Enteroaggregative Escherichia coli is a major cause of diarrhea in diverse populations worldwide. EAEC has a characteristic "stacked-brick" adherence pattern to intestinal epithelial cells which is mediated the aggregative adherence fimbria (AAF). The AraC-like regulator AggR has been found to regulate expression of the genes encoding the AAF and several other virulence associated genes. Multiple epidemiologic studies have found an association between possession of aggR and EAEC disease. However, the exact factor(s) responsible for diarrheal disease remain unclear. A microarray approach was used to identify AggR-regulated genes in EAEC strain 042. Nineteen previously unrecognized genes were found to be regulated by AggR. Three of these genes were chosen for further study based on a high prevalence in an EAEC strain collection. Two of the genes (orf3 and orf4) were found to cause an increase in resistance to cationic antimicrobial peptides. The third (orf61) is a novel membrane damaging toxin that has hemolytic and leukotoxic activity.