44
Epizootiology
Bacteriophages of Lactococcus garvieae have been found in seawater and sediment,
but after defi ning 14 phage types (among 111 isolates), it was concluded that there
was not any correlation between phage type and geographical source of the isolates
(Park et al. 1998 ).
Pathogenicity
Experimental infections with organisms likely to correspond with Lactococcus garvieae have been achieved by injection of 10
4 to 10
5 cells (Cook and Lofton 1975 ),
and by exposure of fi sh for 10 min to 10
6 bacteria (Robinson and Meyer 1966 ). Cells
have been found in the spleen within 2-hours of infection (Young et al. 2012a ).
Thereafter, disease becomes established, and death ensues. Adherence of cells of
Lactococcus garvieae to intestinal and brain gangliosides has been documented in
yellowtail (Shima et al. 2006 ). Then, the pathogen becomes internalised and survives within the phagosomes of macrophages (Young et al. 2012a ). Questions have
been asked about the genes of Lactococcus garvieae that are needed for survival in
fi sh, and as a result of signature-tagged mutagenesis, mutants were found which
could not be recovered from rainbow trout after challenge. Sequence analysis
pointed to roles including the pathogenesis of transcriptional regulatory proteins
homologous to GidA and MerR, metabolic enzymes asparagine synthetase A and
α–acetolactate synthase, the ABC transport system of glutamine, the calciumtransporting ATPase, and the dltA locus involved in alanylation of teichoic acid
(Menéndez et al. 2007 ).
Capsules have been reported , with encapsulated cultures being more virulent
(Barnes et al. 2002 ) and less effi cient at fi xing complement compared to nonencapsulated isolates (Barnes and Ellis 2004 ). Non-encapsulated cultures were
more susceptible to normal rainbow trout serum than capsulated isolates (Barnes
et al. 2002 ). Two capsular types have been found among Lactococcus garvieae, one
of which produces a well developed capsule, whereas the second demonstrates a
micro-capsule which contains fi mbrial-type components projecting from the cell
surface (Ooyama et al. 2002 ).
Disease Control
Vaccines Using formalin-inactivated capsulated and uncapsulated cells of
Lactococcus garvieae, which were applied to yellowtail by i.p. injection, long-term
protection resulted with challenge with a capsulated culture (Ooyama et al. 1999 ).
Because of differences in antibody response (to uncapsulated but not capsulated
cultures), these workers concluded that the capsule affected immunogenicity, and
the protective antigens were most likely to be on the surface of uncapsulated cells
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)
Epizootiology
Bacteriophages of Lactococcus garvieae have been found in seawater and sediment,
but after defi ning 14 phage types (among 111 isolates), it was concluded that there
was not any correlation between phage type and geographical source of the isolates
(Park et al. 1998 ).
Pathogenicity
Experimental infections with organisms likely to correspond with Lactococcus garvieae have been achieved by injection of 10
4 to 10
5 cells (Cook and Lofton 1975 ),
and by exposure of fi sh for 10 min to 10
6 bacteria (Robinson and Meyer 1966 ). Cells
have been found in the spleen within 2-hours of infection (Young et al. 2012a ).
Thereafter, disease becomes established, and death ensues. Adherence of cells of
Lactococcus garvieae to intestinal and brain gangliosides has been documented in
yellowtail (Shima et al. 2006 ). Then, the pathogen becomes internalised and survives within the phagosomes of macrophages (Young et al. 2012a ). Questions have
been asked about the genes of Lactococcus garvieae that are needed for survival in
fi sh, and as a result of signature-tagged mutagenesis, mutants were found which
could not be recovered from rainbow trout after challenge. Sequence analysis
pointed to roles including the pathogenesis of transcriptional regulatory proteins
homologous to GidA and MerR, metabolic enzymes asparagine synthetase A and
α–acetolactate synthase, the ABC transport system of glutamine, the calciumtransporting ATPase, and the dltA locus involved in alanylation of teichoic acid
(Menéndez et al. 2007 ).
Capsules have been reported , with encapsulated cultures being more virulent
(Barnes et al. 2002 ) and less effi cient at fi xing complement compared to nonencapsulated isolates (Barnes and Ellis 2004 ). Non-encapsulated cultures were
more susceptible to normal rainbow trout serum than capsulated isolates (Barnes
et al. 2002 ). Two capsular types have been found among Lactococcus garvieae, one
of which produces a well developed capsule, whereas the second demonstrates a
micro-capsule which contains fi mbrial-type components projecting from the cell
surface (Ooyama et al. 2002 ).
Disease Control
Vaccines Using formalin-inactivated capsulated and uncapsulated cells of
Lactococcus garvieae, which were applied to yellowtail by i.p. injection, long-term
protection resulted with challenge with a capsulated culture (Ooyama et al. 1999 ).
Because of differences in antibody response (to uncapsulated but not capsulated
cultures), these workers concluded that the capsule affected immunogenicity, and
the protective antigens were most likely to be on the surface of uncapsulated cells
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)