28
Isolation
Kidney and samples from external and internal lesions were inoculated onto TSA
and cresol red thallium acetate sucrose inulin agar, which is selective for carnobacteria, with incubation at 22 °C for up to 72 h (Loch et al. 2008 ).
Characteristics of the Pathogen
Scrutiny of the characteristics reveal phenotypic similarities to the organisms
reported by Hiu et al. ( 1984 ), Baya et al. ( 1991 ), Starliper et al. ( 1992 ) and Toranzo
et al. ( 1993 ). The taxonomic status of these putative carnobacteria remains to be
fi rmly established. Subsequently, Loch et al. ( 2011 ) recovered 57 carnobacterial
isolates from the kidney, spleen, swimbladder, and/or external ulcers on 51 trout and
salmon broodstock in Michigan, USA. The isolates were phenotyped and the partial
16S rDNA gene sequenced with the result that the majority (29/30 isolates) were
identifi ed as Car. maltoaromaticum, and a solitary culture as Car. divergens, albeit
with evidence of phenotypic and genotypic heterogeneity . In another study, Schaffer
et al. ( 2013 ) sequenced the 16S rDNA gene of 7 isolates from 7 juvenile salmon
sharks from the Californian coast, and recorded a 99 % homology to Car. maltoaromaticum. A 97 % homology value was scored using the large ribosomal DNA intergeneric spacer region (ISR).
Carnobacterium piscicola (and the Lactobacilli)
Lactic acid bacteria may be benefi cial to fi sh as probiotics. Other representatives are
pathogenic to fi sh. Certainly, there is confusion over the role of carnobacteria as fi sh
pathogens.
Box 2.3: Carnobacterium maltaromaticum -Like Organisms
Whitish colonies on TSA comprise nonmotile, asporogenous, facultatively
anaerobic Gram-positive rods of 1.0–1.5 × 0.5 μm in size arranged in pallisades, which produce arginine dihydrolase and ß-galactosidase but not catalase, H 2 S or indole, lysine or ornithine decarboxylase, oxidase or phenylalanine
deaminase, or reduce nitrates. Aesculin is degraded. The methyl red test is
positive. Citrate and malonate are not utilised. Acid is produced from cellobiose, galactose, glucose, lactose, maltose, mannose, salicin, sucrose and trehalose, but not arabinose, adonitol, inositol, raffi nose, rhamnose or xylose.
Growth does not occur on acetate agar or MacConkey agar. Partial sequencing
of the 16S rRNA gene revealed a 97 % homology with Carnobacterium maltaromaticum (Loch et al. 2008 ), which is below the threshold for a confi rmed
identifi cation.
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)
Isolation
Kidney and samples from external and internal lesions were inoculated onto TSA
and cresol red thallium acetate sucrose inulin agar, which is selective for carnobacteria, with incubation at 22 °C for up to 72 h (Loch et al. 2008 ).
Characteristics of the Pathogen
Scrutiny of the characteristics reveal phenotypic similarities to the organisms
reported by Hiu et al. ( 1984 ), Baya et al. ( 1991 ), Starliper et al. ( 1992 ) and Toranzo
et al. ( 1993 ). The taxonomic status of these putative carnobacteria remains to be
fi rmly established. Subsequently, Loch et al. ( 2011 ) recovered 57 carnobacterial
isolates from the kidney, spleen, swimbladder, and/or external ulcers on 51 trout and
salmon broodstock in Michigan, USA. The isolates were phenotyped and the partial
16S rDNA gene sequenced with the result that the majority (29/30 isolates) were
identifi ed as Car. maltoaromaticum, and a solitary culture as Car. divergens, albeit
with evidence of phenotypic and genotypic heterogeneity . In another study, Schaffer
et al. ( 2013 ) sequenced the 16S rDNA gene of 7 isolates from 7 juvenile salmon
sharks from the Californian coast, and recorded a 99 % homology to Car. maltoaromaticum. A 97 % homology value was scored using the large ribosomal DNA intergeneric spacer region (ISR).
Carnobacterium piscicola (and the Lactobacilli)
Lactic acid bacteria may be benefi cial to fi sh as probiotics. Other representatives are
pathogenic to fi sh. Certainly, there is confusion over the role of carnobacteria as fi sh
pathogens.
Box 2.3: Carnobacterium maltaromaticum -Like Organisms
Whitish colonies on TSA comprise nonmotile, asporogenous, facultatively
anaerobic Gram-positive rods of 1.0–1.5 × 0.5 μm in size arranged in pallisades, which produce arginine dihydrolase and ß-galactosidase but not catalase, H 2 S or indole, lysine or ornithine decarboxylase, oxidase or phenylalanine
deaminase, or reduce nitrates. Aesculin is degraded. The methyl red test is
positive. Citrate and malonate are not utilised. Acid is produced from cellobiose, galactose, glucose, lactose, maltose, mannose, salicin, sucrose and trehalose, but not arabinose, adonitol, inositol, raffi nose, rhamnose or xylose.
Growth does not occur on acetate agar or MacConkey agar. Partial sequencing
of the 16S rRNA gene revealed a 97 % homology with Carnobacterium maltaromaticum (Loch et al. 2008 ), which is below the threshold for a confi rmed
identifi cation.
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)