Structure of Flavobacterium psychrophilum populations infecting farmed rainbow trout Oncorhynchus mykiss 

Abstract

Flavobacterium psychrophilum isolated from rainbow trout Oncorhynchus mykiss suffering from bacterial cold-water disease (BCWD) can dissociate into 2 morphological colony types, rough (R) and smooth (S). However, the presence of the 2 morphotypes in disease outbreaks has not yet been investigated thoroughly. We examined the occurrence of R and S morphotypes in rainbow trout from BCWD outbreaks and in unfertilized eggs from a hatchery. The isolated colony types were characterized by pulsed field gel electrophoresis (PFGE), plasmid analysis, and oxolinic acid susceptibility testing. From most outbreaks, both morphotypes were isolated, although the S type only was isolated from the majority of individual fish. PFGE analysis showed both diverse and indistinguishable genetic patterns among the concurrent morphotypes. While PFGE patterns common to both fish and egg isolates were identified, this was not always the case. Resistant and sensitive isolates of both colony types were isolated from individual disease outbreaks. The plasmid pattern was partly associated with the colony type, showing identical or completely different patterns for the R and S types isolated from the same outbreak. The study showed that within a BCWD outbreak, F. psychrophilum cells with different morphology, plasmid content, antibiotic susceptibility, and PFGE pattern can be isolated, suggesting that F. psychrophilum populations infecting rainbow trout in farm environments can be diverse and thus complicate the control of the disease.

Epidemiological cut‐off values for Flavobacterium psychrophilum MIC data generated by a standard test protocol

“…; Dalsgaard & Madsen ; Schmidt et al . ), Finland (Sundell, Heinikainen & Wiklund ), Japan (Izumi & Aranishi ), Spain (Del Cerro, Márque & Prieto ), Turkey (Kum et al . ; Boyacioglu & Akar ; Durmaz, Onuk & Ciftic ) and the UK (Rangdale et al .…”

In vivo adherence of Flavobacterium psychrophilum to mucosal external surfaces of rainbow trout (Oncorhynchus mykiss) fry

“…From these isolates, two rough variants, P7‐9/2R/10 and P1‐10B/2R/10, respectively, were produced by repeated passages in tryptone yeast extract salt (TYES) broth (Holt, Rohovec & Fryer ; Sundell et al . ). All four isolates were used in the in vivo and in vitro experiments.…”

Multilocus Sequence Typing Identifies Epidemic Clones of Flavobacterium psychrophilum in Nordic Countries

“…These observations show that, for the purpose of detecting and monitoring emergent F. psychrophilum genotypes, it is important to examine more than a single colony from an infected fish. To aid in rapid differentiation of clinically relevant STs from coinfections with distinct genotypes, an applicable examination strategy based on phenotypically distinguishable characteristics, such as colony morphology and antimicrobial susceptibility (32), should be set up.…”

“…The 560 Flavobacterium psychrophilum isolates used in the present study (see Table S1 in the supplemental material) were collected between 1983 and 2012 from a wide variety of sources in Denmark (n ϭ 209), Finland (n ϭ 195), Norway (n ϭ 117), and Sweden (n ϭ 36) and included the reference strains NCIMB 1947 T , THC02/90, and JIP02/86 originally isolated outside the Nordic region. The isolates were cultured on Anacker and Ordals medium (28) or TYES agar (29) and identified by using routine diagnostic procedures, i.e., biochemical characterization (30,31), sequencing of 16S rRNA gene or species-specific PCR (32,33). The collection comprised isolates from 10 different fish species: rainbow trout (n ϭ 448), Atlantic salmon (n ϭ 52), brown trout (n ϭ 26), perch (Perca fluviatilis) (n ϭ 11), three-spined stickleback (Gasterosteus aculeatus) (n ϭ 3), coho salmon (n ϭ 2), arctic char (Salvelinus alpinus) (n ϭ 1), brook trout (Salvelinus fontinalis) (n ϭ 1), flounder (Platichthys flesus) (n ϭ 1), and char hybrid (Salvelinus fontinalis ϫ Salvelinus namaycush) (n ϭ 1).…”