50
polysaccharide antigen type Ib (Vandamme et al. 1997 ). By single stranded conformation polymorphism analysis of the interspacer region, 46 isolates from different
hosts and geographical origins were recovered in 5 genotypes, with genotype 1
accommodating cultures from Kuwait. AFLP profi ling of the same cultures led to
the defi nition of 13 genotypes, with Kuwaiti cultures recovered in two clusters
(Olivares-Fuster et al. 2008 ). The genetic diversity of isolates was studied leading to
the recognition of two capsular types (Ia and Ib) and four sequence types (103, 260,
552 and 553). The combined evaluation of serotype, sequence type and pattern of
the presence or absence of cylE and hylB enabled the recognition of nine genetic
profi les, which reportedly enabled better discrimination than previous methods
(Godoy et al. 2013 ). Fifty-one isolates from 27 tilapia farms in China were collected, and analyzed for mobile genetic elements, genetic markers, and virulencerelated genes, with results revealing only one genotype. This points to a similar
origin for all the cultures included in the study. Bacteriophage typing differentiated
all isolates into two distinct molecular types, with the second prevalent in tilapia
culture in China (Zhang et al. 2013 ). Cultures (no = 181) from red hybrid tilapia
( Oreochromis sp.) and golden pompano ( Trachinotus blochii ) in Malaysia were
studied by RAPDs and REP-PCR leading to the delineation of 13 and 9 groups,
respectively. Three cultures from golden pompano were genetically dissimilar to
those from tilapia (Amal et al. 2013 ).
Detection
Nested PCR A nested PCR has been described for the detection of Str. agalactiae
in naturally infected frozen and paraffi n-embedded tissues of tilapia within positivity recorded from adult but not larvae or fry (Jiménez et al. 2011 ). The detection
limit in the absence of fi sh DNA was given as 1.58 fg (Jiménez et al. 2011 ).
LAMP A LAMP detected 2.8 × 10
3 CFU/ml (=2.8 CFU/reaction), and was regarded
as specifi c insofar as it did not recognise other related taxa (Wang et al. 2012 ).
Similarly, a specifi c and sensitive (~20 cells/reaction) LAMP involved four primers
that were designed to target the pathogen’s cfb gene. The assay, which could be used
with diseased tissues, was carried out at 65 °C for 60 min, and stopped at 80 °C for
10 min in a water bath, leading to results that could be observed visually (Ke et al.
2014 ). An accelerated and specifi c colorimetric LAMP with the pre-addition of calcein
was developed for the detection of Str. agalactiae and Str. iniae in tilapia, with positivity refl ecting a clearly observable colour change from orange to green. The LAMP was
reported as 10 times more sensitivity than nested PCRs (Suebsing et al 2013 ).
Pathogenicity
Intraperitoneal injection of 0.5 ml amounts (10
7 CFU/ml) of Str. agalactiae into
Nile tilapia signifi cantly induced T-cell receptor ß chain expression more so than a
higher dose (10
9 CFU/ml). This may have importance in the host response to attack
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)
polysaccharide antigen type Ib (Vandamme et al. 1997 ). By single stranded conformation polymorphism analysis of the interspacer region, 46 isolates from different
hosts and geographical origins were recovered in 5 genotypes, with genotype 1
accommodating cultures from Kuwait. AFLP profi ling of the same cultures led to
the defi nition of 13 genotypes, with Kuwaiti cultures recovered in two clusters
(Olivares-Fuster et al. 2008 ). The genetic diversity of isolates was studied leading to
the recognition of two capsular types (Ia and Ib) and four sequence types (103, 260,
552 and 553). The combined evaluation of serotype, sequence type and pattern of
the presence or absence of cylE and hylB enabled the recognition of nine genetic
profi les, which reportedly enabled better discrimination than previous methods
(Godoy et al. 2013 ). Fifty-one isolates from 27 tilapia farms in China were collected, and analyzed for mobile genetic elements, genetic markers, and virulencerelated genes, with results revealing only one genotype. This points to a similar
origin for all the cultures included in the study. Bacteriophage typing differentiated
all isolates into two distinct molecular types, with the second prevalent in tilapia
culture in China (Zhang et al. 2013 ). Cultures (no = 181) from red hybrid tilapia
( Oreochromis sp.) and golden pompano ( Trachinotus blochii ) in Malaysia were
studied by RAPDs and REP-PCR leading to the delineation of 13 and 9 groups,
respectively. Three cultures from golden pompano were genetically dissimilar to
those from tilapia (Amal et al. 2013 ).
Detection
Nested PCR A nested PCR has been described for the detection of Str. agalactiae
in naturally infected frozen and paraffi n-embedded tissues of tilapia within positivity recorded from adult but not larvae or fry (Jiménez et al. 2011 ). The detection
limit in the absence of fi sh DNA was given as 1.58 fg (Jiménez et al. 2011 ).
LAMP A LAMP detected 2.8 × 10
3 CFU/ml (=2.8 CFU/reaction), and was regarded
as specifi c insofar as it did not recognise other related taxa (Wang et al. 2012 ).
Similarly, a specifi c and sensitive (~20 cells/reaction) LAMP involved four primers
that were designed to target the pathogen’s cfb gene. The assay, which could be used
with diseased tissues, was carried out at 65 °C for 60 min, and stopped at 80 °C for
10 min in a water bath, leading to results that could be observed visually (Ke et al.
2014 ). An accelerated and specifi c colorimetric LAMP with the pre-addition of calcein
was developed for the detection of Str. agalactiae and Str. iniae in tilapia, with positivity refl ecting a clearly observable colour change from orange to green. The LAMP was
reported as 10 times more sensitivity than nested PCRs (Suebsing et al 2013 ).
Pathogenicity
Intraperitoneal injection of 0.5 ml amounts (10
7 CFU/ml) of Str. agalactiae into
Nile tilapia signifi cantly induced T-cell receptor ß chain expression more so than a
higher dose (10
9 CFU/ml). This may have importance in the host response to attack
2 Gram-Positive Bacteria (Anaerobes and ‘Lactic Acid’ Bacteria)