Antibiotic resistance of Staphylococcus aureus in Changsha from 2006-2010

Objectives To investigate the antibiotic resistance of clinical isolates of Staphylococcus aureus in Changsha and to provide guidance for proper use of antibiotics. Methods In total, 572 non-duplicate clinical isolates of S. aureus were collected from 11 hospitals in Changsha from 2006 to 2011. The K-B disk method was used to test the sensitivity of S. aureus to 23 commonly used antibiotics. A chromogenic cephalosporin spot test was used to detect beta lactamases. Resistance to erythromycin and susceptibility to clindamycin was assayed with the D-test. MRSA was screened for using oxacillin and cefoxitin disk diffusion tests. Agar dilution was used to determine the minimal inhibitory concentrations (MIC) of oxacillin, cefoxitin, and vancomycin for S. aureus. Results S. aureus had greater than 50% resistance to 13 of the 23 antibiotics tested; resistance to penicillin and ampicillin was the highest (both were 96.85%). S. aureus had greater than 50% sensitivity to 10 antibiotics. All of the isolates were susceptible to teicoplanin, vancomycin, and linezolid. Of the 572 S. aureus isolates, 523 (91.43%) were beta-lactamase-positive and 342 (59.79%) were methicillin resistant S. aureus (MRSA). Of the 58 isolates resistant to erythromycin but susceptible to clindamycin, 48 (82.76%) produced a positive result on the D-test. For S. aureus, the MIC of oxacillin ranged from 0.125 μg/ml-256 μg/ml, the MIC of cefoxitin ranged from 2 μg/ml-256 μg/ml, and the MIC of vancomycin ranged from 1 μg/ml-2 μg/ml. Conclusion S. aureus in Changsha has multi-drug resistance to commonly used antibiotics and a high resistance to methicillin. Positivity for beta-lactamases, induced resistance to clindamycin, and the rate of MRSA isolation were very high. All of the strains were sensitive to vancomycin, but special attention should be paid to the increased MIC, which is rather high.