The effects of antibiotics on the biofilm formation and antibiotic resistance gene transfer

Recently, a number of microcontaminants were found in aquatic environment and it raises the concerns about their effects to ecosystem. This study investigated if low levels of antibiotics can trigger the biofilm formation and result in the enhanced antibiotic gene transfer. For this purpose, the biofilm formation of enteric bacteria (Escherichia coli), environmental micro-organism (Pseudomonas aeruginosa), and their mixture by ppb level of antibiotics were investigated. In addition, the effects on the conjugation of E. coli with P. aeruginosa in the biofilm structure were also evaluated using biofilm colony-forming unit assay in 96-well plates and ELISA. Interestingly, at 100-1000ppb, the mixed culture was able to reach its highest biofilm biomass and also form the highest number of transconjugants, which is greater than negative controls. This experiment shows that ppb levels of tetracycline and cephradine can alter the transfer rate of the pB10 plasmid among the biofilm biomass at rates 2-5 times faster than without antibiotics, which indicated the facilitated Antibiotic Resistance Gene (ARG) spread by the presence of low-antibiotic residues in the environment.