Transcriptional profile of the intracellular pathogen Brucella melitensis following HeLa cells infection.

Brucella spp. infect hosts primarily by adhering and penetrating mucosal surfaces; however the initial molecular phenomena of this host:pathogen interaction remain poorly understood. Using cDNA microarray analysis, we characterized the transcriptional profile of the intracellular pathogen Brucella melitensis at 4 h (adaptational period) and 12 h (replicative phase) following HeLa cells infection. The intracellular pathogen transcriptome was determined using initially enriched and then amplified B. melitensis RNA from total RNA of B. melitensis-infected HeLa cells. Analysis of microarray results identified 161 and 115 pathogen genes differentially expressed at 4 and 12 h p.i., respectively. In concordance with phenotypic studies, most of the genes expressed were involved in pathogen growth and metabolism, and were down-regulated at the earliest time point (78%), but up-regulated at 12 h p.i. (75%). Further characterization of specific genes identified in this study will elucidate biological processes and pathways to help understand how both host and Brucella interact during the early infectious process to the eventual benefit of the pathogen and to the detriment of the naïve host.