Detection of biocide resistance genes, qac A/B and smr, among isolated Staphylococcus aureus from clinical and non-clinical sources

Extensive use of biocides containing quaternary ammonium compounds (QACs) have led to the emergence of QACs resistant strains of staphylococci. The aim of the present study was to detect two biocide resistance genes, qac A/B and smr and to study their association with the presence of antibiotic resistance genes in isolated S. aureus from different sources. Forty two S. aureus from clinical sources, 11 from unpasteurized diaries, and 32 from nasal swabs out of 150 collected samples were isolated. Susceptibility of the isolates to biocide QACs containing didecyl dimethyl ammonium chloride was determined by the colorimetric broth microdilution test. Polymerase chain reaction was done for detection of qac A/B, smr, bla Z, and mec A genes. Fifty percent of clinical isolates, 36.36% of isolates from unpasteurized diaries and 15.6% of nasal isolates of S. aureus with the MIC range between 1.95-7.81 µg/ml were resistant to QACs. The frequency of qac A/B and smr genes among clinical isolates was 19.4% and 45.2%, respectively, which was significantly higher than their frequency in other samples (2.3% and 20.9%, respectively) (p<0.05). The smr gene with frequency of 15.6% was the dominant gene among the nasal isolates of S. aureus. There was a significant correlation between the presence of at least one of the biocide resistance genes and bla Z in clinical (p=0.04) and food-related isolates (p=0.024) but there wasn’t any significant association between the presence of biocide resistance genes and mec A. It is for the first time that not only the prevalence of qac A/B and smr genes for Iranian S. aureus strains is reported but also to the best of our knowledge is the first time that the presence of smr gene with the frequency of 15.6% is reported for nasal isolates of S. aureus. The present study confirms the previous findings that there is a close relationship between QACs resistance and penicillin resistance. However the presence of qac genes in the S. aureus population and their ability to develop biological resistance or co-resistance with antibiotics highlights the importance of effective infection control strategies.