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Virulence of Renibacterium salmoninarum to Salmonids
Author(s) -
Starliper Clifford E.,
Smith David R.,
Shatzer Teresa
Publication year - 1997
Publication title -
journal of aquatic animal health
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 52
eISSN - 1548-8667
pISSN - 0899-7659
DOI - 10.1577/1548-8667(1997)009<0001:vorsts>2.3.co;2
Subject(s) - virulence , biology , microbiology and biotechnology , trout , serial dilution , salvelinus , veterinary medicine , colony forming unit , bacteria , fish <actinopterygii> , fishery , genetics , medicine , alternative medicine , pathology , gene
Virulence of Renibacterium salmoninarum isolates representing five origins was evaluated in eight salmonid hosts; four origins were of Lake Michigan and the fifth was of the Pacific Northwest. The species type strain, ATCC (American Type Culture Collection) 33209, was also included. Each isolate was grown in a kidney disease medium (KDM2) supplemented with 1 % ATCC 33209 culture metabolite; serial 10‐fold dilutions were prepared, and groups of fish were challenged by intraperitoneal injection with 0.1 mL of each dilution. A 70‐d observation period followed, and bacterial kidney disease (BKD) was diagnosed by the fluorescent antibody technique. Virulence of isolates was quantified as a dose lethal to 50% of fish (LD50) for each host–isolate challenge. In the first set of experiments, 23 isolates were used to challenge groups of brook trout Salvelinus fontinalis . The mean LD50 was 1.087 × 10 6 colony‐forming units per milliliter (cfu/mL; SD = 2.022 × 10 6 ), and the LD50 values ranged from 8.457 × 10 6 to 2.227 × 10 4 cfu/mL. Analysis of variance to evaluate the effect of isolate origin on virulence in brook trout revealed no significant difference ( F = 1.502; P = 0.243). Susceptibilities of the other salmonid hosts were evaluated by challenge with six isolates of R. salmoninarum representing each origin and the species type strain. For many of the host–isolate challenge combinations, time to death was highly dependent on the dilution (number of bacteria) injected. In general, the isolates MCO4M, B26, and A34 (all of Lake Michigan origin) tended to be more virulent. Also, LD50 values were dispersed throughout a wider range among the more susceptible hosts. Lake trout Salvelinus namaycush , rainbow trout Oncorhynchus mykiss , and brook trout were relatively resistant to challenge with the strains, whereas coho salmon O. kisutch , domestic Atlantic salmon Saltno salar , and chinook salmon O. tshawytscha were relatively susceptible. Another challenge evaluated the effect of washing R. salmoninarum MCO4M cells before injection into brook trout. The calculated LD50 value, 2.009 × 10 5 cfu/mL, was similar ( X 2 = 0.878; P = 0.645) to that of the unwashed cells (1.163 × 10 5 cfu/mL). Furthermore, times to death for successive dilutions were similar regardless of whether or not the cells were washed.