Pathogenicity and virulence of bacterial strains associated with summer mortality in marine mussels (Perna canaliculus).

The occurrence of pathogenic bacteria has emerged as a plausible key component of summer mortalities in mussels. In the current research, four bacterial isolates retrieved from moribund Greenshell࣪ mussels, Perna canaliculus, from a previous summer mortality event, were tentatively identified as Vibrio and Photobacterium species using morpho-biochemical characterization and MALDI-TOF MS and confirmed as V. celticus, P. swingsii, P. rosenbergii, and P. proteolyticum using whole genome sequencing. These isolates were utilized in a laboratory challenge where mussels were injected with cell concentrations ranging from 105 to 109 CFU/mussel. Of the investigated isolates, P. swingsii induced the highest mortality. Additionally, results from quantitative polymerase chain reaction analysis, focusing on known virulence genes were detected in all isolates grown under laboratory conditions. Photobacterium rosenbergii and P. swingsii showed the highest expression levels of these virulence determinants. These results indicate that Photobacterium spp. could be a significant pathogen of P. canaliculus, with possible importance during summer mortality events. By implementing screening methods to detect and monitor Photobacterium concentrations in farmed mussel populations, a better understanding of the host-pathogen relationship can be obtained, aiding the development of a resilient industry in a changing environment.

Lactic fermentation of cooked, comminuted mussel, Perna canaliculus.

The endogenous microflora of mussels, filter feeders, can include pathogens with resulting food safety concerns. The aim was to develop a cook-then-ferment technology to extend shelf life and safety of a ready-to-eat mussels. Only after cooking to destroy the mussel's endogenous microflora could an edible product be made as determined by pH decline after fermentation and the fate of common pathogens. Perna canaliculus was bought live at retail on many dates. Fermentation was with commercial lactic cultures incubated under vacuum at 30 °C for four days. Using one culture containing Pediococcus pentosaceus and Staphylococcus carnosus as a model, pH typically declined to 4.5 to 4.7, and common pathogens, Staphylococcus aureus, Salmonella and Vibrio parahaemolyticus were absent or reduced to acceptable levels. The fate of Listeria monocytogenes was studied with five cultures. These were variably effective at inhibition with one clear success, Chr Hansen's T-SC-150 containing a specific strain of Lactobacillus sakei, and flavour-generating Staphylococcus carnosus. This culture's efficacy was confirmed with sterile extracts of LAB challenging L. monocytogenes in vitro. This culture was also the most rapid fermenter by pH fall. Cook-then-ferment technology may be applied to other novel foods to minimise a disruptive endogenous microflora.

Development of a Probiotic Beverage Using Breadfruit Flour as a Substrate.

A fermented beverage was developed using breadfruit flour as a substrate by optimising sucrose, inoculum concentrations, and fermentation temperature in the formulation by utilising the D-optimal mixture design. The optimisation was carried out based on CFU counts, pH, titratable acidity, lactic acid, and sugar concentration of the different fermented breadfruit substrate formulations. Results showed that the optimised values based on the contour plots generated were: 7% breadfruit flour, 1% inoculum, and 15% sugar after fermentation at 30 °C for 48 h. Sensory projective mapping results showed that the fermented breadfruit substrate beverage was characterised by a pale-yellow appearance, fruity flavour, and sweet and sour taste. The hedonic test was not significantly different (p > 0.05) for almost all formulations except for formulation 4 (5% sugar, 3% inoculum, 7% breadfruit flour at 30 °C), which was described as bitter and had the lowest acceptance rating. This study successfully demonstrated the development of a novel fermented breadfruit-based beverage with acceptable sensory characteristics and cell viability using a mixture strain of L. acidophilus and L. plantarum DPC 206.

Multi-strain probiotics enhance immune responsiveness and alters metabolic profiles in the New Zealand black-footed abalone (Haliotis iris).

We assessed whether dietary administration of a multi-strain probiotic (Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc) lead to enhanced immune responsiveness in juvenile New Zealand black-footed abalone (Haliotis iris). Two groups of abalone were fed (1% body weight per day) over a four-month period with different diets. The control diet consisted of a standard commercial pellet feed (AbMax 16), whereas the treatment diet was additionally enriched with the probiotic mix. At the end of the experiment, probiotic-fed animals showed improved growth compared with control-fed abalone in length (32.3% vs 22.3%), width (31.9% vs 20.7%) and wet weight (109.6% vs 72.8%), respectively. Haemolymph sampling was conducted at the beginning of the experiment and after 2 and 4 months. Haemolymph samples were analysed for total haemocyte count (THC) and viability, presence of apoptotic cells and production of Reactive Oxygen Species (ROS). Compared with control abalone, probiotic-fed abalone had significantly higher THC (1.9 × 106 vs 5.6 × 105 cells), higher viability (90.8% vs 75.6%), higher percentage of ROS-positive cells (19.4% vs 0.5%) and higher numbers of non-apoptotic cells (88.0% vs 78.0%), respectively. These results indicate that the probiotic-enriched diet enhanced the immunostimulatory mechanisms, with a simultaneous low-level up-regulation of ROS production as a priming mechanism of the antibacterial defence system. Metabolomics-based profiling of foot muscle tissue additionally revealed that probiotic-fed abalone differentially expressed 17 unique metabolites, including amino acids, fatty acids and TCA cycle related compounds. These data suggest that the probiotic-supplemented diet can also alter central carbon metabolic processes, which may improve the survival, as well as the growth of abalone.