coli multiple antibiotic resistance operon (marRAB) and that repression of marRAB by the winged-helix DNA-binding repressor MarR is alleviated upon exposure to salicylate (1,6,31). Since these initial discoveries, the ability of salicylate to induce antimicrobial resistance in multiple bacterial species has been reported (for a review, see reference 44).Growth of the gram-positive pathogen Staphylococcus aureus with salicylate also induces reduced susceptibility to multiple antimicrobials, including membrane-active cleaners/disinfectants and plant essential oils, the DNA topoisomerase inhibitor ciprofloxacin, the protein synthesis inhibitor fusidic acid, and the DNA-intercalating dye ethidium (14,15,42,43,45,46). The salicylate-induced phenotype is partially due to the activation of antimicrobial efflux and a proton motive forceindependent reduction in antimicrobial accumulation (43).…”

“…Growth of the gram-positive pathogen Staphylococcus aureus with salicylate also induces reduced susceptibility to multiple antimicrobials, including membrane-active cleaners/disinfectants and plant essential oils, the DNA topoisomerase inhibitor ciprofloxacin, the protein synthesis inhibitor fusidic acid, and the DNA-intercalating dye ethidium (14,15,42,43,45,46). The salicylate-induced phenotype is partially due to the activation of antimicrobial efflux and a proton motive forceindependent reduction in antimicrobial accumulation (43).…”