Abstract
BackgroundThe prevalence of antibiotic resistance genes (ARGs) in animal manure poses a threat to environmental safety. Organic fertilizers fermented by livestock and poultry manure are directly applied to farmland and have the potential to cause outbreaks of bacterial resistance in agricultural environments. This study investigated the composition of ARGs in different animal manures and their derived organic fertilizers.ResultsThe results showed that the abundance of several ARGs, such as sul2, TetB-01, TetG-01 and TetM-01, in organic fertilizer samples was 12–96% lower than that in animal manure. However, the abundance of TetK and ermC was higher in animal manure than in organic fertilizers. No correlation between ARGs and environmental factors such as pH, TN, and antibiotics was observed by redundancy analysis (RDA). Procrustes analysis revealed a significant correlation between bacterial community structures and ARG abundance (r = 0.799, p < 0.01). Nonmetric multidimensional scaling (NMDS) analysis suggested that microorganisms in organic fertilizer may be derived from animal manure. Additionally, the abundance of pathogenic bacteria (especially Actinomadura) would increase rather than decrease in manure compared to organic fertilizer.ConclusionThe diversity and abundance of most ARGs significantly decreased from animal manure to organic fertilizer. Microorganisms in the prepared organic fertilizer may mainly be inherited from the animal manure. The results also showed that the pathogens in the prepared organic fertilizer would significantly reduce, but would still cause partial pathogen proliferation.
Highlights
The prevalence of antibiotic resistance genes (ARGs) in animal manure poses a threat to environmental safety
The results showed that the ARG diversity in the organic fertilizer samples was relatively lower than that in the animal manure samples (p < 0.05) (Fig. 1a)
The absolute abundance of ARGs in the animal manure and organic fertilizer samples was in the range of 2.1 × 105 to 7.8 × 105 copies/g and 1.6 × 105 to 7.3 × 105 copies/g, respectively, which was similar to the findings by Zhang et al [30]
Summary
The prevalence of antibiotic resistance genes (ARGs) in animal manure poses a threat to environmental safety. Organic fertilizers fermented by livestock and poultry manure are directly applied to farmland and have the potential to cause outbreaks of bacterial resistance in agricultural environments. ARGs could enter the environment via discharge of animal manure, leading to the contamination of soil, water and crops [12]. Fang et al study found that there were multidrug resistance (MDR) genes in stream water, which were disseminated from pig feedlot to surrounding stream via pig manure fertilization [16]; and Zhang et al study described that cattle manure application increased the abundance of ARGs in plant root, while poultry manure application increased ARGs in rhizosphere, root endophyte and phyllosphere [17]. The continuous increase or high persistence of ARGs in livestock environments may pose potential threats to human health and the ecological environment [18, 19]
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