Effect of composting on the conjugative transmission of sulfonamide resistance and sulfonamide-resistant bacterial population

The effect of composting practice on reducing the health risk of manure-derived antibiotic resistance is mainly assessed based on the abundance of antibiotic resistance determinants. This study evaluated the impact of industrial thermophilic manure composting in controlling the risk of sulfonamide resistance (SR) by identifying the patterns of horizontal gene transfer events via conjugation experiments and analyzing the community distribution of sulfonamide-selectively cultured bacteria (SRB) via 16S rRNA sequencing. Results showed that composting removed 75.9% of sulfonamide residues and inhibited the transfer of SR from manure to an Escherichia coli recipient, with variation according to the resistance gene. Composting decreased the abundances and conjugative transfer of sul2 and intI1 effectively but not that of sul1, which is essential for E. coli SR acquisition, and it was more effective in suppressing the co transfer of sul1 with sul2/intI1 rather than the transfer of sul1 individually. Besides, it was found that SRB community responded more effectively to composting when compared with the total bacterial community. The SRB in raw compost showed a predominance of Proteobacteria, whereas the SRB in mature compost mirrored the total bacteria community. Bacillus anthracis, a major sulfonamide-resistant pathogen, was enriched after composting. Overall, composting failed to reduce the risks of sul1 and sulfonamide-resistant pathogenic bacteria effectively, which should be essential targets to optimize manure composting for decreasing the dissemination of antibiotic resistance. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Composting was effective in reducing sulfonamide residues and inhibiting the transfer of specific antibiotic resistance genes, but was not as effective in reducing the risks of certain resistant pathogens. Further optimization is needed to target sul1 and sulfonamide-resistant pathogenic bacteria for better outcomes in manure composting to decrease antibiotic resistance dissemination.