Aeromonas hydrophila, a pathogen of concern in aquaculture, utilizes quorum sensing mechanism to form biofilms that significantly increase the risk of infection in aquaculture commodity such as Nile tilapia (Oreochromis niloticus). The biofilm structure produced by A. hydrophila not only enhances its resistance to antibiotics but also complicates treatment efforts. In this study, we investigated the anti-quorum-sensing and biofilm disruption activities of bacterial extracts from Streptomyces labedae 20PM against A. hydrophila (in vitro and in vivo). Quantitative analysis showed that the crude extract had stronger anti-quorum-sensing activity in biofilms than the supernatant. Toxicity assessments indicated that both the supernatant and crude extract were non-toxic (24-hour LC50 >1000 ppm). GC-MS analysis identified 2-pentylpiperidine and (S)-2-propylpiperidine as the dominant compounds in the supernatant and crude extract, respectively. In vivo assays, including blood analyses and survival confirmed that incorporating the crude extract and supernatant into fish feed significantly contributed to the prevention and treatment of A. hydrophila infections in Nile tilapia. These findings suggest that the bioactive compounds derived from S. labedae 20PM have strong potential as natural agents for controlling A. hydrophila biofilm formation in aquaculture systems, offering a novel approach to mitigating bacterial infections.

The total synthesis of the complex pentasaccharide repeating unit related to the O-polysaccharide from Aeromonas hydrophila Pt679 is reported. Suitably protected derivatives of the rare β-d-QuiNAc and α-d-Fuc3NAc units are synthesized from d-glucosamine hydrochloride and 1,2;5,6-di-O-isopropylidene-α-l-allofuranose, respectively, and used for stereoselective glycosylation. The 1,2-cis rhamnosidic linkage is successfully accomplished using picoloyl-mediated hydrogen bond-assisted aglycon delivery (HAD method). The target pentasaccharide in the form of its 2-aminoethyl glycoside is ready for further conjugation through the terminal amine functionality without hampering the reducing end stereochemistry.

In aquaculture, the overuse of antibiotic could lead to antimicrobial resistance and destabilize host–microbiota homeostasis. Latilactobacillus sakei, belonging to the genus Latilactobacillus, was included in the list of bacteria that could be used in food in China in 2014. Increasing evidence demonstrated that its antagonistic capacity against a broad spectrum of pathogenic bacteria, indicating its promising potential for application in aquaculture. In this study, the protective effect of three L. sakei (JO12, JO26, JO35), isolated from the intestine of fish and shrimp, on mucosal injury caused by Aeromonas hydrophila in crucian carp under an oral challenge model was investigated. The result showed that compared with LGG, all three L. sakei strains alleviated A. hydrophila induced intestinal barrier damage and inflammation (downregulated intestinal TNF- α /IL-1β, upregulated IL-10, and reduced MyD88) in crucian carp. L. sakei JO35 delivered the greatest improvement in growth and feed efficiency. Compared with the model group, L. sakei JO26 and JO35 significantly decreased the levels of serum acid phosphatase (ACP) and increased intestinal lysozyme, whereas L. sakei JO12 lowerd serum ACP but exacerbated the elevation of intestinal AKP. Microbiome and transcriptome analysis revealed that the protective effect of L. sakei may be associated with the strain’s intestinal colonization capacity and its regulation of phagolysosomal competence (lysosome/phagosome, LAMP) and IgA barrier via pIgR (prominent with JO35).

Chitosan oligosaccharides (COSs), obtained through the hydrolysis of chitosan, exhibit remarkable antibacterial properties. In pursuit of COSs with enhanced antibacterial activity, the enzymatic characteristics of the chitosanase from Bacillus velezensis YB1534 (BvChi) were investigated. The purified BvChi displayed optimal activity at pH 6.0 and 50 °C and showed the highest hydrolytic activity using colloidal chitosan as a substrate, with the presence of Mn2+. The COSs produced by enzymatic hydrolysis of BvChi exhibited a minimum degree of polymerization (DP) of 2, and their antimicrobial activities against certain pathogenic bacteria (Escherichia coli, Staphylococcus aureus, Salmonella typhi 50071, and Aeromonas hydrophila) were evaluated. Among them, the 20 min hydrolysate showed the strongest growth inhibition against all these pathogens, demonstrated by the inhibition zone diameters, and its MIC and MBC values toward A. hydrophila were 0.625 and 1.25 mg/mL, respectively. Thin-layer chromatography (TLC) analysis showed that the hydrolyzed products after 20 min contains more COSs with DP > 5. These findings highlighted the potential of BvChi as a biocatalyst for producing antimicrobial COSs, applicable in food preservation and biomedical fields.

