Luiza Pinheiro1,2, Priscila L Mello1, Ligia M Abraão1, José Eduardo Corrente3, Maria de Lourdes Rs Cunha1. 1. Department of Microbiology & Immunology, Institute of Biosciences of Botucatu, Universidade Estadual Paulista - UNESP, Botucatu 18618-970, Brazil. 2. Departament of Anatomic Pathology, Instituto Lauro de Souza Lima, Bauru 17034-971, Brazil. 3. Department of Biostatistics, Institute of Biosciences of Botucatu, Universidade Estadual Paulista - UNESP, Botucatu 18618-970, Brazil.
Abstract
AIM: To evaluate the adequacy of the disc-diffusion test and E-test® compared with detection of mecA for coagulase-negative staphylococci isolated from blood cultures, nasal swabs and wounds. RESULTS: Agreement between all techniques was observed in 65.7% of cases. The greatest discrepancy between mecA/susceptible E-test was observed for non-epidermidis species. A resistance breakpoint ≤19 mm using the oxacillin disc was found to best classify all coagulase-negative staphylococci isolates; Staphylococcus epidermidis, ≤19 mm (oxacillin) and ≤27 mm (cefoxitin); Staphylococcus haemolyticus and Staphylococcus capitis, ≤21 mm (oxacillin) and ≤18 mm (cefoxitin); Staphylococcus warneri, MICs ≥0.75 mg/l. CONCLUSION: Although no longer recommended by the Clinical Laboratory Standards Institute, we observed some cases in which only the oxacillin disc-diffusion test detected resistance. The discrepancy between phenotypic tests and mecA is probably due to heterogeneity and borderline resistance.
AIM: To evaluate the adequacy of the disc-diffusion test and E-test® compared with detection of mecA for coagulase-negative staphylococci isolated from blood cultures, nasal swabs and wounds. RESULTS: Agreement between all techniques was observed in 65.7% of cases. The greatest discrepancy between mecA/susceptible E-test was observed for non-epidermidis species. A resistance breakpoint ≤19 mm using the oxacillin disc was found to best classify all coagulase-negative staphylococci isolates; Staphylococcus epidermidis, ≤19 mm (oxacillin) and ≤27 mm (cefoxitin); Staphylococcus haemolyticus and Staphylococcus capitis, ≤21 mm (oxacillin) and ≤18 mm (cefoxitin); Staphylococcus warneri, MICs ≥0.75 mg/l. CONCLUSION: Although no longer recommended by the Clinical Laboratory Standards Institute, we observed some cases in which only the oxacillin disc-diffusion test detected resistance. The discrepancy between phenotypic tests and mecA is probably due to heterogeneity and borderline resistance.