Frequency Assay of qnr Genes in Enterobacteriaceae Isolated from Hospital and Urban Wastewaters in Karaj City

Document Type : Research Paper


1 MSc. Graduate Student, Dept. of Microbiology, Karaj Branch, Islamic Azad University, Karaj, Iran

2 Assist. Prof., Dept. of Microbiology, Karaj Branch, Islamic Azad University, Karaj, Iran

3 Assist. Prof., Ecology and Environmental Pollution Control Research Group, Research Institute of Petroleum Industry, Tehran, Iran


In recent years, because of excessive and unregulated use of antibiotics, the threat of acquisition of antibiotic resistance by pathogens is growing. Hospitals are hotspots for antimicrobial-resistant bacteria (ARB) and will be ejected from hospitals via wastewater systems. The aim of this study was the frequency assay of qnr plasmid’s genes in quinolone resistant Entrobacteriaceae strains isolated from urban and hospital wastewaters. A total of 99 Entrobacteriaceae strains were isolated from urban and hospital wastewater in Alborz province during the spring of 2019. Bacterial strains were identified by standard microbiological and biochemical tests. The antimicrobial susceptibility test to ciprofloxain, levofloxacin, ofloxacin, norfloxacine and nalidxic acid was determined by Kirby-Bauer method and the frequency of quinolone resistance genes (qnrA, qnrB, qnrS) was investigated by PCR. Among the organisms cultured, Escherichia coli was the most common organism followed by Escherichia coli (inactive) and Citrobacter freundii. The most antibiotic resistance was observed against nalidixic acid.  Most of the isolates (61%) harboured the qnrA gene. qnrB and qnrS genes were found in 31% and 8% of isolates respectively. One isolate has both qnrA and qnrB genes. Most of the strains that contain qnrA and qnrB genes were isolated from hospital and urban wastewater respectively. Antimicrobial resistance should now be seen as an environmental pollutant and new wastewater treatment processes must be assessed for their capability in eliminating antimicrobial-resistant bacteria, especially from hospital effluents. Also, unregulated use of antibiotics should be stopped.


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