Practical disk diffusion method for detection of inducible clindamycin resistance in Staphylococcus aureus at a tertiary care hospital: implications for clinical therapy.

The increase in incidence of variety of infections due to Staphylococcus aureus and especially methicillin resistant Staphylococcus aureus has highlighted on the need for better agents to treat such infections. Also the resistance to antimicrobial agents among staphylococci is an increasing problem. The macrolide-lincosamide-streptogramin B (MLS(B)) groups of antibiotics are commonly used in the treatment of staphylococcal infections with clindamycin being the preferred agent. This study demonstrates a simple phenotypic method (D-test) for detecting inducible clindamycin resistance in erythromycin resistant strains of staphylococcus aureus & coagulase negative Staphylococcus. A total of 181 erythromycin resistant staphylococcal isolates were obtained from various clinical specimens. Among the Staphylococcus aureus isolates, 38 (25.4%) were methicillin resistant Staphylococcus aureus (MRSA) and 112 (74.6%) were methicillin sensitive staphylococcus aureus (MSSA). Constitutive resistance was seen in 56 (37.3%) of isolates. Of these 18 (47.4%) were MRSA and 38 (33.9%) were MSSA. Inducible resistance was seen in 25 (16.6%) isolates, in which 11(28.9%) were methicillin resistant Staphylococcus aureus & 14 (12.6%) were methicillin sensitive staphylococcus aureus. It is likely that the true percentage of clindamycin resistance is being underestimated, since testing for inducible resistance is not being routinely performed. So the test should be done routinely in all the labs to avoid therapeutic failures.