The Effect of Rehabilitation of Northern Elephant Seals (Mirounga angustirostris) on Antimicrobial Resistance of Fecal Bacteria
IAAAM 2005
Robyn A. Stoddard1; E. Rob Atwill1; Spencer Jang1; Patricia A. Conrad1; Frances M. Gulland2; Judy Lawrence2
1School of Veterinary Medicine, University of California, Davis, CA, USA; 2The Marine Mammal Center, Golden Gate National Recreation Area, Sausalito, CA, USA


Rehabilitation of marine mammals involves treatment, often with antimicrobials, of clinical conditions and supportive care of the animals prior to release. Certain commensal bacteria, such as Escherichia coli, are known to have a pronounced ability to acquire and disseminate antimicrobial resistance, especially in the face of antimicrobial usage.4 The resistant bacteria can pass on resistance to pathogenic bacteria within the gastrointestinal tract or in the environment once they are shed.1,7 Antimicrobial resistant bacteria are a concern because they limit the treatment choices and cause an increase in mortality, morbidity, and cost of treatment.8 To the best of our knowledge, there are no published data on the effects of drug usage during rehabilitation on the bacterial flora of marine mammals.

The goal of this study was to determine if rehabilitation alters the antimicrobial sensitivity of E. coli within the gastrointestinal tract of northern elephant seals (Mirounga angustirostris). Rectal swabs were performed on juvenile northern elephant seals during admit and release physical exams at The Marine Mammal Center (TMMC) in Sausalito, CA. Based on their symptoms and laboratory results, seals were given appropriate antimicrobials as needed. No animal was placed on an antimicrobial solely for the purpose of this study. As a control, rectal swabs were performed on age matched, free-ranging elephant seals. Rectal swabs were used to isolate three E. coli colonies per swab using standard culture and identification techniques.2,3,5 Antimicrobial susceptibility was done using the broth microdilution method.6 Statistical significance was determined by chi square analysis.

During this study, 52 animals that were released from rehabilitation from TMMC were sampled. At the time of admission, E. coli isolates from 31 animals showed no antimicrobial resistance and 19 animals showed resistance to only one antimicrobial. The most common antimicrobial that the isolates were resistant to was tetracycline (n=13). There were two animals which had multi-drug resistant E. coli upon admission to rehabilitation. At release from rehabilitation, 88% of seals (n=50) had an increase in the number of antimicrobials to which their E. coli isolates were resistant and 48% of the seals had E. coli isolates that were resistant to four or more antimicrobials. The prevalence of seals with E. coli isolates that showed an increase in resistance at release was unaffected (p=0.293) by whether (90.3%, n=31) or not (84.2%, n=19) the animal received antimicrobials. The prevalence of seals with multidrug resistant E. coli was also unaffected by antimicrobial use (p=0.322): 52.6% of seals that did not receive antimicrobials left rehabilitation with E. coli that were resistant to four or more antimicrobials, while 45.2% of seals that received antimicrobials had E. coli that were resistant to four or more antimicrobials at release. Despite the increased resistant bacteria in seals being released from rehabilitation, there was little antimicrobial resistance in E. coli isolates from seals sampled on their natal beaches (4.5%, n=66). The impact of releasing marine mammals back into the wild that are shedding antimicrobial resistant bacteria is not known and therefore antimicrobials should only be used in wild animals when necessary.


This project was supported in part by the California Department of Fish and Game's Oil Spill Response Fund through the Oiled Wildlife Care Network at the Wildlife Health Center, School of Veterinary Medicine, University of California, Davis and the John H. Prescott Marine Mammal Rescue Assistance Grant Program, National Marine Fisheries Service.


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5.  Nachamkin I. 1999. Campylobacter and Arcobacter, p. 716-726. In P. R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover, and R. H. Yolken (eds.), Manual of Clinical Microbiology. ASM Press, Washington, D.C.

6.  National Committee for Clinical Laboratory Standards. Performance Standards for Antimicrobial Disk and Dilution Susceptibility Tests for Bacteria Isolated from Animals, Approved Standards. NCCLS Document M31-A2 . 2002. Wayne, PA, NCCLS.

7.  Salyers AA. 1996. Antibiotic Resistance Transfer in the Mammalian Intestinal Tract: Implications for Human Health, Food Safety, and Biotechnology (Molecular Biology Intelligence Unit), p. 1-191. Springer-Verlag, New York City.

8.  Williams R. 2002. Resistance as a worldwide problem, p. 223-238. In K. Lewis, A. A. Salyers, H. W. Taber, and R. G. Wax (eds.), Bacterial Resistance to Antimicrobials. Marcel Dekker, Inc., New York City.

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Robyn A. Stoddard

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