Prevalence of pleuromutilin antibiotic resistance genes in different laying hen breeding stages in China.

Antimicrobial resistance is a rapidly evolving and extremely complex issue, particularly due to the use of various types of antimicrobials within human, animal, and environmental sectors. Pleuromutilin antibiotics are used to prevent and control respiratory diseases in the rearing stage of hen chicks, but the current status of pleuromutilin resistance in the laying hen breeding process is unclear. ATP-binding cassette transporters encoded by lsa(A), lsa(E), lsa(C) and vga(D) can be transferred by plasmids and transposons, thereby posing a potential dissemination risk. To investigate pleuromutilin resistance in the laying hen production chain in China, 95 samples from five environmental types were collected in four breeding stages to determine the abundances of the main resistance genes by qPCR, i.e. lsa(A), lsa(E), lsa(C) and vga(D). The abundance (5.16 log10GC/g) and detection rate (100%) of lsa(E) was highest in all of the samples, thereby suggesting high contamination with the lsa(E) gene across the large-scale laying hen breeding environment and feces. The lsa(A) (6.02 log10GC/g) and lsa(E) (6.18 log10GC/g) genes were most abundant in flies, and the abundance of vga(D) (4.50 log10GC/g) was highest in dust (P < 0.05). In addition to feces, flies and dust were important sources of contamination with pleuromutilin resistance along the laying hen production chain. In summary, we determined the abundances of four pleuromutilin resistance genes in the laying hen production chain and provided direct evidence of pleuromutilin resistance transmission and environmental contamination. In particular, the chicken breeding stage needs further attention.