Antimicrobial Resistance Prevalence in Bacteria Isolated from Harbour Seal Pups (Phoca vitulina) Stranded in the Netherlands: A First Screening
Antibiotics are the most successful drugs used for fighting bacterial diseases in humans and animals. Its use in humans and animals leads to the selection of resistance genes. Similar resistance genes found in humans are also found in pristine ecosystems without any record of antibiotic contamination.1
The Netherlands is a good example where human populations in coastal areas continue to increase. Therefore, coastal ecosystems may become increasingly important as reservoirs of or sentinels for infectious organisms2 and antimicrobial resistance (AMR). Since many marine mammal species share the coastal environment with humans and consume the same food, they also may serve as sentinels for ocean and human health.3
Little is known on the antimicrobial susceptibility patterns in free ranging and/or stranded marine mammals, more specifically in harbor seals in the Netherlands. In this study, we revealed the prevalence of AMR in bacteria isolated from the rectum of harbour seal pups and weaners admitted for rehabilitation at the Seal Rehabilitation and Research Center (SRRC) in Pieterburen, the Netherlands. Rectal swabs for bacterial culture were collected during health assessment from 100 harbor seals including pups and weanlings during summer 2015. All animals had stranded alive along the Dutch coast and islands with the exception of the island of Texel and the province of Zeeland and were transported to the SRRC. Within 48 hours after collection swabs were streaked onto different plates to screen for Methicillin Resistant Staphylococcus aureus (MRSA), Extended Spectrum Beta-Lactamase (ESBL) and B-lactamase hyper producing gram-negative bacteria, and Vancomycin Resistant Enterococci (VRE).
ESBL-producing organisms were isolated from 4 pups but no MRSA and VRE were found. Subsequently, the whole genome of the four isolates was sequenced on the MiSeq and the genomes were compared to genomes obtained from human isolates by a core genome multi-locus sequence typing (cgMLST) approach. In addition, the presence of resistance genes was determined. E. coli isolates of this study contained genes causing resistance against aminoglycosides, beta-lactams, macrolides-lincosamide-streptogramin, sulphonamides, tetracyclines and trimethoprim. Furthermore, cgMLST revealed that two of the four E. coli isolates cluster together. These isolates were obtained from seals admitted on the same day and stranded at the same place. Moreover, isolates from seals differ only in 40 of 2764 analyzed genes from human E. coli isolates.
In conclusion, prevalence of MRSA, VRE and ESBL-producing E. coli in harbor seal pups is low. E. coli isolates found in them are closely related to those found in human and contain resistance genes that are also found in human isolates.
The authors wish to thank Izore for the financial support, the staff and volunteers of the SRRC that helped with the sample collection and Estee Hoogendorp and Erwin Raangs for their help in generating the WGS data.
* Presenting author
1. Martinez JL. Environmental pollution by antibiotics and by antibiotic resistance determinants. Environ Pollut. 2009a;157:2893–2902.
2. Bogomolni AL, Gast RJ, Ellis JC, Dennett M, Pugliares KR, Lentell BJ, Moore MJ. Victims or vectors: a survey of marine vertebrate zoonoses from coastal waters of the Northwest Atlantic. Dis Aquat Organ. 2008;81:13–38.
3. Bossart G. Marine mammals as sentinel species for oceans and human health. Vet Pathol. 2011;48:676–690.