Presence of the optrA Gene in Methicillin-Resistant Staphylococcus sciuri of Porcine Origin

A total of 57 methicillin-resistantStaphylococcus aureus (MRSA) isolates and 475 methicillin-resistant coagulase-negative staphylococci (MRCoNS) collected from pigs in the Guangdong province of China in 2014 were investigated for the presence of the novel oxazolidinone-phenicol resistance geneoptrA . TheoptrA gene was detected in 6.9% (n = 33) of the MRCoNS, all of which wereStaphylococcus sciuri isolates, but in none of the MRSA isolates. FiveoptrA -carrying methicillin-resistant (MR)S. sciuri isolates also harbored the multiresistance genecfr . Pulsed-field gel electrophoresis (PFGE) anddru typing of the 33optrA -carrying MRS. sciuri isolates revealed 25 patterns and 5 sequence types, respectively. S1 nuclease PFGE and Southern blotting confirmed thatoptrA was located in the chromosomal DNAs of 29 isolates, including 1cfr -positive isolate. The remaining four isolates harbored a ∼35-kb pWo28-3-like plasmid on whichoptrA andcfr were located together with other resistance genes, as confirmed by sequence analysis. Six different types of genetic environments (types I to VI) of the chromosome-borneoptrA genes were identified; these types had theoptrA gene and its transcriptional regulatoraraC in common. Tn558 was found to be associated witharaC-optrA in types II to VI. TheoptrA gene in types II and III was found in close proximity to theccr gene complex of the respective staphylococcal cassette chromosomemec element (SCCmec ). Since oxazolidinones are last-resort antimicrobial agents for the control of serious infections caused by methicillin-resistant staphylococci in humans, the location of theoptrA gene close to theccr complex is an alarming observation.