SEARCHOTHERveterinary medicine, aquaculture

other·veterinary medicine, aquaculture, microbiology, infectious disease·PMC10055933

Impact of Infection with Flavobacterium psychrophilum and Antimicrobial Treatment on the Intestinal Microbiota of Rainbow Trout

Pathogens · 5 authors, 3 centres

AI SUMMARY

FIDELITY 88%

POPULATIONRainbow trout juveniles (Oncorhynchus mykiss), 30–40 g, housed at 10°C

INTERVENTIONProphylactic oral florfenicol (10 mg/kg BW/day) or erythromycin (75 mg/kg BW/day) for 10 days, followed by intraperitoneal infection with Flavobacterium psychrophilum FPG101 (1 × 10^8 cfu/fish)

COMPARISONUntreated fish mock-infected with sterile Cytophaga broth (control) and untreated fish infected with F. psychrophilum

This summary was generated by AI from a single paper. It has not been reviewed by a clinician and is not clinical advice. Verify against the source before acting on it.

AGENT 01 · STRUCTURED SUMMARY

TRACE TO SOURCE

“

TL;DR

This study examined how prophylactic antibiotic treatment (florfenicol and erythromycin) and infection with Flavobacterium psychrophilum alter the intestinal microbiota of rainbow trout juveniles. Both antibiotics and infection reduced beneficial bacteria like Mycoplasma while increasing potential pathogens such as Aeromonas, Pseudomonas, and Acinetobacter, with the microbiome not recovering by day 24 post-infection. These findings highlight the need for cautious antibiotic use in aquaculture due to lasting disruption of gut microbial communities.

Full summary

3,678 CHARS

**Background:** The intestinal microbiota plays critical roles in metabolism, nutrition, and immunity in fish. Rainbow trout are highly susceptible to bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum, which can cause up to 90% mortality in fry and up to 20% in juveniles/adults. Florfenicol is commonly used to treat BCWD, but its effects on gut microbiota composition over time are poorly understood. This study aimed to evaluate the impact of prophylactic oral florfenicol and erythromycin treatment on intestinal microbiota composition and subsequent susceptibility to F. psychrophilum infection in rainbow trout juveniles.

**Methods:** Rainbow trout juveniles (30–40 g) were housed in 12 tanks (50 fish/tank) at 10.0 ± 1.0°C. Four groups (triplicate tanks each) were established: untreated mock-infected control (Ca), untreated infected (Cb), florfenicol-treated infected (F; 10 mg/kg/day), and erythromycin-treated infected (E; 75 mg/kg/day). Antibiotics were administered orally for 10 consecutive days. Fish were then injected intraperitoneally with F. psychrophilum FPG101 (1 × 10^8 cfu/fish) or sterile Cytophaga broth (controls). Intestinal contents were collected at days −11, 0, 12, and 24 post-infection (p.i.). The V3–V4 region of the 16S rRNA gene was sequenced using Illumina MiSeq. Splenic bacterial load was quantified using rpoC qPCR on days 3, 6, 9, and 12 p.i. Survival was monitored for 24 days.

**Key Results:** A total of 15,422,986 sequences were processed, reduced to 4,022,717 after bioinformatics, with a mean of 33,804 sequences per sample (subsampled to 3,838). At the phylum level, the top five taxa were Proteobacteria (44%), Tenericutes (35%), Spirochaetota (11%), Desulfobacterota (6%), and Firmicutes (2%). At the genus level, Mycoplasma (35%), Brevinema (11%), Acinetobacter (10%), Aeromonas (6%), and Pseudomonas (5%) dominated. Alpha diversity was significantly affected by diet, time, and diet × time interaction (p < 0.01 for all indices). Fish infected with F. psychrophilum (Cb) had decreased alpha diversity and high Mycoplasma abundance. Florfenicol-treated fish (F) had increased alpha diversity compared to controls at day 24 p.i. Both antibiotic-treated groups showed increased abundance of potential pathogens: Acinetobacter, Pseudomonas (group F), and Aeromonas (group E). Mycoplasma disappeared after antibiotic treatment but reappeared by day 24. Beta diversity was significantly affected by diet and time (p < 0.001). Cumulative survival was 95% (group E), 91% (group F), and 90% (group Cb), with no significant differences between groups. Splenic F. psychrophilum was first detected on day 3 p.i. (1.61–1.80 log10 rpoC copies/reaction), with a significant increase in group F on day 12 p.i. compared to days 6 and 9.

