Peculiarities of Vesiculation in Virulent and Avirulent LPS-Defective Strains of Francisella tularensis of Various Subspecies

The aim of the study was to compare outer membrane vesicles (OMVs) and their composition in virulent and avirulent (LPS-defective) strains of Fracisella tularensis of various subspecies. Materials and methods. The vesiculation process in F. tularensis bacteria was studied using transmission electron microscopy. OMVs preparations were obtained and characterized by their composition using immunological methods: antibody neutralization test, immunochromatographic analysis, dot and immunoblotting. Results and discussion. It has been found that all natural virulent strains with the S type lipopolysaccharide (LPS) are able to produce two forms of vesicles – spherical and tubular (“tubes”), specific for F. tularensis. OMVs formation has not been registered in avirulent LPS-defective strains. It is revealed that vesicles of strains of various subspecies show their own individual morphological features. The tubes of F. tularensis subsp. mediasiatica are larger in size as compared to those of the subsp. holarctica strain. This is probably the reason why vesicle preparations from F. tularensis subsp. mediasiatica obtained using filters with a diameter of pores being 0.22 μm contained a significantly reduced number of tubular forms. A method of disinfection of bacterial suspensions using gentamycine, which does not affect the morphology and antigenic activity of vesicles, is proposed. A comparative study of several series of concentrated OMVs preparations obtained from different strains has revealed that all samples had antigenic activity in the precipitation Ouchterlony test, antibody neutralization test, immunochromatografic assay, dot-blot and immunoblotting. Immunodominant antigen – LPS and several major antigenic proteins have been detected in the preparations. Differences in the composition of vesicle proteins in the strains of various F. tularensis subspecies have been identified.

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