Inducible Clindamycin Resistance in Staphylococcus aureus Isolated from Clinical Samples

Increasing frequency of methicillin resistant Staphylococcus aureus (MRSA) infections and changing patterns in antimicrobial resistance have led to renewed interest in the use of macrolide-lincosamide-streptogramin (MLS) antibiotics to treat such infections. Inducible macrolides, lincosamides, type B streptogramins (MLS(Bi)) resistance has to be identified to avoid clinical failure of clindamycin therapy. Hence we wanted to study the incidence of inducible clindamycin resistance in MRSA and methicillin susceptible Staphylococcus aureus (MSSA). Staphylococcus aureus was isolated in 1049 patients over a period of two years from various clinical materials. All the isolates were tested for inducible clindamycin resistance by disc diffusion induction test (D-zone test). A total of 726 MSSA and 323 MRSA were tested for the inducible clindamycin resistance (MLS(Bi)) by D-zone test. Inducible resistance to clindamycin (MLS(Bi)) where D test was positive was observed in 42.1% of MRSA and 3.4% of MSSA. Inducible resistance to clindamycin (MLS(Bi)) was found to be higher in MRSA than MSSA isolates. Clindamycin is one of the important alternative antibiotics to treat MRSA infections in resource poor countries. To avoid treatment failure with clindamycin, prior D testing is necessary.