Abstract
The use of antimicrobials in intensive poultry production is becoming increasingly common because of its high throughput of meat and egg products. However, the profile of antibiotic resistance genes (ARGs) and the underlying mechanisms in different breeding scale farms were not fully explored. The study examined the profiles of ARGs in layer manure from three free-range and 12 intensive layer farms with different scales (N500, N5000, N10000, and N20000). A quantitative PCR (qPCR) array was used to quantify ARGs, and microbial community structure was analyzed by 16S rRNA gene sequencing. A total of 48 ARGs, belonging to seven major types, were identified in the layer manure samples, with sul2, tetM-01, and ermB being the predominant ones. The abundance, diversity, and mobility potential of ARGs in layer manure changed significantly with the increasing of the breeding scale. The abundances of total ARGs had significantly positive correlations with mobile genetic elements (MGEs), suggesting the mobility potential of ARGs in layer manure samples. Bacterial abundance did not show significant differences among the five group manure samples. However, bacterial diversity showed an increasing trend along the breeding scale. Pathogenic Bacteroidetes increased in the largest-scale layer manure samples and showed significant positive correlations with most ARGs. Network analysis revealed significant co-occurrence patterns between ARGs and microbial taxa, indicating ARGs had a wide range of bacterial hosts. Proteobacteria and Firmicutes were potential hosts for tetracycline and macrolide-lincosamide-streptogramin B (MLSB) resistant genes. Our results indicated that the expansion of the breeding scale of a farm promotes the abundance, diversity, and mobility potential of ARGs in layer manure.
Highlights
Most of the antibiotics used in humans or poultry are not fully metabolized, and they are discharged into the external environment through the application of manure, soil leakage, surface run-off, and escape into the atmospheric particulate matter (Udikovic-Kolic et al, 2014; McEachran et al, 2015)
Forty-eight antibiotic resistance genes (ARGs) were detected in layer manure from 15 layer farms with different breeding scales
The relative abundance of ARGs within their bacterial community was represented by their proportion relative to the 16S rRNA gene for each layer manure sample
Summary
As the pillar industry of agriculture, plays a vital role in improving the living standards of the population (Xia et al, 2017). With the intensive development of the breeding industry, antibiotics are often added to feed to promote animal growth or improve animal immunity (Qian et al, 2018). The abuse of antibiotics could induce the occurrence of antibiotic resistance genes (ARGs) in animal gut (Rodriguez-Rojas et al, 2013; Hu et al, 2014). Driven by the “One Health” concept, which emphasizes the interdependence of human, animal, and environmental health, ARGs are regarded as emerging environmental pollutants and are a major public health concern (Pruden et al, 2006; Sanderson et al, 2016), especially when found in pathogens infecting humans (Jiang et al, 2017). The emergence in recent years of “superbugs” with multidrug resistance highlights the seriousness of bacterial resistance in the livestock breeding environment (Nagarajan et al, 2018, Gu et al, 2020)
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