Objective: To determine the shift of susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) isolates to vancomycin in recent years.
Methods: Antimicrobial susceptibility was determined by disk diffusion test (K-B method). The t-test was used to compare the mean diameters of zone of inhibition.
Results: The clinical isolates of MRSA from 1994 to 2000 were 218, 187, 292, 237, 351, 886 and 652 in number respectively. The mean diameters (mm) of the inhibition zone of MRSA isolates each year were 19.9, 19.1, 18.6, 17.4, 18.4, 18.2 and 17.8. Comparison of the diameters of the inhibition zone of MRSA isolates (K-B method) showed that the mean diameter of the inhibition zone from the 652 MRSA isolates in 2000 was much less than that of the 218 MRSA isolates in 1994 and the difference was significant (P < 0.001). The resistant rates to chloramphenicol, ciprofloxacin, erythromycin, gentamicin, tetracycline and trimethoprim/sulfamethoxazole were 44.0%, 73.7%, 89.1%, 65.7%, 61.0% and 67.0%.
Conclusion: Our observation demonstrated that the susceptibility of MRSA to vancomycin gradually decreased from 1994 to 2000. It is important to monitor the antimicrobial susceptibility of Staphylococcus aureus to vancomycin.