EsxA might as a virulence factor induce antibodies in patients with Staphylococcus aureus infection

Staphylococcus aureus (S. aureus) is an important human pathogen, which commonly causes the acquired infectious diseases in the hospital and community. Effective and simple antibiotic treatment against S. aureus-related disease becomes increasingly difficult. Developing a safe and effective vaccine against S. aureus has become one of the world's hot spots once again. The key issue of developing the vaccine of S. aureus is how to find an ideal key pathogenic gene of S. aureus. It was previously suggested that EsxA might be a very important factor in S. aureus abscess formation in mice, but clinical experimental evidence was lacking. We therefore expressed EsxA protein through prokaryotic expression system and purified EsxA protein by Ni-affinity chromatography. ELISA was used to detect the anti-EsxA antibodies in sera of 78 patients with S. aureus infection and results showed that the anti-EsxA antibodies were positive in the sera of 19 patients. We further analyzed the EsxA positive antibodies related strains by antimicrobial susceptibility assay and found that all of the corresponding strains were multi-drug resistant. Among those multi-drug resistant strains, 73.7% were resistant to MRSA. The results indicated EsxA is very important in the pathogenesis of S. aureus. We suggested that the EsxA is very valuable as vaccine candidate target antigens for prevention and control of S. aureus infection.

Expression of fljB: z66 on a linear plasmid of Salmonella enterica serovar typhi is dependent on FliA and FlhDC and regulated by OmpR

Salmonella enterica serovar Typhi z66-positive strains have two different flagellin genes, fliC:d/j and fljB:z66, located on the chromosome and on a linear plasmid, respectively. To investigate the mechanism underlying the expressional regulation of fljB:z66, gene deletion mutants of the regulators FliA, FlhDC, and OmpR were constructed in this study. The expression levels of fliC and fljB:z66 were analyzed by qRT-PCR in the wild-type strain and mutants at high and low osmolarity. The results show that the expression levels of both fljB:z66 and fliC were greatly reduced in fliA and flhDC mutants under both high and low osmotic conditions. In the ompR mutant, the expression levels of fljB:z66, fliC, fliA, and flhD were increased at low osmotic conditions. SDS-PAGE and western blotting analysis of the secreted proteins revealed that the FljB:z66 was almost absent in the fliA and flhDC mutants at both high and low osmolarity. In the wild-type strain, the fljB:z66 was more highly expressed under high-osmolarity conditions than under low-osmolarity conditions. However, this difference in expression disappeared in the ompR mutant. Translational expression assay of FljB:z66 showed that the FljB:z66 expression was decreased in ompR mutant at both low and high osmolarity. These results suggest that the expression of fljB:z66 in S. enterica serovar Typhi is dependent on FliA and FlihDC, and OmpR can regulate the expression and secretion of FljB:z66 in different osmolarity.