Induction of TNF-alpha mRNA in murine macrophages by virulent and avirulent strains of Salmonella choleraesuis serovar typhimurium and serovar Choleraesuis

Association of a regulatory gene, slyA with a mouse virulence of Salmonella serovar Choleraesuis

The influence of slyA gene, originally found in Salmonella serovar Typhimurium as a regulatory gene for the expression of virulence genes, on a mouse virulence of S. serovar Choleraesuis was investigated by using an slyA-defective mutant. The defective mutant was constructed by the insertion of a kanamycin-resistance gene (aph) into the cloned slyA gene, and the homologous recombination with the intact slyA gene on the chromosome. The mutant strain showed the LD50 value for BALB/c mouse approximately 10(5) higher than that of the parent strain. The increase of the LD50 value was the same order as that shown by the mutation of the slyA gene of S. serovar Typhimurium, although LD50 of the wild-type strain of S. serovar Choleraesuis was 40-fold higher than that of S. serovar Typhimurium. The time course of infection observed in the mice organs also proved the clear difference of the virulence between the parent and the mutant strains. These results suggested that the slyA gene product functions as a virulence-associated regulator also in S. serovar Choleraesuis.

Production of chemokines in vivo in response to microbial stimulation

Members of the chemokine gene superfamily are known to play a central role in leukocyte extravasation; however, their involvement in acute inflammation in response to micro-organisms has not yet been well studied. We have therefore investigated the role of murine macrophage-inflammatory protein (muMIP) 1alpha and muMIP-2 in the inflammatory response mounted against the bacteria Salmonella enteritidis and the Sacchromyces cerevisiae cell wall component, zymosan. Leukocyte extravasation was monitored in murine s.c. air pouches. Both agonists induced accumulation of leukocytes in a dose- and time-dependent manner, with the response peaking after 4 h and declining thereafter. The inflammatory exudate comprised mainly neutrophils; however, an increase in eosinophil accumulation was also observed in response to zymosan. The production of both muMIP-1alpha and muMIP-2 increased with time in response to both the agonists, although production was more sustained in response to the bacteria. Prior treatment of mice with neutralizing Abs against muMIP-1alpha or muMIP-2, either alone or in combination, failed to attenuate the accumulation of leukocytes in response to the agonists. In contrast, the anti-muMIP-2 Abs significantly inhibited leukocyte recruitment in response to S. enteritidis in complement-deficient mice. Taken together, these data show that while muMIP-1alpha and muMIP-2 are produced in response to phagocytosis of micro-organisms in s.c. tissue, under these circumstances components of the complement pathway appear to play a dominant role in the recruitment of neutrophils.

Study of the role of the htrB gene in Salmonella typhimurium virulence

We have undertaken a study to investigate the contribution of the htrB gene to the virulence of pathogenic Salmonella typhimurium. An htrB::mini-Tn10 mutation from Escherichia coli was transferred by transduction to the mouse-virulent strain S. typhimurium SL1344 to create an htrB mutant. The S. typhimurium htrB mutant was inoculated into mice and found to be severely limited in its ability to colonize organs of the lymphatic system and to cause systemic disease in mice. A variety of experiments were performed to determine the possible reasons for this loss of virulence. Serum killing assays revealed that the S. typhimurium htrB mutant was as resistant to killing by complement as the wild-type strain. However, macrophage survival assays revealed that the S. typhimurium htrB mutant was more sensitive to the intracellular environment of murine macrophages than the wild-type strain. In addition, the bioactivity of the lipopolysaccharide (LPS) of the htrB mutant was reduced compared to that of the LPS from the parent strain as measured by both a Limulus amoebocyte lysate endotoxin quantitation assay and a tumor necrosis factor alpha bioassay. These results indicate that the htrB gene plays a role in the virulence of S. typhimurium.