Association of florfenicol residues with the abundance of oxazolidinone resistance genes in livestock manures.

• The positive detection rate of ARGs was 89.17 % in 157 livestock farms. • Of the tested ARGs, optr A was the most frequently detected in samples. • Poultry and swine manure had higher ARG diversity and abundance than bovine manure. • Florfenicol residues in manures may lead to occurrence of linezolid resistance genes. Livestock and poultry manures are major reservoirs of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs). Linezolid is a clinical medicine for humans and has never been approved for use in livestock. Interestingly, three linezolid resistance genes (cfr , optr A, and poxt A) have been detected in bacteria of animal origin, arousing public concern. This study investigated the abundance of three ARGs, cfr , optr A, and poxt A, in manures from 157 large-scale farms in China using real-time quantitative polymerase chain reaction. The residual concentrations of linezolid, florfenicol, tiamulin, and valnemulin were determined using ultra-high performance liquid chromatography-tandem mass spectrometry. A total of 140 livestock farms were tested positive for ARGs, and the positive detection rate was 89.17 %. Optr A was the most commonly detected ARG. The diversity and abundance of ARGs were significantly higher in poultry and swine manure than in bovine manure. Redundancy analysis presented a strong association between florfenicol and all the three ARGs targeted in the study, and tiamulin showed a significant correlation with optr A. Our results indicated that the residual concentration of florfenicol had a major effect on the distribution of the three ARGs in livestock manures, and extensive use of florfenicol may lead to the production of linezolid resistance genes. [ABSTRACT FROM AUTHOR]