The Emergence And Increase Of Antimicrobial Resistance Affect Virulence In Non-typhoid Salmonella

With in-depth study of bacterial resistance mechanisms, it is not only prove that the emergence of bacterial resistance to antibiotics with the relevant of long-term selective pressure of a range of antibiotic in the environment and resistance gene through plasmid or chromosomal disseminated widely or spread between the flora, also found that there may be some correlation between the bacterial antimicrobial resistance and its biological characteristics, especially for the virulence of the bacteria. As an important pathogens, Salmonella is significance in human-animal suffering, medical, veterinary and public health. Therefore, in order to investigate the emergence and increase of antimicrobial resistance affect virulence non-typhoid Salmonella, this study carried out as following:1> One antimicrobial sensitivity non-typhoid Salmonella isolates was selected as the parental strain, using the broth dilution method for the determination of the minimum inhibitory concentration of tetracycline, doxycycline, chloramphenicol, and kanamycin. Antimicrobial-resistant strains was built by the multi-step induction method with sub-inhibitory concentrations in vitro. The resistant phenotype of15construction strains and parental strains were determined by K-B method, and PCR was used to detect the distribution of resistance genes of genomic DNA and plasmid DNA in different strains. The results showed that Salmonella can produce to antimicrobial resistance mutations on long-term and low-dose exposure, the formation of the corresponding drug-resistant strains and resistance is relatively stable, but failed to obtain the corresponding resistance gene.2、The median lethal dose(LD50) of five non-typhoid Salmonella with different resistance profiles (ie, the parent strain and of resistant strains of DOX, TET+DOX, TET+DOX+CHL, TET+DOX+CHL+KAN)were determined by Cole’s improved method. The results showed that non-typhoid Salmonella pathogenicity in Kunming mice, the LD50was no significant difference between the different infected group and both in order of magnitude of108CFU.3、The kunming mouse were intraperitoneal injecction by non-typhoid Salmonella pathogenicity with different resistance profiles in LD50, collected blood and the production of pathological of the heart, liver, spleen, lung, kidney of mice in each group after infection24h,96h,168h. The CD3+CD4+, CD3+CD8+cell content of peripheral blood was were measured by flow cytometry, the concentrations of IFN-y and IL-4of serum were detected by ELISA. Autopsy results show that Salmonella infection can lead to typical enteritis and liver and spleen enlargement in mice; the results of pathological damages show that Salmonella infection can lead to systemic sepsis and inflammation in the spleen and kidney, and multiple drug-resistant strains more severe inflammatory response. The results of T lymphocyte showed that, the CD3+CD4+and CD3+CD8+cell content of each infected group is both lower than control group at different times, and CD4+/CD8+ratio is higher than the control group, indicating that non-typhoid Salmonella infection can lead to immune suppression; but the CD3+CD4+and CD3+CD8+cells content as well as CD4+/CD8+ratio is not difference significantly between each infection group, that the with the emergence and increase of antimicrobial resistance, the cellular immune did not change significantly. The detection of cytokine results showed that the concentrations of IFN-γ and IFN-γ/IL-4ratio in mice infected with non-typhoid Salmonella were increased,but the concentrations of IL-4were unchanged, indicating that the non-typhoid Salmonella infection main cause of Th1type of inflammatory response; results of the comparison between the different resistance profiles of Salmonella strains showed that the multiple drug-resistant strains inflammatory response was more severe.4、the distribution of plasmid virulence gene spvR, spvA, spvB, spvC, spvD and rck of16non-typhoid Salmonella with different resistance profiles were detected by PCR, the results all were negative.In summary, with the emergence and increase of antimicrobial resistance, the biological characteristics (LD50and virulence genes) of strains were not changed significantly; from the view of host, non-typhoid Salmonella of different resistance profiles infection, the pathological damages of multiple drug-resistant strains is more serious; immunological analysis results show that the emergence and increase of antimicrobial resistance have no significant effect on T cell immunity, but multi-drug-resistant strains induced Th1-type inflammatory response is more evident.