Coinfection by Group C Streptococcus dysgalactiae subsp. equisimilis and Flavobacterium davisii in Nile Tilapia, from the United States

Authors: Shoemaker, Craig; Lafrentz, Benjamin; Beck, Benjamin; Paulson, Matthew; Garcia, Julio; HECKMAN, TAYLOR - University Of California, Davis; SOTO, ESTEBAN - University Of California, Davis

Submitted to: European Association of Fish Pathologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2022
Publication Date: 10/17/2022
Citation: Shoemaker, C.A., Lafrentz, B.R., Beck, B.H., Paulson, M.D., Garcia, J.C., Heckman, T.I., Soto, E. 2022. Coinfection by Group C Streptococcus dysgalactiae subsp. equisimilis and Flavobacterium davisii in Nile Tilapia, from the United States. European Association of Fish Pathologists. https://doi.org/10.48045/001c.38695.
DOI: https://doi.org/10.48045/001c.38695

Interpretive Summary: Streptococcal disease and columnaris disease are common in tilapia aquaculture across the globe, likely responsible for worldwide losses in the billion-dollar range annually. Coinfections are also common but often overlooked or not reported. In the present study, we describe the clinical presentation of streptococcosis and columnaris co-infection in diseased Ivory Coast Nile tilapia (Oreochromis niloticus). The study determined the gram-positive bacteria isolated was Group C Streptococcus dysgalactiae subsp. equisimilis using phenotypic and genetic analysis. The co-isolated gram-negative bacteria was genetically typed using multiplex polymerase chain reaction (genetic test) as Flavobacterium davisii. To our knowledge, this is the first report of both bacteria co-occurring in tilapia in the United States.

Technical Abstract: Streptococcal disease and columnaris disease are common in tilapia aquaculture across the globe. Coinfections are also common but often overlooked or not reported. In the present study, we describe the clinical presentation of streptococcosis and columnaris co-infection in diseased Ivory Coast Nile tilapia (Oreochromis niloticus), and the phenotypic (Lancefield grouping, hemolytic pattern, biochemical characteristics, antibiotic susceptibility) and genotypic (multilocus sequence analysis for streptococci and multiplex PCR for flavobacteria) characterization of its etiological agents, namely Group C Streptococcus dysgalactiae subsp. equisimilis and Flavobacterium davisii. We further fulfilled Koch’s postulates with the S. dysgalactiae subsp. equisimilis isolate in genetically improved Nile tilapia.