195
Characteristics of the Pathogen
The 8 bacterial cultures were identifi ed from phenotype and sequencing of the 16S
rRNA gene.
The snakehead isolates contained two plasmids of ~5,000 and ~10,000 bp (Liu
and Li 2012 ).
Pathogenicity
The pathogenicity of one isolate, HYL1, was assessed intraperitoneally in healthy
snakehead fi ngerlings (weight = ~16 g) and zebra fi sh (weight = ~ 2 g) maintained in
static water at 25 °C [half the water was changed every second day] (Liu and Li
2012 ). The fi sh were monitored over 14 days, and HYL1 led to the development of
similar disease signs to those observed in the fi sh farm with 100 % mortalities in
snakehead and zebra fi sh when injected with 1.15 × 10
7 and 2.7 × 10
6 CFU/fi sh,
respectively (Liu and Li 2012 ). Chen et al. ( 2012 reported) LD
50 values of 1.4 × 10
4
and 6.4 × 10
6 CFU/ g of snakehead, with isolates producing elastase, haemolysin
and lecithinase.
Box 4.7: Aer. schubertii
Cultures comprise short motile, fermentative Gram-negative rods occurring
singly or in pairs, which produce arginine dihydrolase, catalase, lysine decarboxylase, oxidase and phenylalanine deaminase, but not H 2 S, indole or ornithine decarboxylase. Nitrates are reduced to nitrites. The methyl red test is
positive, but not so the Voges Proskauer reaction. Gelatin, lipids (Tween 80)
and starch but not aesculin are degraded. Acid is produced from D-glucose,
glycerol, maltose and trehalose, but not L-arabinose, cellobiose, m -inositol,
lactose, D-mannitol, melibiose, melezitose, raffi nose, L-rhamnose, ribose,
D-sorbitol, sucrose or D-xylose. Growth occurs in 0 and 1 % but not 6.0 %
(w/v) NaCl. Resistance occurs to the vibriostatic agent, O/129. A phylogenetic tree constructed with 16S rRNA gene sequences (99 % homology with
Aer. schubertii) bores similarities to that derived from gyrB-rpoD0dnaJ concatenated sequences (100 % homology with Aer. schubertii) in which the
snakehead isolates formed a single cluster with the type strain of Aer. schubertii ATCC 43700
T (Liu and Li 2012 ).
Aeromonas schubertii
Characteristics of the Pathogen
The 8 bacterial cultures were identifi ed from phenotype and sequencing of the 16S
rRNA gene.
The snakehead isolates contained two plasmids of ~5,000 and ~10,000 bp (Liu
and Li 2012 ).
Pathogenicity
The pathogenicity of one isolate, HYL1, was assessed intraperitoneally in healthy
snakehead fi ngerlings (weight = ~16 g) and zebra fi sh (weight = ~ 2 g) maintained in
static water at 25 °C [half the water was changed every second day] (Liu and Li
2012 ). The fi sh were monitored over 14 days, and HYL1 led to the development of
similar disease signs to those observed in the fi sh farm with 100 % mortalities in
snakehead and zebra fi sh when injected with 1.15 × 10
7 and 2.7 × 10
6 CFU/fi sh,
respectively (Liu and Li 2012 ). Chen et al. ( 2012 reported) LD
50 values of 1.4 × 10
4
and 6.4 × 10
6 CFU/ g of snakehead, with isolates producing elastase, haemolysin
and lecithinase.
Box 4.7: Aer. schubertii
Cultures comprise short motile, fermentative Gram-negative rods occurring
singly or in pairs, which produce arginine dihydrolase, catalase, lysine decarboxylase, oxidase and phenylalanine deaminase, but not H 2 S, indole or ornithine decarboxylase. Nitrates are reduced to nitrites. The methyl red test is
positive, but not so the Voges Proskauer reaction. Gelatin, lipids (Tween 80)
and starch but not aesculin are degraded. Acid is produced from D-glucose,
glycerol, maltose and trehalose, but not L-arabinose, cellobiose, m -inositol,
lactose, D-mannitol, melibiose, melezitose, raffi nose, L-rhamnose, ribose,
D-sorbitol, sucrose or D-xylose. Growth occurs in 0 and 1 % but not 6.0 %
(w/v) NaCl. Resistance occurs to the vibriostatic agent, O/129. A phylogenetic tree constructed with 16S rRNA gene sequences (99 % homology with
Aer. schubertii) bores similarities to that derived from gyrB-rpoD0dnaJ concatenated sequences (100 % homology with Aer. schubertii) in which the
snakehead isolates formed a single cluster with the type strain of Aer. schubertii ATCC 43700
T (Liu and Li 2012 ).
Aeromonas schubertii