Antibiofilm activity of coral-associated bacteria against different clinical M serotypes of Streptococcus pyogenes

Streptococcus pyogenes is the frequent cause of purulent infections in humans. Formation of a biofilm is one of the important aspects of its pathogenicity. Streptococcus pyogenes biofilm communities tend to exhibit significant tolerance to antimicrobial challenge during infections. Exploring novel targets against biofilm-forming pathogens is therefore an important alternative treatment measure. We attempted to screen marine bacteria, especially coral-associated bacteria (CAB), for antibiofilm activity against streptococcal biofilm formation. The bacterial biofilms were quantified by crystal violet staining. Of 43 CAB isolates, nine clearly demonstrated antibiofilm activity. At biofilm inhibitory concentrations (BIC), biofilm formation was reduced up to 80%, and sub-BIC (0.5 and 0.25 BIC) significantly reduced biofilm formation by up to 60% and 40-60%, respectively. Extracts of Bacillus horikoshii (E6) displayed efficient antibiofilm activity. As quorum sensing (QS) and cell surface hydrophobicity (CSH) are crucial factors for biofilm formation in S. pyogenes, the CAB were further screened for QS inhibition properties and CSH reduction properties. This study reveals the antibiofilm and QS inhibition property of CAB.