Prevalence, Antimicrobial Resistance and Genetic Similarity Among Salmonella enterica from California Sea Lions and Sympatric Animals in the Channel Islands, California
IAAAM Archive
Robyn A. Stoddard1; Frances M. Gulland1; Robert L. DeLong2; Ryan K. Jenkinson2; Spencer Jang3; Barbara A. Byrne3
1The Marine Mammal Center, Golden Gate National Recreation Area, Sausalito, CA, USA; 2National Marine Mammal Laboratory, National Oceanic and Atmospheric Administration, Seattle, WA, USA; 3School of Veterinary Medicine, University of California, Davis, CA, USA


Salmonella enterica is a zoonotic pathogen that has been isolated from the intestinal tract of multiple species of free-ranging marine mammals throughout the world.1-5 The highest reported prevalence of Salmonella spp. in free-ranging animals was 40% in juvenile California sea lions (Zalophus californianus) in the Channel Islands in California in 1975.3 The goal of this study was to determine if the prevalence of Salmonella spp. was still high in California sea lions in the Channels Islands and to investigate potential sources by comparing the prevalence, antimicrobial sensitivity and pulsed field gel electrophoresis (PFGE) patterns among Salmonella spp. from these sea lions and other animal species that inhabit these islands.

In 2005 and 2006 fecal samples were collected from juvenile California sea lions, northern elephant seals (Mirounga angustirostris) and Western gulls (Larus occidentalis) in the Channel Islands. In addition, adult male California sea lions were sampled in Seattle, WA for comparison. Salmonella spp. isolation and identification was performed using standard techniques.6 Antimicrobial susceptibility of isolates was done using the broth microdilution method7. PFGE was performed following published PulseNet protocols.8

During this study, 90 juvenile and 50 adult California sea lions, 30 juvenile northern elephant seals, and 87 Western gulls were cultured for Salmonella spp. Of the juvenile California sea lions that were sampled, 21% (n=19) were positive for Salmonella spp., with a majority of the positive animals being found on San Miguel Island in 2005 (n=14). The serotypes found in these animals were Montevideo, Newport, Reading, and Enteritidis. None of the 50 adult California sea lions sampled were shedding Salmonella spp. Of the juvenile northern elephant seals sampled, 87% (n=26) were harboring Salmonella spp. Seals had the same serotypes of Salmonella spp. as sea lions, with the addition of the serotype Saint Paul. Only 9% (n=8) of Western Gulls were shedding Salmonella spp. which were all the same serotypes found in the sea lions and seals. Only one Salmonella spp. isolate was found to have antimicrobial resistance and that was from a Western gull. The PFGE patterns of the same serotypes of Salmonella spp. from the different animals were very similar.

The marine mammals of the Channel Islands appear to harbor Salmonella spp. at a higher rate compared to marine mammals observed in other studies. The high prevalence of shedding in northern elephant seals was astonishing considering Salmonella spp. had only been isolated from 3 out of 165 seals sampled in northern California.4 The similar PFGE patterns suggest there may be transmission, direct or indirect, of Salmonella spp. between species as has been demonstrated with New Zealand fur seals and feral pigs2. Researchers and veterinarians should exercise increased caution when working with these animals due to the zoonotic potential of Salmonella spp.


This project was supported by the West Coast Center for Oceans and Human Health as part of the National Oceanic and Atmospheric Administration Oceans and Human Health Initiative. We would like to thank Tracey Goldstein for assistance in sampling animals.


1.  Baker JR, A Hall, L Hiby, R Munro, I Robinson, HM Ross, J F Watkins. 1995. Isolation of salmonellae from seals from UK waters. Vet. Rec. 136:471-472.

2.  Fenwick SG, PJ Duignan, CM Nicol, MJ Leyland, JE Hunter. 2004. A comparison of Salmonella serotypes isolated from New Zealand sea lions and feral pigs on the Auckland Islands by pulsed-field gel electrophoresis. J. Wildl. Dis. 40:566-570.

3.  Gilmartin WG, PM Vainik, VM Neill. 1979. Salmonellae in feral pinnipeds off the Southern California coast. J. Wildl. Dis. 15:511-514.

4.  Stoddard RA, FMD Gulland, ER Atwill, J Lawrence, S Jang, PA Conrad. 2005. Salmonella and Campylobacter spp. in Northern Elephant Seals, California. Emerg. Infect. Dis. 11:1967-1969.

5.  Vedros NA, J Quinlivan, R Cranford. 1982. Bacterial and fungal flora of wild northern fur seals (Callorhinus ursinus). J. Wildl. Dis. 18:447-456.

6.  Bopp CA, FW Brenner, PI Fields, JG Wells, NA Strockbine. 2003. Escherichia, Shigella, and Salmonella, p. 654-671. In P.R. Murray, E. J. Baron, J.H. Jorgensen, M.A. Pfaller, and R.H. Yolken (eds.), Manual of Clinical Microbiology. ASM Press, Washington, D.C.

7.  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.

8.  Centers for Disease Control and Prevention. One-day (24-48 h) standardized laboratory protocol for molecular subtyping of Escherichia coliO157:H7, non-typhoidal Salmonella serotypes, and Shigella sonneiby pulsed field gel electrophoresis (PFGE). 1-13. 8-1-0005. Atalanta, Georgia, CDC.

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Robyn A. Stoddard

MAIN : Infectious Diseases : Salmonella in Sea Lions
Powered By VIN