Gene Expression Microarrays and Host Pathogen Interaction

Bacterial pathogens adapt to their host environments predominantly by switching on complex transcriptional programs, and whole-genome microarray experiments promise to uncover this complexity. By monitoring microbial gene expression arrays, one can predict the functions of uncharacterized genes, probe the physiological adaptations made under various environmental conditions, identify virulence-associated genes, and predict the effects of drugs. Increased experimental efficiency permits high throughput and whole-genome expression profiling of pathogens and hosts [68]. Such a gene expression approach has recently been used for characterization of the etiological agent of plague, Yersinia pestis. This pathogen must acclimatize itself to temperature shifts between the temperature (26 °C) for flea blockage and the body temperature (37 °C) of warm-blooded hosts during its life cycle [69]. The array results provided a genome-wide profile of gene transcription induced by temperature shift and shed light on the pathogenicity and host-microbe interaction of this deadly pathogen. Gene expression microarrays promise to accelerate our understanding of the host side of the host-patho gen interaction. The complex interaction between host and pathogen has attracted the particular attention of researchers and is now being explored using microar-rays [70, 71]. The basic model consists of ex vivo measurement of gene expression of host cells before and after they are infected with a microorganism. Moreover, in gene expression experiments the bacteria can be used as 'sensors' to report the environment they experience at selected phases during the infection pathogen-esis. For example, Shigella flexneri can be used to probe the cytoplasmic compartment of macrophages, whereas Salmonella enterica and M. tuberculosis describe different modified phagosomal vacuoles. As more expression profiles are obtained for pathogens adapted to the intracellular environment, the construction of more complete pictures of intracellular parasitism become more readily available [72].

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