Oxacillin and Cefoxitin-Susceptible Methicillin Resistant Staphylococcus aureus. Cuirolo A, Fernandez-Caniggia L, Gardella N, Gutkind G, Rosato AE, Mollerach M.

CUIROLO A; FERNÁNDEZ CANIGGIA L; GARDELLA N; FERNÁNDEZ S; GUTKIND G; ROSATO A; MOLLERACH M

INTERNATIONAL JOURNAL OF ANTIMICROBIAL AGENTS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2011 vol. 37 p. 178 - 179

0924-8579

The ability to accurately identify methicillin resistant Staphylococcus aureus (MRSA) is critical in managing both hospital-acquired and community-acquired infections. Even if oxacillin-disk diffusion has been the traditional method for methicillin-resistance screening, the 30 µg-cefoxitin disk was shown to be more efficient for predicting methicillin resistance, consequently, the Clinical Laboratory Standards Institute (CLSI) recommended that cefoxitin should be preferred over oxacillin for the recognition of MRSA. Detection of the mecA gene is the reference method, but this is not feasible in most clinical laboratories throughout the world. Disk diffusion test (DDT) is easy to handle and is the mostly used method for routine MRSA detection. In addition, the heterogeneous resistance phenotype may further complicate the detection of MRSA by conventional methods. We investigated a hetero-resistant strain (SA454) recovered from a patient suffering a surgical site infection after a nephrectomy procedure in December 2009 at a Hospital in city of Buenos Aires, Argentina. The patient presented different underlying diseases including diabetes Type II, obesity and hypertension. Neither oxacillin/cefoxitin DDT nor the oxacillin agar screening method detected mecA mediated oxacillin resistance. PBP2a detection was the only phenotypic test useful to predict β-lactams resistance in this isolate. However, the availability of this commercial kit for every clinical lab in developing countries may pose a problem. Despite 30 μg cefoxitin disk diffusion method has been proposed as an efficient method for the detection of methicillin resistance, but, in the case, it did not permit MRSA recognition. Detection of these isolates could represent a major challenge for the clinical microbiology laboratory; however, clinical relevance and therapeutic implications of these isolates remain to be determined.