<i>Flavobacterium oreochromis</i> From Farmed Tambaqui ( <i>Colossoma macropomum</i> ): Insights Into Genetic, Phenotypic and Pathogenic Diversity

Flavobacterium spp. are the etiological agents of columnaris disease. Although there is evidence that columnaris poses a significant threat to the farming of tambaqui (Colossoma macropomum), there remains a large gap in understanding the genetic and phenotypic diversities of columnaris-causing bacteria (CCB). This study was designed to identify diversity traits of CCB from tambaqui reared in Brazil. From 26 CCB outbreaks previously identified as F. columnare with MALDI-TOF were prospected. A multiplex PCR was conducted to confirm the bacterial species, while REP-PCR was used to determine the differences in genetic patterns (GP), and putative virulence genes were accessed using PCR (norB, trx and gtf). All isolates were identified as F. oreochromis by multiplex PCR. REP-PCR identified 4 genetic variants (GP₁, GP₂, GP₃ and GP₄), with GP₃ being the most frequent. All the putative virulence genes were detected in all analysed strains. One strain representing each GP was subjected to the description of phenotypic traits (growth patterns, morphology and pathogenicity). The pathogenicity and patterns of virulence were assessed and achieved for all GP, and AMFO14 (GP₃) displayed the highest frequency. Based on recent taxonomic advances on Flavobacterium spp. from freshwater fish worldwide, this study provides unprecedented insights regarding CCB retrieved from tambaqui.