Competency of common northern sea otter (Enhydra lutris kenyoni) prey items to harbor Streptococcus lutetiensis and S. phocae

Abstract

Streptococcus lutetiensis and S. phocae have been associated with significant morbidity and mortality in northern sea otters Enhydra lutris kenyoni in Alaska, USA, but the route and mechanism(s) of transmission remain unknown. The goal of this study was to determine the competence of common northern sea otter prey to harbor 2 species of pathogenic Streptococcus bacteria. Prey items (bay mussels Mytilus trossulus, butter clams Saxidomus giganteus, Dungeness crab Metacarcinus magister and black turban snails Tegula funebralis) were exposed to known concentrations of exponential phase cultures of S. lutetiensis and S. phocae in seawater for 24 h. A quantitative PCR assay was developed targeting the sodA gene of both S. lutetiensis and S. phocae to quantify DNA in the prey samples. Results (mean ± SD) revealed that butter clams had the highest concentration of bacteria (4.32 × 107 ± 8.20 × 106 CFU ml-1 of S. lutetiensis, 1.20 × 108 ± 2.08 × 107 CFU ml-1 of S. phocae), followed by mussels (4.26 × 107 ± 1.66 × 107 CFU ml-1, 1.16 × 108 ± 5.39 × 107 CFU ml-1), snails (1.90 × 107 ± 5.26 × 106 CFU ml-1, 5.97 × 107 ± 2.07 × 107 CFU ml-1) and crab (1.46 × 107 ± 0 CFU ml-1, 1.64 × 107 ± 0 CFU ml-1). All prey species harbored higher concentrations of S. phocae than S. lutetiensis.