Effects of sequential exposure to Ciprofloxacin and Sulfamethoxazole in marine microbial biofilms

Conference poster, 2011

Many human pharmaceuticals are emitted into the aquatic environment after usage and antibiotics belong to a commonly detected group. Designed to be effective at low concentrations, it is hence likely that environmentally realistic concentrations of antibiotics directly affect environmental microbes. Also, antibiotic resistance is increasingly recognized as a potential threat to human health. In particular there is concern that resistance will develop in natural bacterial communities and spread to pathogenic bacteria. To test whether environmentally realistic concentrations of antibiotics affect natural communities and lead to tolerance developments, a flow through microcosm experiment was performed in 2010. Long-term effects of two antibiotics were studied on periphytic biofilms (communities of predominantly microalgae and bacteria), established in aquaria from the indigenous micro-biota found in the natural seawater in the Gullmar fjord on the Swedish west coast. During the first two weeks the communities were continuously exposed to either Ciprofloxacin (CIP) or Sulfamethoxazole (SMX) at nominal concentrations of 1nmol/L. Afterwards the exposure regimes were changed, so that communities previously exposed to CIP were exposed to SMX (1, 14, 200nmol/L) instead and vice versa for communities originally exposed to SMX. This second phase lasted five days. At the end of each exposure regime the communities were sampled and assessed with respect to various ecotoxicological endpoints. Chl a content and pigment patterns were used to describe the effects on the algal part of the communities, while effects on bacteria were investigated using bacterial production (3H-Leucin incorporation) and bacterial catabolic profiling (Biolog Ecoplates). Samples were also taken to study the genetic profiles of the exposed communities.