Detection and virulence of Lactococcus garvieae and L. petauri from four lakes in southern California

Taylor Abraham, Zeinab Yazdi, Eric Littman, Khalid Shahin, Taylor I. Heckman, Eva Marie Quijano Cardé, Diem Thu Nguyen, Ruixue Hu, Mark Adkison, Tresa Veek, Kavery Mukkatira, Christine Richey, Kevin Kwak, Haitham H. Mohammed, Cesar Ortega, Ruben Avendaño-Herrera, William Keleher, Véronique LePage, Ian Gardner, Timothy J. WelchEsteban Soto

Research output: Contribution to journalArticlepeer-review

Abstract

Objective: The first objective of the study aimed to detect the presence of Lactococcus petauri, L. garvieae, and L. formosensis in fish (n = 359) and environmental (n = 161) samples from four lakes near an affected fish farm in California during an outbreak in 2020. The second objective was to compare the virulence of the Lactococcus spp. in Rainbow Trout Oncorhynchus mykiss and Largemouth Bass Micropterus salmoides. Methods: Standard bacterial culture methods were used to isolate Lactococcus spp. from brain and posterior kidney of sampled fish from the four lakes. Quantitative PCR (qPCR) was utilized to detect Lactococcus spp. DNA in fish tissues and environmental samples from the four lakes. Laboratory controlled challenges were conducted by injecting fish intracoelomically with representative isolates of L. petauri (n = 17), L. garvieae (n = 2), or L. formosensis (n = 4), and monitored for 14 days postchallenge (dpc). Result: Lactococcus garvieae was isolated from the brains of two Largemouth Bass in one of the lakes. Lactococcus spp. were detected in 14 fish (8 Bluegills Lepomis macrochirus and 6 Largemouth Bass) from 3 out of the 4 lakes using a qPCR assay. Of the collected environmental samples, all 4 lakes tested positive for Lactococcus spp. in the soil samples, while 2 of the 4 lakes tested positive in the water samples through qPCR. Challenged Largemouth Bass did not show any signs of infection postinjection throughout the challenge period. Rainbow Trout infected with L. petauri showed clinical signs within 3 dpc and presented a significantly higher cumulative mortality (62.4%; p < 0.0001) at 14 dpc when compared to L. garvieae (0%) and L. formosensis (7.5%) treatments. Conclusion: The study suggests that qPCR can be used for environmental DNA monitoring of Lactococcus spp. and demonstrates virulence diversity between the etiological agents of piscine lactococcosis.

Original languageEnglish
Pages (from-to)187-198
Number of pages12
JournalJournal of Aquatic Animal Health
Volume35
Issue number3
DOIs
Publication statusPublished - Sept 2023

Keywords

  • emerging
  • lactococcosis
  • salmonids

ASJC Scopus subject areas

  • Aquatic Science

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