Fate of antibiotic resistant E. coli in anoxic/aerobic membrane bioreactor treating municipal solid waste leachate

• Fate of ARB/ARG in the itMBR treating landfill leachate was investigated.
• High OLR/limited DO promoted high multiple antibiotic resistant Escherichia coli in itMBR.
• itMBR environments did not induce resistant gene mutation in E. coli to quinolone.
• HGT of IncF plasmids plays an important role in promotion of MAR E. coli in itMBR.

This study aims to investigate fate of antibiotic resistant bacteria/genes in the anoxic/aerobic membrane bioreactor (itMBR) treating leachate. Three different operations were carried out by variation of organic loading rates and daily sludge returned. The Escherichia coli isolates were examined for susceptibility to 13 antibiotics. High organic loading rate and limited oxygen condition promoted high prevalence of multiple antibiotic resistant (MAR) E. coli. Tetracycline, chloramphenicol and sulfamethoxazole/trimethoprime were antibiotics which E. coli could develop resistance to under less oxygen available condition. Occurrence of co-resistance of antibiotic pair possibly induced in bio-cake formation most especially were aminoglycosides/sulfonamide, tetracycline/sulfonamide, phenicol/sulfonamide, sulfonamide/beta-lactams and sulfonamide/nitrofuran. Conversely, high dissolved oxygen in aeration tank gave negative impact on MAR E. coli. The environmental condition in itMBR did not induce the occurrence of gene mutation to quinolone resistance of E. coli. High occurrence of qnrA gene transferring among E. coli in anoxic condition especially class I integron was found highly whereas that of replicons in IncF plasmids showed easy occurrence in dense biomass such as biocake of anoxic incline plates/MBR surface membrane. In conclusion, horizontal transfer phenomenon of IncF plasmids among E. coli and others in Enterobacteriaceae plays an important role in MAR enhancement in E. coli in itMBR.