244
pathogen from as little as 24 h to as long as 19 days had been reported by different
studies. Survival in unsterilised brackish water was between 16 and 25 days (Smith
1962 ; McCarthy 1980 ). In unsterilised sea water, the organism could be recovered
from between 24 h and 8 days (McCarthy 1980 ). If sterilised water samples were
used, survival time in the absence of competing –antagonistic –organisms was
invariably greatly increased. For example, survival times in fresh water of up to 63
days were reported (Cornick et al. 1969 ), and in sea water up to 24 days (Lund
1967 ). Using whole cells and DNA released into lake water micocosms, with media
and PCR for detection, Deere et al. ( 1996a ) cultured Aer. salmonicida for <4 weeks,
but found the DNA remained intact for >13 weeks. This discrepancy between the
results of culturing and other techniques opens a veritable Pandora’s box. Why
should intact DNA be found 2+ months after culturing techniques indicated that the
population of Aer. salmonicida had disappeared?
Using a laboratory-based microcosm and culturing, direct counts, respiratory
activity (the reduction of tetrazoliums to coloured formazans; after Effendi and
Austin 1993 ), iFAT, epifl uorescence microscopy and the direct viable count techniques (by incorporating yeast extract and nalidixic acid; after Kogure et al. 1979 ),
Effendi and Austin ( 1994 ) confi rmed the emerging view that cells of Aer. salmonicida remained after plates counts reached zero. These workers determined that survival was maximal in brackish conditions, i.e. salinity = 25‰, notably on
substrates – especially on wood but also in sediment – rather than in the water colTable 5.2 (continued)
Type of experimental system
Temperature
(°C)
Survival
time
References
Sterilised water:
7–19 days
Smith ( 1962 )
20
2 days
Lund ( 1967 )
10
1
–10
2 A. salmonicida cells/ml
15
ca. 3 days
Allen ( 1982 )
10
5
–10
6 A. salmonicida cells/ml
15
>3 days
Allen ( 1982 )
Seawater
–
2 days
Williamson ( 1929 )
–
24–30 h
Duncan ( 1932 )
20
5–6 days
Lund ( 1967 )
11–13
8 days
McCarthy ( 1980 )
–
<10 days
Rose et al. ( 1990b )
20
6 days
Effendi and Austin
( 1991 )
Tap water
3–4 days
Horne ( 1928 )
–
3 days
Williamson ( 1929 )
–
4 days
Duncan ( 1932 )
20
3 days
Lund ( 1967 )
Mixtures of water types:
50 % sea water + 50 % tap water
19 h
Arkwright ( 1912 )
25 % sea water + 75 % tap water
45–67 h
Arkwright ( 1912 )
5 Aeromonadaceae Representative (Aeromonas salmonicida)
pathogen from as little as 24 h to as long as 19 days had been reported by different
studies. Survival in unsterilised brackish water was between 16 and 25 days (Smith
1962 ; McCarthy 1980 ). In unsterilised sea water, the organism could be recovered
from between 24 h and 8 days (McCarthy 1980 ). If sterilised water samples were
used, survival time in the absence of competing –antagonistic –organisms was
invariably greatly increased. For example, survival times in fresh water of up to 63
days were reported (Cornick et al. 1969 ), and in sea water up to 24 days (Lund
1967 ). Using whole cells and DNA released into lake water micocosms, with media
and PCR for detection, Deere et al. ( 1996a ) cultured Aer. salmonicida for <4 weeks,
but found the DNA remained intact for >13 weeks. This discrepancy between the
results of culturing and other techniques opens a veritable Pandora’s box. Why
should intact DNA be found 2+ months after culturing techniques indicated that the
population of Aer. salmonicida had disappeared?
Using a laboratory-based microcosm and culturing, direct counts, respiratory
activity (the reduction of tetrazoliums to coloured formazans; after Effendi and
Austin 1993 ), iFAT, epifl uorescence microscopy and the direct viable count techniques (by incorporating yeast extract and nalidixic acid; after Kogure et al. 1979 ),
Effendi and Austin ( 1994 ) confi rmed the emerging view that cells of Aer. salmonicida remained after plates counts reached zero. These workers determined that survival was maximal in brackish conditions, i.e. salinity = 25‰, notably on
substrates – especially on wood but also in sediment – rather than in the water colTable 5.2 (continued)
Type of experimental system
Temperature
(°C)
Survival
time
References
Sterilised water:
7–19 days
Smith ( 1962 )
20
2 days
Lund ( 1967 )
10
1
–10
2 A. salmonicida cells/ml
15
ca. 3 days
Allen ( 1982 )
10
5
–10
6 A. salmonicida cells/ml
15
>3 days
Allen ( 1982 )
Seawater
–
2 days
Williamson ( 1929 )
–
24–30 h
Duncan ( 1932 )
20
5–6 days
Lund ( 1967 )
11–13
8 days
McCarthy ( 1980 )
–
<10 days
Rose et al. ( 1990b )
20
6 days
Effendi and Austin
( 1991 )
Tap water
3–4 days
Horne ( 1928 )
–
3 days
Williamson ( 1929 )
–
4 days
Duncan ( 1932 )
20
3 days
Lund ( 1967 )
Mixtures of water types:
50 % sea water + 50 % tap water
19 h
Arkwright ( 1912 )
25 % sea water + 75 % tap water
45–67 h
Arkwright ( 1912 )
5 Aeromonadaceae Representative (Aeromonas salmonicida)