Monitoring the Drug-resistance of Staphylococcus aureus Isolates from Nasal Carriers of Pharmaceutical Company with Emphasis on daptomycin Resistance

Background and Objectives:Staphylococcus aureus is considered as a normal flora by colonization in the nose and skin of carriers, yet it is as a major cause of nosocomial infections and a life-threatening pathogen. The present study aimed to determine the frequency and comparison of the minimum inhibitory concentration of daptomycin with teicoplanin and linezolid against vancomycin-resistant S. aureus isolates Materials and Methods:In this cross-sectional study, samples were taken from the anterior nasal part of 95 two drug companies staff in Gorgan during 2018-2019, using sterile swabs. Being cultured on Mannitol salt agar, the suspected colonies were identified through Gram staining, as well as catalase, coagulase, DNase tests and PCR. After identifying S. aureus isolates, broth microdilution test was used according to CLSI M100-S25(2015) criteria to determine the minimum inhibitory concentration(MIC) of antibiotics. Results:The frequency of vancomycin-resistant S. aureus isolates was 26.3 %. MICs levels showed that 91.5% isolates of S.aureus tested were susceptible to daptomycin (MIC, ≤1 μg/mL), while 95.8% (MIC, ≤4μg/mL) and 86.3% (MIC, ≤8μg/mL) of isolates were categorized as susceptible to linezolid and teicoplanin, respectively. The concentration of daptomycin that inhibited 90% of isolates (MIC90) was 2μg/mL, 2-folds higher than linezolid (MIC90=1μg/ml) and 8-folds lower than teicoplanin (MIC90= 0.25μg/mL). There was a significant difference between the frequency of daptomycin/linezolid- resistance(P<0.05). Conclusion:We conclude that daptomycin has a beneficial effect on S. aureus isolates but linezolid possesses more potent in vitro activity than the rest of agents.