Occurrence of antibiotics and antibiotic-resistant bacteria (ARB) in the Nervión river

Abstract

The main hydrometeorological, microbiological and physico-chemical characteristics of the Nervión river were monitored during a year, including 10 antibiotics and the presence of bacteria resistant to these antibiotics among faecal coliforms (FC) and total aerobic bacteria at 22ºC (TAB22). The characteristics of the river water were variable without a clear seasonal component, strongly influenced by rainfall, with a good quality for drinking water production throughout the year according to the physico-chemical parameters. The antibiotic resistant bacteria isolated from the water of the Nervión river were especially resistant to β-lactams and macrolide antibiotics, highlighting the absence of resistance to derivatives of tetracyclines among strains of TAB22. A third of the isolated strains were multi-resistant to antibiotics with a seasonal component in its presence, with multi-resistant FC more abundant during summer and multi-resistant TAB22 more abundant during winter. The presence of antibiotics in the waters of the Nervión river was not very significant, with total absence of β-lactams, minocycline and ciprofloxacin. Erythromycin and clarithromycin can be considered ubiquitous with mean concentrations of 2.5±2.3 ngL-1 and 5.7±4.6 ngL-1 respectively, and the presence of sulfamethoxazole and trimethoprim was also noticeable with maximum concentrations of 78.3 ngL-1 for sulfamethoxazole. Dilution due to the increase of rainfall was observed for several analysed antibiotics, but without significant seasonal differences.