Abstract
Clindamycin is one of the alternative antibiotics in the therapy of Staphylococcus aureus, particularly in methicillin resistant S. aureus (MRSA) infections. But inducible clindamycin resistance (iMLSB) has been described as a cause of clinical failure of such infections. The present study attempted to evaluate the prevalence of inducible clindamycin resistance among S. aureus isolates in a tertiary care centre in north eastern India. The study was carried out in the department of Microbiology, Era’s Lucknow Medical College and Hospital, Lucknow, India, during a period of one year from December 2008 to November 2009. It was a prospective cross sectional study. In total, 260 S. aureus isolates were subjected to routine antibiotic susceptibility testing, including cefoxitin (30 mg), by the Kirby Bauer disc diffusion method. Inducible resistance to clindamycin was tested by double disk diffusion assay (D test) as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Overall, inducible clindamycin resistance was detected among sixty (23.2%) isolates, while 16(6.15%) showed constitutive resistance and the remaining 39 (15%) exhibited a MS phenotype. Inducible resistance and constitutive resistance were higher in MRSA than methicillin-susceptible S. aureus (MSSA). Therefore, owing to the high percentage of inducible clindamycin resistance, we recommend that a screening test such as the D test should be included in routine susceptibility testing for S. aureus. Key words: Double disk diffusion assay (D test), inducible clindamycin resistance (iMLSB),Staphylococcus aureus.
Highlights
Resistance to antimicrobial agents among Staphylococcus aureus isolates has become an everincreasing problem among hospitalized patients, persons in long-term care facilities and ambulatory outpatients
Most S. aureus which are resistant to erythromycin are resistant to clindamycin which is known as constitutive resistance (Drinkovic et al, 2001)
Some S. aureus isolates are susceptible to clindamycin in vitro, they may not be effective in vivo when the strain is resistant to erythromycin
Summary
Resistance to antimicrobial agents among Staphylococcus aureus isolates has become an everincreasing problem among hospitalized patients, persons in long-term care facilities and ambulatory outpatients. Most S. aureus which are resistant to erythromycin are resistant to clindamycin which is known as constitutive resistance (Drinkovic et al, 2001). Some S. aureus isolates are susceptible to clindamycin in vitro, they may not be effective in vivo when the strain is resistant to erythromycin. This may be due to presence of inducible macrolidelincosamide-streptogramin B resistance (iMLSB). The presence of inducible clindamycin resistance (iMLSB) can be detected in erythromycin resistant strains by the double disk diffusion assay (D test)
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