Development of a surface plasmon resonance (SPR) assay for rapid detection of Aeromonas hydrophila

A comprehensive understanding of the influence and molecular mechanism of exeA on the pathogenicity in Aeromonas hydrophila

Aeromonas hydrophila is a serious human and animal co-pathogenic bacterium. The type II secretion system (T2SS), a key virulence factor, is vital for the secretion of exotoxins from the bacterium. exeA gene is important for the assembly of the T2SS. However, the role of exeA in the pathogenesis of A. hydrophila is not yet clear. In this study, we constructed a stable A. hydrophila strain with exeA mutation (∆exeA-AH) using homologous recombination. Compared to wild type A. hydrophila (WT-AH), the median lethal doses (LD50) significantly increased in ∆exeA-AH. Biological properties of ∆exeA-AH were analyzed to explain the reasons for changes in virulence. The results showed that there was a significant decline in biofilm formation capacity, no significant differences were found in growth ability, hemolytic activity, motility and external structure. In order to further investigate the molecular mechanism of decreased virulence, WT-AH and ∆exeA-AH were subjected to transcriptomic analysis and validated by realtime fluorescence quantitative polymerase chain reaction and western blot. The results showed that the mutation of exeA affected the assembly of T2SS and biofilm formation capacity by decreasing the uptake capacity of iron ions. However, the abilities of T6SS, Sec system, Tat system, signaling peptidase and Lol system were enhanced, hindering further reduction in virulence. In summary, exeA mutation led to a reduction in virulence by impairing the function of T2SS and the ability of biofilm formation but impeded further decline by enhancing T6SS, Sec system, Tat system, signaling peptidase and Lol system.

flgL mutation reduces pathogenicity of Aeromonas hydrophila by negatively regulating swimming ability, biofilm forming ability, adherence and virulence gene expression

Aeromonas hydrophila is a serious human and animal co-pathogenic bacterium. Flagellum, a key virulence factor, is vital for bacterium tissue colonization and invasion. flgL is a crucial gene involved in the composition of flagellum. However, the impact of flgL on virulence is not yet clear. In this study, we constructed a stable mutant strain (△flgL-AH) using homologous recombination. The results of the attack experiments indicated a significant decrease in the virulence of △flgL-AH. The biological properties analysis revealed a significant decline in swimming ability and biofilm formation capacity in △flgL-AH and the transmission electron microscope results showed that the ∆flgL-AH strain did not have a flagellar structure. Moreover, a significant decrease in the adhesion capacity of ∆flgL-AH was found using absolute fluorescence quantitative polymerase chain reaction (PCR). The quantitative real-time PCR results showed that the expression of omp and the eight flagellum-related genes were down-regulated. In summary, flgL mutation leads to a reduction in pathogenicity possibly via decreasing the swimming ability, biofilm formation capacity and adhesion capacity, these changes might result from the down expression of omp and flagellar-related genes.

Common carp intelectin 3 (cITLN3) plays a role in the innate immune response

Intelectin is a lectin with the capacity to recognize and bind to carbohydrates. In this study, we successfully cloned cITLN3 from common carp, which consists of a signal peptide domain, a FReD domain, and an intelectin domain. The expression levels of cITLN3 were detected in various organs of common carp, including the liver, head kidney, spleen, foregut, midgut, and hindgut, with the highest expression observed in the liver. Following infection with Staphylococcus aureus (S. aureus) or Aeromonas hydrophila (A. hydrophila), the expression level of cITLN3 was significantly upregulated in all organs of common carp. Subsequently, we expressed and purified the recombinant cITLN3 protein using an E. coli expression system. The cITLN3 could aggregate both gram-positive and gram-negative bacteria in the presence of Ca2+, with a stronger affinity for gram-positive bacteria. Moreover, our study demonstrated that cITLN3 displayed a higher binding affinity towards PGN compared to LPS. Furthermore, we observed that cITLN3 had the potential to inhibit bacterial proliferation in common carp and safeguard intestinal integrity during bacterial stimulation. And the results also indicated that cITLN3 might played a role in the Toll-like receptors (TLRs) signaling pathway activation.