Browsing by Author "Flemming, Leonard (Leonard Arnold)"

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    Molecular characterisation of Flavobacterium spp. and investigation of their biofilm-forming capacity in the tilapia aquaculture system
    (Stellenbosch : University of Stellenbosch, 2006-04) Flemming, Leonard (Leonard Arnold); Chenia, H. Y.; Rawlings, D. E.; University of Stellenbosch. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Fish infections caused by pathogenic Flavobacterium spp. are a major problem in the aquaculture industry worldwide, often leading to large economic losses. Thirty-two Flavobacterium spp. isolates, obtained from various diseased fish species and biofilm growth, were characterised genetically using 16S rRNA gene sequencing, 16S rRNA gene PCR restriction fragment length polymorphism (RFLP), randomly amplified polymorphic DNA (RAPD) PCR, repetitive extragenic palindromic (REP) element PCR, plasmid profiling, whole cell protein (WCP) and outer membrane protein (OMP) analyses. The biofilm-forming capability of five genetically heterogeneous Flavobacterium spp. study isolates was investigated using a modified microtiter-plate adherence assay, as well as flow cell studies. Experimental infection studies with Mozambique tilapia (Oreochromis mossambicus) were carried out in order to determine the virulence of the Flavobacterium spp. study isolates. 16S rRNA gene sequence analysis showed the Flavobacterium spp. study isolates were closely related, and 97% sequence similarity was shared with published F. johnsoniae sequences. A high degree of genetic heterogeneity was displayed by the Flavobacterium spp. study isolates following RAPD-PCR, REP-PCR and OMP analysis, however, based on the results obtained by plasmid profiling and WCP analysis, the isolates appeared genetically very homogeneous. The biofilm phenotype was displayed by all five Flavobacterium spp. isolates tested and varied from weakly to strongly adherent. No specific correlation was observed between the RAPD, REP and/or OMP profiles and degree of adherence displayed by Flavobacterium spp. isolates. However, a specific WCP profile (profile B), exhibited by 48% of the Flavobacterium spp. isolates, was linked to strong adherence. Experimental infection studies showed that Flavobacterium spp. isolates displayed variable levels of virulence, which could not be linked to biofilm formation, nor specific genotypes. This is the first reported isolation and characterisation of Flavobacterium spp. isolated from diseased fish in Southern Africa, and there appears to be significant diversity amongst the isolates which is not geographically linked nor host related.