Microbiological quality of and antimicrobial resistance in commercial probiotic products for food animals in Thailand

Abstract

A total of 45 commercial probiotic products for food animals were investigated for the number of viable cells, bacterial species and the presence of antimicrobial resistance (AMR) genes. All products were enumerated for viable bacterial cells of Lactobacillus, Bacillus and Enterococcus. Confirmation of species was carried out by multiplex Polymerase Chain Reaction (PCR) for Lactobacillus (n=20), Enterococcus (n=20), and Amplified Ribosomal DNA Restriction Analysis (ARDRA) for Bacillus (n=190). The presence of Clostridium species was examined by PCR. The contamination of E. coli and Salmonella was also determined. Minimal Inhibitory Concentrations (MICs) for 14 antimicrobials was examined in the bacterial isolates obtained (n=64). The presence of 111 genes encoding resistance to clinically important antibiotics was tested in probiotic products (n=45). Possible resistance gene transferability was investigated in the isolates with resistance phenotype. The results showed that 34 of 45 products (75.5%) were incorrectly labeled in either numbers of viable cells or bacterial species or both. None of the products tested were contaminated with E. coli and Salmonella. Thirty-three out of 64 isolates (51.6%) exhibited resistance to at least one antimicrobial agent. Resistance to chloramphenicol (21%) was highest among probiotic bacteria, followed by trimethoprim (17%), clindamycin (16%) sulfamethoxazole (15%), ampicillin (10%), erythromycin (9%), vancomycin (9%), tetracycline (8%), ciprofloxacin (6%), streptomycin (5%) and kanamycin (5%). Sixteen in 45 products (35.5%) were positive to at least one AMR genes, including genes encoding resistance to β-lactamase (blaOXA-1-like and blaSHV), ciprofloxacin [oqxAB, qnrD, aac(6’)-Ib-cr, qrnB, and qnrS), streptomycin (aadA1, aadA2, aadE and strA-strB), gentamicin [aac(3)-II and aac(6’)-aph(2’’)], kanamycin [ant(4’)-Ia and aph(3’)-IIIa], tetracycline (tetA, tetB, tetL and tetM), chloramphenicol (catA and cmlA), macrolide (mefA), trimethoprim (dfrA12 and dfrA14), sulfonamide (sul1) and vancomycin (vanC). Almost AMR genes detected in probiotic products were not correlated to AMR phenotype of probiotic bacteria found in these products. Three streptomycin- resistant Lactobacillus isolates could horizontally transfer their resistance determinants. The findings demonstrated that the probiotic products could serve as reservoirs for spread of AMR genes and may not yield benefits to animals as claimed. The observations highlight the need for the adequate quality control of probiotic products.