Prevalence of antibiotic resistant genes in selected activated sludge processes in Isfahan Province, Iran

Document Type : Original Article


Department of Environmental Health Engineering, School of Nursing and Health, Urmia University of Medical Sciences, Urmia, Iran


Wastewater treatment plants are one of the main sources of dissemination of antibiotic resistance genes (ARGs) into the environment. The present study was conducted to determine the prevalence and removal of ARGs in different wastewater treatment processes. A total of 36 samples from raw and final effluent of different activated sludge processes were collected and analyzed. Molecular analysis was conducted on the samples for the detection of encoding genes resistant to three groups of antibiotics (tetracycline, erythromycin, and sulfonamide). The results of this study showed that all ARGs were identified in activated sludge processes (average 70%). Comparison of different activated sludge processed showed that the removal percentage patterns were A-B process, conventional process, and extended aeration process, respectively. The results of this study showed that ARGs were present in relatively high levels in activated sludge process. The results also indicated that the activated sludge process did not contribute to effective reduction of ARGs. However, this revealed the major role of the activated sludge process in the distribution of ARGs in the environment. Thus, it seems that the improvement of the process is necessary for ARGs control in activated sludge process. 


1. Zhang XX, Zhang T, Fang HH. Antibiotic resistance genes in water environment. Appl Microbiol Biotechnol 2009; 82(3): 397-414.
2. Gao P, Munir M, Xagoraraki I. Correlation of tetracycline and sulfonamide antibiotics with corresponding resistance genes and resistant bacteria in a conventional municipal wastewater treatment plant. Sci Total Environ 2012; 421-422: 173-83.
3. Bouki C, Venieri D, Diamadopoulos E. Detection and fate of antibiotic resistant bacteria in wastewater treatment plants: a review. Ecotoxicol Environ Saf 2013; 91: 1-9.
4. Kummerer K. Significance of antibiotics in the environment. J Antimicrob Chemother 2003; 52(1): 5-7.
5. Tao R, Ying GG, Su HC, Zhou HW, Sidhu JP. Detection of antibiotic resistance and tetracycline resistance genes in Enterobacteriaceae isolated from the Pearl rivers in South China. Environ Pollut 2010; 158(6): 2101-9.
6. Sarmah AK, Meyer MT, Boxall AB. A global perspective on the use, sales, exposure pathways, occurrence, fate and effects of veterinary antibiotics (VAs) in the environment. Chemosphere 2006; 65(5): 725-59.
7. Wright GD. The antibiotic resistome: the nexus of chemical and genetic diversity. Nat Rev Microbiol 2007; 5(3): 175-86.
8. Aali R, Nikaeen M, Khanahmad H, Hassanzadeh A. Monitoring and comparison of antibiotic resistant bacteria and their resistance genes in municipal and hospital wastewaters. Int J Prev Med 2014; 5(7): 887-94.
9. Wang HH, Schaffner DW. Antibiotic resistance: how much do we know and where do we go from here? Appl Environ Microbiol 2011; 77(20): 7093-5.
10. Huang JJ, Hu HY, Lu SQ, Li Y, Tang F, Lu Y, et al. Monitoring and evaluation of antibiotic-resistant bacteria at a municipal wastewater treatment plant in China. Environ Int 2012; 42: 31-6.
11. Auerbach EA, Seyfried EE, McMahon KD. Tetracycline resistance genes in activated sludge wastewater treatment plants. Water Res 2007; 41(5): 1143-51.
12. Munir M, Wong K, Xagoraraki I. Release of antibiotic resistant bacteria and genes in the effluent and biosolids of five wastewater utilities in Michigan. Water Res 2011; 45(2): 681-93.
13. Rosenblatt-Farrell N. The landscape of antibiotic resistance. Environ Health Perspect 2009; 117(6): A244-A250.
14. Szczepanowski R, Linke B, Krahn I, Gartemann KH, Gutzkow T, Eichler W, et al. Detection of 140 clinically relevant antibiotic-resistance genes in the plasmid metagenome of wastewater treatment plant bacteria showing reduced susceptibility to selected antibiotics. Microbiology 2009; 155(Pt 7): 2306-19.
15. Pruden A, Pei R, Storteboom H, Carlson KH. Antibiotic resistance genes as emerging contaminants: studies in northern Colorado. Environ Sci Technol 2006; 40(23): 7445-50.
16. Munir M, Xagoraraki I. Levels of antibiotic resistance genes in manure, biosolids, and fertilized soil. J Environ Qual 2011; 40(1): 248-55.
17. Iwane T, Urase T, Yamamoto K. Possible impact of treated wastewater discharge on incidence of antibiotic resistant bacteria in river water. Water Sci Technol 2001; 43(2): 91-9.
18. Reinthaler FF, Posch J, Feierl G, Wust G, Haas D, Ruckenbauer G, et al. Antibiotic resistance of E. coli in sewage and sludge. Water Res 2003; 37(8): 1685-90.
19. Czekalski N, Berthold T, Caucci S, Egli A, Burgmann H. Increased levels of multiresistant bacteria and resistance genes after wastewater treatment and their dissemination into lake geneva, Switzerland. Front Microbiol 2012; 3: 106.
20. Wright GD. Antibiotic resistance in the environment: a link to the clinic? Curr Opin Microbiol 2010; 13(5): 589-94.
21. Chee-Sanford JC, Aminov RI, Krapac IJ, Garrigues-Jeanjean N, Mackie RI. Occurrence and diversity of tetracycline resistance genes in lagoons and groundwater underlying two swine production facilities. Appl Environ Microbiol 2001; 67(4): 1494-502.
22. Kummerer K. Resistance in the environment. J Antimicrob Chemother 2004; 54(2): 311-20.
23. Samadi N, Aali R, Asgari E, Mirhosaeini H, Shahriari A, Mahmoodi F, et al. Identification of clinically antibiotic resistant genes Aac(3)-IIa and Aac(6')-Ib in wastewater samples by multiplex PCR. Environmental Health Engineering and Management Journal 2015; 2(2): 47-52.
24. Rodriguez-Mozaz S, Chamorro S, Marti E, Huerta B, Gros M, Sanchez-Melsio A, et al. Occurrence of antibiotics and antibiotic resistance genes in hospital and urban wastewaters and their impact on the receiving river. Water Res 2015; 69: 234-42.
25. Aydin S, Ince B, Ince O. Development of antibiotic resistance genes in microbial communities during long-term operation of anaerobic reactors in the treatment of pharmaceutical wastewater. Water Res 2015; 83: 337-44.
26. Lee DY, Seo YS, Rayamajhi N, Kang ML, Lee SI, Yoo HS. Isolation, characterization, and evaluation of wild isolates of Lactobacillus reuteri from pig feces. J Microbiol 2009; 47(6): 663-72.
27. Negreanu Y, Pasternak Z, Jurkevitch E, Cytryn E. Impact of treated wastewater irrigation on antibiotic resistance in agricultural soils. Environ Sci Technol 2012; 46(9): 4800-8.
28. Knapp CW, Zhang W, Sturm BS, Graham DW. Differential fate of erythromycin and beta-lactam resistance genes from swine lagoon waste under different aquatic conditions. Environ Pollut 2010; 158(5): 1506-12.
29. Knapp CW, Dolfing J, Ehlert PA, Graham DW. Evidence of increasing antibiotic resistance gene abundances in archived soils since 1940. Environ Sci Technol 2010; 44(2): 580-7.