51
by pathogens (Nithikulworawong et al. 2012 ). The presence of a polysaccharide
capsule is important for virulence, and the CpsA protein, which is a likely transcriptional regulator, has a role in capsule synthesis and unspecifi ed cell wall-associated
factors (Hanson et al. 2012 ). The duodenase-1 gene, which is involved in the
immune response, appears to have an important role in conferring disease resistance
in hybrid tilapia (Shen et al. 2015 ).
The water temperature has a direct relationship to the outcome of infection, and
in one study 0, 50 and 70 % mortalities were recorded among populations of tilapia
challenged with Str. agalactiae, and maintained at 20, 25 and 30 °C, elevating water
temperature increases the severity of disease (Kayansamruaj et al. 2014 ; Zhao et al.
2015 ). Conversely, rainbow trout remained asymptomatic at 12 °C (Sepahi et al.
2013 ). Haemolytic activity was 5-fold higher when the pathogen was grown at
35 °C compared to 28 °C. Similarly, expression of cylE ß-haemolysin cytolysin),
cfb (CAMP [Christie Atkins Munch-Petersen] factor) and PI-2b (pili backbone)
was higher at 35 °C than 28 °C. Between 6 and 96 h after infection, at the higher
temperature, tilapia showed profound infl ammation, which was attributed to a
30–40 fold increase in upregulation of the infl ammatory-related genes cyclooxygenase- 2 , IL-1 ß and TNF- α . In short, massive infl ammatory type responses lead to
acute mortalities at higher water temperatures (Kayansamruaj et al. 2014 ).
Metabolomics revealed difference in the metabolic response of the tilapia according
to the water temperature at which the fi sh were maintained. Thus, there was an
increase in metabolites in the liver with increase in water temperature – 36 to 45
metabolites with less amino acids – particularly of L-proline – but more carbohydrates at 25 and 30 °C, respectively. Thus, the application of L-proline by injection
or orally led to an increase in amino acid metabolism, and a concomitant reduction
in mortalities (Zhao et al. 2015 ).
Disease Control
Vaccine Development Formalin-killed cells and a culture extract containing 50 %
protein conjugated to alum , administered intraperitoneally, protected tilapia against
challenge with a virulent strain, with protection correlated by the presence of
humoral antibodies (Eldar et al. 1995c ). Of relevance for vaccine development,
western blots indicated that only a few proteins were actually protective (Eldar et al.
1995c ). Using ECPs and encapsulated formalin-inactivated cells, which were
administered to Nile tilapia by i.p. injection, Pasnik et al. ( 2005a ) reported good
protection even after 6 months when challenged . Also, there was demonstrable antibodies produced in the vaccinates, with a 55 kDa ECP antigen being implicated in
vaccine effi cacy (Pasnik et al. 2005b ). Bath vaccination was less successful, with an
RPS of 34 % compared to 80 % after administration intraperitoneally (Evans et al.
2004 ).
A live attenuated vaccine was developed by continuous passage of a culture
in vitro, and the non-virulent variant evaluated in tilapia. Following administration
Streptococcaceae Representatives
by pathogens (Nithikulworawong et al. 2012 ). The presence of a polysaccharide
capsule is important for virulence, and the CpsA protein, which is a likely transcriptional regulator, has a role in capsule synthesis and unspecifi ed cell wall-associated
factors (Hanson et al. 2012 ). The duodenase-1 gene, which is involved in the
immune response, appears to have an important role in conferring disease resistance
in hybrid tilapia (Shen et al. 2015 ).
The water temperature has a direct relationship to the outcome of infection, and
in one study 0, 50 and 70 % mortalities were recorded among populations of tilapia
challenged with Str. agalactiae, and maintained at 20, 25 and 30 °C, elevating water
temperature increases the severity of disease (Kayansamruaj et al. 2014 ; Zhao et al.
2015 ). Conversely, rainbow trout remained asymptomatic at 12 °C (Sepahi et al.
2013 ). Haemolytic activity was 5-fold higher when the pathogen was grown at
35 °C compared to 28 °C. Similarly, expression of cylE ß-haemolysin cytolysin),
cfb (CAMP [Christie Atkins Munch-Petersen] factor) and PI-2b (pili backbone)
was higher at 35 °C than 28 °C. Between 6 and 96 h after infection, at the higher
temperature, tilapia showed profound infl ammation, which was attributed to a
30–40 fold increase in upregulation of the infl ammatory-related genes cyclooxygenase- 2 , IL-1 ß and TNF- α . In short, massive infl ammatory type responses lead to
acute mortalities at higher water temperatures (Kayansamruaj et al. 2014 ).
Metabolomics revealed difference in the metabolic response of the tilapia according
to the water temperature at which the fi sh were maintained. Thus, there was an
increase in metabolites in the liver with increase in water temperature – 36 to 45
metabolites with less amino acids – particularly of L-proline – but more carbohydrates at 25 and 30 °C, respectively. Thus, the application of L-proline by injection
or orally led to an increase in amino acid metabolism, and a concomitant reduction
in mortalities (Zhao et al. 2015 ).
Disease Control
Vaccine Development Formalin-killed cells and a culture extract containing 50 %
protein conjugated to alum , administered intraperitoneally, protected tilapia against
challenge with a virulent strain, with protection correlated by the presence of
humoral antibodies (Eldar et al. 1995c ). Of relevance for vaccine development,
western blots indicated that only a few proteins were actually protective (Eldar et al.
1995c ). Using ECPs and encapsulated formalin-inactivated cells, which were
administered to Nile tilapia by i.p. injection, Pasnik et al. ( 2005a ) reported good
protection even after 6 months when challenged . Also, there was demonstrable antibodies produced in the vaccinates, with a 55 kDa ECP antigen being implicated in
vaccine effi cacy (Pasnik et al. 2005b ). Bath vaccination was less successful, with an
RPS of 34 % compared to 80 % after administration intraperitoneally (Evans et al.
2004 ).
A live attenuated vaccine was developed by continuous passage of a culture
in vitro, and the non-virulent variant evaluated in tilapia. Following administration
Streptococcaceae Representatives