Involvement of LuxS in Aeromonas salmonicida metabolism, virulence and infection in Atlantic salmon (Salmo salar L)

Quorum sensing is a bacterial density dependent communication system, which regarded to regulate co-operative behaviors of community and mediated by extracellular signal molecules named autoinducers (AI). Among various signals, autoinducer-2 (AI-2) is believed to be the messengers inter species and produced by LuxS. For Aeromonas salmonicida (A. salmonicida), an opportunistic pathogen to many cold-water teleost, little information has been known about the function of AI-2 and LuxS. Therefore, our aim was to preliminarily clarify the function of LuxS in A. salmonicida. The consequences demonstrated that wild type A. salmonicida exhibited AI-2 activity and luxS defective mutant strain fail to produce AI-2 signals. Furthermore, it was suggested that luxS deficiency could impact bacterial morphology, surface properties and virulence dramatically. Challenge experiment showed a tendency that immune factors expressed earlier when Atlantic salmon was infected with ΔluxS strain. Overall, we hypothesis that AI-2 quorum sensing could regulate the expression of A-layer protein coding gene vapA, and then influence bacterial survival ability when suffered from attack of the host immune system. Though additional studies are warranted, our study will supply a new thinking to control the damage caused by A. salmonicida.

Case definition for clinical and subclinical bacterial kidney disease (BKD) in Atlantic Salmon (Salmo salar L.) in New Brunswick, Canada

Bacterial kidney disease (BKD) is considered an important cause of loss in salmon aquaculture in Atlantic Canada. Causative agent of BKD is the Gram-positive bacteria Renibacterium salmoninarum. Infected salmon are often asymptomatic (subclinical infection), and the disease is considered chronic. One of the challenges in quantifying information from farm production and health records is the application of a standardized case definition. Case definitions for farm-level and cage-level clinical and subclinical BKD were developed using retrospective longitudinal data from aquaculture practices in New Brunswick, Canada, combining (i) industry records of weekly production data including mortalities, (ii) field observations for BKD using reports of veterinarians and/or fish health technicians, (iii) diagnostic submissions and test results and (iv) treatments used to control BKD. Case definitions were evaluated using veterinarians' expert judgements as reference standard. Eighty-nine and 66% of sites and fish groups, respectively, were associated with BKD at least once. For BKD present (subclinical or clinical), sensitivity and specificity of the case definition were 75-100% varying between event, fish group, site cycle and level (site pen). For clinical BKD, sensitivities were 29-64% and specificities 91-100%. Industry data can be used to develop sensitive case definitions.

Carbon monoxide stunning of Atlantic salmon (Salmo salar L.) modifies rigor mortis and sensory traits as revealed by NIRS and other instruments

BACKGROUND

Methods of stunning used in salmon slaughter are still the subject of research. Fish quality can be influenced by pre-, ante- and post-mortem conditions, including handling before slaughter, slaughter methods and storage conditions. Carbon monoxide (CO) is known to improve colour stability in red muscle and to reduce microbial growth and lipid oxidation in live fish exposed to CO. Quality differences in Atlantic salmon, Salmo salar L., stunned by CO or percussion, were evaluated and compared by different techniques [near infrared reflectance spectroscopy (NIRS), electronic nose (EN), electronic tongue (ET)] and sensory analysis.

RESULTS

Thawed samples, freeze-dried preparates and NIRS devices proved to be the most efficient combinations for discriminating the treatments applied to salmon, i.e. first the stunning methods adopted, then the back-prediction of the maximum time to reach rigor mortis and finally to correlate some sensory attributes. A trained panel found significant differences between control and CO-stunned salmon: reduced tactile crumbliness, reduced odour and aroma intensities, and reduced tenderness of CO-treated fillets. CO stunning reduced radiation absorbance in spectra of thawed and freeze-dried fillets, but not fillet samples stored in ethanol, where it may have interacted with myoglobin and myosin.

CONCLUSIONS

The good results in a rapid discrimination of thawed samples detected by NIRS suggest suitable applications in the fish industry. CO treatment could mitigate sensory perception, but consumer tests are needed to confirm our findings. © 2015 Society of Chemical Industry.

Molecular cloning of Salmo salar Toll-like receptors (TLR1, TLR22, TLR5M and TLR5S) and expression analysis in SHK-1 cells during Piscirickettsia salmonis infection

In fish, the innate immune system is the primary response against infection. Toll-like receptors (TLRs) recognize pathogens through pathogen-associated molecular patterns (PAMPs), and some target molecules of TLRs are homologous between fish and mammals. Piscirickettsia salmonis is one of the main pathogens affecting the salmon industry in Chile. Better knowledge of mechanisms underlying its invasive capacity and recognition of target cells is crucial for vaccine development. Therefore, Salmo salar L. TLR1, TLR22, membrane TLR5M and soluble TLR5S sequences were cloned, and expression kinetics were analysed by RT-qPCR in salmon head kidney cells (SHK-1) infected with three different P. salmonis preparations: alive, formaldehyde treated, extract. Clearly, all analysed TLRs were expressed and transcription level changes were revealed at 2 hpi, 12 or 16 hpi and 24 hpi depending on P. salmonis infection scheme. Increased IL1-beta expression confirmed TLR pathway response. Furthermore, significant expression modulations of several members of the TLR pathway in this in vitro model suggest that P. salmonis extract rather than formaldehyde-inactivated bacteria might strengthen the salmon immune system.