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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Bioenergy Research » Research » Publications at this Location » Publication #317609
Title: Examination of the Aerobic Microflora of swine feces and stored swine manure

Author
item Whitehead, Terence
item Cotta, Michael

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2015
Publication Date: 3/1/2016
Citation: Whitehead, T.R., Cotta, M.A. 2015. Examination of the aerobic microflora of swine feces and stored swine manure. Journal of Environmental Quality. 45(2):604-608. doi: 10.2134/jeq2015.05.0248.

Interpretive Summary: Antimicrobial compounds have been commonly used as feed additives for domestic animals to reduce infection and promote growth. Recent reports have suggested such feeding practices may result in increased microbial resistance to antibiotics, which can have an impact on human health. While many investigations have centered on antibiotic resistance in E. coli and other aerobic bacteria, little research has been directed towards investigating antibiotic resistance in the commensal aerobic microflora found in the feces and stored manure of domestic animals. We now report on the number of recoverable antibiotic resistant aerobic bacteria that are present in both swine feces and stored manure, as well as identification of antibiotic resistance genes carried by the bacterial strains. These results provide further evidence that the swine gastrointestinal tract and stored swine manure may serve as reservoirs of antibiotic resistance genes.

Technical Abstract: Antimicrobial compounds are commonly used as feed additives for domestic animals to reduce infection and promote growth, but concerns have arisen that such feeding practices may result in increased microbial resistance to antibiotics used in human health. Our previous studies of the commensal anaerobic bacteria in both swine feces and manure storage pits have revealed that these microorganisms may serve as reservoirs of antibiotic resistance genes. However, little is known regarding antibiotic resistance in the aerobic bacteria. These organisms are present in much lower numbers but could add significantly to the resistance gene pool in these ecosystems. Swine feces and manure samples were plated onto various agar media with and without tetracycline, tylosin, or erythromycin, incubated at 37°C, and colonies counted daily. Randomly selected colonies were isolated and characterized by 16S rDNA sequence analyses and additional antibiotic resistance and biochemical analyses. Colonies were recovered at levels of 10**6 to 10**7 CFU/ml, approximately 100-fold lower than numbers obtained under anaerobic conditions. Addition of antibiotics to the media resulted in counts that were 80%-90% of those in control media without added antibiotics. PCR analyses for antibiotic resistance genes demonstrated the presence of a number of different tet resistance genes from the isolates. In conclusion, the recoverable aerobic microflora of swine feces and manure contain high percentages of bacteria resistant to antibiotics, which include both known and novel genera and species, and contain a variety of antibiotic resistance genes. Further analyses of these and additional isolates should provide information on these organisms as potential reservoirs of antibiotic resistance genes in these ecosystems.