Phylogenetic comparison of the virulence and antigenic properties of Streptococcus agalactiae biotypes I and II from Nile tilapia (Oreochromis niloticus) with other vertebrate species
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1
Norwegian University of Life Sciences, Norway
Streptococcus agalactiae, also known as group B streptococcus (GBS), is one of the most important pathogens adversely affecting the expansion of the production of Nile tilapia (Oreochromis niloticus) across the world. This bacterium species is pathogenic to a wide host range of aquatic and terrestrial species. In fish, two S. agalactiae strains commonly referred to as biotypes I and II that are phenotypically, biochemically and geographically distinct have been shown to cause disease in tilapia. Although virulence and antigenic properties of GBS have been extensively studied in higher vertebrates, little is known about the virulence mechanisms and antigenic properties of GBS in tilapia. It is not clear as to whether S. agalactiae biotype I expresses the same virulence and antigenic proteins as biotype II. It is also not clear as to whether the mechanisms used by both biotypes to cause disease in tilapia are comparable to mechanisms seen in higher vertebrates. Hence, in this study we compared by sequence alignments virulence and antigenic proteins expressed by S. agalactiae biotypes I and II from Nile tilapia with isolates from that of different vertebrate species. As a first step, we used the 16 S ribosomal RNA to confirm that the isolates from tilapia used in this study belong to S. agalactiae species. Phenotypic properties of biotypes I and II used in this study were characterized by Gram staining, β-hemolysis, CAMP-test and biochemical tests using the API-20 systems. Thereafter, sequence alignments for the CAMP factor (cfb), β-hemolysis (cyIE), fibrinogen-binding protein A (fbsA) and surface immunogenic protein (SIP) for S. agalactiae biotypes I and II sequenced in this study were compared with sequences from different vertebrate species obtained from different geographical regions in the world deposited in public databanks. Data obtained in this study shows genetic similarities and differences of the virulence and antigenic proteins of S. agalactiae biotypes I and II from tilapia. Our findings also show the genetic differences between isolates from tilapia and vertebrate species from different geographical regions suggesting that different host species and ecosystems could have different impacts on influencing the virulence and antigenic properties for S. agalactiae. Overall, this study shows that S. agalactiae could be using similar mechanisms to cause disease in different vertebrate species, including Nile tilapia, although there are genetic variations in the virulence and antigenic proteins based on bacterial strains, host species and ecological factors.
Keywords:
Streptococcus agalactiae,
biotypes,
Nile tilapia,
Genetic Variation,
Virulence Factors,
Antigenic properties
Conference:
AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.
Presentation Type:
Oral
Topic:
Aquatic Animal Epidemiology
Citation:
Paul
J,
Munang'Andu
HM and
Evensen
O
(2016). Phylogenetic comparison of the virulence and antigenic properties of Streptococcus agalactiae biotypes I and II from Nile tilapia (Oreochromis niloticus) with other vertebrate species.
Front. Vet. Sci.
Conference Abstract:
AquaEpi I - 2016.
doi: 10.3389/conf.FVETS.2016.02.00055
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Received:
30 May 2016;
Published Online:
14 Sep 2016.
*
Correspondence:
Dr. Hetron M Munang'Andu, Norwegian University of Life Sciences, Oslo, Norway, hetron.m.munangandu@nord.no
Prof. Oystein Evensen, Norwegian University of Life Sciences, Oslo, Norway, oystein.evensen@nmbu.no