55
Pathogenicity
When administered i.m. at doses of just over 10
6 cells/fi sh, Str. dysgalactiae led to
clinical disease resembling those of naturally infected fi sh (Nomoto et al. 2004 ).
The pyrogenic, exotoxin G, a superantigen, and streptolysin S genes are regarded as
the most importance virulence traits, with cultures recovered from moribund fi sh
harbouring the streptolysin S structural gene, sagA (Abdelsalam et al. 2010 ).
Streptococcus ictaluri
Characteristics of the Disease
The pathogen has been associated with a range of conditions, including arthritis,
emaciation, myositis, osteolysis and spinal meningitis leading to low level mortalities in channel catfi sh (Camus et al. 2008 ).
Characteristics of the Pathogen
Sequencing of the 16S rRNA gene revealed that the three isolates from diseased
channel catfi sh were most related phylogenetically to Str. iniae, Str. parauberis and
Str. uberis (Shewmaker et al. 2007 ).
Box 2.14: Streptococcus ictaluri
Colonies on TSA supplemented with 5 % (v/v) defi brinated sheep blood comprise α-haemolytic catalase-negative Gram-positive cocci in pairs and short
chains, which grows at optimally at 30 °C, but not at 45 °C or in 6.5 % (w/v)
sodium chloride. Produces alanine-phenylalanine proline arylamidase, alkaline phosphatase, leucine aminopeptidase, pyroglutamic acid arylamidase and
pyroglutamylaminopeptidase, but not arginine dihydrolase, ß-glucosidase,
ß-galactosidase, N -acetyl-ß-glucosaminidase, glycine-L-tryptophan arylamidase or ß-mannosidase. Does not degrade aesculin, arginine, hippurate or
urea. Produces acid from maltose, but not L-arabinose, D-arabitol, cyclodextrin, glycogen, lactose, mannitol, melibiose, melezitose, methyl-ß-Dglucopyranoside, pullulan, raffi nose, sorbitol, sucrose, tagatose or trehalose.
Does not utilise pyruvate. The Voges Proskauer reaction is negative. Tellurite
is not tolerated. Susceptible to vancomycin. The G + C ratio of the DNA is
38.5 mol%. DNA:DNA hybridisation revealed a DNA relatedness of ≤22 %
with other streptococci, namely Str. canis, Str. dysgalactiae subsp. dysgalactiae, Str. iniae, Str. parauberis, Str. pyogenes, Str. uberis and Str. urinalis
(Shewmaker et al. 2007 ).
Streptococcaceae Representatives
Pathogenicity
When administered i.m. at doses of just over 10
6 cells/fi sh, Str. dysgalactiae led to
clinical disease resembling those of naturally infected fi sh (Nomoto et al. 2004 ).
The pyrogenic, exotoxin G, a superantigen, and streptolysin S genes are regarded as
the most importance virulence traits, with cultures recovered from moribund fi sh
harbouring the streptolysin S structural gene, sagA (Abdelsalam et al. 2010 ).
Streptococcus ictaluri
Characteristics of the Disease
The pathogen has been associated with a range of conditions, including arthritis,
emaciation, myositis, osteolysis and spinal meningitis leading to low level mortalities in channel catfi sh (Camus et al. 2008 ).
Characteristics of the Pathogen
Sequencing of the 16S rRNA gene revealed that the three isolates from diseased
channel catfi sh were most related phylogenetically to Str. iniae, Str. parauberis and
Str. uberis (Shewmaker et al. 2007 ).
Box 2.14: Streptococcus ictaluri
Colonies on TSA supplemented with 5 % (v/v) defi brinated sheep blood comprise α-haemolytic catalase-negative Gram-positive cocci in pairs and short
chains, which grows at optimally at 30 °C, but not at 45 °C or in 6.5 % (w/v)
sodium chloride. Produces alanine-phenylalanine proline arylamidase, alkaline phosphatase, leucine aminopeptidase, pyroglutamic acid arylamidase and
pyroglutamylaminopeptidase, but not arginine dihydrolase, ß-glucosidase,
ß-galactosidase, N -acetyl-ß-glucosaminidase, glycine-L-tryptophan arylamidase or ß-mannosidase. Does not degrade aesculin, arginine, hippurate or
urea. Produces acid from maltose, but not L-arabinose, D-arabitol, cyclodextrin, glycogen, lactose, mannitol, melibiose, melezitose, methyl-ß-Dglucopyranoside, pullulan, raffi nose, sorbitol, sucrose, tagatose or trehalose.
Does not utilise pyruvate. The Voges Proskauer reaction is negative. Tellurite
is not tolerated. Susceptible to vancomycin. The G + C ratio of the DNA is
38.5 mol%. DNA:DNA hybridisation revealed a DNA relatedness of ≤22 %
with other streptococci, namely Str. canis, Str. dysgalactiae subsp. dysgalactiae, Str. iniae, Str. parauberis, Str. pyogenes, Str. uberis and Str. urinalis
(Shewmaker et al. 2007 ).
Streptococcaceae Representatives