Expression of Nocardia brasiliensis superoxide dismutase during the early infection of murine peritoneal macrophages

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Abstract:

Nocardia brasiliensis is the main agent of actinomycetoma in Mexico, but little is known about its virulence and molecular pathogenic pathways. These facultative intracellular bacteria are able to survive and divide within the host phagocytic cells, in part by neutralizing the reactive oxygen intermediates. Superoxide dismutase (SOD) participates in the intracellular survival of several bacterial species and, in particular, constitutes one of Nocardia asteroides virulence factors. To clarify SOD participation in the N. brasiliensis early infective process, we report its isolation and the consequent comparison of its transcript level. A 630 bp polymerase chain reaction fragment that included most of the coding sequence of N. brasiliensis sodA was cloned. A competitive assay was developed, allowing comparison of bacterial sod expression in exponential culture and 1 h after infecting peritoneal macrophages from BALB/c mice. At that time, there were viable bacteria in the macrophages. The intracellular bacteria presented a clear decrease in their sod transcript amount, although their 16S rRNA (used as an internal control) and hsp levels were maintained or slightly increased, respectively. These results indicate that sodA transcription is not maintained within the SOS bacterial response induced by phagosomal conditions. Further kinetics will be necessary to precisely define sod transcriptional regulation during N. brasiliensis intra-macrophage growth.Key words: Nocardia brasiliensis, superoxide dismutase, macrophage infection, differential gene expression.

Nocardia brasiliensis est l'agent principal de l'actinomycétome au Mexique, mais ses mécanismes de virulence et pathogenèse n'ont pas encore été élucidés. Ces bactéries intracellulaires peuvent survivre et se multiplier à l'intérieur des phagocytes de l'hôte en partie grâce à la neutralization des dérivés réactifs de l'oxygène. La superoxyde dismutase (SOD) est responsable de la survie à l'intérieur de la cellule de plusieurs espèces bactériennes et l'un des facteurs de la virulence de Nocardia asteroides. Pour étudier la participation de SOD durant les premières étapes de l'infection, nous avons obtenu le gène et comparé par RT-PCR compétitive la quantité de ses transcrits. Un fragment de 630 pb incluant la plupart de la séquence codante de sodA, a été cloné. Une fois monté, l'essai compétitif a permis la comparaison de l'expression de sod dans les bactéries en culture exponentielle et après 1 h d'infection de macrophages péritonéaux de souris BALB/c. A ce temps d'infection, les bactéries présentent une nette diminution des ARN de sod alors que ceux de 16S ARNr (utilizés comme control interne) et de hsp restent constants ou augmentent légèrement. Ces résultats indiquent que la transcription de sodA n'est pas maintenue durant la réponse bactérienne SOS induite par les conditions du phagosome. De plus amples études cinétiques sont nécessaires pour préciser la régulation transcriptionnelle de sod durant la survie de N. brasiliensis à l'intérieur du macrophage.Mots clés : Nocardia brasiliensis, superoxide dismutase, macrophage infecte, expression des gènes.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2006

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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