Detection and analysis of gene expression during infection by in vivo expression technology

Many limitations associated with the use of in vitro models for study of ba cterial pathogenesis can be overcome by the use of technologies that detect pathogen gene expression during the course of infection within an intact a nimal. In vivo expression technology (IVET) accomplishes this with versatil ity: it has been developed with a variety of reporter systems which allow f or either in vivo selection or ex vivo screening. Selectable gene fusion sy stems generally allow for the complementation of a bacterial metabolic defe ct that is lethal in vivo, or for antibiotic resistance during the course o f in vivo antibiotic challenge. In contrast, the screenable gene fusion sys tem uses a site-specific DNA recombinase that, when expressed in vivo, exci ses a selectable gene cassette from the bacterial chromosome. Loss of this cassette can then be either screened or selected for ex vivo. The recombina se-based IVET can be used to detect genes that are transcriptionally induce d during infection, including those expressed transiently or at low levels and, in addition, can be used to monitor the spatial and temporal expressio n of specific genes during the course of infection.