Biofilm formation by Streptococcus pyogenes: modulation of exopolysaccharide by fluoroquinolone derivatives.

Biofilm formation by Streptococcus pyogenes has been demonstrated as a potentially important mechanism contributing to antibiotic treatment failure. S. pyogenes is the frequent cause of purulent infections in humans and also, it could play a significant role in recurrent and chronic infections. S. pyogenes biofilm communities tend to exhibit significant tolerance to antimicrobial challenge during infections. The fluoroquinolone derivatives have been previously reported from our laboratory as effective agents against human bacterial pathogens. Therefore, in the present study, we observed the effect of these fluoroquinolones on biofilm formation. Quantitative analysis using 2,3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide (XTT) at the biofilm inhibitory concentrations (BIC), the compounds 6a, 6c, 7b and 7c reduced 61-71% biofilm and sub-BIC (0.5 and 0.25 BIC) significantly reduced biofilm formation by up to 30-38% and 16-18%, respectively. The Fourier Transform Infrared (FTIR) spectrum of the control and treated S. pyogenes revealed the shift in the chemical entity corresponding to the exopolysaccharide (EPS). The GC/MS analysis showed that the EPS of S. pyogenes has the most abundant neutral sugars l-glucose and d-mannose which is not detected in the fluoroquinolone treated EPS.