title: Collaborative evaluation of an erythromycin-clindamycin combination well for detection of inducible clindamycin resistance in beta-hemolytic streptococci by use of the CLSI broth microdilution method.
abstract: Constitutive or inducible clindamycin resistance can occur in beta-hemolytic streptococci due to the presence of an erm gene. The Clinical and Laboratory Standards Institute (CLSI) has recommended a disk approximation test (D-zone test) with erythromycin and clindamycin disks and a single-well broth test combining erythromycin and clindamycin for detection of inducible clindamycin resistance in staphylococci, but only a disk approximation test for the beta-hemolytic streptococci. This collaborative study assessed two different erythromycin and clindamycin concentration combinations in single wells (1 μg/ml + 0.25 μg/ml [erythromycin plus clindamycin] and 1 μg/ml + 0.5 μg/ml) with three different brands of Mueller-Hinton broth supplemented with 3% lysed horse blood for testing of frozen panels prepared for this study. All labs performed the D-zone test as described by the CLSI. A total of 155 nonduplicate streptococcal isolates (50 group A, 48 group B, 28 group C, and 29 group G isolates) were tested; 99 isolates showed inducible resistance by the D-zone test. There were some differences noted based upon the test medium. The sensitivity of the erythromycin plus clindamycin combination of 1 μg/ml + 0.25 μg/ml was 91 to 100%, while the sensitivity of the combination of 1 μg/ml + 0.5 μg/ml was 95 to 100%. Specificity overall was 98%. The slightly higher sensitivity of the combination of 1 μg/ml + 0.5 μg/ml is recommended. This study has demonstrated that a single-well microdilution test incorporating erythromycin and clindamycin in combination is a sensitive and specific indicator of inducible clindamycin resistance and could be included in routine test panels.
authors.affiliation: Department of Pathology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA. jorgensen@uthscsa.edu
authors.forename: James H
authors.initials: JH
authors.lastname: Jorgensen
authors.forename: M Leticia
authors.initials: ML
authors.lastname: McElmeel
authors.forename: Letitia C
authors.initials: LC
authors.lastname: Fulcher
authors.forename: Lesley
authors.initials: L
authors.lastname: McGee
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Richter
authors.forename: K P
authors.initials: KP
authors.lastname: Heilmann
authors.forename: Mary Jane
authors.initials: MJ
authors.lastname: Ferraro
authors.forename: Jean
authors.initials: J
authors.lastname: Spargo
authors.forename: Anita
authors.initials: A
authors.lastname: Glennen
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D002981:Clindamycin / Q000378:metabolism / Q000494:pharmacology*; D003470:Culture Media / Q000737:chemistry; D024881:Drug Resistance, Bacterial; D004917:Erythromycin / Q000378:metabolism / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests / Q000379:methods; D012680:Sensitivity and Specificity; D013291:Streptococcus / Q000187:drug effects*; D015533:Transcriptional Activation
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D002981:Clindamycin; D004917:Erythromycin