Phenotypic characterization of biofilm formation and efflux pump activity in multi-drug resistant staphylococcus species isolated from asymptomatic students

Abstract

Staphylococcus spp. are one of the major groups of bacterial commensals isolated from skin and mucous membranes. While a variety of Staphylococcal species are present on or in clinically normal individuals, some are also opportunistic pathogens and leading causes of community associated diseases in humans and animals worldwide. The objective of the study was to determine the antimicrobial susceptibility pattern, biofilm formation capability and efflux pump activity in Staphylococcus spp. isolated from nares and armpits of students. A total of 91 swab samples were collected from consenting microbiology students. Characterization of isolates was done using conventional microbiological guidelines yielding 50 Staphylococcal isolates and antimicrobial susceptibility was done following CLSI guidelines. Biofilm formation was detected using the congo red agar method and efflux activity was assayed by a modification of the EtBr cart wheel method using local blue dye. Among the 50 staphylococcal isolates, 7(14%) were coagulase positive while 43(86%) were coagulase negative. Antimicrobial susceptibility pattern of isolates showed resistance of 46(92%) to augmentin, 45(90%) to cloxacillin, 43(86%) to erythromycin, 41(84%) to cefuroxime and 39(78%) to ceftazidime. Resistance to gentamicin and oflaxacin was observed in only 5(10%) of the isolates. Biofilm formation (blackening of medium) was observed in 10(36%) of the 28 multi-drug resistant isolates and 5(83%) of the 6 isolates screened positive for efflux activity (non-retention of blue dye). Biofilm formation and efflux activity have shown to be mechanisms for drug resistance in community-associated staphylococcal isolates with high multi-drug resistance pattern.