Isolation of enteroaggregative escherichia coli (EAggEC) from patients with diarrheal disease in an outbreak case of overseas tour

Twenty four patients out of 78 Cambodia tourists (31%) suffered from diarrhea and/or abdominal pain. Though the stools of 20 patients were examined in some local health centers and institutes, well-known pathogens were detected in only a low level and the cause of the outbreak remained unclear. We suspected the enteroaggregative Escherichia coli (EAggEC) as a cause of this outbreak. We examined E. coli strains isolated from stools of 8 patients (Okayama:7, Aichi:1) at first by the PCR method targeted both the aggR and the astA genes related to the virulence factors of EAggEC. As a result, the E. coli strains with positive aggR and/or astA genes were isolated from 8 patients. And the E. coli strains with positive both aggR gene and clump formation isolated from 3 patients adhered aggregatively to HEp-2 cells and accordingly identified as EAggEC. The plasmid profiles, PFGE patterns and drug resistance patterns of these EAggECs agreed completely. From these results, we concluded that at least 3 patients were infected with EAggEC of the same origin. Though we could not examine all samples from 20 patients, it is possible that the still uncommon EAggEC might be a cause of the outbreak. The E. coli strains with positive aggR gene did not always aggregatively adhered to HEp-2 cells. So we recommend to perform stepwise EAggEC screening tests by the PCR and the clump formation, and final confirmation test by the aggregative adhesion to HEp-2 cells.