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Microbiological studies of Streptococcus sp. biovar 1 (synonym of Enterococcus seriolicida and Lactococcus garvieae), pathogenic for rainbow trout (Oncorhynchus mykiss), and related species of bacteria

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Hawkesford, T (1997) Microbiological studies of Streptococcus sp. biovar 1 (synonym of Enterococcus seriolicida and Lactococcus garvieae), pathogenic for rainbow trout (Oncorhynchus mykiss), and related species of bacteria. PhD thesis, University of Tasmania.

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Abstract

A specific Gram-positive coccus, which was given the epithet Streptococcus sp.
biovar 1, was first isolated from diseased farmed rainbow trout (Oncorhynchus
mykiss) in Tasmania in 1988. The preliminary identification was based on the
morphological, physiological and biochemical characteristics of the Tasmanian
isolates. However, subsequent studies in Japan and Tasmania indicated that these
organisms were more closely related to the genus Enterococcus, especially the fishpathogenic
bacterium known as Enterococcus seriolicida, than to the genus
Streptococcus. Further investigation has indicated that these fish pathogenic isolates
are identical to the species Lactococcus garvieae isolated from cattle.
In December 1993, when this study commenced, the source of Streptococcus sp.
biovar 1 (as it was then known) in Tasmania was unknown, so an environmental
survey of potential sources was undertaken with the view to determining the initial
source of the organism and providing a basis for future control of the disease. The 61
organisms isolated during this survey, as well as ten Australian isolates of
Streptococcus sp. biovar 1, two strains of Enterococcus seriolicida and two strains of
Lactococcus garvieae, were characterised phenotypically using morphological,
physiological, biochemical and immunological techniques. Random amplified
polymorphic DNA polymerase chain reaction (RAPD-PCR) studies were then
undertaken on the ten Australian isolates of Streptococcus sp. biovar 1, two strains of
Enterococcus seriolicida, one strain of Lactococcus garvieae and 18 of the
environmental isolates to investigate the possibility of any genetic similarity.
A specific Gram-positive coccus, which was given the epithet Streptococcus sp.
biovar 1, was first isolated from diseased farmed rainbow trout (Oncorhynchus
mykiss) in Tasmania in 1988. The preliminary identification was based on the
morphological, physiological and biochemical characteristics of the Tasmanian
isolates. However, subsequent studies in Japan and Tasmania indicated that these
organisms were more closely related to the genus Enterococcus, especially the fishpathogenic
bacterium known as Enterococcus seriolicida, than to the genus
Streptococcus. Further investigation has indicated that these fish pathogenic isolates
are identical to the species Lactococcus garvieae isolated from cattle.
In December 1993, when this study commenced, the source of Streptococcus sp.
biovar 1 (as it was then known) in Tasmania was unknown, so an environmental
survey of potential sources was undertaken with the view to determining the initial
source of the organism and providing a basis for future control of the disease. The 61
organisms isolated during this survey, as well as ten Australian isolates of
Streptococcus sp. biovar 1, two strains of Enterococcus seriolicida and two strains of
Lactococcus garvieae, were characterised phenotypically using morphological,
physiological, biochemical and immunological techniques. Random amplified
polymorphic DNA polymerase chain reaction (RAPD-PCR) studies were then
undertaken on the ten Australian isolates of Streptococcus sp. biovar 1, two strains of
Enterococcus seriolicida, one strain of Lactococcus garvieae and 18 of the
environmental isolates to investigate the possibility of any genetic similarity.
In vivo pathogenicity to rainbow trout (Oncorhynchus mykiss) was also studied to
compare the virulence of the Australian isolates of Streptococcus sp. biovar 1 with
that of Lactococcus garvieae. This was performed as two separate experiments. The
first experiment was to establish the LD50 of one of the Tasmanian isolates, including
examination of histopathology to evaluate the tissue tropism of the organism. The
second experiment was to passage Lactococcus garvieae isolated from a case of
bovine mastitis through rainbow trout. Two techniques, direct kidney tissue transfer
and culture and re-isolation, were used to see if the organism could produce disease. The results of all these studies showed that the Australian isolates (Streptococcus sp.
biovar 1) were closely related to, if not identical with, both Lactococcus garvieae and
organisms previously named Enterococcus seriolicida. The results also showed that
none of the isolates from the environment were phenotypically or genotypically the
same as the Australian isolates or Lactococcus garvieae.
Therefore, Streptococcus sp. biovar 1 should probably be reclassified as Lactococcus
garvieae, and, because it is known to be the cause of streptococcosis in many
countries around the world, it must now be considered a major fish pathogen
worldwide.

Item Type: Thesis (PhD)
Keywords: Fish pathogens
Copyright Holders: The Author
Copyright Information:

Copyright 1997 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D)--University of Tasmania, 1999. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:38
Last Modified: 23 May 2017 05:09
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