Rapid accumulation of bacterial genomic data offered an unprecedented opportunity to understand bacterial biology from a holistic view of point. We can thus closely look at the way in which a pathogen is evolved, and these data has been applied to molecular epidemiology and microbial forensics, and screening of novel diagnostic, vaccine and drug targets. The newly developed high-throughput low-cost sequencing technologies, such as 454, Solexa and SOLiD, will promote the acquisition and application of genomic data in new research areas that we dared not imagine previously, such as the metagenomics of human gastric-intestinal tract, for better and comprehensive understanding of human health and disease.