Introduction: Aeromonas infections are an emerging global public health challenge due to their complex pathogenicity and diverse virulence factors. These infections can lead to various conditions in humans, such as gastroenteritis, wound infections, and septicaemia. On February 12, 2024, an outbreak of Aeromonas hydrophila infection in Jinja and Luuka, Uganda, resulted in cases of abdominal pain, diarrhoea, vomiting, and death. This study described the epidemiology of the outbreak and the public health response. Methods: To investigate the outbreak and evaluate the epidemiology and public health response, a mixed-methods study was conducted using secondary data involving 185 individuals. Confirmed cases were identified through positive culture results from gastric aspirates or stool samples. Suspected and probable cases were defined by at least two symptoms, including abdominal pain, vomiting, and diarrhoea, history of exposure, and an epidemiological link to a confirmed case or outbreak cluster occurring between February 12 and 27, 2024. The study also included secondary laboratory investigations, food safety assessments, and an evaluation of timeliness using the 7-1-7 metric. Data analysis was performed using STATA-17. Results: Among 185 individuals investigated, 54.1% were female, the mean age was 23.9 ±18.7years, 103 Aeromonas hydrophila cases were identified, resulting in an attack rate of 55.7%(103/185), including one laboratory-confirmed case. Cases were younger than non-cases (22.1 vs. 26.3 years). The outbreak lasted five days (12–16 February 2024), peaked on 14 February, and had an incubation period of 33–38 hours, indicating a common-source exposure. Eight deaths occurred (case fatality rate: 7.8%). Geographical clustering of cases was observed, with high attack rates in Iziru (48%) and Bugomba (78%) parishes, respectively. Funeral food exposure showed an attributable risk of 9.3/100 and an attributable fraction of 15.7%. A. hydrophila was detected in gastric aspirate and water samples, implicating contaminated water and ill food handlers. Relapse occurred in 30.1% of cases. Conclusion: The outbreak of Aeromonas hydrophila was rapid, geographically clustered, and linked to contaminated water and ill food handlers, with funeral food exposure contributing to the outbreak. High attack, relapse, and fatality rates highlight the need for timely water safety interventions, improved food hygiene, and strengthened outbreak detection and response to prevent future occurrences.

Efficacy of a novel oral bivalent vaccine with fucoidan as adjuvant against Aeromonas hydrophila and Edwardsiella tarda infections in Nile tilapia aquaculture.

Antibacterial properties and mechanisms of anti-lipopolysaccharide factor 1 from Procambarus clarkii.

Dietary supplementation of Bacillus amyloliquefaciens and β-glucan, both individually and in conjunction effected growth performance, skin mucosal immunity, mRNA expression, and disease protection against Aeromonas hydrophila in striped snakehead, Channa striata (Bloch 1793).

Effects of dietary selenium nanoparticles and pennyroyal essential oil on growth performance, immune-biochemical and antioxidant parameters and disease resistance in Nile tilapia, Oreochromis niloticus.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) regulates Aeromonas hydrophila-induced autophagy in yellow catfish (Pelteobagrus fulvidraco).

Bacterial infection triggers CD3ε+ T cell expansion and interaction with macrophages in grass carp (Ctenopharyngodon idella).

Aeromonas hydrophila cellulitis and necrotizing fasciitis from a catfish fin puncture wound, and a review of the literature

Gb-piscidin: A novel antimicrobial and immunostimulant peptide from gilthead seabream (Sparus aurata) - Identification, tissue-specific expression, recombinant production, and biological evaluation.

Neuropeptide FF enhances antimicrobial defense by promoting intestinal barrier function in grass carp (Ctenopharyngodon idella).

Embryonic diazepam exposure induces innate immune toxicity in zebrafish (Danio rerio).

Bacterial infections are increasingly recognised as a major threat to ornamental freshwater shrimp aquaculture. Diseased Neocaridina spp. displaying abnormal swimming, lethargy, hypoxia, cutaneous abrasions, dark-brown lesions, and occasional moulting were investigated. Pure cultures from moribund shrimp yielded Gram-negative, motile, catalase- and oxidase-positive rods producing hemolysis and resistant to vibriostatic agent O/129. Biochemical profiling (API 20E) identified all isolates (KRW1-KRW5) as Aeromonas hydrophila, clustering with A. hydrophila CECT 839 and A. bestiarum CECT 4227, while MALDI-TOF MS confirmed their highest similarity to A. hydrophila CECT 839T DSM. Virulence gene screening revealed the universal presence of aer, alongside variable combinations of ela, hlyA, act, alt, ast, and lip. Pathogenicity assays fulfilled Koch's postulates, linking isolates to 'black disease', with cumulative mortality reaching 100% by Day 4-5 postinfection for strains KRW1 and KRW2, whereas KRW4 was least virulent. Antimicrobial susceptibility testing revealed multidrug resistance, with MAR indices ranging from 0.130 (KRW4) to 0.478 (KRW5). These findings identify A. hydrophila as the etiological agent of black disease in Neocaridina shrimp, underscore its virulence heterogeneity, and highlight the alarming prevalence of antimicrobial resistance in strains circulating in ornamental aquaculture.

