Molecular characterisation of enteroinvasive Escherichia coli O136: K78 isolates from patients of a diarrhoea outbreak in China

Purpose: A diarrhoea outbreak occurred in a kindergarten, which caused 21 relevant infected cases. Our object was to confirm the pathogens and their molecular characterisation. Materials and Methods: Faecal samples from 21 patients were collected on the 3rd day after their symptom onset, and a regular epidemiological investigation was conducted. Bacterial isolation was performed in accordance with standard laboratory protocol, serological and molecular characterisations were determined by serum agglutination test and real-time polymerase chain reaction (PCR) method, respectively. The pulsed field gel electrophoresis (PFGE) and 16S rRNAs were conducted to determine the homology. Results: Eleven enteroinvasive Escherichia coli (EIEC) O136: K78 strains were isolated. The serum agglutination test showed that all strains' serotypes were E. coli (EIEC) O136: K78. Real-time PCR showed that 10 (91%) strains carried the invasion plasmid antigen H gene (ipaH), carried by all four Shigella species and EIEC. The strain that didn't carry the ipaH gene had different biochemical reactions of L-lizyna and L-rhamnose with the other strains. The complete 16S rRNA sequences showed 98.4% identity between ipaH-negative isolate and the others, and the PFGE indicated that the ipaH-negative isolate was not homological with other isolates in this diarrhoea outbreak. Conclusions: The diarrhoea outbreak was caused by E. coli (EIEC) O136: K78.