Peter Robertson

Use of Carnobacterium sp. as a probiotic for Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss, Walbaum)

A strain of Carnobacterium sp., isolated from the intestine of Atlantic salmon, was evaluated for potential use as a probiotic for salmonids. In vitro studies demonstrated antagonism against Aeromonas hydrophila, A. salmonicida, Flavobacterium psychrophilum, Photobacterium damselae subsp. piscicida, Streptococcus milleri, Vibrio anguillarum and V. ordalii but not towards Debaryomyces hansenii, Janthinobacterium lividum, V. alginolyticus, V. harveyi or Yersinia ruckeri. Feeding salmonids with diets containing the probiotic revealed that the isolate remained viable in the gastrointestinal tract. After reverting to feeding with control diets, the isolate was re-isolated from the intestine up to 4 and 10 days in fingerlings and fry, respectively. After feeding with the probiotic for 14 days, challenge by cohabitation indicated effectiveness at reducing disease caused by A. salmonicida, V. ordalii and Y. ruckeri but not V. anguillarum.

Recovery of a new biogroup of Yersinia ruckeri from diseased rainbow trout (Oncorhynchus mykiss, Walbaum)

Cultures of a new biogroup of Yersinia ruckeri, the causal agent of enteric redmouth (ERM), were recovered in England from diseased rainbow trout (Oncorhynchus mykiss, Walbaum), which had been previously vaccinated with a commercial ERM vaccine. The bacterial isolates were confirmed as Y. ruckeri by the results of sequencing the 16S rRNA, but differed from the characteristics of the taxon by positivity for the Voges Proskauer reaction and a general lack of motility, and could not be equated with any of the existing serovars. Cultures were pathogenic in laboratory-based infectivity experiments with 100% mortalities occurring in juvenile rainbow trout (average weight = 10 g) within 4-days of intraperitoneal or intramuscular injection with 10(5) cells/fish. Protection against disease was achieved using a formalin-inactivated whole vaccine prepared against a representative isolate.

Chitinases from Vibrio: activity screening and purification of chiA from Vibrio carchariae

Fourteen species of Vibrio were screened for chitin‐induced chitinase activity in culture medium. V. carchariae, V. alginolyticus 283 and V. campbellii showed high levels of activity. Screening on agar plates containing swollen chitin showed high levels of chitinase activity by the same three species, and also by V. fischeri and V. alginolyticus 284. An affinity purification procedure was developed for the chitinase from V. carchariae. The purified chitinase was active as a monomer with Mr 63 000–66 000, and displayed activity toward polymeric chitin from acetylated chitosan or from crab shells. N‐terminal sequence analysis and immunological cross‐reactivity confirmed that the enzyme belongs to the group A/chiA family of bacterial chitinases.

An enzyme-linked immunosorbent assay (ELISA) for the detection of Vibrio harveyi in penaeid shrimp and water

Plate and dipstick enzyme-linked immunosorbent assays (ELISA) were developed for the rapid detection of Vibrio harveyi from penaeid shrimp and water. The ELISA, which incorporated a polyclonal antiserum produced in a female New Zealand white rabbit, detected 105 cells of V. harveyi/ml. Also, the systems detected V. harveyi in water from Chinese shrimp hatcheries. The systems permitted the recognition of a wide range of V.harveyi isolates, but not those of other taxa. Western blot analysis of bacterial outer membrane proteins (OMP) indicated that a wide epitope was recognised, with many immunoreactive bands in common between isolates of V. harveyi.

PCR and Molecular Detection for Differentiating Vibrio Species

Abstract: Vibriosis is an economically important disease of fish, marine invertebrates (particularly penaeid shrimps), and large marine mammals and is responsible for high mortality rates in aquaculture worldwide. Some Vibrio species are also responsible for zoonoses, whereas others are relatively nonpathogenic. Using 16S‐ and 23S‐based PCR reactions, we obtained species‐specific patterns and a 470‐bp band, respectively. DNA sequences obtained on the 23S rRNA gene allowed us to identify species‐specific probes for Vibrio parahaemolyticus, V. alginolyticus, V. anguillarum and for a cluster of taxonomically related species: V. carchariae/harveyi/campbelii. A phylogenetic tree based on the 23S sequences confirmed previous results obtained by Western blotting.

Prevention of ulcer disease in goldfish by means of vaccination

Abstract A vaccine comprising cells of Aeromonas bestiarum grown in tryptic soy broth and atypical A. salmonicida cells produced in iron-limited and iron-supplemented media protected goldfish Carassius auratus when administered by immersion (dosage ≈ 5 × 107 cells/mL for 60 s) followed after 28 d by an oral booster (dosage = 5 × 107 cells/g of feed), which was fed for 7 d so that each fish received about 1 g of vaccine-containing feed. After challenge by intramuscular injection of a virulent culture of atypical A. salmonicida, the relative percent survival (RPS) was more than 90%. The approach was more successful than using a commercial furunculosis vaccine with or without supplementation with A. bestiarum or atypical A. salmonicida cells. Moreover, a smooth derivative of the virulent rough culture of atypical A. salmonicida was less effective as a vaccine candidate, yielding an RPS of only 65%. Low antibody titers of 1:39–1:396 were found in the vaccinated fish. The vaccinated fish had a significantly hi...

Isolation of Aeromonas salmonicida in association with purple-pigmented bacteria in sediment from a Scottish loch

Aeromonas salmonicida was recovered in close association with an unidentified purple‐pigmented organism, which was isolated from sediment in a Scottish loch during November (1997) and February (1998). However, there has not been any evidence of A. salmonicida infections, specifically furunculosis, associated with the fish in this loch.