36
Serology, although indicating a multiplicity of serotypes, has confi rmed that the
fi sh pathogens are indeed bona fi de representatives of Streptococcus/Enterococcus.
Thereafter, serological techniques have not improved the understanding of the precise taxonomic status of the strains. The organisms described by Cook and Lofton
( 1975 ) and considered as identical to those of Plumb et al. ( 1974 ) were identifi ed as
Group B type 1 b Streptococcus by the CDC, Atlanta. Also, Baya et al. ( 1991 ) identifi ed their isolates as Group B. However, Boomker et al. ( 1979 ) regarded the isolates
as Group D. To further complicate the issue, Kitao et al. ( 1981 ) reported a new
serotype in Japan, which did not react with specifi c antisera to Lancefi eld groups A,
B, C, D, E, F, G, H, K, L, N, O and MG; this conclusion was also reached by Kitao
( 1982a ) and Kusuda et al. ( 1982 ). The confusion was only resolved when a proper
speciation of fi sh pathogenic streptococci began to be developed and has continued
until now with the recognition of some new species, e.g. Str. phocae.
Isolation
Recovery is usually straightforward, involving use of bovine blood tryptose agar
(Naudé 1975 ; Roode 1977 ; Boomker et al. 1979 ), Columbia agar (Appendix in
Chap. 12 ), 5 % (v/v) defi brinated sheep blood agar (Doménech et al. 1996 ), ToddHewitt broth (Appendix in Chap. 12 ), Todd-Hewitt agar (Nomoto et al. 2004 ), nutrient agar supplemented with rabbit blood (Kitao et al. 1981 ), TSA (Teskeredzic et al.
1993 ; Michel et al. 1997 ), 10 % (v/v) horse blood in Columbia agar (Oxoid), 10 %
(v/v) horse serum in Columbia agar (Austin and Robertson 1993 ), yeast extract
glucose agar (Appendix in Chap. 12 ; Michel et al. 1997 ) or BHIA (Minami et al.
1979 ; Ugajin 1981 ; Kusuda et al. 1991 ; Eldar et al. 1994 ). Media may be supplemented with 1 % (w/v) sodium chloride (Austin and Robertson 1993 ). Media should
be inoculated with diseased tissue, notably from the kidney, and incubated at
15–37 °C for up to 7 days (usually 48 or 72 h) when ‘dull grey’ colonies approximately 1–2 mm in diameter develop. These colonies contain cocci in chains. It must
be emphasised that an incubation temperature of 37 °C is in excess of the normal
growth temperature of many fi sh species, notably salmonids. This indicates that the
organisms may well have been derived from warm-blooded animals, and may,
therefore, constitute a public health risk.
Epizootiology
By scrutiny of the early literature, there is evidence that the pathogens abound
throughout the year in the aquatic environment, occurring in water, mud and in the
vicinity of fi sh pens (Kitao et al. 1979 ). Some seasonality has been recorded, with
higher numbers present in seawater during summer. In contrast, greatest numbers
were isolated in mud during autumn and winter (Kitao et al. 1979 ). This is interesting, but unfortunately the authors did not comment further about the reasons for the
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)
Serology, although indicating a multiplicity of serotypes, has confi rmed that the
fi sh pathogens are indeed bona fi de representatives of Streptococcus/Enterococcus.
Thereafter, serological techniques have not improved the understanding of the precise taxonomic status of the strains. The organisms described by Cook and Lofton
( 1975 ) and considered as identical to those of Plumb et al. ( 1974 ) were identifi ed as
Group B type 1 b Streptococcus by the CDC, Atlanta. Also, Baya et al. ( 1991 ) identifi ed their isolates as Group B. However, Boomker et al. ( 1979 ) regarded the isolates
as Group D. To further complicate the issue, Kitao et al. ( 1981 ) reported a new
serotype in Japan, which did not react with specifi c antisera to Lancefi eld groups A,
B, C, D, E, F, G, H, K, L, N, O and MG; this conclusion was also reached by Kitao
( 1982a ) and Kusuda et al. ( 1982 ). The confusion was only resolved when a proper
speciation of fi sh pathogenic streptococci began to be developed and has continued
until now with the recognition of some new species, e.g. Str. phocae.
Isolation
Recovery is usually straightforward, involving use of bovine blood tryptose agar
(Naudé 1975 ; Roode 1977 ; Boomker et al. 1979 ), Columbia agar (Appendix in
Chap. 12 ), 5 % (v/v) defi brinated sheep blood agar (Doménech et al. 1996 ), ToddHewitt broth (Appendix in Chap. 12 ), Todd-Hewitt agar (Nomoto et al. 2004 ), nutrient agar supplemented with rabbit blood (Kitao et al. 1981 ), TSA (Teskeredzic et al.
1993 ; Michel et al. 1997 ), 10 % (v/v) horse blood in Columbia agar (Oxoid), 10 %
(v/v) horse serum in Columbia agar (Austin and Robertson 1993 ), yeast extract
glucose agar (Appendix in Chap. 12 ; Michel et al. 1997 ) or BHIA (Minami et al.
1979 ; Ugajin 1981 ; Kusuda et al. 1991 ; Eldar et al. 1994 ). Media may be supplemented with 1 % (w/v) sodium chloride (Austin and Robertson 1993 ). Media should
be inoculated with diseased tissue, notably from the kidney, and incubated at
15–37 °C for up to 7 days (usually 48 or 72 h) when ‘dull grey’ colonies approximately 1–2 mm in diameter develop. These colonies contain cocci in chains. It must
be emphasised that an incubation temperature of 37 °C is in excess of the normal
growth temperature of many fi sh species, notably salmonids. This indicates that the
organisms may well have been derived from warm-blooded animals, and may,
therefore, constitute a public health risk.
Epizootiology
By scrutiny of the early literature, there is evidence that the pathogens abound
throughout the year in the aquatic environment, occurring in water, mud and in the
vicinity of fi sh pens (Kitao et al. 1979 ). Some seasonality has been recorded, with
higher numbers present in seawater during summer. In contrast, greatest numbers
were isolated in mud during autumn and winter (Kitao et al. 1979 ). This is interesting, but unfortunately the authors did not comment further about the reasons for the
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)