Abstract
Manure compost has been thought of as a potential important route of transmission of antimicrobial-resistant bacteria (ARB) and antimicrobial resistance genes (ARGs) from livestock to humans. To clarify the abundance of ARB and ARGs, ARB and ARGs were quantitatively determined in tetracycline-resistant Escherichia coli (harboring the tetA gene)-spiked feces in simulated composts. In the simulated composts, the concentration of spiked E. coli decreased below the detection limit at day 7. The tetA gene remained in manure compost for 20 days, although the levels of the gene decreased. Next, to clarify the field conditions of manure compost in Japan, the quantities of tetracycline-resistant bacteria, tetracycline resistance genes, and residual tetracyclines were determined using field-manure-matured composts in livestock farms. Tetracycline-resistant bacteria were detected in 54.5% of tested matured compost (6/11 farms). The copy number of the tetA gene and the concentrations of residual tetracyclines in field manure compost were significantly correlated. These results suggest that the use of antimicrobials in livestock constitutes a selective pressure, not only in livestock feces but also in manure compost. The appropriate use of antimicrobials in livestock and treatment of manure compost are important for avoiding the spread of ARB and ARGs.
Highlights
Antimicrobials are used to treat bacterial infections in both humans and animals
Escherichia coli (TC7-1/DH5α) concentration decreased from the initial concentration to below the detection limit (50 CFU/g) at 55 ◦ C one day after spiking, while at 37, 25, and 4 ◦ C, the bacteria survived for 10, 30, and 80 days, respectively (Figure 1a)
The tetracycline resistance gene (tetA) gene copy number significantly decreased from the initial copy number after 5 and 25 days at 55 and 37 ◦ C, respectively (p < 0.05) (Figure 1b)
Summary
Antimicrobials are used to treat bacterial infections in both humans and animals. In livestock animals, antimicrobials are used as growth promoters in several countries, including Japan.The extensive use of antimicrobials in the veterinary fields has led to great selective pressure for the development of antimicrobial-resistant bacteria (ARB) and the acquisition of transmissible antimicrobial resistance genes (ARGs) [1]. Antimicrobials are used to treat bacterial infections in both humans and animals. ARB and ARGs derived from livestock animals can spread to humans via food, contact, and the environment [2], compromising the effective treatment of bacterial infections in humans and constituting an important public health concern. Manure compost is applied for soil amendment and contributes to the spread of ARB and ARGs in the environment [4]. Such applications can lead to ARB and ARGs contamination of vegetables, and to the transmission of ARB and ARGs from livestock to humans via the food chain
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