Analysis of Bacterial Communities Resistant to Ciprofloxacin and Tetracycline in Municipal Activated Sludge

Abstract

Wastewater treatment plants are considered to be reservoirs of antibiotic-resistant bacteria (ARB) outside human and animal bodies. To collect the supporting data, we investigated the existence of ARB in the activated sludge process of municipal wastewater treatment by analyzing communities of sludge bacteria that were incubated with high concentrations of antibiotics (ciprofloxacin or tetracycline) , using the next-generation sequencing technique targeting the 16S rRNA gene. Activated sludge samples were taken from aeration tanks at five municipal wastewater treatment plants (MWWTPs) and one university wastewater treatment plant in Thailand and Japan. Bacterial communities in the sludge samples before incubation were similar among the four MWWTPs in Thailand, but obviously different from those in Japan. The composition of sludge bacteria was markedly changed upon incubation. The concentrations of Enterobacteriaceae species in the sludge samples from two MWWTPs in Thailand increased to 71.3 and 81.4% during incubation with ciprofloxacin, indicating high resistance to this antibiotic. No such increases of specific bacteria families were observed during incubation of the sludge samples with tetracycline, but seven of the top ten dominant families of bacteria were common among the samples from three MWWTPs in Thailand, probably owing to the wide range of sludge bacteria resistant to tetracycline.