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.
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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.