This report was commissioned by the Norwegian Environment Agency.

Report summary

Faecal samples were collected from obtained from whales and seals for analysis of antimicrobial resistance. There were 55 whale samples and 5 seal samples, from which bacteria were cultivated on a variety of culture media. Ten isolates per sample (total 600) were selected for further analysis.

For testing of phenotypic resistance to a selection of antibiotics (ampicillin, cefotaxime, vancomycin, kanamycin, tetracycline, ciprofloxacin, erythromycin and trimethoprim), the standard method for determining minimum inhibitory concentration (MIC) was used. A concentration range of 0.0625 – 32 mg/L was tested. MICs were determined for 285 of the isolates, 239 from whale samples and 46 isolates from seal samples. For each antibiotic, there were isolates which were capable of growing at the maximum concentration tested (32 mg/L). The MIC values for ampicillin and tetracycline were low compared to studies of other environmental samples. The highest number of isolates with an MIC of ≥32 mg/L was seen for trimethoprim, which also had an overall MIC range which was high compared to similar studies. There were observable differences in the distribution of MIC values between the seal and whale samples, though this appears to be due to an overrepresentation of one species in the seal samples.

Molecular testing for a selection of antimicrobial resistance genes (AMRGs) was done using standard PCR methods. The selected AMRGs were mecA, tetA, ermB, nptII, qnrs, dfrA1, vanA, as well as two genes which code for multidrug resistance (MDR) efflux pumps, acrB and mexD. Only nptII failed to produce any amplicons. There was not a strong association between high MIC values and the detection of resistance genes (except for vancomycin and VanA), though this is likely due to the small selection of genes screened for.

The results of this study reveal a snapshot of the antimicrobial susceptibility and resistance genes present in isolates collected from whale and seal samples, and contribute to a growing body of evidence connecting the environment to dissemination of antibiotic resistance. The present study is limited in terms of scale, and continued research is required to fully understand the role of marine mammals in the context of maintenance and spread of antimicrobial resistance.

Suggested citation

Venter, H. (2018) Antimicrobial resistance in the marine environment: MIC profiles of bacteria isolated from whale and seal faeces. Project report, M-1260|2019, GenØk, Tromsø, Norway.