Quinolone resistance genes (qnrA and qnrS) in bacteriophage particles from wastewater samples and the effect of inducing agents on packaged antibiotic resistance genes

Objectives: This study quantifies quinolone antibiotic resistance genes (qnrA and qnrS) in DNA of phage particles isolated from faecally polluted waters and evaluates the influence of phage inducers on the abundance of antibiotic resistance genes in packaged DNA. Methods: qnrA and qnrS were quantified by qPCR in DNA of phage particles isolated from 18 raw urban wastewater samples, 18 river samples and 28 archived samples of animal wastewater. The bacterial fraction of the samples was treated with mitomycin C, ciprofloxacin, EDTA or sodium citrate under different conditions, and the number of resistance genes in DNA of phage particles was compared with the non-induced samples. Results: qnrA was more prevalent than qnrS, with 100% of positive samples in urban wastewater and river and 71.4% of positive samples in animal wastewater. Densities of qnrA ranged from 2.3×10 2 gene copies (GC)/mL in urban wastewater to 7.4×10 1 GC/mL in animal wastewater. qnrS was detected in 38.9% of urban wastewater samples, in 22.2% of river samples and only in one animal wastewater sample (3.6%). Despite the lower prevalence, qnrS densities reached values of 10 3 GC/mL. Both qnr genes and other resistance genes assayed (blaTEM and blaCTX-M) showed a significant increase in DNA of phage particles when treated with EDTA or sodium citrate, while mitomycin C and ciprofloxacin showed no effect under the different conditions assayed. Conclusions: This study confirms the contribution of phages to the mobilization of resistance genes and the role of the environment and certain inducers in the spread of antibiotic resistance genes by means of phages.