Abstract
ABSTRACTFrancisella tularensis is the causative agent of tularemia and a potential bioterrorism agent. In the present study, we isolated, identified, and quantified the proteins present in the membranes of the virulent type A strain, Schu S4, and the attenuated type B strain, LVS (live vaccine strain). Spectral counting of mass spectrometric data showed enrichment for membrane proteins in both strains. Mice vaccinated with whole LVS membranes encapsulated in poly (lactic-co-glycolic acid) (PLGA) nanoparticles containing the adjuvant polyinosinic-polycytidylic acid [poly(I·C)] showed significant protection against a challenge with LVS compared to the results seen with naive mice or mice vaccinated with either membranes or poly(I·C) alone. The PLGA-encapsulated Schu S4 membranes with poly(I·C) alone did not significantly protect mice from a lethal intraperitoneal challenge with Schu S4; however, this vaccination strategy provided protection from LVS challenge. Mice that received the encapsulated Schu S4 membranes followed by a booster of LVS bacteria showed significant protection with respect to a lethal Schu S4 challenge compared to control mice. Western blot analyses of the sera from the Schu S4-vaccinated mice that received an LVS booster showed four immunoreactive bands. One of these bands from the corresponding one-dimensional (1D) SDS-PAGE experiment represented capsule. The remaining bands were excised, digested with trypsin, and analyzed using mass spectrometry. The most abundant proteins present in these immunoreactive samples were an outer membrane OmpA-like protein, FopA; the type IV pilus fiber building block protein; a hypothetical membrane protein; and lipoproteins LpnA and Lpp3. These proteins should serve as potential targets for future recombinant protein vaccination studies.
Highlights
Francisella tularensis is the causative agent of tularemia and a potential bioterrorism agent
Membranes were initially isolated from lysed Schu S4 or live vaccine strain (LVS) strains of F. tularensis using differential centrifugation
We obtained purified fractions of both membranes using the presence or absence of LPS as an indicator of the presence of the respective membrane fractions. This allowed us to obtain high-resolution proteomic analyses of both membrane fractions with little overlap. These studies indicated that the membrane proteins of the two strains were remarkably similar as our analysis identified only two proteins present in F. tualarensis Schu S4 which were not present in LVS, the type IV pilus fiber building block protein (Q5NGF5; gene, FTT_0890c), and a hypothetical lipoprotein (Q5NGE3; gene, FTT_0902)
Summary
Francisella tularensis is the causative agent of tularemia and a potential bioterrorism agent. The low infectious dose, the high potential mortality/morbidity rates, and the ability to be disseminated as an aerosol make this organism a potential agent for bioterrorism; the Centers for Disease Control and Prevention (CDC) has classified F. tularensis as a Tier 1 pathogen [3]. An attenuated type B strain designated the live vaccine strain (LVS) was developed in the Soviet Union and given to the United States in the 1950s [4] This vaccine has been used to immunize those at highest risk of infection, but widespread use of this vaccine was not implemented in the United States due to adverse reactions and residual virulence, and it can be presumed that the vaccine is no longer available for general use for these reasons [2, 5,6,7]. The search for a well-defined, protein-based vaccine able to protect against Schu S4 is ongoing
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
