Frequency of inducible clindamycin resistance among gram-positive cocci in a tertiary hospital, Tehran, Iran

Iranian Journal of Microbiology

Volume 8 - Number 4

Article Type: Original Article

Background and Objectives: Accurate designation of antimicrobial susceptibility pattern of the infecting microorganismsis an important crucial factor in making appropriate therapeutic decisions. Macrolide, lincosamide and streptogramin Bantibiotics are in a family, reserved as an alternative approach in treatment of resistant Gram positive cocci. Amongst them,clindamycin has been considered as the preferred agent due to its excellent pharmacokinetic properties. The inducible resistance to clindamycin in Gram positive staphylococci and streptococci cannot be recognized by routine broth or agar basedsusceptibility tests and D-zone testing is necessary. This study is conducted to evaluate the frequency of inducible clindamycin resistance in Gram positive cocci.Materials and Methods: Using traditional culture methods, 487 isolates of staphylococcus and β-hemolytic streptococcuswere evaluated. If they were resistant to erythromycin and sensitive to clindamycin in primary antibiotic susceptibility testingby Kirby-Bauer method, they were subjected to D-zone testing to detect possible inducible clindamycin resistance.Results: Thirty three out of 172 isolates of Staphylococcus aureus and 50 out of 277 isolates of coagulase-negativestaphylococci (CoNS) were subjected for D-zone testing. Among them 13/33 and 28/50 showed inducible clindamycinresistance, respectively. There was no significant difference in inducible clindamycin resistance regarding to methicillinsusceptibility pattern. Positive D-test was observed in 17.39 and 13.33% of Group B streptococci and Streptococcus spp.,respectively.Conclusion: Considerable number of isolates showed inducible clindamycin resistance in our study which falsely would bereported susceptible if D-zone testing was not performed. Thus, performing D-Zone testing is necessary to avoid misleadingresults which may cause treatment failure