Pine oil cleaner-resistant Staphylococcus aureus: reduced susceptibility to vancomycin and oxacillin and involvement of SigB.

Mutants of Staphylococcus aureus strain COL resistant to a household pine oil cleaner (POC) were isolated on laboratory media containing POC. S. aureus mutants expressing the POC resistance (POC(r)) phenotype also demonstrate reduced susceptibility to the cell wall-active antibiotics vancomycin and oxacillin. The POC(r) phenotype is reliant on the S. aureus alternative transcription factor SigB, since inactivation of sigB abolished expression of elevated POC resistance and the reductions in vancomycin and oxacillin susceptibilities. The isolation of suppressor mutants of COLsigB::kan, which maintain the sigB::kan allele, indicates that the POC(r) phenotype can also be expressed to a lesser degree via a sigB-independent mechanism. These results bolster a growing body of reports suggesting that common disinfectants can select for bacteria with reduced susceptibilities to antibiotics. A series of in vitro-selected glycopeptide-intermediate S. aureus (GISA) isolates also expressed reductions in POC susceptibility compared to parent strains. Viewed collectively, our evidence suggests that mutations leading to the POC(r) phenotype may also be involved with the mechanism that leads to the GISA phenotype.