title: The Fischer 344 rat reflects human susceptibility to francisella pulmonary challenge and provides a new platform for virulence and protection studies.
abstract: BACKGROUND
  The pathogenesis of Francisella tularensis, the causative agent of tularemia, has been primarily characterized in mice. However, the high degree of sensitivity of mice to bacterial challenge, especially with the human virulent strains of F. tularensis, limits this animal model for screening of defined attenuated vaccine candidates for protection studies.
  
  
  RESULTS
  We analyzed the susceptibility of the Fischer 344 rat to pulmonary (intratracheal) challenge with three different subspecies (subsp) of F. tularensis that reflect different levels of virulence in humans, and characterized the bacterial replication profile in rat bone marrow-derived macrophages (BMDM). In contrast to the mouse, Fischer 344 rats exhibit a broader range of sensitivity to pulmonary challenge with the human virulent subsp. tularensis and holarctica. Unlike mice, Fischer rats exhibited a high degree of resistance to pulmonary challenge with LVS (an attenuated derivative of subsp. holarctica) and subsp. novicida. Within BMDM, subsp. tularensis and LVS showed minimal replication, subsp. novicida showed marginal replication, and subsp. holartica replicated robustly. The limited intramacrophage replication of subsp. tularensis and novicida strains was correlated with the induction of nitric oxide production. Importantly, Fischer 344 rats that survived pulmonary infection with subsp. novicida were markedly protected against subsequent pulmonary challenge with subsp. tularensis, suggesting that subsp. novicida may be a useful platform for the development of vaccines against subsp. tularensis.
  
  
  CONCLUSIONS
  The Fischer 344 rat exhibits similar sensitivity to F. tularensis strains as that reported for humans, and thus the Fischer 344 ray may serve as a better animal model for tularemia vaccine development.
authors.affiliation: Department of Biology, University of Texas at San Antonio, South Texas Center for Emerging Infectious Diseases, San Antonio, Texas, United States of America.
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Ray
authors.forename: Ping
authors.initials: P
authors.lastname: Chu
authors.forename: Terry H
authors.initials: TH
authors.lastname: Wu
authors.forename: C Rick
authors.initials: CR
authors.lastname: Lyons
authors.forename: Ashlesh K
authors.initials: AK
authors.lastname: Murthy
authors.forename: M Neal
authors.initials: MN
authors.lastname: Guentzel
authors.forename: Karl E
authors.initials: KE
authors.lastname: Klose
authors.forename: Bernard P
authors.initials: BP
authors.lastname: Arulanandam
mesh_terms: D000818:Animals; D001428:Bacterial Vaccines; D004198:Disease Susceptibility / Q000175:diagnosis*; D005604:Francisella tularensis / Q000254:growth & development / Q000472:pathogenicity*; D006801:Humans; D008168:Lung / Q000382:microbiology*; D008264:Macrophages / Q000382:microbiology; D023421:Models, Animal; D051381:Rats; D011916:Rats, Inbred F344 / Q000382:microbiology*; D014406:Tularemia / Q000628:therapy*; D014774:Virulence
chemical_list: D001428:Bacterial Vaccines