Aminoglycoside and chlorhexidine resistance genes in Staphylococcus aureus isolated from surgical wound infections.

Hamdia Askar1, Wafaa Badawy2  and Enas Hammad11Medical Microbiology and Immunology Department, Faculty of Medicine, Mansoura University, Egypt2MD.MansouraUniversity Students'Hospital,Egypt. Background:   Staphylococcus aureus is a major human pathogen resistant to many antimicrobial agents especially the methicillin-resistant Staphylococcus aureus (MRSA). In surgical site infections, MRSA is known to be an important etiologic factor. Infections range from skin and soft-tissue infections to deep tissue infections such as osteomyelitis, bacteremia, and endocarditis that are much more common in hospital environment. In staphylococci the main mechanism of aminoglycoside resistance is the drug inactivation by aminoglycoside-modifying enzymes (AMEs) and reduced biocide susceptibility is associated with the acquisition of quaternary ammonium compound (qac) gene-encoding for Qac efflux proteins.Aim of the work: To investigate the prevalence of the aminoglycosides resistance genes aac(6′)aph(2″), aph(3′)-IIIa, Ant(4′)-Ia) and the biocide resistance genes (qacA/qacB, qacC) in  S. aureus  isolated from surgical site infections.Methods:  Swabs from 280 infected surgical sites were sent to our laboratory from different surgical words at Mansoura University Hospitals between January 2014 and December 2014. Sixty- six staphylococcal strains were isolated and included in this study. Verification of the presence of methicillin resistance gene (mecA), chlorhexidine MIC and qac resistance genes (qacA/qacB, qacC) were detected by PCR. The presence of aminoglycoside resistance genes [(aac(6′)/aph (2″), ant (4′)-1a and aph(3′)-IIIa)] in S. aureus was also tested by PCR.Results:   Seventeen of the 66 S. aureus isolates (25.75 %) were phenotypically MRSA and mecA gene was detected in 19 S. aureus isolates (28.7 %) by PCR. Aminoglycoside resistant S. aureus were 21/66 (31.8%). AME genes were detected in all aminoglycoside-resistant S. aureus; aac(6′)/aph (2″) was the most frequently detected 11/21(52.4%) followed by aph(3′)-IIIa 6/21 (28.6%) and the least frequent was ant (4′)-1a 4/21(19%). Aminoglycoside resistance in 9 out of the 21 (42.9%) aminoglycoside resistance S. aureus isolates was solely plasmid mediated being lost after plasmid curing. A total of 14 out of the 21 aminoglycoside-resistant S. aureus isolates (66.7 %) carried the mecA gene. Among the 45 aminoglycoside-sensitive S. aureus isolates 5 (11.1%) were mecA positive. Nine of the 21 aminoglycoside-resistant S. aureus isolates (42.9%) were positive for qacA/qacB genes and in all of them mecA gene co-existed. Five aminoglycoside resistant S. aureus isolates were qacC positive (23.8%).  Conclusion: In the Staphylococcus aureus isolated from infected surgical wounds, quaternary ammonium compounds resistance genes were positive at a considerable ratio and co-existed with aminoglycosides and methicillin-resistance genes in S. aureus isolates.