Thermophilic composting is increasingly analyzed regarding its impact on ARGs. This highlights the importance of preventing the contamination of the environment with antibiotic resistance genes (ARGs). There are indications that clinically relevant resistances may be transferred back from environmental to clinical bacteria. The accumulation of multiple resistances with a lack of treatment options is a public health burden, leading to an estimated minimum of 700,000 deaths per year. One of the concerns with the use of human excreta in agriculture are antibiotic resistances that could be introduced into the food chain and thereby promote the antibiotic crisis. Pathogens are usually not adapted to the high temperatures during the thermophilic phase of composting, which leads to their inactivation. Thus, thermophilic composting can be a suitable treatment for the recycling of human excreta. The decrease in both intI1 and korB genes from start to end of composting indicated that thermophilic composting can decrease the horizontal spread of resistance genes. We found low concentrations of the beta-lactamase genes in all samples, with non-significant mean decreases in bla CTX-M and bla TEM copy numbers and a mean increase in bla IMP copy numbers. Beta-lactamase genes bla CTX-M, bla IMP, and bla TEM conferring resistance to broad-spectrum beta-lactam antibiotics, as well as horizontal gene transfer marker genes, intI1 and korB, were quantified using qPCR. We analyzed samples from the start and end of a thermophilic composting trial of human excreta, together with green cuttings and straw, with and without biochar. However, using human excreta as feedstock for composting raises concerns about antibiotic resistances. Thermophilic composting is a suitable treatment for the recycling of organic wastes for agriculture.
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