Finding your niche: what has been learnt from STM studies on GI colonization

The first step in the pathogenesis of all enteric and some systemic infections is colonization of the gastrointestinal (GI) tract. Here, we highlight the barriers to infection faced by bacteria during their attempts to become established in the GI tract, and some of the mechanisms used by microbes to overcome innate host defences. We focus in particular on insights provided by recent studies that used signature-tagged mutagenesis to identify bacterial colonization factors in a range of enteric pathogens. Although some differences in the results can be attributed to variation in methodology, clear themes emerge. For example, whereas each of the pathogens studied use a unique adhesin to establish successful infection in a host, most organisms must express full-length lipopolysaccharide and certain transcription factors. Further understanding of this key step in the disease process could lead to novel methods to combat GI infections, a major cause of morbidity and mortality throughout the world.