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Aeromonas hydrophila is a common zoonotic agent in aquatic environments that causes gastroenteritis and wound infections in both humans and animals through foodborne and hospital-acquired infection. Antimicrobial resistance (AMR) combination with virulence factors enhances treatment challenging. The prevalence and AMR of Aeromonas hydrophila have been increasingly reported, posing a significant threat to both animal and public health. This systematic review and meta-analysis aimed to determine the prevalence of A. hydrophila and its resistance to aquatic food animals. A comprehensive search for relevant studies was conducted on Google Scholar, PubMed, ScienceDirect, and Scopus, following the PRISMA guidelines, covering studies from January 2020 to December 2024. The quality of the included publications was evaluated using the Joanna Briggs Institute critical appraisal tool. Differences in the prevalence and AMR of A. hydrophila were assessed using a random-effect model. A total of 14,077 studies were screened, and 14 publications were included. Bacterial isolation of A. hydrophila was achieved using various standard protocols, involving culture on Rimler-Shotts (RS) agar and Tryptic Soy Agar (TSA), with or without antimicrobials. Subsequent biochemical identification confirmed the isolates. The pool prevalence of A. hydrophila (30.7%, 95% C.I.:17.0-46.3%), and the distribution of virulence genes were 71.2%. The most common resistance observed to penicillin (80.7%), oxytetracycline (69.9%) and macrolides (67.8%). The most prevalent AMR genes identified were bla TEM (67.0%), followed by tetA (63.7%). The increasing presence of A. hydrophila in aquaculture suggests a considerable risk of disease. The prevalence of both A. hydrophila and AMR was higher in Africa than in Asia, indicating regional variations in the AMR pattern. However, monitoring and surveillance of A. hydrophila remained limited. A major limitation of this study was the heterogeneity in effect estimates across the selected studies. Nonetheless, the quality assessment conducted indicated that this variability did not compromise the consistency or reliability of the findings.

Aeromonas is recognized as a human pathogen following ingestion of contaminated food and water. One major problem in Aeromonas identification is that certain species are phenotypically very similar. The antimicrobial resistance is another significant challenge worldwide. We therefore aimed to use mass spectrometry technology for identification and discrimination of Aeromonas species and to screen the antimicrobial resistance of Aeromonas hydrophila (A. hydrophila). A total of 150 chicken meat and water samples were cultured, and then, the isolates were identified biochemically by the Vitek® 2 Compact system. Proteomic identification was performed by MALDI‐TOF MS and confirmed by a microchannel fluidics electrophoresis assay. Principal component analysis (PCA) and single‐peak analysis created by MALDI were also used to discriminate the Aeromonas species. The antimicrobial resistance of the A. hydrophila isolates was determined by Vitek® 2 AST cards. In total, 43 samples were positive for Aeromonas and comprised 22 A. hydrophila, 12 Aeromonas caviae (A. caviae), and 9 Aeromonas sobria (A. sobria) isolates. Thirty‐nine out of 43 (90.69%) Aeromonas isolates were identified by the Vitek® 2 Compact system, whereas 100% of the Aeromonas isolates were correctly identified by MALDI‐TOF MS with a score value ≥2.00. PCA successfully separated A. hydrophila, A. caviae and A. sobria isolates into two groups. Single‐peak analysis revealed four discriminating peaks that separated A. hydrophila from A. caviae and A. sobria isolates. The resistance of A. hydrophila to antibiotics was 95.46% for ampicillin, 50% for cefotaxime, 45.45% for norfloxacin and pefloxacin, 36.36% for ceftazidime and ciprofloxacin, 31.81% for ofloxacin and 27.27% for nalidixic acid and tobramycin. In conclusion, chicken meat and water were tainted with Aeromonas spp., with a high occurrence of A. hydrophila. MALDI‐TOF MS is a powerful technique for characterizing aeromonads at the genus and species levels. Future studies should investigate the resistance of A. hydrophila to various antimicrobial agents. The sequencing results indicated that A. hydrophila is the most prevalent Aeromonas spp. isolated from food and water. MALDI‐TOF MS is a powerful technique used for identification of Aeromonas at the genus and species‐level. Principal component analysis (PCA) and single‐peak analysis are successful tools to discriminate the Aeromonas spp. VITEK® 2 AST Cards can also use as a detective method of antimicrobial resistance.

