Copy numbers of target PMQR genes were normalized to the 16S rRNA copy number (defined as relative abundances) and to 1 g for soil samples or 1 mL for wastewater samples (defined as absolute concentrations: copies per gram or copies per milliliter) to take into account any temporal variations among sites, overall extraction efficiencies, total bacterial community, and potential sample degradation (Graham et al.
A two-tailed Pearson's bivariate correlation analysis was used to compare levels of total PMQR genes in soil and wastewater samples and to compare levels of total PMQR genes and (fluoro)quinolone concentrations.
Among the nine PMQR genes investigated, qnrD, oqxB, and qepA were found in all environmental samples from the target sites; qnrS and oqxA were only detected in wastewater samples; qnrB was found in only three wastewater samples ([F.
Absolute concentrations and relative abundances of the five major PMQR genes (qnrD, oqxB, qepA, qnrS, and oqxA) are shown in Figure 1 and reported in Supplemental Material Tables S3 and S4, respectively (http://dx.
001), and total PMQR genes (sum of five PMQR genes: qnrD, qepA, oqxB, qnrS, and oqxA; r = 0.
The relative abundance of total PMQR genes (sum of the five genes: qnrD, oqxB, qepA, qnrS, and oqxA) and measured concentrations of total (fluoro)quinolones were significantly correlated (r = 0.
We investigated wastewater from seven different swine feedlots and corresponding agricultural soil samples for the presence of PMQR genes.
Although levels of the three PMQR genes (qnrD, oqxB, and qepA) varied among the environmental samples, they were identified in all wastewater samples and corresponding farm soil samples.
Significant correlations were found between some individual (fluoro)quinolones and individual PMQR genes as well as between total (fluoro)quinolones and PMQR genes among all the paired samples, which is consistent with the hypothesis that exposure to antibiotics could lead to selective pressure for resistance genes (Wu et al.
Swine wastewater that contains PMQR genes and (fluoro)quinolone residues and is applied to agricultural fields or released to surrounding rivers might increase the risk that nearby residents will be exposed during farming or through their use of contaminated river water.
A more extensive sampling campaign including crops, waste from humans, and additional river water samples collected at different distances from the point sources would permit a more detailed assessment of the environmental health risk of PMQR genes.