Antimicrobial resistance of enteric bacteria isolated from a sewage treatment plant

Abstract

The present work analysed the frequency of antimicrobial resistant enteric bacteria in a sewage treatment plant in Porto Alegre (RS, Southern Brazil). Water samples were collected every three months, from July/1997 to June /1998, at the inflow, at the facultative stabilization lagoon, at the maturation lagoon and the effluent of the plant. Two sites outside the plant (71a and 71b) were also sampled. Antimicrobial resistance was determined by disc diffusion test on Mueller-Hinton agar, where 18 different antimicrobials were tested. Among the 839 isolated strains, Enterobacter sp (n=348) and Escherichia coli (n=210) were the most frequently observed ones, followed by Proteus sp (n=66), Serratia sp (n=53), Citrobacter sp (n=40), Klebsiella sp (n=37), Yersinia sp (n=32), Shigella sp (n=28) and Salmonella sp (n=25). The total number of bacteria and antimicrobial resistant strains (rs) decreased from inflow (4.69x104cfu/mL;154 rs) to effluent (7.94x103 cfu/mL;49 rs) at the treatment plant. At sites 7a and 7b the number of resistant strains was as high as the inflow. The number of multiresistant strains also reduced significantly from the inflow to the effluent. The present study demonstrates that the sewage treatment system investigated is efficient in decreasing enterobacteria and antimicrobial resistant bacterial numbers, contributing to a lower discharge of multiresistant bacteria into the environment. Key words: enterobacteria, sewage, antimicrobial resistance, aquatic environment