Phenotypic and Genetic Predictors of Pathogenicity and Virulence in Flavobacterium psychrophilum

Krister Sundell*, Lotta Landor, Pierre Nicolas, Johanna Jorgensen, Daniel Castillo, Mathias Middelboe, Inger Dalsgaard, Valentina Laura Donati, Lone Madsen, Tom Wiklund

*Corresponding author for this work

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Abstract

Flavobacterium psychrophilum causes bacterial cold-water disease (BCWD) in farmed rainbow trout (Oncorhynchus mykiss), with the multilocus sequence typing (MLST) clonal complex (CC) CC-ST10 accounting for the majority of outbreaks globally. The development of alternative strategies to antibiotic treatment of BCWD using bacteriophage-based control of F psychrophilum, or virulence factors as targets for therapy, requires knowledge of the phage-sensitivity of outbreak strains and of universal traits contributing to their pathogenicity. To examine the association between virulence and both genetic (MLST sequence type (ST) and PCR-serotype) and phenotypic characteristics (adherence, antibiotic resistance, colony spreading motility, hemolytic and proteolytic activity), the median lethal dose (LD50) of 26 geographically disparate F psychrophilum isolates was determined in rainbow trout. Furthermore, the in vitro sensitivity of the isolates against five bacteriophages was determined by the efficiency of plating (EOP). The tested F psychrophilum isolates were mainly represented by CC-ST10 genotypes (22 out of 26) and showed up to 3-log differences in LD50 (8.9 x 103 to 3.1 x 106 CFU). No association between MLST ST and virulence was found because of a high variation in LD50 within STs. All identified serotypes (0, 1, and 2) were pathogenic, but ten most virulent isolates belonged to serotype 1 or 2. Isolates of high (LD50 <105 CFU), moderate (LD50 = 105-106 CFU), and weak (LD50 > 106 CFU) virulence were similar in phenotypic characteristics in vitro. However, the only non-virulent CC-ST10 isolate was deficient in spreading motility and proteolytic activity, indicating that the characteristics are required for pathogenicity in F. psychrophilum. Univariate correlation studies found only non-significant associations between LD50 and the measured phenotypic characteristics, and the multivariable analysis did neither reveal any significant predictors of virulence. The majority of isolates (16 out of 26) were sensitive to at least four bacteriophages, with up to a 6-log variation in the EOP. Most CC-ST10 isolates (16 out of 22) were sensitive to the examined phages, including 5 out of the 7 most virulent isolates represented by prevalent and antibiotic-resistant STs. Our findings suggest that control of BCWD using lytic phages or interventions targeting shared characteristics of pathogenic F. psychrophilum strains should be further explored.
Original languageEnglish
Article number1711
JournalFrontiers in Microbiology
Volume10
ISSN1664-302X
DOIs
Publication statusPublished - 2019

Keywords

  • Flavobacterium psychrophilum
  • Bacterial cold-water disease
  • Rainbow trout (Oncorhynchus mykiss)
  • Multilocus sequence typing (MLST)
  • Bacteriophage
  • LD50
  • Pathogenicity
  • Virulence

