Phenotype resistance to methicillin, macrolides and lincosamides in staphylococcus aureus, isolated in a hospital in Valledupar, Colombia

Abstract

Introduction: Infections with methicillin-resistant S. aureus are a public health problem due to the multi-resistance profile presented by this pathogen. Objective: To determine resistance phenotypes to methicillin, macrolides and lincosamides in S. aureus. Materials and methods: 50 S. aureus strains, isolated from patients of the Hospital Rosario Lopez Pumarejo in the city of Valledupar, were analyzed. Susceptibility tests to methicillin, erythromycin and clindamycin were performed using microdilution and agar diffusion methods. Methicillin resistance was determined through agar dilution technique and inducible clindamycin resistance D-Test. Results: Methicillin resistance reached 50%, five phenotypes were established in the analyzed macrolides and lincosamides: phenotype sensitive to erythromycin and clindamycin (78%); phenotype resistant to erythromycin and clindamycin (16%) with constitutive resistance for both cMLSB antimicrobials, which lead the resistance phenotypes; phenotype with intermediate resistance to both antimicrobials (2%); the intermediate result phenotype resistant to erythromycin and clindamycin (2%); and the RS phenotype resistant to erythromycin and sensitive to clindamycin (2%) that show inducible iMLSB clindamycin resistance with positive D test. Conclusions: The inducible resistance to macrolides, lincosamides and streptogramines is not established through the standard antimicrobial susceptibility test. Not identifying the inducible resistance can lead to clindamycin treatment failure.