124
The source of Myc. avium may well have been pre-frozen feed (Janse and Kik
2012 ).
Pathogenicity
Overcrowding and handling exacerbate mycobacteriosis caused by Myc. chelonei and
Myc. marinum in zebra fi sh (Ramsay et al. 2009 ). At a water temperature of 12 °C,
experimental infections developed in rainbow trout which were injected, via the i.p.
route, with approximately 10
7 cells of Myc. chelonei subsp. piscarium . Accumulative
mortalities ranged from 20 to 52 %. With juvenile chinook salmon, 98 % mortalities
were recorded within 10 days at a water temperature of 18 °C (Arakawa and Fryer
1984 ). Goldfi sh have been successfully infected within 8 weeks by i.p. injection with
Myc. fortuitum and Myc. smegmatis ATCC 19420 at 10
7 CFU/fi sh and developed
granulomatous lesions, typical of mycobacteriosis (Talaat et al. 1999 ). Similarly,
striped bass were infected using i.p. injections with ~10
5 cells of Myc. gordonae, Myc.
marinum and Myc. shottsii. Myc. marinum caused peritonitis and the development of
extensive granulomas particularly in the kidney, mesenteries and spleen, whereas the
other two mycobacteria led to mild peritonitis, granulomas in the mesenteries which
resolved with time, and persistent infections in the spleen (Gauthier et al. 2003 ). Zebra
fi sh were much more susceptible, with i.p. injection of ~10
3 cells of Myc. marinum
leading to the development of granulomatous mycobacteriosis (Swaim et al. 2006 ).
Evidence has indicated that a novel plasmid-encoded toxic macrolide,
Mycolactone F (Ranger et al. 2006 ) and ECP may well be involved with the pathogenic process (e.g. Chen et al. 1997 , 2001 ). Mycolactone F, being the smallest
mycolactone recognised and has a molecular weight of 700, has been identifi ed in
Myc. marinum and Myc. pseudoshottsii (Ranger et al. 2006 ). Chen et al. ( 1997 )
determined the LD 50 of ECP from Mycobacterium spp. as >400 μg of protein/fi sh to
rainbow trout and Nile tilapia. Head kidney macrophages from naive rainbow trout
demonstrated heightened macrophage activation when incubated with 1–100 μg/ml
of ECP for 48 h (Chen et al. 2001 ).
Disease Control
Vaccine Development Although there are no vaccines commercially available
against fi sh pathogenic mycobacteria, it is recognised that there is a cell-mediated
response in fi sh, i.e. rainbow trout (Bartos and Sommer 1981 ). Immunisation with
Myc. salmoniphilum mixed with Freund’s adjuvant resulted in delayed hypersensitivity reactions. A DNA vaccine involving the Ag85A gene encoding for one of the major
secreted fi bronectin-binding proteins of Myc. marinum and cloned in a eukaryotic
expression vector stimulated a protective (120 days after vaccination) humoral
immune response, but macrophage phagocytosis or respiratory burst activities, in
hybrid striped bass when administered i.m. (RPS = 80 % and 90 % for 25 μg and 50 mg
doses of vaccine, respectively) and to some extent by i.p. (RPS = 20 % for the 25 μg
dose) (Pasnik and Smith 2005 , 2006 ). In an interesting approach, Kato et al. ( 2010 )
injected Japanese founder i.m. with BCG (1.2 × 10
8 CFU/fi sh) and challenged them
3 Aerobic Gram-Positive Rods and Cocci
The source of Myc. avium may well have been pre-frozen feed (Janse and Kik
2012 ).
Pathogenicity
Overcrowding and handling exacerbate mycobacteriosis caused by Myc. chelonei and
Myc. marinum in zebra fi sh (Ramsay et al. 2009 ). At a water temperature of 12 °C,
experimental infections developed in rainbow trout which were injected, via the i.p.
route, with approximately 10
7 cells of Myc. chelonei subsp. piscarium . Accumulative
mortalities ranged from 20 to 52 %. With juvenile chinook salmon, 98 % mortalities
were recorded within 10 days at a water temperature of 18 °C (Arakawa and Fryer
1984 ). Goldfi sh have been successfully infected within 8 weeks by i.p. injection with
Myc. fortuitum and Myc. smegmatis ATCC 19420 at 10
7 CFU/fi sh and developed
granulomatous lesions, typical of mycobacteriosis (Talaat et al. 1999 ). Similarly,
striped bass were infected using i.p. injections with ~10
5 cells of Myc. gordonae, Myc.
marinum and Myc. shottsii. Myc. marinum caused peritonitis and the development of
extensive granulomas particularly in the kidney, mesenteries and spleen, whereas the
other two mycobacteria led to mild peritonitis, granulomas in the mesenteries which
resolved with time, and persistent infections in the spleen (Gauthier et al. 2003 ). Zebra
fi sh were much more susceptible, with i.p. injection of ~10
3 cells of Myc. marinum
leading to the development of granulomatous mycobacteriosis (Swaim et al. 2006 ).
Evidence has indicated that a novel plasmid-encoded toxic macrolide,
Mycolactone F (Ranger et al. 2006 ) and ECP may well be involved with the pathogenic process (e.g. Chen et al. 1997 , 2001 ). Mycolactone F, being the smallest
mycolactone recognised and has a molecular weight of 700, has been identifi ed in
Myc. marinum and Myc. pseudoshottsii (Ranger et al. 2006 ). Chen et al. ( 1997 )
determined the LD 50 of ECP from Mycobacterium spp. as >400 μg of protein/fi sh to
rainbow trout and Nile tilapia. Head kidney macrophages from naive rainbow trout
demonstrated heightened macrophage activation when incubated with 1–100 μg/ml
of ECP for 48 h (Chen et al. 2001 ).
Disease Control
Vaccine Development Although there are no vaccines commercially available
against fi sh pathogenic mycobacteria, it is recognised that there is a cell-mediated
response in fi sh, i.e. rainbow trout (Bartos and Sommer 1981 ). Immunisation with
Myc. salmoniphilum mixed with Freund’s adjuvant resulted in delayed hypersensitivity reactions. A DNA vaccine involving the Ag85A gene encoding for one of the major
secreted fi bronectin-binding proteins of Myc. marinum and cloned in a eukaryotic
expression vector stimulated a protective (120 days after vaccination) humoral
immune response, but macrophage phagocytosis or respiratory burst activities, in
hybrid striped bass when administered i.m. (RPS = 80 % and 90 % for 25 μg and 50 mg
doses of vaccine, respectively) and to some extent by i.p. (RPS = 20 % for the 25 μg
dose) (Pasnik and Smith 2005 , 2006 ). In an interesting approach, Kato et al. ( 2010 )
injected Japanese founder i.m. with BCG (1.2 × 10
8 CFU/fi sh) and challenged them
3 Aerobic Gram-Positive Rods and Cocci