Measurement of bacterial gene expression in vivo

The complexities of bacterial gene expression during mammalian infection ca nnot be addressed by in vitro experiments. We know that the infected host r epresents a complex and dynamic environment, which is modified during the i nfection process, presenting a variety of stimuli to which the pathogen mus t respond if it is to be successful. This response in involves hundreds of ivi (in vivo-induced) genes which have recently been identified in animal a nd cell culture models using a variety of technologies including in vivo ex pression technology, differential fluorescence induction, subtractive hybri dization and differential display Proteomic analysis is beginning to be use d to identify IVI proteins, and has benefited from the availability of geno me sequences for increasing numbers of bacterial pathogens. The patterns of bacterial gene expression during infection remain to be investigated. Are ivi genes expressed in an organ-specific or cell-type-specific fashion? New approaches are required to answer these questions. The uses of the immunol ogically based in vivo antigen technology system, in situ PCR and DNA micro array analysis are considered. This review considers existing methods for e xamining bacterial gene expression in vivo, and describes emerging approach es that should further our understanding in the future.