Assessment of methicillin and clindamycin resistance patterns in staphylococcus aureus isolated from a tertiary hospital in Turkey

In order to detect the methicillin susceptibility and determine the prevalence of constitutive and inducible clindamycin resistance in Staphylococcus aureus strains, a total of 254 S. aureus isolates, including 139 (54.7%) methicillin-sensitive and 115 (45.3%) methicillin-resistant, were tested for clindamycin and erythromycin by Kirby-Bauer's disk diffusion method. The disk diffusion induction test or D-test was performed on erythromycin-resistant and clindamycin-sensitive strains using the disk diffusion method. The erythromycin-resistant and clindamycin-sensitive strains with a D-shaped zone around the clindamycin disk were considered positive for inducible clindamycin resistance. If a strain was found to be both erythromycin-resistant and clindamycin-resistant, it was considered to have constitutive clindamycin resistance. Overall, ten (3.9%) strains, including two methicillin-resistant S. aureus and eight methicillin-sensitive S. aureus, were found to be erythromycin-resistant and clindamycin-sensitive according to the disk diffusion method and all of these strains showed inducible clindamycin resistance by the D-test method. Constitutive clindamycin resistance was detected in 100 of all MRSA strains. In conclusion, the presence of inducible clindamycin-resistant strains may lead to clindamycin treatment failure in patients with S. aureus infection. The D-test method should be used for antimicrobial susceptibility testing of clindamycin.