Inhibitory effect of marine cyanobacterial extract on biofilm formation and virulence factor production of bacterial pathogens causing vibriosis in aquaculture

Abstract

Emergence of extended antibiotic resistance among bacterial pathogens often leads to the failure of existing antibiotics to treat bacterial infections; therefore, there is an urgent need to look for novel alternative treatment measures. The aim of this study was to evaluate the anti-quorum sensing (QS) potential of Synechococcus sp., to prevent the onset of bacterial infections as an alternate to antibiotics. A total of 110 marine cyanobacterial strains were screened for their anti-QS activity against biomarker strain Chromobacterium violaceum (ATCC 12472) and aquatic bacterial pathogens Vibrio harveyi (MTCC 3438) and Vibrio vulnificus (MTCC 1145). Of the 110 strains tested, the extract of unicellular algae Synechococcus sp. (Q-25) exhibited the efficient reduction in the production of violacein pigment of C. violaceum to the level of 82 %, bioluminescence of V. harveyi to 91 % and protease in V. vulnificus to 63 %. In V. harveyi and V. vulnificus, it exhibited a significant reduction of 71 and 84 % in biofilm formation and 66 and 68 % in EPS production, respectively, without any antibacterial activity. Confocal laser scanning microscopic and light microscopic analyses further confirmed that the Q-25 extract effectively prevented initial attachment as well as disrupting the architecture of mature biofilm, when compared to their untreated controls. In addition, the characterization of active principle by gas chromatography–mass spectrometry analysis confirmed the presence of stable bioactive compound hexadecanoic acid in the extract. Hence, this study clearly revealed the antibiofilm and QS inhibitory potential of the cyanobacterium, Synechococcus sp.