Cite this

Sundell, K., Landor, L., Nicolas, P., Jorgensen, J., Castillo, D., Middelboe, M., ... Wiklund, T. (2019). Phenotypic and Genetic Predictors of Pathogenicity and Virulence in Flavobacterium psychrophilum. Frontiers in Microbiology, 10, [1711]. https://doi.org/10.3389/fmicb.2019.01711
Sundell, Krister ; Landor, Lotta ; Nicolas, Pierre ; Jorgensen, Johanna ; Castillo, Daniel ; Middelboe, Mathias ; Dalsgaard, Inger ; Donati, Valentina Laura ; Madsen, Lone ; Wiklund, Tom. / Phenotypic and Genetic Predictors of Pathogenicity and Virulence in Flavobacterium psychrophilum. In: Frontiers in Microbiology. 2019 ; Vol. 10.
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title = "Phenotypic and Genetic Predictors of Pathogenicity and Virulence in Flavobacterium psychrophilum",
abstract = "Flavobacterium psychrophilum causes bacterial cold-water disease (BCWD) in farmed rainbow trout (Oncorhynchus mykiss), with the multilocus sequence typing (MLST) clonal complex (CC) CC-ST10 accounting for the majority of outbreaks globally. The development of alternative strategies to antibiotic treatment of BCWD using bacteriophage-based control of F psychrophilum, or virulence factors as targets for therapy, requires knowledge of the phage-sensitivity of outbreak strains and of universal traits contributing to their pathogenicity. To examine the association between virulence and both genetic (MLST sequence type (ST) and PCR-serotype) and phenotypic characteristics (adherence, antibiotic resistance, colony spreading motility, hemolytic and proteolytic activity), the median lethal dose (LD50) of 26 geographically disparate F psychrophilum isolates was determined in rainbow trout. Furthermore, the in vitro sensitivity of the isolates against five bacteriophages was determined by the efficiency of plating (EOP). The tested F psychrophilum isolates were mainly represented by CC-ST10 genotypes (22 out of 26) and showed up to 3-log differences in LD50 (8.9 x 103 to 3.1 x 106 CFU). No association between MLST ST and virulence was found because of a high variation in LD50 within STs. All identified serotypes (0, 1, and 2) were pathogenic, but ten most virulent isolates belonged to serotype 1 or 2. Isolates of high (LD50 <105 CFU), moderate (LD50 = 105-106 CFU), and weak (LD50 > 106 CFU) virulence were similar in phenotypic characteristics in vitro. However, the only non-virulent CC-ST10 isolate was deficient in spreading motility and proteolytic activity, indicating that the characteristics are required for pathogenicity in F. psychrophilum. Univariate correlation studies found only non-significant associations between LD50 and the measured phenotypic characteristics, and the multivariable analysis did neither reveal any significant predictors of virulence. The majority of isolates (16 out of 26) were sensitive to at least four bacteriophages, with up to a 6-log variation in the EOP. Most CC-ST10 isolates (16 out of 22) were sensitive to the examined phages, including 5 out of the 7 most virulent isolates represented by prevalent and antibiotic-resistant STs. Our findings suggest that control of BCWD using lytic phages or interventions targeting shared characteristics of pathogenic F. psychrophilum strains should be further explored.",
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language = "English",
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journal = "Frontiers in Microbiology",
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publisher = "Frontiers Media S.A.",

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Phenotypic and Genetic Predictors of Pathogenicity and Virulence in Flavobacterium psychrophilum. / Sundell, Krister; Landor, Lotta; Nicolas, Pierre; Jorgensen, Johanna; Castillo, Daniel; Middelboe, Mathias; Dalsgaard, Inger; Donati, Valentina Laura; Madsen, Lone; Wiklund, Tom.

In: Frontiers in Microbiology, Vol. 10, 1711, 2019.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Phenotypic and Genetic Predictors of Pathogenicity and Virulence in Flavobacterium psychrophilum

