[Effects of Low-level Nutrition and Trace Antibiotics on the Fitness Cost of Plasmids Bearing Antibiotic Resistance].

The effects of nutrition and antibiotic level on fitness costs of plasmid containing antibiotic resistance in drinking water system were investigated in this study. Three plasmids harboring different antibiotic resistances, i.e. pACYC184, RP4, and PBR322, were selected. It was found that the antibiotic resistance imposed cost on the fitness of all plasmids at different nutrition levels, which was universal. Moreover, the fitness costs were larger at lower nutrition levels. Besides, the fitness costs of plasmid bearing antibiotic resistance were also affected by trace antibiotics. In this study, when exposed to antibiotics (lower than 50% MIC), the fitness costs of plasmid imposed to the bacteria were more apparent than the injury or inhibition effect by antibiotics. The plasmids were unstable. Therefore, it was inferred that the plasmid containing antibiotic resistance imposed large fitness costs on bacteria in drinking water system (with low-level nutrition and ng·L level antibiotic), and it was not stable. Thus, the risk of plasmid bearing antibiotic resistance transmission and spread in drinking water system was low.