Abstract

Staphylococcus aureus especially Methicillin Resistant Staphylococcus aureus (MRSA) is challenging as a hospital pathogen, as it is not only resistant to Methicillin but to most of the first line antibiotics used for treatment. This usually limits the choice for treatment to Clindamycin, Vancomycin and Linezolid. The latter two being the second line antibiotics need to be kept as reserve drugs. Clindamycin is tolerable, cheaper, available as oral preparations, has good tissue penetration, hence a good choice for skin and bone infections. On routine antibiotic testing  by Disc-Diffusion Clindamycin may appear sensitive, but resistance is expressed after induction with Erythromycin, leading to treatment failure, making Clindamycin unpopular in the treatment of MRSA. These strains can be picked out  by adopting a simple method, D-test. A total  of 1086 Staphylococcus aureus strains isolated from various clinical specimens were tested for antibiotic sensitivity by Kirby Bauer disc diffusion method, Methicillin resistance was detected using Cefoxitin (30µg) disc, and D-test was done on those isolates which were erythromycin resistant. Among the 1086 isolates, 402 were MRSA, out of which 271 (67.4%) were truly sensitive to Clindamycin (after testing for inducible resistance). Only 32.6% need to be treated with Linezolid or Vancomycin. Hence by doing D-test routinely, majority of isolates could be treated with Clindamycin without fear of treatment failure and inadvertent use of Linezolid could be avoided.

Keywords: Methicillin Resistant Staphylococcus aureus, Clindamycin, Inducible resistance, D-test, Linezolid.