Occurrence of antimicrobial-resistant Escherichia coli in sewage treatment plants of South India

Antibiotics received by sewage treatment plants may be the causative factor in spreading antibiotic resistance bacteria in the aquatic environment. The current study investigates the distribution of antimicrobial-resistant Escherichia coli (E. coli) in four sewage treatment plants (STPs) in South India receiving hospital and domestic wastewater in different proportions. A total of 221 E. coli isolates were checked for antimicrobial resistance against 16 antimicrobials. Among the antimicrobials tested, ampicillin (AMP) and cefazolin (CFZ) showed resistance between 20% and 90%, nalidixic acid (NAL) and ciprofloxacin (CIP) showed resistance between 15% and 75% and chloramphenicol (CHL) showed resistance between 2% and 20%. Based on the observations, there is no significant difference between the wastewater inlet and outlet, suggesting that treatment process was not effective in reducing the resistance. In conclusion, the trends of antimicrobial resistance pattern show that the levels of resistance were slightly higher in hospital wastewater than domestic wastewater.