Background. Enteroaggregative Escherichia coli is emerging as an increasingly recognized cause of persistent, mildly inflammatory diarrhea in the United States, especially among patients with AIDS, as well as among children, for whom it is accompanied by growth shortfalls.

Methods. We describe a novel model of disease induced in neonatal and weaned C57BL/6 mice by pathogenic strains of enteroaggregative E. coli 042 and JM221.

Results. Enteroaggregative E. coli caused growth impairment (up to 47%), persistent stool shedding (for 13 weeks), and a substantial tissue burden of organisms (150,000 organisms per milligram of tissue), as well as histopathological changes in the colonic epithelium (days 4 and 6 of infection) using the model. Undernutrition in neonatal mice, as well as in weaned mice, intensified infection by 1–4 logs, as assessed by quantitative polymerase chain reaction for fecal shedding of organisms. Growth impairment was dependent on both microorganism burden and challenge dose.

Conclusions. Both neonatal and weaned mice provide models for a vicious cycle of enteroaggregative E. coli infection that causes growth shortfalls and undernutrition, thus worsening infection. Hence, these neonatal and weaned mice provide the opportunity to dissect mechanisms of this cycle in childhood malnutrition, as well as to define the role played by innate and acquired host defenses in this important infection.