Inappropriate use of antibiotics in pig feed could cause accelerated emergence of antibiotic resistance genes, and agricultural application of swine waste could spread antibiotic resistance genes to the surrounding environment, according to Juan Li of China Agricultural University in Beijing and co–authors there and at China National Center for Food Safety Risk Assessment, Chinese Center for Disease Control and Prevention, Chinese Academy of Science, Beijing Center for Disease Control and Prevention and Capital Medical University.

In a paper soon to be published in Environmental Health Perspectives, the researchers explain that their study was conducted to investigate the distribution of plasmid–mediated quinolone resistance (PMQR) genes from pig feedlots and their surrounding environment.

They used a culture–independent method to identify PMQR genes and estimate their levels in wastewater from seven swine feedlot operations and corresponding wastewater-irrigated farm fields. Concentrations of fluoroquinolones in wastewater and soil samples were determined by ultra-performance liquid chromatography-electrospray tandem mass spectrometry.

The predominant PMQR genes in the samples were qnrD, qepA and oqxB, whereas qnrS and oqxA were present only in wastewater samples. Absolute concentrations of all PMQR genes combined ranged from 1.66 × 10⁷ to 4.06 × 10⁸ copies per mL in wastewater and 4.06 × 10⁶ to 9.52 × 10⁷ copies per gram in soil.

Concentrations of fluoroquinolones ranged from 4.57 to 321ng per mL in wastewater and below detection limit to 23.4ng per g in soil.

Significant correlations were found between the relative abundance of PMQR genes and fluoroquinolone concentrations (r=0.71' p=0.005) and the relative abundance of PMQR genes in paired wastewater and agricultural soil samples (r=0.91; p=0.005).

Wastewater from pig farms may be a source of PMQR genes that could facilitate the spread of antibiotic resistance, concluded Li and co–authors. They add that, to their knowledge, this is the first study to examine the occurrence of PMQR genes in animal husbandry environments using a culture–independent method.

Reference

Li J., Wang T., Shao B., Shen J., Wang S, and Wu Y. 2012. Plasmid-mediated quinolone resistance genes and antibiotic residues in wastewater and soil adjacent to swine feedlots: potential transfer to agricultural lands. Environ. Health Perspect. [ahead of print]. http://dx.doi.org/10.1289/ehp.1104776

Further Reading

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