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Methods

D-163 ICAAC Sept 12-15 2010 Boston.

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Methods

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  1. D-163 ICAAC Sept 12-15 2010 Boston Detection of inducible macrolide-lincosamide-streptogramin B resistance in Staphylococcusspecies: Vitek 2 ICR test (AST-P610) versus double disc method (D-zone test).Timothy Vanwynsberghe, Annick Smismans, Johan FransLaboratory of microbiology, Imelda hospital Bonheiden, Belgium Imeldalaan 9 2820 Bonheiden BELGIUM +32015505460 Results (2) Introduction Methods • Methylation by a ribosomal methylase encoded by erm genes results in resistance to macrolide, lincosamide and streptograminB (MLSB phenotype). • This phenotype can be expressed either constitutively or inducible (iMLSB). Clindamycin may be clinically ineffective in case of inducible resistance despite low minimal inhibitory concentrations. • The double disc induction test or “D-test” (CLSI, M100-S20) is recommended to determine iMLSB resistance in Staphylococcus spp. • The ‘advanced expert system’ (AES) of the Vitek 2 (bioMérieux) provides recently a Vitek 2 ICR test for the detection of the iMLSB phenotype, which is available on the AST-P610 card (bioMérieux). • The aim of the study was to compare the accuracy of this test with the golden standard D-test to omit manual confirmation testing. 55 Consecutive patient samples with Staphylococcus spp. (34 S. aureus and 21 coagulase-negative staphylococci) identified on Vitek 2 with the GP card were tested for inducible clindamycine resistance by Vitek 2 ICR test (AST-P610 card) and compared to the CLSI double disk reference test. Sensitivity, specificity, positive predictive value and negative predictive value were calculated for the Vitek 2 ICR test. • These values were comparable with data provided by the manufacturer1. • The categorical agreement was 98%. • One very major error (VME: D-test +, Vitek 2 ICR -) was found which fell within CLSI limits (VME ≤ 3%)2. • In this study the prevalence of iMLSB resistance was 56.4% which was similar to a former local study concerning iMLSB resistance (58.4%)3. Results Conclusions The Vitek 2 ICR test is an acceptable method to detect iMLSB resistance. References 1 Leclercq R. et al. (France), ICAAC 2009 2 Clark, R.B., M.A. Lewinski, M.J. Loeffelholz, and R.J. Tibbetts, 2009. Cumitech 31A, Verification and validation of procedures in the clinical microbiology laboratory. Coordinating ed., S.E. Sharp. ASM Press, Washington, DC. 3 Geerts I. et al. (Belgium), ECCMID 2010 We noted a sensitivity of 97%, a specificity of 100%, a positive predictive value of 100% and a negative predictive value of 96%.

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