To investigate the molecular basis of the emergence of Aeromonas hydrophila responsible for an epidemic outbreak of motile aeromonad septicemia of catfish in the Southeastern United States, we sequenced 11 A. hydrophila isolates that includes five reference and six recent epidemic isolates. Comparative genomics revealed that recent epidemic A. hydrophila isolates are highly clonal, whereas reference isolates are greatly diverse. We identified 55 epidemic-associated genetic regions with 313 predicted genes that are present in epidemic isolates but absent from reference isolates and 35% of these regions are located within genomic islands, suggesting their acquisition through lateral gene transfer. The epidemic-associated regions encode predicted prophage elements, pathogenicity islands, metabolic islands, fitness islands and genes of unknown functions, and 34 of the genes encoded in these regions were predicted as virulence factors. We found two pilus biogenesis gene clusters encoded within predicted pathogenicity islands. A functional metabolic island that encodes a complete pathway for myo -inositol catabolism was evident by the ability of epidemic A. hydrophila isolates to use myo -inositol as a sole carbon source. Testing of A. hydrophila field isolates found a consistent correlation between myo -inositol utilization as a sole carbon source and the presence of an epidemic-specific genetic marker. All epidemic isolates and one reference isolate shared a novel O-antigen cluster. Altogether we identified four different O-antigen biosynthesis gene clusters within the 11 sequenced A. hydrophila genomes. Our study reveals new insights into the evolutionary changes that have resulted in the emergence of recent epidemic A. hydrophila strains.

Among several Aeromonas spp., causing diseases in fishes, Aeromonas hydrophila is the most predominant and pathogenic one. This study represents the first molecular detection, virulence profiling, and antibiogram analysis of Aeromonas hydrophila isolated from stinging catfishes (shing; Heteropneustes fossilis ) and shark catfishes (pangasius; Pangasianodon hypophthalmus ) in Bangladesh. Whole fish samples (n = 140) were collected from fish farming areas of Trishal upazila (stinging catfish 50; shark catfish 20) and Muktagachha upazila (stinging catfish 50; shark catfish 20), under Mymensingh district. Isolation and identification were accomplished through cultural, morphological, biochemical and finally, polymerase chain reaction (PCR) using genus- and species-specific primers, targeting 16S rDNA gene. Out of 140 samples, 38 (27.14%) isolates were found positive for A. hydrophila via conventional and PCR. The PCR-based virulence profiling showed that aer A (44.73%), hly A (39.74%), asa 1 (39.47%), ahy B (60.52%), act (21.5%), ast (28.94), alt (47.36%), ser (44.73%), lip (50%), gcat (23.68%), and asc V (21.05%) genes were detected, however, no aex T was detected. Antibiotic susceptibility test (using disc diffusion method) revealed that highest resistance (other than Penicillin Group) against Aztreonam and Cefuroxime (73.68%), and lowest against Gentamicin and Azithromycin (5.26%). MDR was detected in 71.05% isolates, and 92.11% isolates had MAR index ≥ 0.2. Statistically significant associations were observed between phenotypic resistance and specific virulence genes p ≤ 0.05. It could be concluded that MDR and virulent potential A. hydrophila are prevalent in stinging and shark catfishes of Mymensingh region, which might be a serious threat to sustainable aquaculture, food safety and public health.

