Plausible challenges of methicillin and clindamycin resistance detection in Staphylococcus aureus

Accurate detection and therapeutic challenges are still on the debate for methicillin-resistant Staphylococcus aureus (MRSA). Working on clindamycin, researchers serendipitously spotted the D test and the era of macrolide-lincosamide (ML) resistance commenced. We aimed to i) assess usage of other antibiotics other than cefoxitin for the detection of MRSA, ii) evaluate various surrogate therapeutic options, and iii) determine phenotypic and genotypic aspects of inducible and constitutive clindamycin resistance in S. aureus. Disk diffusion agar assay and molecular method were used to assess MRSA detection. Efficacy of linezolid, vancomycin, mupirocin, teicoplanin, fusidic acid, and rifampin was analyzed by E-test. Various phenotypes of macrolide-lincosamide-streptogramin B (MLSB) resistance were detected by performing D-test followed by PCR assay for ermA, ermB and ermC genes coding for macrolide resistance. The cefoxitin disc yielded the best sensitivity value (100%) over oxacillin, imipenem, and mempenem. All isolates were completely sensitive to linezolid and teicoplanin. Among MRSA isolates, 6.2%, 1.5%, and 17.1% strains had intermediate and complete resistance to vancomycin, fusidic acid, and rifampin respectively. Fifty-six isolates were clindamycin susceptible and diverse resistance outlooks were the major outcome of our study with 20.6% isolates demonstrated two distinct induction phenotypes (D and D+) and 45% isolates showed non-induction (HD,R) phenotypes. ermA gene alone and in combination with ermC was found to be more prevalent among inducible as well as constitutive clindamycin- resistant isolates.