Abstract
BackgroundFlavobacterium psychrophilum causes serious fish diseases such RTFS and BCWD, affecting the aquaculture industry worldwide. Commercial vaccines are not available and control of the disease depends on the use of antibiotics. Reliable methods for detection and identification of different isolates of this bacterium could play an important role in the development of good management strategies. The aim of this study was to identify genetic markers for discrimination between isolates. A selection of eight VNTRs from 53 F. psychrophilum isolates from Norway, Chile, Denmark and Scotland were analyzed. The results were compared with previous work on the same pathogen using MLST for genetic differentiation.ResultsThe VNTR analysis gave a separation between the F. psychrophilum isolates supporting the results of previous MLST work. A higher diversity was found among the Chilean isolates compared to those from Norway, which suggests a more homogenous reservoir in Norway. Transgenerational transmission of F. psychrophilum from other countries, exporting salmon embryos to Chile, may explain the differences in diversity. The same transmission mechanisms could also explain the wide geographical distribution of identical isolates in Norway. But, this could also be a result of movement of smolts and embryos. The selected VNTRs are stable genetic markers and no variation was observed after several passages on agar plates at different temperatures.ConclusionsThese VNTRs are important additions for genotyping of F. psychrophilum isolates. Future studies on VNTRs of F. psychrophilum should include isolates from more host species from a wider geographical area. To get a more robust genotyping the VNTRs should be used in concert with MLST. Future studies of isolates with high and low virulence should focus on identifying virulence markers using VTNRs and MLST.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-015-0469-7) contains supplementary material, which is available to authorized users.
Highlights
Flavobacterium psychrophilum causes serious fish diseases such rainbow trout fry syndrome (RTFS) and bacterial cold water disease (BCWD), affecting the aquaculture industry worldwide
Variable number of tandem repeats (VNTR) The 12 pairs of variable number of tandem repeats (VNTR)-primers were tested using Deoxyribonucleic acid (DNA) extracted from the type strain (NCIMB 1947), five Norwegian, and five Chilean isolates of F. psychrophilum
The primers for VNTR-7 and VNTR-13 did not produce the expected Polymerase chain reaction (PCR) products, but a new set of primers yielded these products with the exception of the isolate No10-35-T-W
Summary
Flavobacterium psychrophilum causes serious fish diseases such RTFS and BCWD, affecting the aquaculture industry worldwide. Commercial vaccines are not available and control of the disease depends on the use of antibiotics. Flavobacterium psychrophilum causes bacterial cold water disease (BCWD) and rainbow trout fry syndrome (RTFS) in the fresh water phase of salmonid production worldwide [1]. Pers.) flavobacteriosis is still a major problem in the salmonid production in Chile, and the control of the disease is dependent on the use of antibiotics [2]. Since the first reports of flavobacteriosis, the disease caused by F. psychrophilum (former name Cytophaga psychrophila) in the 1940s in North America, the pathogen has emerged in several countries causing severe outbreaks on salmonids and other fresh water species [5, 6]. It has been shown that F. psychrophilum can be transgenerational transmitted and, to prevent spreading and disease outbreaks it is necessary to develop specific and sensitive methods for detection of the bacterium [7].
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