Hfq Regulates Efflux Pump Expression and Purine Metabolic Pathway to Increase Trimethoprim Resistance in Aeromonas veronii

Aeromonas veronii (A. veronii) is a zoonotic pathogen. It causes clinically a variety of diseases such as dysentery, bacteremia, and meningitis, and brings huge losses to aquaculture. A. veronii has been documented as a multiple antibiotic resistant bacterium. Hfq (host factor for RNA bacteriophage Qβ replication) participates in the regulations of the virulence, adhesion, and nitrogen fixation, effecting on the growth, metabolism synthesis and stress resistance in bacteria. The deletion of hfq gene in A. veronii showed more sensitivity to trimethoprim, accompanying by the upregulations of purine metabolic genes and downregulations of efflux pump genes by transcriptomic data analysis. Coherently, the complementation of efflux pump-related genes acrA and acrB recovered the trimethoprim resistance in Δhfq. Besides, the accumulations of adenosine and guanosine were increased in Δhfq in metabonomic data. The strain Δhfq conferred more sensitive to trimethoprim after appending 1 mM guanosine to M9 medium, while wild type was not altered. These results demonstrated that Hfq mediated trimethoprim resistance by elevating efflux pump expression and degrading adenosine, and guanosine metabolites. Collectively, Hfq is a potential target to tackle trimethoprim resistance in A. veronii infection.

Evaluation of the Adhesive Potential of Bacteria Isolated from Meat-Related Sources

Microbial adhesion constitutes the transition of microorganisms from a planktonic mode to a static one. It promotes the formation of biofilm which is responsible for spoilage, foodborne diseases, and corrosion in the food processing industry. In this study, the adhesive potential of fourteen meat-borne bacterial isolates belonging to seven different genera was investigated. All strains were found able to colonize polystyrene surfaces with different levels of firmness. Significant variations were determined in assays of bacterial hydrophobicity and motility. Among the 14 strains, Pseudomonas fragi, Aeromonas salmonicida II, Serratia liquefaciens, Citrobacter braakii, Pseudomonas putida, and Aeromonas veronii had a strong hydrophobic force, while the isolates of Lactobacillus genus showed the most hydrophilic property. In terms of motility, Citrobacter braakii and Escherichia coli exhibited exceptional swarming and swimming abilities, whilst conservatively weak performances were observed in the Lactobacillus strains. Furthermore, the majority of the isolates were predominantly electron donors and weak electron acceptors. Overall, a high level of correlation was observed between biofilm-forming ability with cell surface hydrophobicity and Lewis acid–base properties, whereas the contribution of motility in bacterial adhesion could not be confirmed. Research on the adhesive performance of foodborne bacteria is potentially conducive to developing novel control strategies, such as food processing equipment with specific surfaces, not facilitating attachment.

A New Outbreak in Sea Bass Farming in Turkey: Aeromonas veronii

Turkey produces most of the European sea bassin Europe and bacterial diseases are the main cause of economic loss during the production cycle. This research presents the first extended study of the Aeromonas veronii infection in sea bass on the Turkish coast of the Aegean Sea. An outbreak was observed in three different sea bass farms and diseased fish with clinical symptoms were sampled. Abdominal distention, hemorrhages on the body and anus, enlarged spleen and liver, and hemorrhages in the internal organs were detected from clinical and pathological examinations. Biochemical and molecular identification confirmed the pathogen to be A.veronii.The histopathological observations demonstrated that the pathogen caused bacterial colonies in the fibrous connective tissue, granuloma, and vacuolar degeneration.The primary causes of the disease were proved through an infection experiment. 80% and 90% mortality were calculated in 0.85 x 108 CFU ml-1 and 1.28 x 108 CFU ml-1 experimentally infected groups with clinical and pathological signs of the disease respectively. Recently, the pathological symptoms of the disease had been confused with pasteurellosis infection in cage farms but the presence of A.veronii has been confirmed in the current study. A detailed study is needed to investigate the overall status of the disease in the Aegean Sea in order to design an appropriate preventive strategy.

Characterisation of Extracellular Enzyme-Producing Microorganisms From the Gut of Nile Tilapia, Oreochromis niloticus (Linnaeus, 1758)

The current priority in the aquaculture industry is to replace fish meal with cheaper but efficient protein sources like plant-based feedstuffs to support global expansion and sustainability. Hence, research has focused on finding novel ways to increase the digestibility of plant-based diets. Exogenous enzymes have emerged as an excellent alternative to improve nutrient digestibility of the diet in animals, including fish. The present study aims to explore exogenous enzyme-producing bacteria in the gastrointestinal (GI) tract of Nile tilapia (Oreochromis niloticus (Linnaeus, 1758)). Two Gram-negative enzyme-producing (amylase, xylanase, and lipase) bacterial strains viz. Aeromonas veronii ONKP1 (GenBank accession no. MN602971) and Stenotrophomonas maltophilia ONKP2 (GenBank accession no. MN602972) were identified by biochemical tests and 16s RNA analysis. They are capable of utilising citrate, maltose, glucose, and gelatine. Besides, A. veronii ONKP1 can utilise mannitol, sucrose, and lactose, whereas S. maltophilia ONKP2 is catalase and urease positive. Aeromonas veronii ONKP1 was superior in terms of enzyme production to S. maltophilia ONKP2. Stenotrophomonas maltophilia ONKP2 is a rarely reported strain, specifically from healthy fish. Amylase, xylanase, and lipase could be used as feed additives for fermenting plant products and producing prebiotics like xylooligosaccharides. Further, this study might help understand the role of gut-associated bacteria viz. A. veronii and S. maltophilia, in fish nutrition.