Original Research

Detection of virulence factors of South African Lactococcus garvieae isolated from rainbow trout, Oncorhynchus mykiss (Walbaum)

Cornelia M. Meyburgh, Robert R. Bragg, Charlotte E. Boucher
Onderstepoort Journal of Veterinary Research | Vol 85, No 1 | a1568 | DOI: https://doi.org/10.4102/ojvr.v85i1.1568 | © 2018 Cornelia M. Meyburgh, Robert R. Bragg, Charlotte E. Boucher | This work is licensed under CC Attribution-NoDerivatives 4.0
Submitted: 20 October 2017 | Published: 04 October 2018

About the author(s)

Cornelia M. Meyburgh, Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, South Africa
Robert R. Bragg, Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, South Africa
Charlotte E. Boucher, Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, South Africa


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Abstract

Lactococcus garvieae is a Gram-positive bacterium that causes mortalities in freshwater and marine fish worldwide and therefore results in severe economic losses in the aquaculture industry. Apart from the apparent integral role of the exopolysaccharide (EPS) capsule in pathogenesis, factors associated with virulence of this bacterium are poorly understood. However, recent studies have indicated that the ability of L. garvieae to cause disease does not depend on the presence of the EPS capsule. Lack of knowledge of virulence factors, pathogenesis and serology of L. garvieae is an impediment to the development of effective typing methods and control measures. This study, therefore, aimed to detect the presence of EPS capsules and other putative virulence factors in South African L. garvieae fish pathogenic isolates and a non-virulent isolate, and to identify possible candidates for subunit vaccine development. No indication of the presence of the EPS capsule was detected by negative staining or amplification of the EPS biosynthesis gene cluster in the virulent isolates or the avirulent strain, discrediting the notion that the EPS capsule is the sole determinant of virulence. However, a set of putative virulence factor genes was detected in all isolates, and candidates for subunit vaccine development (enolase, lactate dehydrogenase phosphoenolpyruvate-protein phosphotransferase) were identified by identification of extracellular proteins of virulent strains.

Keywords

aquaculture; bacterial infection; virulence factors; capsule

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