[The role of lipopolysaccharide in toxicity of Francisella genus bacteria].

It was demonstrated that the lipopolysaccharides (LPS) preparations, which were isolated from all representatives of Francisella Genus bacteria, i.e. F. tularensis, F. novicida, F. novicida-like and F. philomiragia by using the method of R.P. Darveau, R.E. Hancock (1983), were not toxic for white rats and white mice. A comparative study of toxicity of live F. tularensis bacteria (both wild and LPS-defective strains) made it possible to establish a direct correlation between the toxicity of microbes and LPS chemotype. It was found that only typical strains, which synthesize the wild-type S-LPS, caused the death of white rats and white mice in 24 hours after intraperitoneal contamination (10(9), 10(10) CFU/animal). Live bacteria of F tularensis R-mutants were not able to induce a lethal infection of rats and retained only residual virulence for mice. Other representatives of Francissela genus possessed less pronounced pathogenic properties. Thus, the toxic effect was registered, in case of white rats, only for F. novicida but not for F. novicida-like or F. philomiragia. At the same time, the two last mentioned species displayed a certain degree of virulence at high challenge doses (10(9), 10(10) CFU/animal) in respect to white mice. F. philomiragia, which generated lipoolygosaccharide (LOS) with an unusual structure, was found to be least pathogenic (25-75% of dead mice). The toxicity of bacteria, killed experimentally by different means (heating, UV-light, chloroform, acetone and formalin), was studied to define the role of bacterial proteins in the realisation of F. tularensis toxic potential in vivo. No lethal effect was exerted on experimental animals by killed microbes or purified LPS preparations. Finally, the study results show a priority role of the LPS molecule in the toxic effect of F. tularensis, which is possible in vivo only if structurally valuable molecules of live bacterial cells are available.