Agar dilution method for detection of inducible clindamycin resistance in Staphylococcus spp.
We describe the development and validation of an agar dilution method for the detection of inducible clindamycin resistance by using 227 previously characterized erythromycin-resistant, clindamycin-susceptible Staphylococcus sp. isolates. Mueller-Hinton agar with defibrinated horse blood containing a range of erythromycin concentrations (1 to 8 mg/liter) combined with clindamycin at 0.5 mg/liter was used to determine the optimal concentration that produced growth of inducible isolates while inhibiting that of isolates without the inducible phenotype. A concentration of clindamycin of 0.5 mg/liter with erythromycin at 1 mg/liter was the optimal combination for detection of inducible resistance and resulted in a sensitivity of 100% (95% confidence interval [CI], 97.9 to 100) and a specificity of 100% (95% CI, 93.0 to 100). Attention must be paid to ensuring that a sufficient inoculum has been used, since an inoculum below the standard 10(7) bacteria/ml may result in false-negative results. This method has been incorporated into routine use in our laboratory.
Fernandes
Clarence J
CJ
Department of Microbiology, Royal North Shore Hospital, Sydney, New South Wales, Australia.
O'Sullivan
Matthew V N
MV
Cai
Yongwei
Y
Kong
Fanrong
F
Zeng
Xianyu
X
Gilbert
Gwendolyn L
GL
Kotsiou
George
G
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002981:Clindamycin / Q000494:pharmacology*; D003470:Culture Media / Q000737:chemistry; D024881:Drug Resistance, Bacterial; D004917:Erythromycin / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D008826:Microbial Sensitivity Tests / Q000379:methods*; D012680:Sensitivity and Specificity; D013210:Staphylococcus / Q000187:drug effects*
D000900:Anti-Bacterial Agents; D003470:Culture Media; D002981:Clindamycin; D004917:Erythromycin