Transduction of the plasmid encoding antiseptic resistance gene qacB in Staphylococcus aureus

The plasmid-borne qacA and qacB genes encode a multidrug efflux protein. The proteins encoded by qacA and qacB mediate efflux of cationic antiseptic agents such as quaternary ammonium compounds. In methicillin-resistant Staphylococcus aureus (MRSA), qacA and qacB are widely prevalent and decrease antiseptic susceptibility. However, it is difficult to find the plasmids encoding qacA or qacB in community-associated MRSA (C-MRSA) isolated from patients with impetigo. Most MRSA, the strains causative of impetigo, carry the plasmid-borne exfoliative toxin-producing gene etb. To find the reason for the paucity of qacA or qacB in MRSA isolated from patients with impetigo, we performed transfer experiments of the plasmid pTZ2162qacB encoding qacB. The pTZ2162qacB was transferred to S. aureus strain RN4220 by transduction, although no pTZ2162qacB was transferred by conjugation. Additionally, pTZ2162qacB was transduced to MRSA carrying etb, and was coexistence with the plasmid encoding etb. Our results showed that pTZ2162qacB was horizontally transferred by transduction and was compatible with the plasmid encoding etb. Consequently, there will be risk of the emergence of C-MRSA with decreased antiseptic susceptibility among patients with impetigo.