Aeromonas species are important pathogens of fishes and aquatic animals capable of infecting humans and other animals via food. Due to the paucity of pan-genomic studies on aeromonads, the present study was undertaken to analyse the pan-genome of three clinically important Aeromonas species (A. hydrophila, A. veronii, A. caviae). Results of pan-genome analysis revealed an open pan-genome for all three species with pan-genome sizes of 9181, 7214 and 6884 genes for A. hydrophila, A. veronii and A. caviae, respectively. Core-genome: pan-genome ratio (RCP) indicated greater genomic diversity for A. hydrophila and interestingly RCP emerged as an effective indicator to gauge genomic diversity which could possibly be extended to other organisms too. Phylogenomic network analysis highlighted the influence of homologous recombination and lateral gene transfer in the evolution of Aeromonas spp. Prediction of virulence factors indicated no significant difference among the three species though analysis of pathogenic potential and acquired antimicrobial resistance genes revealed greater hazards from A. hydrophila. In conclusion, the present study highlighted the usefulness of whole genome analyses to infer evolutionary cues for Aeromonas species which indicated considerable phylogenomic diversity for A. hydrophila and hitherto unknown genomic evidence for pathogenic potential of A. hydrophila compared to A. veronii and A. caviae.

Aeromonas hydrophila is an opportunistic pathogen that is highly important for freshwater fish. In the present study, two freshwater fish species Nile tilapia ( Oreochromis niloticus ) and Mullet ( Mugil cephalus ) collected from various fish farms in Kafrelsheikh Governorate, Egypt. The fish samples were examined to determine Aeromonas hydrophila presence ( A. hydrophila ). In addition, a treatment trial was conducted involving four groups of Nile tilapia fish, which treated with florfenicol (FFC) and oxytetracycline (OTC) based on the antimicrobial susceptibility test results. According to the findings, 12 (20%) A. hydrophila strains were isolated from a total of 60 collected fish samples (30 of Nile tilapia and Mullet with percentages of 30% and 10%, respectively). Based on species-specific 16 S rRNA genes, six (6) isolates were identified as A. hydrophila and carried aerolysin ( aer A) and hemolysin ( hyl A) virulence genes, with percentages of 83.3% and 50%, respectively. Whereas, the antimicrobial resistance gene results were bla TEM with percent (100%) and aadA 1 (83.3%). Histopathological changes were significantly reduced in all assessed organs (liver, spleen, kidney, and gills) in the FFC group compared to the OTC-treated group. The prevalence of virulent and multidrug-resistant A. hydrophila in aquaculture poses significant risks to fish health, economic productivity, and public health.

Necrotizing fasciitis (NF) caused by flesh-eating bacteria is associated with high case fatality. In an earlier study, we reported infection of an immunocompetent individual with multiple strains of Aeromonas hydrophila (NF1–NF4), the latter three constituted a clonal group whereas NF1 was phylogenetically distinct. To understand the complex interactions of these strains in NF pathophysiology, a mouse model was used, whereby either single or mixed A. hydrophila strains were injected intramuscularly. NF2, which harbors exotoxin A (exoA) gene, was highly virulent when injected alone, but its virulence was attenuated in the presence of NF1 (exoA-minus). NF1 alone, although not lethal to animals, became highly virulent when combined with NF2, its virulence augmented by cis-exoA expression when injected alone in mice. Based on metagenomics and microbiological analyses, it was found that, in mixed infection, NF1 selectively disseminated to mouse peripheral organs, whereas the other strains (NF2, NF3, and NF4) were confined to the injection site and eventually cleared. In vitro studies showed NF2 to be more effectively phagocytized and killed by macrophages than NF1. NF1 inhibited growth of NF2 on solid media, but ExoA of NF2 augmented virulence of NF1 and the presence of NF1 facilitated clearance of NF2 from animals either by enhanced priming of host immune system or direct killing via a contact-dependent mechanism.

