Dissemination of Antibiotic Resistance Genes in Representative Broiler Feedlots Environments: Identification of Indicator ARGs and Correlations with Environmental Variables

Abstract

Livestock operations are known to harbor elevated levels of antibiotic resistance genes (ARGs) that may pose a threat to public health. Broiler feedlots may represent an important source of ARGs in the environment. However, the prevalence and dissemination mechanisms of various types of ARGs in the environment of broiler feedlots have not previously been identified. We examined the occurrence, abundance and variation of ARGs conferring resistance to chloramphenicols, sulfonamides and tetracyclines in the environments of two representative types of broiler feedlots (free range and indoor) by quantitative PCR, and assessed their dissemination mechanisms. The results showed the prevalence of various types of ARGs in the environmental samples of the broiler feedlots including manure/litter, soil, sediment, and water samples, with the first report of five chloramphenicol resistance genes (cmlA, floR, fexA, cf r, and fexB) in broiler feedlots. Overall, chloramphenicol resistance genes and sulfonamides sul genes were more abundant than tetracyclines tet genes. The ARG abundances in the samples from indoor boiler feedlots were generally different to the free range feedlots, suggesting the importance of feeding operations in ARG dissemination. Pearson correlation analysis showed significant correlations between ARGs and mobile genetic element genes (int1 and int2), and between the different classes of ARGs themselves, revealing the roles of horizontal gene transfer and coselection for ARG dissemination in the environment. Further regression analysis revealed that fexA, sul1 and tetW could be reliable indicator genes to surrogate anthropogenic sources of ARGs in boiler feedlots (correlations of fexA, sul1 and tetW to all ARGs: R = 0.95, 0.96 and 0.86, p < 0.01). Meanwhile, significant correlations were also identified between indicator ARGs and their corresponding antibiotics. In addition, some ARGs were significantly correlated with typical metals (e.g., Cu, Zn, and As with fexA, fexB, cf r, sul1, tetW, tetO, tetS: R = 0.52−0.71) and some environmental parameters (e.g., TOC, TN, TP, NH 3 −N with fexA, fexB, cf r, sul1, tetW, tetO, tetQ, tetS: R = 0.53−0.87) (p < 0.01). Further redundancy analysis demonstrated that the distribution and transportation of ARGs from the boiler feedlots to the receiving environments were correlated with environmental variables. The findings highlight the contribution of some chemicals such as antibiotics and metals to the development of ARGs in broiler feedlots environments; and the observed ARG dissemination mechanism in the broiler feedlots facilitates the development of effective mitigation measures.

Discharge of swine wastes risks water quality and food safety: Antibiotics and antibiotic resistance genes from swine sources to the receiving environments

“…All collected samples were transported to the laboratory in a cooler for immediate processing following the protocol previously described (He et al, 2014). Briefly, aqueous samples for chemical analysis and ARG analysis were processed within 24 h. For ARG analysis, successive filtration of aqueous samples was filtered through 0.45 μm membrane filters which were stored at −80°C for later DNA extraction.…”

“…All qPCR assays were performed on ViiA™ 7 Real-Time PCR System (ABI, USA) using SYBR Green Real Time QPCR Kit (TOYOBO, Japan). The detailed DNA extraction, purification and ARG determination methods can be referred to our previous study (He et al, 2014;Su et al, 2014aSu et al, , 2014b). …”

“…The transfer of antibiotic resistance determinants from human and livestock sources to the environment has gained attention in the scientific community in the past decade (Silbergeld et al, 2008;Storteboom et al, 2010;Wright, 2010), with antibiotic resistance genes (ARGs) considered as emerging environmental contaminants (Pruden et al, 2006). Human wastes are nowadays better treated by centralized wastewater treatment plants than animal wastes with simple treatment systems such as lagoon and digester or even without any treatment before their discharge into the environment (McKinney et al, 2010;Liu et al, 2012;Zhou et al, 2013;He et al, 2014;Su et al, 2014b;Chen et al, 2015). In comparison with other livestock animals (broiler and cattle), antibiotics are commonly used as growth promoter in swine farming (Zhou et al, 2013;Durso and Cook, 2014), thus swine feedlots are of particular concern as potential hot spots for promoting the dissemination of antibiotic resistance (Gotz and Smalla, 1997;Cole et al, 2000;Binh et al, 2008).…”

“…Since sulfonamides, tetracyclines, macrolides and florfenicol are commonly used in livestock production (Zhou et al, 2013), and such use is perceived to contribute to the development of antibiotic resistance (van den Bogaard and Stobberingh, 2000), sul sulfonamide resistance genes and tet tetracycline resistance genes were the most frequently reported ARGs in diverse livestock operations such as swine and broiler feedlots (McKinney et al, 2010;Koike et al, 2007;Wu et al, 2010;He et al, 2014), followed by erm macrolide-lincosamides-streptogramin B resistance genes (Chen et al, 2007(Chen et al, , 2010. Although chloramphenicol has been banned in food-producing animals since 1994, its alternative antibiotic florfenicol was widely used and their resistance genes (cmlA, floR, fexA, cfr, and fexB) were prevalent in swine feedlots and their surrounding environments (Li et al, 2013).…”

Multi-biomarker responses as indication of contaminant effects in Gambusia affinis from impacted rivers by municipal effluents

“…The concentrations of eight metals including chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb) in the surface water samples were measured by using inductively coupled plasma-mass spectrometry (ICP-MS, Agilent 7700, Agilent) (He et al, 2014).…”