Fate of Horizontal-Gene-Transfer Markers and Beta-Lactamase Genes during Thermophilic Composting of Human Excreta

Abstract

Thermophilic composting is a suitable treatment for the recycling of organic wastes for agriculture. However, using human excreta as feedstock for composting raises concerns about antibiotic resistances. 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. Beta-lactamase genes blaCTX-M, blaIMP, and blaTEM conferring resistance to broad-spectrum beta-lactam antibiotics, as well as horizontal gene transfer marker genes, intI1 and korB, were quantified using qPCR. We found low concentrations of the beta-lactamase genes in all samples, with non-significant mean decreases in blaCTX-M and blaTEM copy numbers and a mean increase in blaIMP copy numbers. 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. Thus, thermophilic composting can be a suitable treatment for the recycling of human excreta.

Special Issue “Multidrug-Resistant Bacteria in the Environment, Their Resistance and Transfer Mechanisms”

“…Werner and coworkers found low concentrations of beta-lactamase genes in samples prior to, during and after thermophilic composting, as well as a decline in the horizontal gene transfer marker genes, intI1 and korB, from the start to the end of composting. Thus, thermophilic composting can decrease the horizontal spread of ARGs and could be a suitable treatment for the recycling of human excreta [11].…”