37
presence of streptococci in the aquatic environment. Conceivably, the organisms
may have been released from infected fi sh and were being merely retained in the
water and underlying sediment. Alternatively with the inconclusive taxonomic status of the fi sh pathogenic streptococci at the time, it would be diffi cult to conclude
that any environmental isolates correspond precisely to the description of the fi sh
pathogens. Therefore, any environmental isolates could be merely indicators of an
unsanitary condition and not necessarily imply the presence of fi sh pathogenic
strains. However, this evades the question about the precise source of infection.
Minami ( 1979 ) determined that streptococci, with similarities to the fi sh pathogens,
were present in fresh and frozen fi sh used for yellowtail diets. This worker reported
that the isolates were pathogenic, and could survive for over 6 months in the frozen
state. The suggestion was made, therefore, that the contaminated diets served as an
important source of infection. The importance of food-borne infection was further
highlighted by Taniguchi ( 1982a , b , 1983 ).
It is recognised that streptococcicosis may be transmitted by contact with infected
fi sh. In this context, Robinson and Meyer ( 1966 ) transmitted the disease by cohabiting an infected golden shiner with healthy specimens of the same species. The
healthy fi sh succumbed to streptococcicosis, and died within 5 days. Some host
specifi city to Gram-positive cocci in chains exists, insofar as trout suffer heavy
mortalities whereas Mozambique bream ( Sarotherodon mossambicus), banded
bream ( Tilapia sparramanii), carp ( Cyprinus carpio) and largemouth bass
( Micropterus salmoides) do not (Boomker et al. 1979 ). It has been established that
challenge with low-virulence isolates or low doses of high-virulence isolates
together with cell-free culture supernatants are suffi cient to establish infection
(Kimura and Kusuda 1979 ). The toxic activity of supernatants was further
researched, and two fractions were demonstrated to have a signifi cant effect on
pathogenicity (Kimura and Kusuda 1982 ). These were recovered in Todd-Hewitt
broth after incubation at 30 °C for 48 h. The fraction, although not toxic by oral
administration (presumably the compounds were digested), produced damage, i.e.
exophthalmia and petechial haemorrhages, following percutaneous injection of
yellowtails.
Development of Vaccines
A formalised suspension of ß-haemolytic Streptococcus was successful when
applied to rainbow trout by immersion or by injection with or without FCA (Sakai
et al. 1987 ; 1989 ). A RPS of 70 % was achieved, which was superior to the results
of Iida et al. ( 1982 ). Yet, only low titres of agglutinating antibody occurred in fi sh
vaccinated by injection. Conversely, antibodies were not detected in trout, which
were vaccinated by immersion (Sakai et al. 1987 ; 1989 ). A toxoid enriched whole
cell Enterococcus vaccine, administered to turbot by i.p injection and immersion,
gave long term protection, with RPS of 89–100 % and 67–86 % recorded for 45 g
and 150 g fi sh, respectively (Toranzo et al. 1995 ).
Gram-Positive Cocci in Chains: The Early Literature
presence of streptococci in the aquatic environment. Conceivably, the organisms
may have been released from infected fi sh and were being merely retained in the
water and underlying sediment. Alternatively with the inconclusive taxonomic status of the fi sh pathogenic streptococci at the time, it would be diffi cult to conclude
that any environmental isolates correspond precisely to the description of the fi sh
pathogens. Therefore, any environmental isolates could be merely indicators of an
unsanitary condition and not necessarily imply the presence of fi sh pathogenic
strains. However, this evades the question about the precise source of infection.
Minami ( 1979 ) determined that streptococci, with similarities to the fi sh pathogens,
were present in fresh and frozen fi sh used for yellowtail diets. This worker reported
that the isolates were pathogenic, and could survive for over 6 months in the frozen
state. The suggestion was made, therefore, that the contaminated diets served as an
important source of infection. The importance of food-borne infection was further
highlighted by Taniguchi ( 1982a , b , 1983 ).
It is recognised that streptococcicosis may be transmitted by contact with infected
fi sh. In this context, Robinson and Meyer ( 1966 ) transmitted the disease by cohabiting an infected golden shiner with healthy specimens of the same species. The
healthy fi sh succumbed to streptococcicosis, and died within 5 days. Some host
specifi city to Gram-positive cocci in chains exists, insofar as trout suffer heavy
mortalities whereas Mozambique bream ( Sarotherodon mossambicus), banded
bream ( Tilapia sparramanii), carp ( Cyprinus carpio) and largemouth bass
( Micropterus salmoides) do not (Boomker et al. 1979 ). It has been established that
challenge with low-virulence isolates or low doses of high-virulence isolates
together with cell-free culture supernatants are suffi cient to establish infection
(Kimura and Kusuda 1979 ). The toxic activity of supernatants was further
researched, and two fractions were demonstrated to have a signifi cant effect on
pathogenicity (Kimura and Kusuda 1982 ). These were recovered in Todd-Hewitt
broth after incubation at 30 °C for 48 h. The fraction, although not toxic by oral
administration (presumably the compounds were digested), produced damage, i.e.
exophthalmia and petechial haemorrhages, following percutaneous injection of
yellowtails.
Development of Vaccines
A formalised suspension of ß-haemolytic Streptococcus was successful when
applied to rainbow trout by immersion or by injection with or without FCA (Sakai
et al. 1987 ; 1989 ). A RPS of 70 % was achieved, which was superior to the results
of Iida et al. ( 1982 ). Yet, only low titres of agglutinating antibody occurred in fi sh
vaccinated by injection. Conversely, antibodies were not detected in trout, which
were vaccinated by immersion (Sakai et al. 1987 ; 1989 ). A toxoid enriched whole
cell Enterococcus vaccine, administered to turbot by i.p injection and immersion,
gave long term protection, with RPS of 89–100 % and 67–86 % recorded for 45 g
and 150 g fi sh, respectively (Toranzo et al. 1995 ).
Gram-Positive Cocci in Chains: The Early Literature