Biofilm Formation and Prevalence of Biofilm-Related Genes Among Clinical Strains of Multidrug-Resistant <i>Staphylococcus aureus</i>

Abstract

The biofilm-forming <i>Staphylococcus aureus</i> strains are responsible for causing a number of diseases. With the emergence of multidrug resistance they constitute a catastrophic threat to medicine. The ability of 65 clinical strains of multidrug-resistant <i>S. aureus</i> (MDRSA) to form biofilm <i>in vitro</i> was examined in this study and analyzed in relation to SCC<i>mec</i>, <i>spa</i> type, microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), and <i>ica</i> genes. Results obtained from crystal violet and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays showed that all MDRSA strains tested form biofilm but, of 65 strains, only 18 strains (28%) were found to form a biofilm with high metabolic activity and a great amount of biomass. The high proportion of MDRSA isolates in our study made no significant difference for <i>ica</i> and MSCRAMMs genes according to biofilm-forming capacity, except for <i>fib</i>, <i>icaA</i>, and <i>cna</i> gene. In addition, this study demonstrated that strains carrying SCC<i>mec</i> type I showed a significantly decreased biofilm viability compared with the strains harboring SCC<i>mec</i> type II and type IV, but SCC<i>mec</i> type could not serve as a good predictor of biofilm formation. However, we found that significantly weaker metabolic activity was detected in the biofilm of isolates with <i>spa</i> type t011.