Abstract
An outbreak of severe diarrheal illness was recently reported in northeastern Oklahoma, and Shiga toxin–producing Escherichia coli serotype O111 was identified as the etiological agent. Our results indicated that this isolate is unable to decarboxylate lysine, a characteristic that is shared with other outbreak-linked O111 isolates. Therefore, further investigation is recommended to determine whether the lysine decarboxylase test could be used to identify a subset of pathogenic E. coli, particularly Shiga toxin–producing E. coli O111 isolates, that have the potential of causing human infections and outbreaks.