Comparative on characteristics and pathogenicity of four strains of Aeromonas schubertii isolated from snakehead hybrid

Abstract:

[Background] Aeromonas schubertii is a gram-negative short rod-shaped bacterium. It is a human-animal-fish co-infected conditional pathogen and can cause various human diseases, which has been reported frequently in recent years. [Objective] In order to provide references for the prevention and control of A. schubertii caused diseases in aquaculture , the physiological and biochemical characteristics, pathogenicity as well as the sensitivity to common antibiotics of the 4 strains of A. schubertii (WL-4, ZL-1, ZL-13, D075) isolated from hybrid snakehead have been analyzed and compared. [Methods] The physiological and biochemical characteristics of the strains were detected by automatic microorganism identification instrument, the gyrB and 16S rRNA gene sequences of the strains were compared by PCR and sequencing. The expression of virulence factor was tested by modified plate method and the carrying status of virulence gene and antibiotic resistance gene were detected by PCR. The differences of pathogenicity for 4 strains were analyzed by artificial injection infection. The minimum inhibitory concentration of 15 antimicrobial agents against the strains were measured by double microdilution method. [Results] As ATCC43700, a human origin strain, was used as a reference strain, the physiological and biochemical characteristics of these 5 A. schubertii were basically the same and the similarity of the gyrB and 16S rRNA genes of them were 99.57% and 100% respectively. five strains are clustered into one group though cluster analysis. All of them showed hemolytic activity, protease activity and lipase activity, but there are differences on virulence genes among 5 strain. ATCC43700 carried hlyA, ela, lip, ahal and act, while WL-4, ZL-1, ZL-13 and D075 carried hlyA, ela, lip, ahal and aer. four strains isolated from snakehead hybrid showed different pathogenicity. The mortality rate of hybrid snakehead by artificial injection of WL-4, ZL-1, ZL-13 and D075 at 1.2×105 CFU/mL solution was 30%, 40%, 70% and 80% respectively. The antibiotic sensitivity and antibiotic resistance gene are also different among them. [Conclusion] There are differences on pathogenicity and antibiotic sensitivity among the four strains of A. schubertii from hybrid snakehead. The results of this study are helpful to further research on the pathogenesis of A. schubertii and the prevention and control methods against it in aquaculture.