**Clinical Implications:** Prophylactic oral treatment with florfenicol and erythromycin, as well as F. psychrophilum infection, significantly altered the intestinal microbiota composition of rainbow trout juveniles, with effects persisting at least 24 days post-infection. Both antibiotics reduced beneficial Mycoplasma and Brevinema while increasing potentially pathogenic genera (Aeromonas, Pseudomonas, Acinetobacter). The presence of Sphingomonas in florfenicol-treated fish suggests possible florfenicol degradation capacity. Neither antibiotic significantly improved survival against F. psychrophilum infection, though treated groups had numerically higher survival. These findings support cautious use of antibiotics in aquaculture and highlight the need for alternatives such as probiotics and prebiotics to preserve gut health and reduce antimicrobial resistance risks.

PICO

PPOPULATION

Rainbow trout juveniles (Oncorhynchus mykiss), 30–40 g, housed at 10°C

IINTERVENTION

Prophylactic oral florfenicol (10 mg/kg BW/day) or erythromycin (75 mg/kg BW/day) for 10 days, followed by intraperitoneal infection with Flavobacterium psychrophilum FPG101 (1 × 10^8 cfu/fish)

OOUTCOME

Intestinal microbiota composition (alpha and beta diversity via 16S rRNA gene sequencing), splenic bacterial load (rpoC qPCR), and cumulative survival

STUDY TYPE

other

SPECIALTY

veterinary medicine

SUMMARISED BY

AI pipeline

FIDELITY CHECK

88% · B

ORIGINAL PAPER

PMC10055933

Impact of Infection with Flavobacterium psychrophilum and Antimicrobial Treatment on the Intestinal Microbiota of Rainbow Trout

Pathogens

READ THE FULL PAPER

JUMP TO SECTION

ABSTRACT

The diversity and composition of intestinal microbiota in rainbow trout have been studied using next-generation sequencing (NGS), although few studies have examined the effects of antimicrobials. We evaluated the effect of antibiotics florfenicol and erythromycin and infection with or without Flavobacterium psychrophilum on the intestinal microbiota in rainbow trout juveniles (30–40 g) using NGS. Prophylactic oral antibiotic treatments were administered for 10 days before groups of fish were injected intraperitoneally with virulent F. psychrophilum . Intestinal content (allochthonous bacteria) was collected at day −11, 0, 12, and 24 p.i., and the v3–v4 region of the 16S rRNA gene was sequenced using Illumina MiSeq. Before prophylactic treatment, Tenericutes and Proteobacteria were the most abundant phyla identified and Mycoplasma was the most abundant genus. Fish infected with F. psychrophilum had decreased alpha diversity and a high abundance of Mycoplasma . Fish administered florfenicol had increased alpha diversity compared to the control at day 24 p.i., although both florfenicol and erythromycin-treated fish had a higher abundance of potential pathogens, specifically Aeromonas , Pseudomonas, and Acinetobacter . Mycoplasma disappeared after treatment but appeared again after day 24. This study demonstrates that prophylactic oral treatment with antibiotics florfenicol and erythromycin as well as F. psychrophilum infection changed the composition of intestinal microbiota in rainbow trout juveniles that did not recover by day 24 p.i. and further long-term effects on the host need to be investigated.

CITATION EXPORT

David Huyben, Maureen Jarau, Janet MacInnes et al.. Impact of Infection with Flavobacterium psychrophilum and Antimicrobial Treatment on the Intestinal Microbiota of Rainbow Trout. Pathogens. (2023). https://doi.org/10.3390/pathogens12030454

AUTHORS

5 · 3 CENTRES

David Huyben, Maureen Jarau, Janet MacInnes, Roselynn Stevenson, John Lumsden

1Department of Animal Biosciences, University of Guelph, Guelph, ON N1G 2W1, Canada
2Department of Pathobiology, University of Guelph, ON N1G 2W1, Canada
3Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada

EDITOR / REVIEWER

Po-Lin Chen, Roberto Bermúdez Pose, Lawrence S. Young