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.

Survival and adaptation of Streptococcus phocae in host environments

“…mussels) that might accumulate S . phocae and are the prey of several marine mammalian species such as sea otters [ 40 , 41 ]. Further studies are required to identify factors that influence the survival rate of S .…”

Habitat associations between Streptococcus bovis/equinus complex and Streptococcus phocae, the causative agents of strep syndrome in sea otters, and the marine environment

“…The relationship between bacterial presence and sand may also be associated with the presence of bivalves. Clams are a preferred sea otter diet item, and experiments have shown that clams can harbor the bacteria (Rouse et al, 2021). Other than in the case of substrate size and bay effect, the results of our logistic regression modeling did not reveal a relationship between SBEC and S .…”

“…Published primers targeting a portion of the superoxide dismutase ( sodA ) gene were used to detect S . phocae (Alber et al, 2004) and SBEC (Rouse et al, 2021). Reactions were prepared using 10–12.5 µl of master mix (5Prime Hot Master Mix or OneTaq Hot Start2X), 1 µl forward primer, 1 µl reverse primer, template DNA from bay mussels (500–1000 µg) or positive control bacteria (250–350 µg), and the final reaction volume brought to 25 µl with PCR‐grade water.…”

“…Each PCR run contained a known positive control and a negative (no template) control. Cycling parameters for SBEC were 94°C for 2 min, 30 cycles of 94°C for 30 s, 57°C for 30 s, 72°C for 30 s, and a final elongation step at 72°C for 5 min (Rouse et al, 2021). For S .…”

“…Additionally, in laboratory experiments, common sea otter prey (clams, mussels, crab, and snails) were able to accumulate SBEC and S . phocae , which suggests prey could be an infection source (Rouse et al, 2021). Streptococcus phocae has also been shown to colonize sea otters through skin wounds (Bartlett et al, 2016).…”