Molecular approaches to bacterial detection and species/subspecies characterization: The diarrheagenic Escherichia coli groups

Classical bacterial identification methods have worked well for defining most bacterial pathogens. Recent evidence, however, indicates that only some strains of a particular species are pathogenic (eg, the diarrheagenic classes of Escherichia coli) and that these pathogens cannot be identified by standard bacteriologic techniques. Molecular approaches have been developed that serve as adjuncts to existing bacteriologic procedures for identifying pathogenic varieties within a species. This short review is focused on defining the six classes of E. coli that cause different diarrheal disease syndromes and the best current molecular methods for identifying these pathogens from the background nonpathogenic E. coli. Identification of E. coli diarrheagenic pathogens with these molecular tools will ultimately allow for better definition of each pathogenic class and a clearer understanding of their relative importance in causing diarrheal diseases worldwide. In addition, we list several current applications of additional molecular methods that are useful in the epidemiologic study of enteric diseases.