SURVIVAL OF B. PERTUSSIS IN HUMAN MACROPHAGES INVOLVES BACTERIAL VIRULENCE MODULATION AND THE EXPRESSION OF GENES IMPLICATED IN IRON STRESS RESPONSE

VALDEZ, HUGO; LAMBERTI YANINA; GORGOJO JUAN PABLO; ALVAREZ HAYES, JIMENA; RODRIGUEZ, MARÍA EUGENIA

Baltimore

Simposio; 9th International Bordetella Symposium; 2010

We recently showed that the encounter of B. pertussis with human macrophages in the absence of opsonic antibodies leads to the intracellular survival of a significant number of bacteria which, after a lag period, are able to replicate inside early endosomes. This ability to replicate seems to require bacterial adaptation to the intracellular environment. Only 24 hours after uptake the number of bacteria start to increase. The goal of this study was to gain a first insight into the adaptive genetic mechanisms utilized by B. pertussis to survive and eventually grow inside macrophages. In this approach we focused on two groups of genes usually implicated in pathogen adaptation to the phagosomal environment: genes involved in bacterial virulence and eventual host cell intoxication, and genes involved in iron homeostasis, one of the main stressors intracellular pathogens has to face. Using semi-quantitative RT-PCR we determined the mRNA expression of selected genes indicatives of i) iron stress response (irp1-3, fumC, sodA) (Vidakovics, et al. J. Proteome Res. 2007: 2518-2528), and ii) bacterial virulence phase (cyaA, bipA, vrg-6). By comparing gene expression of infecting bacteria and bacteria that has been inside the human macrophage for up to 48 h the following major results were obtained: (i) fumC, irp1-3, and sodA were found significantly upregulated in bacteria inside the cell suggesting either iron starvation or the need to regulate toxic amounts of free iron in the phagosomal environment; ii) cyaA was found downregulated while bipA was upregulated in bacteria inside the cell suggesting a possible intermediate virulence state in intracellular bacteria. Accordingly, no vrg-6 expression was observed. These results constitute the first indication that B. pertussis undergoes an adaptive response that enables its intracellular growth