Potential impact of emerging bacterial pathogens on shellfish production

Identifier:  TDX:4676

Handle: https://hdl.handle.net/20.500.11797/TDX4676

Authors:  Rahman, Faiz Ur

Abstract:
Arcobacter-like species are rod-shaped gram-negative bacteria found ubiquitously in nature. They are considered zoonotic pathogens and have potential of causing diseases in their hosts. This thesis studied the role of Arcobacter-like species in shellfish production by isolating them from Pacific oyster (Crassostrea gigas) during mortality and non-mortality episodes. It was found that OsHV-1 and V. aestuarianus were found in C. gigas only in mortality episodes samples, while V. splendidus clade and Arcobacter-like spp. were present in both mortality and non-mortality episodes. Genetic profiling and phylogenetic analysis of the isolates revealed that mainly Malaciobacter marinus was present in the samples from mortality episodes, while it was not isolated from samples of non-mortality episodes. M. marinus was identified as a potential pathogen for C. gigas by in-vivo and in-vitro bacterial challenge experiments. Results showed that mortality in C. gigas was 15% higher when both V. aestuarianus and M. marinus were experimentally infecting the animal, suggesting a potential synergistic role of M. marinus. Additionally, two M. marinus isolated from mortality episode were studied with the hemocytes of Mediterranean mussel (Mytilus galloprovincialis) and C. gigas. It was found that M. marinus was moderately pathogenic to early larvae of M. galloprovincialis, while in adult lysosomal membrane stability was decreased in M. galloprovincialis and C. gigas hemocytes, indicating stress given to the host. ROS and lysozyme were released as defense response to the bacteria in the host.