Analysis of virulence and inflammatory potential of Shigella flexneri purine biosynthesis mutants.
Several Shigella flexneri mutants with defects in aromatic amino acid and/or purine biosynthesis have been evaluated as vaccines in humans or in animal models. To be suitable as a vaccine, a mutant has to show virulence attenuation, minimal reactogenicity, and a good immunogenic potential in animal models. With this aim, we have constructed five S. flexneri 5 (wild-type strain M90T) mutants with inactivation of one or two of the loci purEK, purHD, and guaBA, governing early or late steps of purine biosynthesis. The mutants have been analyzed in vitro in cell cultures and in vivo in the Sereny test and in the murine pulmonary model of shigellosis. M90T guaBA, M90T guaBA purEK, M90T guaBA purHD, and M90T purHD purEK gave a negative result in the Sereny test. In contrast, in the murine pulmonary model all of the strains had the same 50% lethal dose as the wild type, except M90T guaBA purHD, which did not result in death of the animals. Nevertheless, bacterial counts in infected lungs, immunohistochemistry, and reverse transcription-PCR analysis of mRNAs for tumor necrosis factor alpha (TNF-alpha), gamma interferon (IFN-gamma), interleukin-1beta (IL-1beta), IL-6, IL-12, and inducible nitric oxide synthase (iNOS) revealed significant differences among the strains. At 72 h postinfection, M90T guaBA purHD still induced proinflammatory cytokines and factors such as IL-1beta, IL-6, TNF-alpha, and iNOS, along with cytokines such as IL-12 and IFN-gamma. Moreover, in the absence of evident lesions in murine tissues, this mutant highly stimulated major histocompatibility complex class II expression, showing a significant ability to activate the innate immunity of the host.
Cersini
Antonella
A
Dipartimento di Biologia Cellulare e dello Sviluppo, Sezione di Scienze Microbiologiche, Università La Sapienza, 00185 Rome, Italy.
Martino
Maria Celeste
MC
Martini
Irene
I
Rossi
Giacomo
G
Bernardini
Maria Lina
ML
D000281:Administration, Intranasal; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015169:Colony Count, Microbial; D004195:Disease Models, Animal; D004405:Dysentery, Bacillary / Q000382:microbiology / Q000503:physiopathology; D005260:Female; D006367:HeLa Cells; D006801:Humans; D007249:Inflammation / Q000503:physiopathology*; D008168:Lung / Q000276:immunology / Q000382:microbiology; D008171:Lung Diseases / Q000382:microbiology / Q000503:physiopathology; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D011687:Purines / Q000096:biosynthesis*; D012763:Shigella flexneri / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000472:pathogenicity*; D014774:Virulence
D001426:Bacterial Proteins; D011687:Purines; C030985:purine