Abstract

Objective: To perform a laboratory investigation to identify and characterize the causative pathogens of a diarrheal outbreak in the south of Iran in July 2015. Methods: Laboratory investigation was done through standard cultures and molecular methods for causative agent and possible source identification. Antibiotic resistant patterns, extended-spectrum β-lactamase (ESBL) production ability and plasmid profiling were used to characterize the isolated pathogens. Results: Out of 16 stool samples received in the lab, 14 were positive for enteroaggregative E. coli (EAEC), enteroinvasive E. coli (EIEC) and non-O157 enterohaemorrhagic E. coli (EHEC). Of 5 EIEC isolates, 3 were similar in terms of plasmid patterns and ESBL production ability and virulence genes (ipaH+ and virF+). The EAEC isolates were positive for at least one of two virulence genes, agg and aap. Out of 7 EAEC isolates, 2 had the same patterns of plasmid profiles, antibiotic resistance and virulence gene (aap+). Of the 7 EAEC isolates, four had ESBL production ability. The two non-O157 EHEC isolates were positive for stx2 virulent gene and were also susceptible to all tested antibiotics. Conclusions: Laboratory investigation showed that the outbreak was caused by mixed diarrheagenic E. coli pathogroups, possibly due to waste contamination of drinking water.

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