Fate of tetracycline, sulfonamide and fluoroquinolone resistance genes and the changes in bacterial diversity during composting of swine manure

This study monitored the abundance of antibiotic resistant genes (ARGs) and the bacterial diversity during composting of swine manure spiked with chlortetracycline, sulfadiazine and ciprofloxacin at two different levels and a control without antibiotics. Resistance genes of tetracycline (tetQ, tetW, tetC, tetG, tetZ and tetY), sulfonamide (sul1, sul2, dfrA1 and dfrA7) and fluoroquinolone (gyrA and parC) represented 0.02–1.91%, 0.67–10.28% and 0.00005–0.0002%, respectively, of the total 16S rDNA copies in the initial composting mass. After 28–42 days of composting, these ARGs, except parC, were undetectable in the composting mass indicating that composting is a potential method of manure management. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis of bacterial 16S rDNA of the composting mass indicated that the addition of antibiotics up to 100, 20 and 20 mg/kg of chlortetracycline, sulfadiazine and ciprofloxacin, respectively, elicited only a transient perturbation and the bacterial diversity was restored in due course of composting.

► Tet genes represented 0.02–1.91% of the total 16S rDNA copies in the initial composting mass. ► Sulfonamide resistance genes represented 0.67–10.28% of the total 16S rDNA copies. ► QRDR region of the parC gene was persistent in the composting mass after 56 days of composting. ► All the tested ARGs, except parC, were undetectable after 28–42 days of composting. ► Addition of antibiotics elicited only a transient perturbation on bacterial diversity.