Novel proteins and their corresponding nucleotide sequences in enteroaggregative Escherichia coli (EAEC) are provided. In particular, Aap and the five gene cluster (aat) of the AA probe region of the pAA plasmid of EAEC 042 have been identified, sequenced, and further characterized. The use of these novel proteins and their corresponding nucleotide sequences for diagnosis, therapy, and prevention of EAEC infections is also provided.