title: Virulence of Francisella spp. in chicken embryos.
abstract: We examined the utility of infecting chicken embryos as a means of evaluating the virulence of different Francisella sp. strains and mutants. Infection of 7-day-old chicken embryos with a low dose of F. novicida or F. tularensis subsp. holarctica live vaccine strain (LVS) resulted in sustained growth for 6 days. Different doses of these two organisms were used to inoculate chicken embryos to determine the time to death. These experiments showed that wild-type F. novicida was at least 10,000-fold more virulent than the LVS strain. We also examined the virulence of several attenuated mutants of F. novicida, and they were found to have a wide range of virulence in chicken embryos. Fluorescent microscopic examination of infected chicken embryo organs revealed that F. tularensis grew in scattered foci of infections, and in all cases the F. tularensis appeared to be growing intracellularly. These results demonstrate that infection of 7-day-old chicken embryos can be used to evaluate the virulence of attenuated F. tularensis strains.
authors.affiliation: Department of Biochemistry and Microbiology, PO Box 3055 STN CSC, University of Victoria, Victoria, British Columbia, V8W 3P6, Canada.
authors.forename: Eli B
authors.initials: EB
authors.lastname: Nix
authors.forename: Karen K M
authors.initials: KK
authors.lastname: Cheung
authors.forename: Diana
authors.initials: D
authors.lastname: Wang
authors.forename: Na
authors.initials: N
authors.lastname: Zhang
authors.forename: Robert D
authors.initials: RD
authors.lastname: Burke
authors.forename: Francis E
authors.initials: FE
authors.lastname: Nano
mesh_terms: D000818:Animals; D001431:Bacteriological Techniques; D002642:Chick Embryo / Q000382:microbiology*; D015169:Colony Count, Microbial; D005603:Francisella / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D005604:Francisella tularensis / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000662:veterinary; D008856:Microscopy, Fluorescence; D011201:Poultry Diseases / Q000382:microbiology; D014406:Tularemia / Q000382:microbiology / Q000662:veterinary; D014774:Virulence / Q000235:genetics