Characterization of Some Genotypic and Phenotypic Traits of Biofilm Producing Clinical Isolates of Methicillin Resistant Staphylococcus Epidermidis

Abstract

Staphylococcus epidermidis is a major commensal bacterium. Various strains of methicillin resistant S. epidermidis are capable of forming biofilms and it is found to be associated with many hospital-acquired infections. Bacterial biofilms, which are micro-colonies encased in extracellular polysaccharide material, mediated by gene products of the icaADBC operon, are the sources of many bacterial infections which is so difficult to respond to routine treatments. In this research, we investigated the biofilm forming capacity of a 100 methicillin resistant staphylococcus epidermidis isolates, isolated from different clinical specimens delivered to the Diagnostic Microbiology Laboratories and Surveillance Laboratory, Faculty of Medicine, Alexandria University, in relation to the icaADBC gene cluster. Also, the minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) assays were used to evaluate the antibiotic sensitivity patterns of these MRSE isolates in their planktonic and biofilm phases to Vancomycin and Linezolid. The results showed that only 27 isolates (27%) produced detectable biofilm, and icaADBC gene was detected in only 5 of these isolates. Moreover, there was no statistical association between the presence of the gene and the biofilm status. All 27 biofilm producing isolates were susceptible to both Vancomycin and Linezolid in their planktonic state, but the MBEC values of Vancomycin were higher than those of Linezolid in almost all strains, with an agreement between both MBEC values in 15/27 (55.5%) of isolates and disagreement in 12/27 (44.5%) of isolates, and this was statistically significant (p<0.05). In conclusion, this study indicates that the presence of icaADBC gene is not always associated with in-vitro formation of biofilm. Although Vancomycin and Linezolid continued to be effective for planktonic MRSE infection, their sub-MIC concentrations can induce biofilm formation.