The effect of rehabilitation of northern elephant seals (Mirounga angustirostris) on antimicrobial resistance of commensal Escherichia coli Robyn A. Stoddard a,b, *, E. Rob Atwill c , Patricia A. Conrad a , Barbara A. Byrne a,d , Spencer Jang d , Judy Lawrence b , Brenda McCowan c , Frances M.D. Gulland b a Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA 95616, USA b The Marine Mammal Center, Marin Headlands, 1065 Fort Cronkhite, Sausalito, CA 94965, USA c Population Health and Reproduction, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA 95616, USA d Microbiology Laboratory, William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, One Shields Avenue, Davis, CA 95616, USA 1. Introduction The potential for marine mammals to be a source of disease for humans has been recognized since the 1970s (Smith et al., 1978). Marine mammals are known carriers of zoonotic bacteria including Brucella spp., Vibrio spp., Leptospira spp., Escherichia coli, Mycobacter- ium spp., and Salmonella enterica, with reports of some of these bacteria having antimicrobial resistance (Smith et al., 1978; Johnson et al., 1998; Cowan et al., 2001). There is a public health concern associated with marine mammals due to their close proximity to locations where humans recreate and collect food sources such as mussels, clams, and oysters, as well as the potential for exposure of humans caring for animals during rehabilitation. Veterinary Microbiology 133 (2009) 264–271 ARTICLE INFO Article history: Received 27 July 2006 Received in revised form 6 July 2008 Accepted 16 July 2008 Keywords: Escherichia coli Antimicrobial drug resistance Northern elephant seal Mirounga angustirostris ABSTRACT The aim of this study was to determine if antimicrobial drug use increases resistance of commensal gastrointensinal Escherichia coli of wild northern elephant seals (Mirounga angustirostris) treated in rehabilitation, and, if so, identify the risk factors involved. Minimum inhibitory concentration (MIC) levels of twelve antimicrobial drugs were determined for 289 E. coli isolates from 99 seals sampled at admission and 277 isolates obtained at release from rehabilitation using broth microdilution. Prevalence of E. coli antimicrobial resistance, MIC 50 , MIC 90 , and clustering of MIC values were determined for seals and the data were analyzed using Fisher’s exact test, ordinal logistic regression and negative binomial regression. At release from rehabilitation 77.8% of the seals had antimicrobial resistant E. coli compared to 38.4% of the seals at admission. The MIC 90 for amoxicillin-clavulanic acid, chloramphenicol, enrofloxacin, ticarcillin-clavulanic acid, and trimethoprim-saulfamethoxazole were at levels considered to be sensitive at admission but they increased to levels of resistance at release. E. coli were grouped into four clusters by their MIC values, with increasing levels of resistance going from Cluster 1 to 4. A primary risk factor associated with the probability of a seal having E. coli in Clusters 3 and 4 was time in rehabilitation, regardless of whether the animal received treatment with antimicrobial drugs, suggesting nosocomial infection. The results of this study provide evidence that increased levels of hygiene and appropriate use of antimicrobial therapy might be important in the rehabilitation of wild animals to prevent rise in the prevalence of antimicrobial resistant bacteria. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author at: Department of Veterinary Sciences, The Marine Mammal Center, Marin Headlands, 1065 Fort Cronkhite, Sausalito, CA 94965, USA. Tel.: +1 404 639 2053; fax: +1 415 289 7376. E-mail address: StoddardR@tmmc.org (R.A. Stoddard). Contents lists available at ScienceDirect Veterinary Microbiology journal homepage: www.elsevier.com/locate/vetmic 0378-1135/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetmic.2008.07.022