Screening for antimicrobial- and heavy metal resistant bacteria in copper contaminated areas
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A One heath approach is essential to examine the role of the marine environment in the selection and spread of antimicrobial resistance. Norwegian aquaculture used high amounts of antimicrobials during the 80s and 90s, which facilitated widespread resistance among fish pathogens. Moreover, fish farms have since their beginning used copper containing coating as anti-fouling agents on the fish nets, in addition to copper supplements in the fish feed. Consequently, some fish farms have high concentrations of copper in det sediments beneath the pens. Several studies have reported that even sublethal concentrations of heavy metals can facilitate co-selection of antimicrobial resistance and heavy metal resistance. This study applied Vibrio spp. as indicator of antimicrobial- and heavy metal resistance in copper contaminated areas. Six different locations were sampled twice. These represented four different areas in regard of aquaculture activity; Active aquaculture, Non-active aquaculture, Non-aquaculture and Unpolluted. In total, 70 samples, including sediments, seawater, marine fauna and marine algae, were examined for the presence of Vibrio spp. and Escherichia coli. The sediments were examined for heavy metals, where sediments from Active aquaculture areas held exstensively toxic mean concentration with 272.3 mg/kg dry weight (d.w.) copper, significant higher than Non active (24.4 mg/kg d.w.), Non-aquaculture (34.8 mg/kg d.w.) and Unpolluted (2.28 mg/kg d.w.), and moderate toxic mean concentration with 424.6 mg/kg d.w. zinc, also significant higher than Non-active (70.7 mg/kg d.w.), Non-aquaculture (144.6 mg/kg d.w.) and Unpolluted (16.4 mg/kg d.w.). The majority of the retrieved 350 Vibrio splendidus and 72 Vibrio anguillarum isolates were susceptible to all the antimicrobials tested for. Increased minimum inhibition concentrations (MIC) to oxytetracycline and copper were seen for some isolates from Active aquaculture, however only one- to two-fold higher than from Non-active and Non-aquaculture areas. Several antimicrobial- and heavy metal resistance genes were found across the different examined areas, with exception of the nlpE gene encoding a copper sensing lipoprotein inducing efflux pumps, that were only found in one isolate from one location with aquaculture. The majority of the 336 E. coli isolates were susceptible to all antimicrobial tested for. The Active aquaculture areas conferred highest number of E. coli, and most of the resistant E. coli. Many factors, such as weather and topography, can influence the inflow of E. coli from sewage and run-offs from land. No association was found between the detected phenotypic and genotypic resistance traits in V. splendidus and in E. coli in any of the examined areas. Importantly, a higher sample size including more locations is needed to determine whether any possible indicated differences are significant. In conclusion, the high proportion of susceptible isolates found in this project, indicates that the prevalence of selectable resistance mechanisms in the examined marine vibrios from copper contaminated areas are low.