Quorum quenching and anti-biofilm activities of halotolerant Bacillus strains isolated in different environments in Algeria.

Aims: The current study aimed to screen Bacillus strains with wide-spectrum quorum quenching (QQ) activity against N-acyl-l-homoserine lactones (AHLs), helpful in controlling virulence traits in Gram-negatives, including biofilm formation and also with anti-biofilm activity against Gram-positives.

Methods And Results: A total of 94 halotolerant strains of Bacillus isolated from soil and salt-lake sediment samples in Algeria were examined for the presence of QQ activity against AHLs, the presence of the aiiA gene, encoding an AHL lactonase enzyme typical of Bacillus spp., antimicrobial and anti-biofilm activities against Pseudomonas aeruginosa and Streptococcus mutans. Of all strains of Bacillus spp. isolated, 48.9% showed antibacterial activity. In addition, 40% of these isolates showed a positive QQ activity against long-chain AHLs, of which seven strains presented the aiiA gene. Among the species with broad-spectrum QQ activity, the cell extract of Bacillus thuringiensis DZ16 showed antibiofilm activity against P. aeruginosa PAO1, reducing 60% using the Amsterdam active attachment (AAA) biofilm cultivation model. In addition, the cell extract of B. subtilis DZ17, also presenting a broad-spectrum QQ activity, significantly reduced Strep. mutans ATCC 25175 biofilm formations by 63% and 53% in the xCELLigence and the AAA model, respectively, without affecting growth. Strain DZ17 is of particular interest due to its explicit halophilic nature because it can thrive at salinities in the range of 6%-30%.

Conclusions: B. thuringiensis DZ16 and B. subtilis DZ17 strains have interesting antibacterial, QQ, and anti-biofilm activities. The high range of salinities accepted by these strains increases their biotechnological potential. This may open up their use as probiotics, the treatment and prevention of conventional and emerging infectious diseases.

Significance And Impact Of Study: The use of safe, economical and effective probiotics is limited to control the infections related to multi-resistant bacteria. In our study, we provide two promising agents with QQ, anti-biofilm and antibacterial activities.