Enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAggEC) are a group of E. coli characterized by the ability to adhere to cultured cell monolayers with an aggregative or 'stacked brick' adhesion phenotype. These strains of E. coli are distinct from other pathogenic groups of E. coli. Epidemiological evidence suggests that strains of EAggEC are a significant cause of protracted diarrhoea in children, and may cause diarrhoea in adults. The group is heterogeneous, comprising a diverse range of serotypes that possess a variety of putative virulence factors. These include an enterotoxin similar to the heat-stable enterotoxin of enterotoxigenic E. coli, putative haemolysins and toxins, and various types of fimbriae and outer membrane proteins that may be involved in the adhesion process. The role of these factors in the production of disease is unclear. Diagnosis of EAggEC infection is problematic; serotyping alone cannot identify strains of E. coli expressing an EAggEC phenotype. Currently, EAggEC are identified by either cell adhesion tests or DNA-based tests involving gene probes or polymerase chain reaction (PCR) for detecting the genes encoding cell adhesion. The nature and significance of strains of E. coli expressing an EAggEC phenotype are poorly understood. This article reviews the current literature and speculates on the direction of future studies to define this emerging group of bacteria.