The discovery of antibiotics has radically changed the treatment of bacterial infections, making the increasing antibiotic resistance one of the top ten greatest threats to the global health. The main focus of antibiotic resistance research has, until recently, been focused on clinical settings and human and veterinary aspects. It has become more evident that the environment plays a vital role in the evolution, dissemination and prevalence of antibiotic resistant bacteria and genes. Aquatic ecosystems are a known mixing ground for clinical and environmental bacteria and can be a source and reservoir for resistance genes. The transfer of resistance between environmental and clinically important bacteria occurs, and surveillance of the environment is therefore important to better understand this flow of resistance.
The purpose of this thesis was to investigate the occurrence of antibiotic resistant bacteria and genes in aquatic environments in Ås and Nordre Follo municipalities in Norway. Water samples were collected from three different locations was filtered and plated out on Brilliance™ ESBL and CRE chromogenic agar plates selecting for Extended spectrum β-lactamase (ESBL) producing and carbapenem resistant bacteria. Bacterial colonies were isolated, and DNA was extracted, followed by 16S PCR and identification by Sanger sequencing. Multiplex and Singelplex PCR with ESBL-specific primers were utilized to screen for specific ESBL-genes, which were confirmed by sequencing. Selected bacterial strains were chosen for antimicrobial susceptibility testing using five different classes of antibiotics. Illumina MiSeq was utilized for whole genome sequencing (WGS) for three selected bacteria, followed by screening for antibiotic resistance and virulence genes, multidrug efflux pumps and metal resistance genes. Several bacteria genera were detected by selective agar plates and identified by 16S rRNA, including the genera Pseudomonas, Serratia, Herbaspirillum, Aeromonas, Shewanella, Chitinophaga and Pandoraea. The susceptibility testing revealed a high amount of resistance to Penicillins and four different Multidrug resistant (MDR) isolates. The bacteria showing the highest amount of resistance was Pandoraea sp., which demonstrated clinical resistance to five out of seven antibiotics tested. The screening for resistance in the three WGS bacteria, Pseudomonas aeruginosa, Chitinophaga silvatica and Pandoraea sp., revealed several β-lactamases. This included the class D β-lactamases blaOXA-50, blaOXA-158 and two bla genes, and the class C β-lactamases blaPDC-202 and blaPAO. Several genes conferring metal resistance and genes for multidrug efflux pumps were also discovered. Together, the results obtained in this work indicate an occurrence of antibiotic resistant bacteria and resistance genes, including several blaOXA-variants, in the aquatic environments in Ås and Nordre-Follo municipalities
