Investigation of Gowharrood River Contamination to Antibiotic Resistant Bacteria

Wastewaters and agricultural effluents are among the main sources of antibiotics and antibiotic resistant microorganisms. Rivers as the sink for the effluents may distribute this kind of contamination in the environment. This study aimed to investigate the variation of antibiotic resistant bacteria density in Gowharrood River. The water and sediment samples were taken at three points along the river (focused on river course in Rasht city), in autumn 2016 and in winter, spring and summer 2017. The number of heterotrophic and coliform bacteria were counted in the Nutrient agar and Eosine-Methylene Blue agar media containing 100 µg/mL of cephalexin, gentamicin, doxycyclin, ciprofloxacin, and trimetoprim antibiotics, respectively. pH and EC were also measured in water samples. Data for bacteria number were analyzed by repeated measures of factorial arrangement in a completely randomized design by SAS software package. As the river passes through the city, pH and EC of water increase. The average EC value of river water in spring and summer seasons was more than 2.5 times its value in autumn and winter seasons. The number of heterotrophic and coliform bacteria in both water body and sediment increased as the river passed throutgh the city. The average density of antibiotic resistant heterotrophic and coliform bacteria in the river water was 3.74 and 2.79 (Log CFU/mL) respectively, and the average density of antibiotic resistant heterotrophic and and coliform bacteria in sediment samples was 5.74 and 5.37 (Log CFU/g) respectively. Resistance pattern of both heterotrophic and coliform bacteria to antibiotics in both sediment and water samples was as follows: cephalexin> gentamicin> ciprofloxacin> doxycyclin> trimetoprim. Seasonal variation patterns for river water and sediment coliforms and sediment heterotrophic bacteria were as follows: winter>autumn>summer>spring. According to the results of this study, Gowharrood river is contaminated with antibiotic resistant, especially cephalexin resistant, bacteria and if the water of this river is used in aquaculture and irrigation of downstream agriculture fields, the antibiotic resistant bacteria and their antibiotic resistance genes may be spread in the other ecosystems and finally may enter the human food chain.