The role of exotoxin A in the pathogenesis of Pseudomonas aeruginosa burn wound infection
Fogle, Matthew R.
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Pseudomonas aeruginosa, gram-negative opportunistic pathogen, causes severe infections in immunocompromised hosts. The mortality rate among P. aeruginosa-infected bum patients may reach as high as 50%. Due to their immunocompromised status, passive rather than active immunization may be more effective in protecting burn patients against infection. As a potential multivalent Ab-based therapy, specific polyclonal antibodies against four P. aeruginosa virulence factors, including exotoxin A (ETA), were prepared. In this study, we analyzed the in vivo effects of ETA and the ability of ETA antibody (ETA-Ab) to neutralize these effects. Adult mice injected with purified ETA suffered 100% mortality. The cytosolic DNA ofthe hepatocytes of these mice was fragmented indicating ETA-induction of apoptosis. In addition, multiprobe RNase protection assays showed that ETA up-regulates the expression of the genes for the proinflammatory cytokines as well as the apoptosis genes in the livers of ETAinjected mice. No mortality was detected among animals that were injected with ETAAb after ETA injection. In addition, the ETA-induced hepatocyte DNA fragmentation and the upregulation ofthe above-described genes were eliminated. The role of ETA during a P. aeruginosa infection was examined by determining the in vivo virulence of P aeruginosa PA103 and its isogenic, ETA-deficient mutant PA103Ù::toxA using the thermally injured mouse model. The lethality of PA103Ù::toxA was significantly reduced compared to PA103. In addition, PA103Ù::toxA was defective in its spread within the bumed skin, as well as in the livers and spleens of infected mice. These results suggest that: (1) part of ETA lethality is due to induced apoptosis in hepatocytes, (2) specific cytokines are produced in response to ETA, (3) ETA-Ab neutralizes these effects, and (4) ETA contributes to the spread of P. aeruginosa during bum wound infection.