In this study, the antimicrobial effect of the T. zygis essential oil (EO) was investigated on 68 bacterial and two yeast isolates belonging to 20 different families, including foodborne, ready-to-eat food, aquatic, and collection strains that are important for food safety and aquaculture. First, the chemical composition of the oil was analyzed using GC-MS to better understand its potential bioactivity. The major components of the T. zygis EO were identified as thymol (38.82%), β-cymene (21.66%), γ-terpinene (6.51%), carvacrol (6.36%) and linalool (6.25%) and the total of these components constituted 79.6% of the essential oil. In terms of antimicrobial activity, the disk diffusion test revealed inhibition in 66 out of 70 tested strains, with strong inhibition observed in 62 strains, moderate inhibition in four, and no inhibition in the remaining four. It showed strong antimicrobial activity against species known to be foodborne and fish pathogens such as Aeromonas hydrophila, Aeromonas salmonicida, Escherichia coli, Pseudomonas putida, Salmonella enterica, Staphylococcus aureus, Streptococcus iniae, Klebsiella pneumoniae, Edwardsiella tarda, Lactococcus garvieae, Yersinia ruckeri, Vibrio parahaemolyticus, Vibrio anguillarum, and Vibrio gigantis. In addition, it has been determined that the T. zygis EO has strong antifungal activity against yeast species such as Candida albicans and Saccharomyces cerevisiae. Antimicrobial activity levels were attributed to the high levels of phenolic components, especially thymol. In conclusion, this study has shown that the essential oil derived from T. zygis exhibits broad-spectrum antimicrobial activity and an effective natural bioprotective agent for both Gram-positive and Gram-negative bacteria and yeast species. In addition, this study provides an original contribution to the literature through a comprehensive evaluation of its effect on microorganisms isolated from various sources. Future studies should focus on the stability, sensory properties, and mechanisms of action of the T. zygis essential oil, particularly in diverse seafood applications.

Bacterial load estimation of Aeromonas hydrophila in experimentally infected Indian catfish, Clarias magur and its correlation with disease progression

Macroalgae plays a significant role in the formulation of innovative and environmentally sustainable approaches to address food challenges. Specifically, green macroalgae serve as dietary supplements aimed at improving the health, growth, and feeding efficiency of various species of marine and freshwater fishes, as well as mollusks. The effects of Chaetomorpha linum extract (CLE) on growth performance, physiological responses, and disease resistance are studied in Bellamya bengalensis against Aeromonas hydrophila. In this experiment, adult B. bengalensis (4412 ± 165.25 mg) were randomly divided into 15 rectangular glass aquariums (35 snail/aquaria; 45 L capacity) and their basal diet was supplemented with different levels of CLE, including 0 (CLE0), 1 (CLE1), 2 (CLE2), 3 (CLE3), and 4 (CLE4) g/kg for 60 days. The growth performance in the CLE3 dietary group was significantly higher that of the CLE0 group, exhibiting both linear and quadratic trends in relation to dietary CLE levels (p < 0.05). The activities of pepsin, amylase, and lipase were found to be highest in CLE3 and lowest in CLE0. Both linear and quadratic responses to dietary CLE levels in digestive enzymes were observed (p < 0.05). The activities of superoxide dismutase and catalase in the hepatopancreas were found to be elevated in snails due to the synergistic effect of the supplemented CLE diet. Among different levels of diet given, CLE2-supplemented snails showed an increase in their enzyme activity (p < 0.05). Interestingly, all the CLE-treated snails expressed elevated levels of mucus lysozyme and mucus protein when compared to control (p < 0.05). Additionally, hepatopancreatic acid phosphatase and alkaline phosphatase activity were elevated in snails consuming CLE3 (p < 0.05). The transcription levels of immune-related genes, including mucin-5ac and cytochrome, were significantly elevated in snails that were fed a diet supplemented with 2-4 g of CLE/kg. Furthermore, the transcription level of the acid phosphatase-like 7 protein gene also increased in snails receiving CLE-supplemented diets. After a 14-day period of infection, snails that consumed a diet supplemented with 3-4 g/kg of CLE exhibited a notable increase in survival rates against virulent A. hydrophila. Based on the above findings, it is suggested that a diet supplemented with 3 g/kg of CLE may enhance growth, antioxidant and immune defense, and disease resistance in the freshwater snail B. bengalensis.

Outbreaks of Aeromonas hydrophila cause major losses in African catfish (Clarias gariepinus) farming, while antibiotic raises resistance concerns. This study evaluated bacteriophages from a diseased catfish pond as local biocontrol agents. In vitro, phages reduced bacterial density by over 50% within 24 h (P&lt;0.05). In vivo, phage treatment significantly improved survival compared with infected controls (P&lt;0.05) and moderated hematological disruption. After infection, clinical signs were milder in phage-treated fish than in non-treated control. These results indicate that locally sourced phages can mitigate A. hydrophila infection and support future disease management in C. gariepinus aquaculture.