ARS | Publication request: Identification and virulence of Chryseobacterium indologenes isolated from diseased yellow perch (Perca flavescens)

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 5, 2012
Publication Date: March 1, 2013
Citation: Wei Pridgeon, Y., Klesius, P.H., Garcia, J.C. 2013. Identification and virulence of Chryseobacterium indologenes isolated from diseased yellow perch (Perca flavescens). Journal of Applied Microbiology. 114:636-643.

Interpretive Summary: In January of 2012, mortality among yellow perch was observed in a US fish farm, with symptoms of gross skin lesions below the dorsal fin as well as the caudal peduncle. Diseased fish were sent to Aquatic Animal Health Research Unit, USDA-ARS for pathogen identification. Fifteen Gram-negative bacteria isolates were recovered from the skin lesions of diseased yellow perch. Based on biochemical tests, ten isolates were identified as Chryseobactertium indologenes. Based on results of fatty acid methyl ester analysis, thirteen isolates were identified as Chryseobacterium. Based on sequencing results of partial 16S rRNA gene, thirteen isolates were identified as C. indologenes. Multiple sequence alignment analysis revealed that the partial 16S rRNA or the 16S-23S ISR sequence of the thirteen isolates shared 100% identity with each other. When healthy yellow perch were exposed to the fifteen isolates by bath immersion, only C. indologenes isolates killed 10% to 20% of fish, whereas other isolates were avirulent. When yellow perch were exposed to C. indologenes by intraperitoneal injection, mortality was dose-dependent, with LD50 and LD95 values of 1.5 × 108 and 3.2 × 108 CFU/fish, respectively. This is the first report on the isolation of C. indologenes from diseased yellow perch. Virulence studies suggested that C. indologenes could become pathogenic to yellow perch.

Technical Abstract: Fifteen Gram-negative bacteria isolates were recovered from the skin lesions of diseased yellow perch (Perca flavescens). Based on API 20NE test results, ten isolates were found to share 67.2% to 99.9% homologies with Chryseobactertium indologenes. Based on results of fatty acid methyl ester analysis, thirteen isolates were found to share similarities with C. indologenes and other species of Chryseobacterium. Based on sequencing results of partial 16S rRNA gene, thirteen isolates shared 99% identities (e value = 2e-50) with the 16S rRNA sequence of C. indologenes (GenBank HQ259684). Based on the 16S-23S rRNA intergenic spacer region (ISR) sequence, the thirteen isolates shared 88% identity (e value = 1e-165) with the 16S-23S ISR sequence of C. indologenes (GenBank EU014570). T-coffee multiple sequence alignment revealed that the partial 16S rRNA or the 16S-23S ISR sequence of the thirteen isolates shared 100% identity with each other. When healthy yellow perch were exposed to the fifteen isolates by bath immersion (~ 6 × 107 CFU/ml for one hour), only C. indologenes isolates killed 10% to 20% of fish, whereas other isolates were avirulent. When yellow perch were exposed to C. indologenes by intraperitoneal injection, mortality was dose-dependent, with LD50 and LD95 values of 1.5 × 108 and 3.2 × 108 CFU/fish, respectively. This is the first report on the isolation of C. indologenes from diseased yellow perch. Virulence studies suggested that C. indologenes could become pathogenic to yellow perch.