AU - Sundell, Krister

AU - Landor, Lotta

AU - Nicolas, Pierre

AU - Jorgensen, Johanna

AU - Castillo, Daniel

AU - Middelboe, Mathias

AU - Dalsgaard, Inger

AU - Donati, Valentina Laura

AU - Madsen, Lone

AU - Wiklund, Tom

PY - 2019

Y1 - 2019

N2 - Flavobacterium psychrophilum causes bacterial cold-water disease (BCWD) in farmed rainbow trout (Oncorhynchus mykiss), with the multilocus sequence typing (MLST) clonal complex (CC) CC-ST10 accounting for the majority of outbreaks globally. The development of alternative strategies to antibiotic treatment of BCWD using bacteriophage-based control of F psychrophilum, or virulence factors as targets for therapy, requires knowledge of the phage-sensitivity of outbreak strains and of universal traits contributing to their pathogenicity. To examine the association between virulence and both genetic (MLST sequence type (ST) and PCR-serotype) and phenotypic characteristics (adherence, antibiotic resistance, colony spreading motility, hemolytic and proteolytic activity), the median lethal dose (LD50) of 26 geographically disparate F psychrophilum isolates was determined in rainbow trout. Furthermore, the in vitro sensitivity of the isolates against five bacteriophages was determined by the efficiency of plating (EOP). The tested F psychrophilum isolates were mainly represented by CC-ST10 genotypes (22 out of 26) and showed up to 3-log differences in LD50 (8.9 x 103 to 3.1 x 106 CFU). No association between MLST ST and virulence was found because of a high variation in LD50 within STs. All identified serotypes (0, 1, and 2) were pathogenic, but ten most virulent isolates belonged to serotype 1 or 2. Isolates of high (LD50 <105 CFU), moderate (LD50 = 105-106 CFU), and weak (LD50 > 106 CFU) virulence were similar in phenotypic characteristics in vitro. However, the only non-virulent CC-ST10 isolate was deficient in spreading motility and proteolytic activity, indicating that the characteristics are required for pathogenicity in F. psychrophilum. Univariate correlation studies found only non-significant associations between LD50 and the measured phenotypic characteristics, and the multivariable analysis did neither reveal any significant predictors of virulence. The majority of isolates (16 out of 26) were sensitive to at least four bacteriophages, with up to a 6-log variation in the EOP. Most CC-ST10 isolates (16 out of 22) were sensitive to the examined phages, including 5 out of the 7 most virulent isolates represented by prevalent and antibiotic-resistant STs. Our findings suggest that control of BCWD using lytic phages or interventions targeting shared characteristics of pathogenic F. psychrophilum strains should be further explored.

AB - Flavobacterium psychrophilum causes bacterial cold-water disease (BCWD) in farmed rainbow trout (Oncorhynchus mykiss), with the multilocus sequence typing (MLST) clonal complex (CC) CC-ST10 accounting for the majority of outbreaks globally. The development of alternative strategies to antibiotic treatment of BCWD using bacteriophage-based control of F psychrophilum, or virulence factors as targets for therapy, requires knowledge of the phage-sensitivity of outbreak strains and of universal traits contributing to their pathogenicity. To examine the association between virulence and both genetic (MLST sequence type (ST) and PCR-serotype) and phenotypic characteristics (adherence, antibiotic resistance, colony spreading motility, hemolytic and proteolytic activity), the median lethal dose (LD50) of 26 geographically disparate F psychrophilum isolates was determined in rainbow trout. Furthermore, the in vitro sensitivity of the isolates against five bacteriophages was determined by the efficiency of plating (EOP). The tested F psychrophilum isolates were mainly represented by CC-ST10 genotypes (22 out of 26) and showed up to 3-log differences in LD50 (8.9 x 103 to 3.1 x 106 CFU). No association between MLST ST and virulence was found because of a high variation in LD50 within STs. All identified serotypes (0, 1, and 2) were pathogenic, but ten most virulent isolates belonged to serotype 1 or 2. Isolates of high (LD50 <105 CFU), moderate (LD50 = 105-106 CFU), and weak (LD50 > 106 CFU) virulence were similar in phenotypic characteristics in vitro. However, the only non-virulent CC-ST10 isolate was deficient in spreading motility and proteolytic activity, indicating that the characteristics are required for pathogenicity in F. psychrophilum. Univariate correlation studies found only non-significant associations between LD50 and the measured phenotypic characteristics, and the multivariable analysis did neither reveal any significant predictors of virulence. The majority of isolates (16 out of 26) were sensitive to at least four bacteriophages, with up to a 6-log variation in the EOP. Most CC-ST10 isolates (16 out of 22) were sensitive to the examined phages, including 5 out of the 7 most virulent isolates represented by prevalent and antibiotic-resistant STs. Our findings suggest that control of BCWD using lytic phages or interventions targeting shared characteristics of pathogenic F. psychrophilum strains should be further explored.

KW - Flavobacterium psychrophilum

KW - Bacterial cold-water disease

KW - Rainbow trout (Oncorhynchus mykiss)

KW - Multilocus sequence typing (MLST)

KW - Bacteriophage

KW - LD50

KW - Pathogenicity

KW - Virulence

U2 - 10.3389/fmicb.2019.01711

DO - 10.3389/fmicb.2019.01711

M3 - Journal article

VL - 10

JO - Frontiers in Microbiology

JF - Frontiers in Microbiology

SN - 1664-302X

M1 - 1711

ER -