Abstract
Antimicrobial resistance in bacteria is a global health threat in human and veterinary medicine1,2, with a rapid emergence and expansion worldwide. Wildlife species can play an important role as reservoirs for these organisms3, posing a hazard to humans and domestic animals regarding transmission of antimicrobial-resistant bacteria or resistance determinants4. Information regarding prevalence and transmission pathways is especially lacking for marine species, which are highly vulnerable to the introduction of treated sewage5 in natural waters and to the enhanced horizontal transmission of resistance mechanisms naturally occurring in aquatic ecosystems6. The investigation of different marine and coastal animals of the North and Baltic Sea of Schleswig-Holstein, Germany and the western Baltic Sea of Denmark for antimicrobial-resistant E. coli shall determine the current situation in these areas. Up to now, 144 rectal/cloacal and faecal swabs were collected from different sea fish, coastal birds and marine mammals. The collected swabs were incubated in Mossel bouillon and the suspensions were streaked on antibiotic-containing MacConkey agar plates. Tested antibiotics included ampicillin, cephalothin, chloramphenicol, ciprofloxacin, colistin, gentamicin, sulfamethoxazole, and tetracycline. The bacterial colonies that grew on the antibiotic-containing agar plates were screened for presumptive coliform bacteria identification via three different selective agar plates (Gassner, MacConkey and Chromocult agar). E. coli species confirmation was performed by PCR assay. These isolates were tested in disk diffusion tests for their resistance against 14 antibiotics or antibiotic combinations including amoxicillin/clavulanic acid (20/10 µg), ampicillin (10 µg), cefazolin (30 µg), cefpodoxime (10 µg), chloramphenicol (30 µg), ciprofloxacin (5 µg), florfenicol (30 µg), gentamicin (10 µg), kanamycin (30 µg), nalidixic acid (30 µg), sulfisoxazole (300 µg), streptomycin (10 µg), tetracycline (30 µg) and trimethoprim (5 µg). Resistant E. coli were present in 29.9% of the samples. With 50% positive samples, birds had the highest occurrence of resistant E. coli, followed by the marine mammals with 25.5% positive samples. No resistant E. coli were identified in the fish samples. The most frequent resistances detected were against streptomycin and ampicillin. Gentamicin and kanamycin resistances had the lowest occurrence (all data as of October 26th 2018). The high resistance occurrences in the sampled birds and marine mammals were unexpected. Further investigations of virulence factors and resistance genes of the collected E. coli isolates will allow the evaluation of potential risk factors for the transmission of these resistant bacteria or their resistant determinants to livestock, companion animals and humans. Furthermore, the obtained data might elucidate differences regarding antimicrobial resistance prevalence and profiles according to different aquatic systems (North and Baltic Sea).
Acknowledgements
The authors wish to thank Martin Altemüller, NABU Waterfowl Reserve Wallnau, Nils Kobarg and Uwe Schwippert, Förderverein Integrierte Station Geltinger Birk, all involved members of the Stranding network of Schleswig-Holstein, Thomas Lang and his colleagues, Thünen Institute of Fisheries Ecology, and our colleagues at the ITAW, especially Abbo van Neer, for their support in collecting fecal and rectal swabs as well as Iris Oltrogge, LMQS, for her excellent technical assistance.
* Presenting author
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