title: Frequency of inducible clindamycin resistance among gram-positive cocci in a tertiary hospital, Tehran, Iran.
abstract: OBJECTIVE
  Accurate designation of antimicrobial susceptibility pattern of the infecting microorganisms is an important crucial factor in making appropriate therapeutic decisions. Macrolide, lincosamide and streptogramin B antibiotics 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 based susceptibility tests and D-zone testing is necessary. This study is conducted to evaluate the frequency of inducible clindamycin resistance in Gram positive cocci.
  
  
  METHODS
  Using traditional culture methods, 487 isolates of staphylococcus and β-hemolytic streptococcus were evaluated. If they were resistant to erythromycin and sensitive to clindamycin in primary antibiotic susceptibility testing by Kirby-Bauer method, they were subjected to D-zone testing to detect possible inducible clindamycin resistance.
  
  
  RESULTS
  Thirty three out of 172 isolates ofStaphylococcus aureusand 50 out of 277 isolates of coagulase-negative staphylococci (CoNS) were subjected for D-zone testing. Among them 13/33 and 28/50 showed inducible clindamycin resistance, respectively. There was no significant difference in inducible clindamycin resistance regarding to methicillin susceptibility pattern. Positive D-test was observed in 17.39 and 13.33% of Group B streptococci andStreptococcusspp., respectively.
  
  
  CONCLUSIONS
  Considerable number of isolates showed inducible clindamycin resistance in our study which falsely would be reported susceptible if D-zone testing was not performed. Thus, performing D-Zone testing is necessary to avoid misleading results which may cause treatment failure.
authors.affiliation: Department of Pathology and Laboratory Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hiva
authors.initials: H
authors.lastname: Saffar
authors.affiliation: Department of Pathology and Laboratory Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Afsaneh
authors.initials: A
authors.lastname: Rajabiani
authors.affiliation: Department of Pathology, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Alireza
authors.initials: A
authors.lastname: Abdollahi
authors.affiliation: School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Shirin
authors.initials: S
authors.lastname: Habibi
authors.affiliation: Department of Pathology and Laboratory Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Baseri
keywords: D-test; Inducible clindamycin resistance; Staphylococci; Streptococci