Microbiological quality and possible role as a source of antimicrobial resistance genes of commercial probiotic products for livestock and aquatic animals

The reduction of antimicrobial use is one of the most important action to combat antimicrobial resistance (AMR) crisis. Probiotic products are among alternatives to antibiotics that have been increasingly used in food animal production. Therefore, this study aims to determine the microbiological quality and the presence of resistance genes in some probiotics available for livestock and aquatic animals in Thailand. Nine commercial-probiotic products for livestock and aquatic animals were examined for the number of probiotic bacterial strains as indicated on the product labels. Confirmation of species was performed by multiplex PCR for Lactobacillus and Enterococcus and Amplified Ribosomal DNA Restriction Analysis (ARDRA) for Bacillus. The contamination of pathogenic bacteria (i.e. Escherichia coli and Salmonella enterica) and the presence of 56 genes that encode resistance to clinically-important antibiotics were determined. The results showed that none of the products tested were contaminated with E. coli and Salmonella. Inaccurate labelling in either numbers or species of bacteria was a common issue among the probiotic products tested. Some products did not contain the species as claimed on the label. B. licheniformis and B. sphaericus were commonly misidentified as B. subtilis. Of seven products claimed to contain B. subtilis, six were found to contain B. subtilis cluster consisting B. pumilus, B. amyloliquefaciens and B. atropheus and one was positive to B. licheniformis. Contamination of L. rhamnosus and L. casei-group was frequently found. E. faecium was mislabeled as Streptococcus faecium. Resistance genes encoding resistance to sulphonamides, streptomycin and tetracycline were observed in three products. One product contained both sul1 and aadA2 and one carried tetA and tetM. The study is currently being undertaken to find horizontal transfer of genes in probiotic samples. While the use of probiotics in food animals may generate beneficial effects, it can also pose risks as a source of resistance genes. The results highlight the need to regulate the production and the use of probiotics to assure their quality and reduce their potential contribution to the spread of AMR.

Abstract presented at the 3rd International Symposium on Alternatives to Antibiotics 2019.