Culture-free supernatant of potential probiotic Bacillus albus attenuates the expression of biofilm-associated virulence determinants in Burkholderia thailandensis and Staphylococcus aureus.
Abstract
The role of native bacterial probiotics in the Chinese traditional fermentation starter, Qubing, has not been previously studied. In this investigation, 22 bacterial strains were isolated from Qubing, and potential probiotic candidates were selected for their antibiofilm activity against Burkholderia thailandensis and Staphylococcus aureus. The most resistant bacterial isolates were highly tolerant of simulated harsh conditions, including acid, bile salts, and gastric juice. Many isolates exhibited bile-salt hydrolase activity, suggesting that they reduce cholesterol levels by deconjugating bile acids. Furthermore, numerous isolates exhibit greater auto-aggregation and hydrophobicity, enabling adhesion to the gastrointestinal tract and facilitating colonization while preventing pathogen invasion. Moreover, culture-free supernatants (CFSs) from the isolates showed considerable antibacterial effect against B. thailandensis and S. aureus. Tricine-SDS gel electrophoresis revealed protein bands at 8 kDa, indicating bacteriocin-like activity. The proteolytic, amylolytic, lipolytic, and cellulolytic activities were observed in the majority of isolates, whereas a few isolates demonstrated β-galactosidase, phytase, and exopolysaccharide production. Almost all isolates demonstrated notable cholesterol assimilation and free radical-scavenging activities. The absence of antibiotic resistance and the non-hemolytic properties underscore safety. Bacillus subtilis QB-07 and Bacillus albus QB-10 were identified as potential isolates by principal component analysis. The B. albus QB-10 CFS showed a dose-dependent reduction in biofilm formation by the tested bacterial pathogens, confirmed by microscopic observation (CLSM and SEM). RT-qPCR studies exhibited that CFS differentially regulates biofilm-associated virulence gene expression in tested pathogens. Thus, the promising probiotic B. albus CFS could serve as an alternative source for identifying novel antibiofilm peptides in the future.