Antimicrobial resistance of Staphylococcus aureus isolated from human and food against Linezolid, Quinupristin-Dalfopristin, Quinolones and Imipenem

Staphylococcus aureus is a versatile pathogen of humans and animals that has evolved resistance to all classes of antimicrobials. A total of 293 S. aureus isolates including 71 obtained from human and 222 recovered from food against crucial antimicrobial agents used in human and veterinary practice were examined for the antimicrobial resistance profiles. The in vitro activities of new agents (linezolid and quinupristin-dalfopristin), quinolones (ofloxacin, norfloxacin, levofloxacin, moxifloxacin) and imipenem against the isolates were performed by standard disk diffusion method. The 293 isolates demonstrated very low levels of resistance to imipenem (0.7%), followed by quinupristin-dalfopristin (1.7%) but had the highest activity against linezolid (6.8%) and moxifloxacin (5.5%). Over 9.9% of clinical isolates showed resistance to three or more antimicrobial agents. Only 1.8% of food isolates were multidrug resistant (>= 3 antibiotics). The differences between clinical and food isolates in the results of antimicrobial resistance were statistically significant. Besides, comparing the resistance to each antimicrobial agent between the two group isolates, there were statistically significant differences (P<0.05). Because S. aureus has a remarkable propensity to develop or acquire resistance to antimicrobial agents, it is important to continually monitor antimicrobial susceptibilities of isolates from clinical and food sources.