Identification of Streptococcus phocae pathotypes by comparing virulence-associated traits of harbor seal isolates in primary airway epithelial cell models
Final Report Abstract
Marine mammals are indicators for the status of the marine ecosystem. They are threatened by numerous factors such as infectious diseases. It is assumed that they increase with climate change and other threats that have suppressive effects on the immune system of marine mammals, e.g. chemical pollution. One of the most frequently isolated bacteria are betahemolytic streptococci, of which one is Streptococcus phocae. S. phocae is also known as a serious pathogen of sea otters, minks and Atlantic salmon. While it has been isolated from at least 16 marine mammalian species, its pathogenicity and contribution to disease in marine mammals is largely unknown. This project aimed to identify different pathotypes of S. phocae isolated from marine mammals by combining genome analyses with infection experiments focusing on adherence, invasion, cytotoxicity and cytokine production in marine mammal host. We were further interested in the ability of S. phocae to survive in host environments such as blood and seawater. We sequenced the genomes of 19 S. phocae isolates and selected three different ones (based on their colony morphology, hemolysis, host origin and genetic differences) to perform all the experiments. The isolates originated from harbor seals, grey seals and harbor porpoises. Our results showed that S. phocae can survive in seawater for at least 11 and 28 days at 16 °C and 4 °C, respectively. It is able to grow in blood of harbour and grey seals, but not in porcine blood. Furthermore, S. phocae is adherent and invasive to cells from seals and pigs, while the portion of invasive cells was higher in seal derived cells. Macrophages of harbour seals were more efficient in killing S. phocae than porcine macrophages. Genome analyses of 19 isolates revealed a core genome of 1,232-1,432 core genes and 8-787 unique genes for each isolate. Different profiles of virulence genes, typical for streptococci, were identified. Accordingly, phenotypic differences indicated different pathotypes of S. phocae. Two out of three isolates showed stronger hemolysis, cytotoxicity and cytokine production in seal macrophages than the third one. Genetic analyses of virulence genes revealed that Streptolysin O – a known cyto- and hemolysin - might be one key virulence factor of S. phocae that is also responsible for the observed phenotypes, as it was present in the first ones, but not in the latter one. Our results indicate that S. phocae has strategies enabling it to adapt to the marine environment and seal hosts. This study furthermore combines for the first time genetic and phenotypic characteristics of S. phocae from marine mammals revealing at least two pathotypes and gives first insights into its pathogenicity. This might help in further studies to understand the interaction with its marine host.
Publications
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Streptococcal Infections in Marine Mammals. Microorganisms, 9(2), 350.
Numberger, Daniela; Siebert, Ursula; Fulde, Marcus & Valentin-Weigand, Peter
