Community composition effects low non-therapeutic antibiotic concentrations

The aim of this study was to discern possible effects on bacterial community composition of low non-therapeutic dosages of a variety of antibiotics. As inoculum source we used washed cells sampled from a wastewater treatment plant (in the activated sludge basin). Cells were diluted to 1e5 cells per ml at start in artificial lake water medium, containing only natural assimilable organic carbon at 0.1-0.5 mg C per L. To this were added individual antibiotics, either at 0.1 or 1 mg C per L. Communities were incubated in the dark at 21 degrees C for 8 days with 180 rpm rotary shaking, then sampled for community analysis using V3V4 amplicon sequencing. As negative control we used incubations without any carbon added. All treatments were conducted in biological triplicates. Three samples from the inoculum itself at start without incubation were processed similarly.We find inhibitory effects of all antibiotics and relevant community changes that are dependent on the used antibiotic. The tested antibiotics included: ampicillin, chloramphenicol, erythromycin, gentamicin, penicillin, nalidixic acid and sulfomethoxazole.