Water Environ R

iotics in the environment. in test s ent... icipal s trolled through the use of antimicrobials such as antibiotics. Pri-mary resistance is naturally present in micro-organisms such as the resistance of Pseudomonas aeruginosa against penicillin G. The resistance is ‘‘inherited ” by organisms of the same species through cell division (vertical resistance transfer). In contrast, secondary resistance develops during therapy/contact of a micro-organism with an antibiotic. Plasmid mediated resistance is transferable be-at a later time point. Resistance can then reach the environment with the potential of adversely affecting aquatic and terrestrial organisms. It might reach humans again through drinking water. The history of resistance due to the use of antibiotics as growth promoters and the lessons there to be learned has only recently been described in more detail (Edquist and Pedersen, 2001; Lord Soulsby of Swaffham Prior, 2008). As for the presence of antibiotics in the environment, the issue of resistance was nearly always ad-dressed in publications describing the presence of antibiotics in the environment (e.g. Nygaard et al., 1992; Samuelsen et al.