Elimination of the risks of colistin resistance gene (mcr-1) in livestock manure during composting

Since its discovery in Escherichia coli , the emergence and rapid spread of the plasmid-mediated colistin resistance gene mcr - 1 have become a public health concern. Livestock manure is a potentially important reservoir of mcr - 1 because colistin has been widely used in livestock production. Efforts made to accurately quantify the prevalence of mcr - 1 in livestock manure and the dynamic changes therein during thermophilic composting have been few and far between. In this study, mcr - 1 in 51 collected samples from four kinds of livestock manures was detected and quantified. In total, 16 manure samples were found to be mcr - 1 positive, with a detection frequency of 31% in 51 samples. The numbers of mcr - 1 gene copies in 12 positive manure samples with a high prevalence of mcr - 1 were 10 7 –10 9 copies/g dry weight. During composting, >90% of mcr - 1 in the manure was eliminated in 15 days at high temperature (44–65 °C), and mcr - 1 was completely undetectable after 22 days. The reduction of mcr - 1 following manure composting may be ascribed to the decreased number of potential mcr - 1 –harboring bacteria, Enterobacteriaceae and Pseudomonas . The results indicated that thermophilic composting effectively eliminated mcr - 1 and inhibited its spread from livestock manure to the environment.