Molecular characterization and pathogenicity of Francisella noatunensis subsp. orientalis isolated from cultured tilapia (Oreochromis sp.) in Taiwan

Abstract

Francisella noatunensis subsp. orientalis is a causative agent of systemic granulomatous disease in tilapia. The present study was designed to understand the genetic and phenotypic diversities among Taiwanese Fno isolates obtained from tilapia (n = 17) and green Texas cichlid (Herichthys cyanoguttatus) (n = 1). The enzymatic profiles of the isolates were studied using the API ZYM system. Phylogenetic tree analysis of the 16S rRNA and housekeeping gene and pulsed‐field gel electrophoresis (PFGE) were carried out to determine the genotypic characters of all isolates. The phylogenetic tree showed similarity of 99%–100% nucleotide sequences of 16S rRNA and housekeeping genes compared to the Fno references genes from GenBank database. Comparatively, the results revealed an identical profile of enzymatic and PFGE pattern which was distincted from that of F. philomiragia. To understand the pathogenicity, the isolates were intraperitoneal injected to tilapia the gross lesions were observed concomitant with natural outbreak. Median lethal dose upon Nile tilapia and red tilapia were 9.06 × 103 CFU/fish and 2.08 × 102 CFU/fish, respectively. Thus, our data provide understanding the epidemiology of Taiwanese Fno isolates, and help in development of future control and prevention.

Whole cell inactivated autogenous vaccine effectively protects red Nile tilapia (Oreochromis niloticus) against francisellosis via intraperitoneal injection

“…Francisella noatunensis subsp. orientalis is one of the most pathogenic bacteria for tilapia (Klinger‐Bowen et al, ; Pulpipat, Lin, Chen, Wang, & Chen, ; Ramírez‐Paredes, Thompson, et al, ; Soto et al, ) and one of the main challenges that this industry currently faces globally. Nevertheless, despite the relevance of this pathogen, there are still no commercial vaccines available for its prevention and control.…”

Immune Responses and Protective Efficacy of a Formalin-Killed Francisella Noatunensis Subsp. Orientalis Vaccine Evaluated through Intraperitoneal and Immersion Challenge Methods in Oreochromis Niloticus

“…Vaccination is an effective and environmentally safe method to control and prevent the outbreak of fish diseases [24]. Fno AOD104086 is a local strain which belongs to the clonal group of Fno isolates that cause francisellosis in Taiwanese tilapia [5]. Owing to the high virulence of this strain, it was selected as the candidate strain for combination with the oil-based adjuvant Montanide TM ISA 763 AVG for the development of the first vaccine in Taiwan.…”

“…The Fno AOD104086 strain was originally isolated from cultured tilapia in Taiwan, and has been described in a previous study [5]. The Fno strain was recovered from the 20% skim milk stock solution and cultured on cysteine heart agar supplemented with 2% hemoglobin (CHAH) (BD BBL, Sparks, MD, USA) at 25 • C for 72 h. A single colony was sub-cultured in modified brain heart infusion broth (BD BBL, Sparks, MD, USA) at 25 • C with shaking at 150 rpm for 60 h, as previously published [18].…”

“…To evaluate the resistance of vaccinated fish to the Fno vaccine strain, at six weeks post primary immunization, control and vaccinated fish were challenged by the IP route and immersion method with a dose of 10 LD 50 (median lethal dose) in each group (n = 30 with duplications). The LD 50 dose used in the IP injection was approximately 10 4 CFU/fish, similar to that in a previous study [5], whereas the LD 50 dose used in the immersion method was around 10 7 CFU/mL of water as described in a previously published protocol [21]. Before challenge, all fish were starved for 24 h and anesthetized with MS222 (100 mg/L).…”

“…The disease causes high morbidity, with mortalities ranging from 20% to 95%, resulting in significant economic losses in tilapia farming worldwide [1][2][3]. Tilapia francisellosis was initially reported in Taiwan in 2005 as a Francisella-like bacterium in cultured tilapia [4] and is still considered a major threat in Taiwanese tilapia farming [5] along with other bacterial diseases like streptococcosis [6,7]. However, streptococcosis usually occurs in the summer season, while Fno generally causes disease outbreaks in the winter season.…”