Inducible clindamycin resistance in Staphylococcus aureus: Reason for treatment failure.

ABSTRACT

Emergence of methicillin resistance in Staphylococcus aureus (S.aureus) has left us with very few therapeutic alternatives available to treat staphylococcal infection. The widespread use of macrolide-lincosamide-streptogramin B (MLSB) antibiotics has led to an increase in number of staphylococcal strains acquiring resistance to MLSB antibiotics. This study was done to investigate the infections by hospital and community acquired “erythromycin- induced clindamycin resistant” strains or D-test positives of clinical isolates of Staphylococcus aureus (S.aureus) in a hospital. Three hundred isolates of S.aureus were subjected to routine antibiotic susceptibility testing including Cefoxitin (30µg) by modified disc diffusion method. Inducible resistance to clindamycin in S.aureus was tested by D-test as per CLSI guidelines. Among 300 S.aureus isolates, 114 (38%) were methicillin resistant Staphylococcus aureus (MRSA) and 186 (62%) methicillin susceptible Staphylococcus aureus (MSSA). Forty one (13.67%) isolates showed induced clindamycin resistance, 49(16.33%) showed constitutive resistance and 94 (31.33%) showed the MS phenotype. Inducible resistance and constitutive resistance were found to be higher in MRSA compared to MSSA (22.81%, 23.68% and 8.1%, 11.8% respectively). D-test should be included as a part of routine antibiotic susceptibility testing to detect induced clindamycin resistance to prevent treatment failure.