ABSTRACT
This study aimed to identify and characterize isolates of Francisella salimarina associated with an outbreak on a marine fish farm in Brazil and to analyse their genetic variability and antimicrobial susceptibility. In 2021, diseased cobias (Rachycentron canadum, n = 10) and dusky groupers (Epinephelus marginatus, n = 10) were sampled and subjected to bacteriological and pathological examinations. The isolates obtained were morphologically and biochemically characterized and identified by matrix-assisted laser desorption/ionization-time of flight (MALDI-ToF) and 16S rRNA gene sequencing. The genetic diversity of these isolates was analysed using repetitive extragenic palindromic-polymerase chain reaction (REP-PCR). Antimicrobial susceptibility was assessed using the disk diffusion technique. Macroscopically, the fish presented skin ulcerations, ocular lesions, hepatomegaly and splenomegaly. A pleomorphic, gram-negative, catalase- and oxidase-positive bacterium was isolated from seven cobias and two groupers. The 16S rRNA gene sequences showed >99% coverage and identity with other deposited sequences of F. salimarina. The results of the biochemical analysis corresponded to these bacterial species. Histologically, granulomas were observed in the spleen, liver and heart of the cobias (n = 6), and necrotizing and fibrinous dermatitis and myositis were identified in some groupers (n = 2). The isolates exhibited the same banding pattern when REP-PCR was performed, indicating that they were clonally related. Finally, the antibiogram test, no inhibition halo was observed for amoxicillin and trimethoprim-sulfamethoxazole. To our knowledge, this is the first report of F. salimarina infection in cobias and dusky groupers.
ABSTRACT
Edwardsiella tarda is a crucial pathogenic bacterium in tropical aquaculture. This bacterium was recently isolated from tambaqui (Colossoma macropomum), a commercially important fish species in Brazil. This study assessed the antimicrobial susceptibility, pathogenicity, and genetic diversity of the tambaqui-derived E. tarda isolates. Fourteen bacterial isolates isolated from tambaqui were identified as E. tarda by using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and dnaJ gene sequencing. Antimicrobial susceptibility tests were conducted against seven drugs using the disc diffusion assay. The pathogenicity test conducted by intraperitoneal injection of 2.4 × 107 colony-forming units (CFU) fish-1 of E. tarda (ED38-17) into tambaqui juveniles eventually revealed that neither clinical signs nor death were present. However, splenomegaly and whitish areas in the spleen and kidneys were observed. The histological investigation also revealed granulomatous splenitis, nephritis, and hepatitis occurring internally. Repetitive extragenic palindromic-PCR fingerprinting separated the 14 isolates into three genetic groups. The antibiogram revealed that all E. tarda isolates were wild-type (WT) to florfenicol (FLO), norfloxacin (NOR), neomycin (NEO), erythromycin (ERY), and oxytetracycline (OXY); however, some were non-wild-type to sulfamethoxazole/trimethoprim (7.1%) and amoxicillin (21.4%). Therefore, through experimental infection, E. tarda ED38-17 could induce pathogenic effects in C. macropomum. Additionally, three distinct genetic types were found, and the E. tarda isolates were WT to FLO, NOR, NEO, ERY, and OXY. These findings raise awareness of a bacteria causing unseen lesions, a pathogen that will potentially impact tambaqui aquaculture in the future.
ABSTRACT
This study aimed to evaluate the effects of Saccharomyces cerevisiae var. boulardii (SB) for sows on their productive performance, colostrum and milk composition, and litter performance, in tropical humid climatic conditions. A total of 105 sows (Topigs Norsvin®) were allotted to a 5 × 3 completely randomized factorial design, with five diets (control diet; SBGL4 and SBGL8: 0.04 and 0.08% SB supplementation from the 90th day of gestation until 24th day of lactation; SBL4 and SBL8: 0.04 and 0.08% SB supplementation during lactation) and three parity order groups (PO: 1st and 2nd; 3rd and 4th; 5th to 7th), considering each sow and their litter as experimental unit. Sows above the 5th PO that fed control diet had a lower daily milk production (DMP), number of weaned piglets (NWP), and daily weight gain of litter (DWGL) than sows from 1st to 4th PO that fed the same diet (P < 0.05). Dietary supply of SBGL4 and SBGL8 to older sows provided a higher DMP, NWP, and DWGL when compared to sows of same PO that fed the control diet (P < 0.05). Dietary supply of SBGL4, SBGL8, SBL4, and SBL8 provided a higher dry matter and protein contents in sows' milk of 1st and 2nd PO when compared to sows from same PO that fed control diet (P < 0.05). Dietary supply of SB enhances milk yield of older sows and their litter performance, as well as the dry matter and protein content of younger sows' milk in tropical humid climatic conditions.
