AUTHOR=Agga Getahun E. , Kasumba John , Loughrin John H. , Conte Eric D. 

TITLE=Anaerobic Digestion of Tetracycline Spiked Livestock Manure and Poultry Litter Increased the Abundances of Antibiotic and Heavy Metal Resistance Genes

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.614424

DOI=10.3389/fmicb.2020.614424

ISSN=1664-302X

ABSTRACT=<p>Anaerobic digestion is used for the treatment of animal manure by generating biogas. Heavy metals cause environmental pollutions and co-select for antimicrobial resistance. We evaluated the impact of mesophilic anaerobic digestion of cattle manure (CM), swine manure (SM) and poultry litter (PL) on the concentrations of seven tetracycline [<italic>tet</italic>(A), <italic>tet</italic>(B), <italic>tet</italic>(G), <italic>tet</italic>(M), <italic>tet</italic>(O), <italic>tet</italic>(Q), and <italic>tet</italic>(W)], macrolide [<italic>erm</italic>(B)], methicillin (<italic>mec</italic>A and <italic>mec</italic>C), copper (<italic>cop</italic>B, <italic>pco</italic>A, <italic>pco</italic>D, and <italic>tcr</italic>B) and zinc (<italic>czr</italic>C) resistance genes, and three bacterial species (<italic>E. coli</italic>, <italic>Enterococcus</italic> spp. and <italic>Staphylococcus aureus</italic>). The total bacterial population and total abundance of the seven <italic>tet</italic> genes significantly increased in the three manure types after digestion. Concentration of <italic>tet</italic>(M) was strongly correlated with that of <italic>erm</italic>(B) and enterococci. As concentration of tetracyclines declined during anaerobic digestion, that of four <italic>tet</italic> genes (A, B, Q, and W) and 16S rRNA increased, that of <italic>tet</italic>(M) decreased, and that of <italic>tet</italic>(G) and <italic>tet</italic>(O) did not change. Concentrations of <italic>cop</italic>B and <italic>pco</italic>A did not change; while that of <italic>pco</italic>D did not change in the PL, it increased in the SM and CM. While the concentration of enterococci remained unchanged in CM, it significantly increased in the PL and SM. Concentrations of <italic>tcr</italic>B significantly increased in the three manure types. While concentrations of <italic>S. aureus</italic> significantly increased in the CM and PL, that of SM was not affected. Concentrations of <italic>mec</italic>C significantly increased in all manure types after digestion; while <italic>mec</italic>A concentrations did not change in the SM, they significantly increased in CM and PL. While concentration of <italic>czr</italic>C remained low in the CM, it increased in the PL but declined in the SM. In conclusion, while mesophilic anaerobic digestion of animal manure decreased concentration of tetracyclines, it increased the concentrations of total bacteria, <italic>tet</italic> genes, <italic>E. coli</italic>, enterococci and <italic>S. aureus</italic> and methicillin resistance genes. It did not have any effect on concentrations of heavy metals; concentrations of heavy metal resistance genes either increased or remained unaffected depending on the animal species. This study showed the need for post-digestion treatments of animal manure to remove bacteria, antibiotic resistance genes, heavy metals and their resistance genes.</p>