Objective: This study was undertaken to assess the frequency of the phenotypic expression of the inducible resistance to clindamycin which was due to the expression of the erm genes in various clinical isolates of the Staphylococcus species.
Materials and methods: This was a cross sectional study conducted in the Dept. of Microbiology and Immunology, Veer Chandra Singh Garhwali Govt. Medical Sciences and Research Institute, Srikot, Uttarakhand, from July 2010 to December 2011. A total of 373 consecutive, non duplicate strains of Staphylococci isolated from various clinical samples like pus, wound swab, blood, urine and other body fluids, were tested. The isolates which had a discordant resistance pattern (clindamycin-sensitive and erythromycin-resistant) by Kirby Bauer Disk Diffusion method were selected and subjected to the D-test for inducible clindamycin resistance, as per the Clinical and Laboratory Standards Institutes (CLSI) guidelines.
Results: Among the 373 clinical isolates of Staphylococci which were studied, 134 isolates showed a discordant resistance pattern. Among these discordant strains, 45 (33.6%) isolates were D-test positive, which had inducible clindamycin resistance and belonged to the inducible macrolide lincosamide streptogramin- B phenotype (MLSBi). 89 (66.4%) isolates were D-test negative and they belonged to the macrolide streptogramin phenotype (MS). Among the MLSBi phenotypes, 6 (13.3%) isolates were methicillin-resistant Staphylococcus aureus (MRSA), 13 (28.9%) were Methicillin-sensitive S.aureus (MSSA) and 26 (57.8%) were coagulase negative staphylococci (CONS).
Conclusion: The D-test is a simple, effective and an important method for the phenotypic detection of inducible clindamycin resistance and it should be used routinely, as it will help in guiding the empirical therapy. The possible clinical failures can thus be avoided.
Keywords: Clindamycin; D-Test; Erythromycin; MLSBi; Staphylococci.