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. 2004 Feb;72(2):908-15.
doi: 10.1128/iai.72.2.908-915.2004.

Generation of Yersinia Pestis Attenuated Strains by Signature-Tagged Mutagenesis in Search of Novel Vaccine Candidates

Free PMC article

Generation of Yersinia Pestis Attenuated Strains by Signature-Tagged Mutagenesis in Search of Novel Vaccine Candidates

Yehuda Flashner et al. Infect Immun. .
Free PMC article


In a search for novel attenuated vaccine candidates for use against Yersinia pestis, the causative agent of plague, a signature-tagged mutagenesis strategy was used and optimized for a subcutaneously infected mouse model. A library of tagged mutants of the virulent Y. pestis Kimberley53 strain was generated. Screening of 300 mutants through two consecutive cycles resulted in selection of 16 mutant strains that were undetectable in spleens 48 h postinfection. Each of these mutants was evaluated in vivo by assays for competition against the wild-type strain and for virulence following inoculation of 100 CFU (equivalent to 100 50% lethal doses [LD50] of the wild type). A wide spectrum of attenuation was obtained, ranging from avirulent mutants exhibiting competition indices of 10(-5) to 10(-7) to virulent mutants exhibiting a delay in the mean time to death or mutants indistinguishable from the wild type in the two assays. Characterization of the phenotypes and genotypes of the selected mutants led to identification of virulence-associated genes coding for factors involved in global bacterial physiology (e.g., purH, purK, dnaE, and greA) or for hypothetical polypeptides, as well as for the virulence regulator gene lcrF. One of the avirulent mutant strains (LD50, >10(7) CFU) was found to be disrupted in the pcm locus, which is presumably involved in the bacterial response to environmental stress. This Kimberley53pcm mutant was superior to the EV76 live vaccine strain because it induced 10- to 100-fold-higher antibody titers to the protective V and F1 antigens and because it conferred efficacious protective immunity.


FIG. 1.
FIG. 1.
Accumulation of Y. pestis strain Kimberley53 in mice organs following s.c. infection. Groups of eight OF1 female mice were infected s.c. with three different doses of Y. pestis Kimberley53. At different times three mice were sacrificed, and bacteria were extracted from the spleen (solid symbols) and liver (open symbols) of each mouse for counting (by plating on BHI and BIN agar media). (A, B, and C) Survival and bacterial counts in organs following infection with 103, 104, and 105 CFU/mouse, respectively. The arrows indicate times when the first morbidity signs were observed.

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