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.

The industrial processing of broiler chickens has become increasingly automated to scale up meat production. However, certain procedures may cause rupture of the gastrointestinal tract, contaminating the products. The objective of this study was to evaluate the efficiency of the removal of visible contaminated broiler carcasses from the slaughter line based on their microbiological quality compared to non-contaminated ones. Carcasses were analyzed for Escherichia coli and aerobic mesophilic microorganisms counts, as well as Salmonella spp. detection. Carcasses with gastrointestinal contamination had significantly higher counts of aerobic mesophilic microorganisms and E. coli than those without contamination. However, carcasses without visible contamination also showed high counts of bacteria, indicative of the hygiene and sanitary concerns during slaughter. Salmonella spp. were detected in both types of carcasses, with no significant difference in the frequency of positive samples. The most frequently identified serovar was Salmonella Minnesota. The most frequently detected bacteria were E. coli, Klebsiella pneumoniae, Citrobacter freundii, and Pseudomonas aeruginosa. In conclusion, both contaminated and non-contaminated carcasses exhibited high bacterial counts, including potentially pathogenic microorganisms, highlighting the need for post-evisceration steps to reduce microbial contamination.

Vibrio vulnificus is an opportunistic pathogen in humans and exhibits pathogenic behavior in several aquaculture fish species. To date, in Brazil, there are no reports of V. vulnificus outbreaks in farmed fish. However, in 2019, sorubim (Pseudoplatystoma sp.) in the grow-out phase with clinical signs and cumulative mortality of 40% was registered. We aimed to identify and characterize the etiological agents of this outbreak. Seven moribund fish were sampled for bacteriological studies, and isolates were obtained from the brain and kidneys. Bacterial identification using matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF/MS) revealed V. vulnificus. One isolate, RP4, was used for identification via dnaJ and 16S rRNA gene sequencing and antimicrobial susceptibility evaluation. Sorubim juveniles were experimentally challenged with RP4 isolate via intracelomic injection (IC, 10⁷ colony-forming units [CFU] fish⁻¹) and immersion bath (IB, 10⁶ CFU mL⁻¹ for 30 min). Identities to V. vulnificus of dnaJ and 16S rRNA genes by BLAST analysis were higher than 92% and 98%, respectively. Susceptibility to oxytetracycline, florfenicol, and other antimicrobial molecules was also observed. In the IC-challenged group, the mortality rate was 100% with V. vulnificus recovered from fish organs (brain, liver, spleen, and kidney). Additionally, splenic endothelium alterations were observed in the IC group. On the contrary, the control and IB groups did not develop any clinical signs, mortality, or bacterial recovery after 7 days of challenge. To the best of our knowledge, this is the first report of pathogenic V. vulnificus in farmed Pseudoplatystoma sp.

Streptococcus agalactiae and Francisella orientalis are major bacterial pathogens affecting Nile tilapia ( Oreochromis niloticus ) worldwide, leading to substantial economic losses in aquaculture. This study investigated the spatial and temporal distribution of these pathogens in tilapia production units of Brazil and identified risk factors associated with their occurrence. Between 2019 and 2024, 257 tilapia production units across Brazil were monitored, resulting in 395 bacteriological examinations and 10,161 fish evaluated. Water temperature and fish weight were recorded, and bacterial isolates were identified by MALDI‐ToF and serotyping. Spatial and temporal analyses were conducted, alongside risk prediction modeling. S. agalactiae was detected in 69.2% of production units, with serotype Ib widely distributed nationwide and serotype III restricted to the Northeast, where its occurrence increased over time. F. orientalis was detected in 23.3% of production units, predominantly during colder months in the South and Southeast regions. Seasonal analysis revealed that S. agalactiae occurred year‐round with minimal detection in August, whereas F. orientalis peaked in July. Spatial clustering revealed high‐risk areas overlapping with major tilapia production zones. Water temperature and fish weight were significant predictors for all three pathogens ( S. agalactiae Ib/III and F. orientalis ). Coinfections at the fish level were rare, although concurrent pathogens presence within production units were observed. Overall, the study provides a comprehensive assessment of the seasonal and regional dynamics of S. agalactiae and F. orientalis in tilapia production units of Brazil. These findings underscore the need for strengthened biosecurity measures and region‐specific disease surveillance strategies to mitigate the impact of these pathogens.

Nile tilapia (Oreochromis niloticus) and tambaqui (Colossoma macropomum) are the two most produced freshwater fishes in Brazil. This study investigated the potential pathogenicity of Streptococcus agalactiae and Francisella orientalis, previously isolated from diseased Nile tilapia, to tambaqui. Experimental infection trials were conducted in juvenile tambaqui at a dose of approximately 10⁷ CFU fish⁻¹, assessing clinical signs, mortality, bacterial recovery, and histopathological changes. Results demonstrated that S. agalactiae exhibited high pathogenicity to tambaqui, causing rapid disease progression, high mortality (83.33%) within 48 h post-infection, and severe lesions in multiple organs, under the experimental conditions. In contrast, F. orientalis infection did not result in mortality or clinical signs, despite bacterial recovery and granulomatous inflammation observed in the tissues. This study highlights the need to consider the potential impact of these pathogens in tambaqui farming.