Antibiotic resistance of probiotics isolated from Chinese corn stover silage

One of the most important drivers of the emergence of antimicrobial resistance is the irrational usage of antibiotics. But alongside some indirect sources such as feeding Chinese corn stover silage could also transmit resistant genes to animals. This study was aimed at assessing the antibiotic resistance phenotypes, drug resistance genes and mediated drug resistance mechanisms. A total of 37 isolates were obtained by selective medium and identified by 16S rDNA sequencing including Lactobacillus acidophilus (n = 3), Lactobacillus amylovorus (n = 4), Weissella confusa (n = 3), Acetobacter pasteurianus (n = 9), Lactobacillus buchneri (n = 6), Enterococcus faecium (n = 8) and Lactobacillus reuteri (n = 4). Antimicrobial resistance of all isolates to 12 antibiotics was determined using the agar dilution method. Widespread resistance to ampicillin, erythromycin, clindamycin, kanamycin, streptomycin, levofloxacin and ciprofloxacin was observed. The presence of relevant resistance genes was examined by PCR, and the genes pbp5, blaZ, bla TEM, mecA, mexI, tetW, ermB, msrA, msrC, ermC, vatE, aacA-aphD, aphA1, aadA1, aadA2 and vanX were detected. All the isolated strains had multiple drug resistance, and harboured related drug-resistant genes; therefore, the use of probiotics in animal feed should be standardized to reduce the risks of horizontal transmission of drug resistance genes to animal products and human population. Highlights Fermentation bacteria isolated from the silage were identified. Lactobacillus strains isolated from the silage exhibited antimicrobial resistance. Feeding Chinese corn stover silage transmits resistant genes to animals. Standardization of probiotics in animal feed is crucial to avoid horizontal drug resistance.