Virulence, Antibiotic Resistance, and Phylogenetic Relationships of Aeromonas spp. Carried by Migratory Birds in China

Exploring Aeromonas veronii in Migratory Mute Swans (Cygnus olor): A Debut Report and Genetic Characterization

Aeromonas veronii (A. veronii) is a ubiquitous bacterium in terrestrial and aquatic environments. It has a significant impact on animal and human health, with it becoming an emerging crucial pathogen worldwide. However, there have been no reports of mute swan infections. In the present study, after an observation of pathological changes, one bacterial strain isolated from a dead migratory mute swan was identified as A. veronii HNZZ-1/2022 based on its morphology, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and sequence analysis of the 16S rRNA and gyrB genes. To explore its pathogenicity, virulence gene detection and a gosling infection experiment were subsequently carried out, respectively. Six virulence genes for cytotonic enterotoxins (alt), lateral elastase (ela), lipase (lip), cytotoxic enterotoxin (act), aerolysin (aerA), and polar flagellin (fla) were present in the template DNA of A. veronii HNZZ-1/2022. Experimentally infected goslings exhibited hemorrhages of various different degrees in multiple organs. The half-maximal lethal dose (LD50) value of A. veronii strain HNZZ-1/2022 was estimated to be 3.48 × 108 colony forming units (CFUs) per mL for goslings. An antimicrobial susceptibility test showed that the A. veronii HNZZ-1/2022 strain was resistant to meropenem, ampicillin, and enrofloxacin. To date, this is the first report of A. veronii in migratory mute swans, thus expanding the currently known host spectrum. These results suggest that the migratory mute swan is a new host for A. veronii and demonstrate the need for extensive surveillance and research of A. veronii to minimize its transmission between animals, the environment, and humans.

Antibacterial activity and mechanism of rose essential oil against Aeromonas veronii isolated from Northern snakehead (Channa argus)

AIMS

To investigate and identify the antibacterial action and mechanism of rose essential oil (REO) against Aeromonas veronii isolated from Northern snakehead for the first time by the phenotypic and metabolic analysis.

METHODS AND RESULTS

The 2-fold broth microdilution and spread-plate method identified that the minimum inhibitory concentration and minimum bactericidal concentration of REO against A. veronii were 1.25 μl ml-1 and REO impaired the growth in a concentration-dependent manner, indicating that REO possessed a significant bacteriostatic activity. Electron microscopy and live-dead cell staining found that REO caused a severe disruption of cellular morphology and increased the membrane permeability. Additionally, REO treatment induced the leakage of intracellular biomolecules such as proteins and nucleic acids from the bacteria. Metabolomics analysis showed that compared with the control, the REO treatment group exhibited a total of 190 differential metabolites (118 down-regulated and 72 up-regulated), which involved in the main metabolic pathways such as biotin metabolism, arginine biosynthesis, glutathione metabolism, lysine degradation, and histidine metabolism and the TCA cycle. These results verified that REO disturbed the metabolic processes of A. veronii to achieve the bacteriostatic effect.

CONCLUSION

The rose essential oil exhibited the effective antibacterial activity against A. veronii via breaking the cellular structure, increasing the membrane permeation and disrupting the metabolic processes.

Identification and specificity validation of unique and antimicrobial resistance genes to trace suspected pathogenic AMR bacteria and to monitor the development of AMR in non-AMR strains in the environment and clinical settings

The detection of developing antimicrobial resistance (AMR) has become a global issue. The detection of developing antimicrobial resistance has become a global issue. The growing number of AMR bacteria poses a new threat to public health. Therefore, a less laborious and quick confirmatory test becomes important for further investigations into developing AMR in the environment and in clinical settings. This study aims to present a comprehensive analysis and validation of unique and antimicrobial-resistant strains from the WHO priority list of antimicrobial-resistant bacteria and previously reported AMR strains such as Acinetobacter baumannii, Aeromonas spp., Anaeromonas frigoriresistens, Anaeromonas gelatinfytica, Bacillus spp., Campylobacter jejuni subsp. jejuni, Enterococcus faecalis, Escherichia coli, Haemophilus influenzae, Helicobacter pylori, Klebsiella pneumonia subsp. pneumoniae, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica serovar Typhimurium, Thermanaeromonas toyohensis, and Vibrio proteolyticus. Using in-house designed gene-specific primers, 18 different antibiotic resistance genes (algJ, alpB, AQU-1, CEPH-A3, ciaB, CMY-1-MOX-7, CMY-1-MOX-9, CMY-1/MOX, cphA2, cphA5, cphA7, ebpA, ECP_4655, fliC, OXA-51, RfbU, ThiU2, and tolB) from 46 strains were selected and validated. Hence, this study provides insight into the identification of strain-specific, unique antimicrobial resistance genes. Targeted amplification and verification using selected unique marker genes have been reported. Thus, the present detection and validation use a robust method for the entire experiment. Results also highlight the presence of another set of 18 antibiotic-resistant and unique genes (Aqu1, cphA2, cphA3, cphA5, cphA7, cmy1/mox7, cmy1/mox9, asaI, ascV, asoB, oxa-12, acr-2, pepA, uo65, pliI, dr0274, tapY2, and cpeT). Of these sets of genes, 15 were found to be suitable for the detection of pathogenic strains belonging to the genera Aeromonas, Pseudomonas, Helicobacter, Campylobacter, Enterococcus, Klebsiella, Acinetobacter, Salmonella, Haemophilus, and Bacillus. Thus, we have detected and verified sets of unique and antimicrobial resistance genes in bacteria on the WHO Priority List and from published reports on AMR bacteria. This study offers advantages for confirming antimicrobial resistance in all suspected AMR bacteria and monitoring the development of AMR in non-AMR bacteria, in the environment, and in clinical settings.

OmpR (TCS response regulator) of Aeromonas veronii plays a major role in drug resistance, stress resistance and virulence by regulating biofilm formation

Aeromonas veronii (A. veronii), a highly pathogenic bacteria with a wide range of hosts, widely exists in the environment of humans, animals and aquatic animals, and can cause a variety of diseases. In this study, the receptor regulator ompR in the envZ/ompR of two-component system was selected to construct a mutant strain (Δ ompR) and a complement strain (C-ompR) to explore the regulatory effect of ompR on the biological characteristics and virulence of TH0426. The results showed that the ability of biofilm formation and osmotic stress of TH0426 were significantly reduced (P < 0.001), the resistance to ceftriaxone and neomycin were slightly down-regulate when the ompR gene was deleted. At the same time, animal pathogenicity experiments showed that the virulence of TH0426 was significantly down-regulated (P < 0.001). These results indicated that ompR gene regulates the biofilm formation of TH0426, and regulates some biological characteristics of TH0426, including drug sensitivity, resistance to osmotic stress, and also affects its virulence.