Detection of Inducible Clindamycin Resistance in Staphylococci by Disk Diffusion Induction Test
Sureerat Chelae MSc*, Varaporn Laohaprertthisarn BSc*, Manthana Phengmak MSc*, Urairat Kongmuang PhD*, Sineenart Kalnauwakul MD*
Affiliation : * Microbiology Unit, Department of Pathology, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, Thailand
Objective : To detect inducible clindamycin (CL) resistance in staphylococci by disk diffusion induction test
(D-test).
Material and Method: One thousand one hundred eighty clinical isolates of staphylococci were tested for
inducible CL resistance by placing erythromycin (E) disk and clindamycin disk 12 mm apart (edge to edge)
on Mueller-Hinton agar plate inoculated with staphylococci. The flattening of CL zone (D-shaped zone) near
E disk indicated an inducible CL resistance was observed after 18-24 h of incubation.
Results : Inducible CL resistance was detected in 9.9% of staphylococci isolates. It was found in methicillin-
resistant Staphylococcus aureus (MRSA) more than methicillin-sensitive Staphylococcus aureus (MSSA) and
coagulase-negative staphylococci (CoNS) 35.9%, 4.7%, and 5.5%, respectively.
Conclusion : To avoid misinterpretation of CL result, D-test is recommended for routine detecting of inducible
CL resistance in staphylococci. It provides the confident laboratory report of CL as resistant (D-shaped zone
positive) or as susceptible (D-shaped zone negative) particular for E resistant isolates.
Keywords : Clindamycin, Drug resistance, D-test, Methicillin-resistant Staphylococcus aureus, Microbial sensitivity tests, Staphylococcus aureus
