Sami Nikoskelainen

Immune enhancement in rainbow trout (Oncorhynchus mykiss) by potential probiotic bacteria (Lactobacillus rhamnosus)

The present study assessed the immune enhancement of fish by a lactic acid bacterium (LAB) Lactobacillus rhamnosus (ATCC 53103). The bacterium was administered orally at five different doses 7.9 x 10(4) (LAB4), 2.1 x 10(6) (LAB6), 2.8 x 10(8) (LAB8), 1.9 x 10(10) (LAB10) and 9.7 x 10(10) (LAB11) CFU/g feed to rainbow trout for two weeks and the feed was changed to un-supplemented diet. From the onset of feeding supplemented diets at 1, 2, 3 and 4 weeks, blood and mucus samples were taken. During the LAB feeding period L. rhamnosus persisted in the fish intestine and in the tank water in high numbers. However, L. rhamnosus disappeared from the intestine, skin mucus and tank water within one week after the change to the non-supplemented feed. In comparison to untreated control fish, respiratory burst activity of blood cells was raised significantly in the LAB4 treated group on week 2. Serum-mediated killing of Escherichia coli was increased significantly in group LAB6 on week 2. Serum immunoglobulin levels were significantly raised only in LAB8 group on week 1 and in LAB4 and LAB8 at the end of the trial. The results show that rainbow trout immune parameters were enhanced by using probiotic bacteria.

Protection of rainbow trout (Oncorhynchus mykiss) from furunculosis by Lactobacillus rhamnosus

The present study aimed to investigate the potential probiotic properties in fish of a lactic acid bacterium intended for human use: Lactobacillus rhamnosus (ATCC 53103). A probiotic for human use was specifically chosen since it is known to be safe for human use, which is of major importance because the fish are meant for human consumption. The bacterium was administered at two different doses (109 and 1012 CFU/g feed) to rainbow trout for 51 days. Sixteen days after the start of the Lactobacillus feeding, the fish were challenged with Aeromonas salmonicida ssp. salmonicida, which causes furunculosis. During the challenge trial the mortality was monitored. L. rhamnosus reduced the fish mortality significantly, from 52.6% in the control to 18.9% and 46.3% in the 109 CFU/g feed and the 1012 CFU/g feed groups, respectively. From this, it was concluded that the tested strain may be a promising probiotic for fish without subsequent risk for human consumption.

Characterization of the Properties of Human- and Dairy-Derived Probiotics for Prevention of Infectious Diseases in Fish

ABSTRACT The present study aimed to investigate the potential probiotic properties of six lactic acid bacteria (LAB) intended for human use, Lactobacillus rhamnosus ATCC 53103,Lactobacillus casei Shirota, Lactobacillus bulgaricus, L. rhamnosus LC 705, Bifidobacterium lactis Bb12, and Lactobacillus johnsonii La1, and one for animal use, Enterococcus faecium Tehobak, for use as a fish probiotic. The strains for human use were specifically chosen since they are known to be safe for human use, which is of major importance because the fish are meant for human consumption. The selection was carried out by five different methods: mucosal adhesion, mucosal penetration, inhibition of pathogen growth and adhesion, and resistance to fish bile. The adhesion abilities of the seven LAB and three fish pathogens, Vibrio anguillarum, Aeromonas salmonicida, and Flavobacterium psychrophilum, were determined to mucus from five different sites on the surface or in the gut of rainbow trout. Five of the tested LAB strains showed considerable adhesion to different fish mucus types (14 to 26% of the added bacteria). Despite their adhesive character, the LAB strains were not able to inhibit the mucus binding of A. salmonicida. Coculture experiments showed significant inhibition of growth of A. salmonicida, which was mediated by competition for nutrients rather than secretion of inhibitory substances by the probiotic bacteria as measured in spent culture liquid. All LAB except L. casei Shirota showed tolerance against fish bile. L. rhamnosus ATCC 53103 and L. bulgaricus were found to penetrate fish mucus better than other probiotic bacteria. Based on bile resistance, mucus adhesion, mucus penetration, and suppression of fish pathogen growth,L. rhamnosus ATCC 53103 and L. bulgaricus can be considered for future in vivo challenge studies in fish as a novel and safe treatment in aquaculture.

Bacteriolytic activity of rainbow trout (Oncorhynchus mykiss) complement

The total bacteriolytic activity comprising of the classical, alternative and possible lectine pathways as well as the bacteriolytic activity of the alternative pathway (AP) of rainbow trout (Oncorhynchus mykiss) complement was assessed in temperatures ranging from 0 to 35 degrees C against a recombinant strain Escherichia coli containing two reporter genes gfp and lucFF. At 35 degrees C there was no difference between the total (TC) activity and the activity of the AP, but at 10 degrees C the TC was notably higher than the AP. Total activity peaked at 30 degrees C and gradually grew smaller towards 0 degrees C. The activity of the AP was similarly temperature-dependent, but CB50 value was found to be beyond measurable range at temperatures below 10 degrees C. When compared to human serum complement, the peak human TC activity at 37 degrees C was four times higher than the TC of rainbow trout at 30 degrees C. Human TC activity was 10.1-fold lower at 25 degrees C when compared to the activity at 37 degrees C. At 37 degrees C the human AP bacteriolytic activity was 4.5-fold less effective than human TC, but at 25 degrees C there was no difference between human TC and AP. In contrast to previous reports where AP activity of fish was assayed as hemolytic activity our study showed that the bacteriolytic activity of AP was lower than that of TC and very low at temperatures below 10 degrees C suggesting that the earlier proposed particular importance of AP in fish should be reconsidered.

Exposure to Increased Ambient Ultraviolet B Radiation has Negative Effects on Growth, Condition and Immune Function of Juvenile Atlantic Salmon (Salmo salar)

Atlantic salmon (Salmo salar) parr were exposed in two outdoor experiments, ranging in duration from 52 to 137 days, to spectral treatments: (1) natural sunlight (=present ambient UVB level), (2) solar radiation supplemented with enhanced UVB radiation from lamps simulating 20% or 8% stratospheric ozone loss or (3) UVB‐depleted sunlight achieved by screening with Mylar‐D film. The growth, condition and immune function of the salmon were quantified after treatments. Exposure to enhanced UVB radiation retarded growth, and decreased hematocrit value and plasma protein concentration. Further, enhanced UVB radiation affected plasma immunoglobulin concentration. The results demonstrate that juvenile Atlantic salmon are not able to fully adapt to increased ambient UVB levels in long‐term exposures, and the interference with immune system function suggests a negative effect of UVB on disease resistance in Atlantic salmon.

Resistance to bacterial infectious diseases in rainbow trout (Oncorhynchus mykiss)

Individually tagged rainbow trout representing 15 full-sibling families were sequentially challenged twice with Aeromonas salmonicida causing furunculosis: first as cohabitation and then as injected intraperitoneally. The bleeding procedure prior to challenges caused the outbreak of cold water disease by Flavobacterium psychrophilum. Before and after the outbreak and challenges, 11 immunological parameters were measured from blood samples. The immunological responses predicted the fate of the fish since nearly all the initial responses were lower in individuals which later died from cold water disease than in survivors. Fish died from furunculosis had impaired respiratory burst (RB) response to A. salmonicida. Fish that had initially the highest responses survived in the outbreak and challenges. The outbreak and challenges resulted in these individuals higher and faster responses compared with initial values. Unlike in mammals, the number of monocytes, but not that of granulocytes, in rainbow trout blood correlated well with the whole blood RB activity. The fish families differed markedly from each other in capacity to resist the induced diseases.