An earlier report described a human case of necrotizing fasciitis (NF) caused by mixed infection with 4 Aeromonas hydrophila strains (NF1–NF4). While the NF2, NF3, and NF4 strains were clonal and possessed exotoxin A (ExoA), the NF1 strain was determined to be phylogenetically distinct, harboring a unique type 6 secretion system (T6SS) effector (TseC). During NF1 and NF2 mixed infection, only NF1 disseminated, while NF2 was rapidly killed by a contact-dependent mechanism and macrophage phagocytosis, as was demonstrated by using in vitro models. To confirm these findings, we developed 2 NF1 mutants (NF1ΔtseC and NF1ΔvasK); vasK encodes an essential T6SS structural component. NF1 VasK and TseC were proven to be involved in contact-dependent killing of NF2 in vitro, as well as in its elimination at the intramuscular injection site in vivo during mixed infection, with overall reduced mouse mortality. ExoA was shown to have an important role in NF by both NF1-exoA (with cis exoA) and NF2 during monomicrobial infection. However, the contribution of ExoA was more important for NF2 than NF1 in the murine peritonitis model. The NF2ΔexoA mutant did not significantly alter animal mortality or NF1 dissemination during mixed infection in the NF model, suggesting that the ExoA activity was significant at the injection site. Immunization of mice to ExoA protected animals from NF2 monomicrobial challenge, but not from polymicrobial infection because of NF2 clearance. This study clarified the roles of T6SS and ExoA in pathogenesis caused by A. hydrophila NF strains in both mouse peritonitis and NF models in monomicrobial and polymicrobial infections.

Aeromonas hydrophila poses significant health and economic challenges in aquaculture owing to its pathogenicity and prevalence. Overuse of antibiotics has led to multidrug resistance and environmental pollution, necessitating alternative strategies. This study investigated the antibacterial and antibiofilm potentials of quercetin against A. hydrophila. Efficacy was assessed using various assays, including antibacterial activity, biofilm inhibition, specific growth time, hemolysis inhibition, autoaggregation, and microscopic evaluation. Additionally, docking analysis was performed to explore potential interactions between quercetin and virulence proteins of A. hydrophila, including proaerolysin, chaperone needle-subunit complex of the type III secretion system, and alpha-pore forming toxin (PDB ID: 1PRE, 2Q1K, 6GRK). Quercetin exhibited potent antibacterial activity with 21.1 ± 1.1 mm zone of inhibition at 1.5 mg mL−1. It also demonstrated significant antibiofilm activity, reducing biofilm formation by 46.3 ± 1.3% at the MIC and attenuating autoaggregation by 55.9 ± 1.5%. Hemolysis was inhibited by 41 ± 1.8%. Microscopic analysis revealed the disintegration of the A. hydrophila biofilm matrix. Docking studies indicated active hydrogen bond interactions between quercetin and the targeted virulence proteins with the binding energy -3.2, -5.6, and -5.1 kcal mol⁻1, respectively. These results suggest that quercetin is an excellent alternative to antibiotics for combating A. hydrophila infection in aquaculture. The multifaceted efficacy of quercetin in inhibiting bacterial growth, biofilm formation, virulence factors, and autoaggregation highlights the potential for aquaculture health and sustainability. Future research should delve into the precise mechanisms of action and explore synergistic combinations with other compounds for enhanced efficacy and targeted interventions.

Co-infection of Lactococcus garvieae and Aeromonas hydrophila , has been confirmed from diseased Nile Tilapia ( Oreochromis niloticus ), Chithralada strain cultured in a freshwater rearing pond of Alappuzha district of Kerala, India. The aetiological agents behind the disease outbreak were bacteriologically proven and confirmed by 16SrRNA sequencing and phylogenetic analysis. PCR detection of the virulent genes, showed existence of adhesin and hemolysin in L. garvieae and aerolysin in A. hydrophila strain obtained. To fulfil Koch’s postulates, challenge experiments were conducted and median lethal dose (LD 50 ) of L. garvieae and A. hydrophila was calculated as 1 × 10 5.91 CFU per mL and 1 × 10 5.2 CFU per mL respectively. Histopathologically, eyes, spleen, and kidney were the predominantly infected organs by L. garvieae and A. hydrophila . Out of the 13 antibiotics tested to check antibiotic susceptibility, L. garvieae showed resistance to almost 7 antibiotics tested, with a resistance to Ciprofloxacin while A. hydrophila was found resistant to Streptomycin and Erythromycin. Understanding the complex interaction between Gram-positive and Gram-negative bacteria in the disease process and pathogenesis in fish host will contribute to efficient treatment strategies. As a preliminary investigation into this complex interaction, the present study is aimed at phenotypic and genotypic characterization, pathogenicity evaluation, and antibiotic susceptibility of the co-infecting pathogens in a diseased sample of freshwater-farmed Nile tilapia.