Prevalence of virulence genes and antibiotic susceptibility of Bacillus used in commercial aquaculture probiotics in China

Disease is a significant constraint faced by aquaculture, and its prevention and control bring together a hub of recent research. Several resources and resorts have been applied to prevent diseases in aquaculture. Probiotics are known to be beneficial natural derivatives that have several benefits in aquaculture. Currently, several commercial probiotics are used in the aquaculture industry that contains one or more live microorganisms. In the aquaculture industry, Bacillus species is one of the most widely used probiotic organisms. They are considered distinctive and are found to be natural members of the gut microbiota of some fish species. The safety of beneficial microorganisms is essential since some of these organisms are reported to harbor traits that might be transferable to their hosts. In this study, the safety of some Bacillus-based commercial probiotics used in aquaculture in terms of virulence and drug resistance were assessed. Commercial Bacillus species after isolation were screened for the presence of virulence genes (nheA, nheB, nheC, hblA, hblC, hblD, cytK, and entFM) and one emetic gene (ces), as well as their resistance to some antibiotics. Most isolates did not possess any of the virulence genes assessed. Nonetheless, three isolates harbored the nheABC and entFM enterotoxin genes, while two had the hblA, hblC, hblD, cytK genes. None of the isolates possessed the ces emetic gene. Antibiotic resistance assessment revealed most of the isolates to be resistant to β-lactam antibiotics, including penicillin, ampicillin, oxacillin, cefuroxime, and ceftriaxone, and also to minocycline.