21
© Springer International Publishing Switzerland 2016
B. Austin, D.A. Austin, Bacterial Fish Pathogens,
DOI 10.1007/978-3-319-32674-0_2
Chapter 2
Gram-Positive Bacteria (Anaerobes
and ‘Lactic Acid’ Bacteria)
Abstract A wide range of aerobic and anaerobic Gram-positive taxa have been
associated with fi sh diseases with new pathogens including Lactococcus lactis
subsp. lactis. Lactococcosis and streptoccoccosis have developed into signifi cant
constraints of many fi sh species over a wide geographical area. Recent research has
aimed to improve diagnostics by use of sensitive and specifi c molecular methods
and disease control especially by vaccination, probiotics and plant products.
Keywords Anaerobes • Lactococcosis • Streptococcosis • Pseudokidney disease •
Weisellosis
Anaerobes
Although only two species of anaerobic bacteria, namely Clostridium botulinum
and Eubacterium tarantellae , have been implicated as fi sh pathogens, it is likely
that detailed bacteriological investigations, including the use of suitable methods,
may reveal that anaerobes cause more widespread problems than has been hitherto
realised. In the fi rst place, fi sh disease diagnostic laboratories do not normally use
anaerobic methods. Therefore, it is unlikely that isolation of an offending anaerobic
pathogen would ever be achieved. Consequently, the true cause of disease may not
be recognised, or may be attributed to an aerobic secondary invader. Although there
is no evidence that anaerobic pathogens have been missed, there are puzzling cases
of mortalities among fi sh populations for which the aetiological agent has never
been determined. It is recognised that anaerobes occur widely in the natural environment, and are commonplace in aquatic sediments (Davies 1969 ; RouhbakhshKhaleghdoust 1975 ) and in the gastro-intestinal tract of fi sh (Sakata et al. 1978 ,
1980 ; Trust et al. 1979 ; Austin 2006 ), where they would be readily available for
initiation of a disease cycle. Of relevance, Trust and colleagues recovered
Actinomyces, Bacteroides, Fusobacterium and Peptostreptococcus from grass carp,
goldfi sh and rainbow trout. Subsequently, Sakata et al. ( 1980 ) described two groups
of anaerobes from the intestines of freshwater fi sh, i.e. ayu, goldfi sh and tilapia, in
Japan. These Gram-negative, non-motile, asporogenous rods were considered to be
© Springer International Publishing Switzerland 2016
B. Austin, D.A. Austin, Bacterial Fish Pathogens,
DOI 10.1007/978-3-319-32674-0_2
Chapter 2
Gram-Positive Bacteria (Anaerobes
and ‘Lactic Acid’ Bacteria)
Abstract A wide range of aerobic and anaerobic Gram-positive taxa have been
associated with fi sh diseases with new pathogens including Lactococcus lactis
subsp. lactis. Lactococcosis and streptoccoccosis have developed into signifi cant
constraints of many fi sh species over a wide geographical area. Recent research has
aimed to improve diagnostics by use of sensitive and specifi c molecular methods
and disease control especially by vaccination, probiotics and plant products.
Keywords Anaerobes • Lactococcosis • Streptococcosis • Pseudokidney disease •
Weisellosis
Anaerobes
Although only two species of anaerobic bacteria, namely Clostridium botulinum
and Eubacterium tarantellae , have been implicated as fi sh pathogens, it is likely
that detailed bacteriological investigations, including the use of suitable methods,
may reveal that anaerobes cause more widespread problems than has been hitherto
realised. In the fi rst place, fi sh disease diagnostic laboratories do not normally use
anaerobic methods. Therefore, it is unlikely that isolation of an offending anaerobic
pathogen would ever be achieved. Consequently, the true cause of disease may not
be recognised, or may be attributed to an aerobic secondary invader. Although there
is no evidence that anaerobic pathogens have been missed, there are puzzling cases
of mortalities among fi sh populations for which the aetiological agent has never
been determined. It is recognised that anaerobes occur widely in the natural environment, and are commonplace in aquatic sediments (Davies 1969 ; RouhbakhshKhaleghdoust 1975 ) and in the gastro-intestinal tract of fi sh (Sakata et al. 1978 ,
1980 ; Trust et al. 1979 ; Austin 2006 ), where they would be readily available for
initiation of a disease cycle. Of relevance, Trust and colleagues recovered
Actinomyces, Bacteroides, Fusobacterium and Peptostreptococcus from grass carp,
goldfi sh and rainbow trout. Subsequently, Sakata et al. ( 1980 ) described two groups
of anaerobes from the intestines of freshwater fi sh, i.e. ayu, goldfi sh and tilapia, in
Japan. These Gram-negative, non-motile, asporogenous rods were considered to be