Types of eae genes in non-O157 Shiga toxin-producing Escherichia coli strains

Abstract

Objective To analyze the subtypes of eae genes in various non-O157 Shiga toxin-producing Escherichia coli (STEC)strains isolated in China. Methods The complete nucleotide sequences of 10 eae genes were amplified by PCR and sequenced. The BLASTn software was used to analyze the sequences for eae gene subtyping. A phylogenetic tree was constructed based on the 10 eae gene sequences together with the gene sequences of 30 different subtypes in GenBank and those of STEC strains of 7 prevalent serotypes (O157∶H7, O26∶H11, O103∶H2, O111∶H8, O145∶H28, O45∶H2 and O121∶H19) using MEGA 5.0. Multilocus sequence typing (MLST) was performed on the 10 STEC strains with reference to the Escherichia coli (E.coli) MLST website (http: //mlst.warwick.ac.uk/mlst/dbs/Ecoli) for the typing of multiple loci. A minimum spanning tree (MST) was constructed using the BioNumerics software to investigate the phylogenetic relationships between the 10 eae gene-positive STEC strains in this study and hemolytic uremic syndrome-associated enterohemorrhagic E. coli (HUSEC) strains as well as all human STEC strains of O157, O26, O45, O103, O111, O121 and O145 serotypes submitted to the E. coli MLST website database. Results The complete nucleotide sequences of eae genes in 10 non-O157 STEC strains were 2.8 kb in length and belonged to 3 known subtypes. The predominant subtype was β1, accounting for 60% of the 10 STEC strains (6/10), followed by θ and γ1 subtypes with two strains in each type. The eae gene sequences in certain strains were identical to those of the prevalent serotypes. Seven sequence types (STs) were identified from the 10 STEC strains carrying eae gene. Conclusion The eae genes harbored by the non-O157 STEC strains isolated from different specimens in China were diverse and had close phylogenetic relationships with the highly pathogenic and prevalent STEC strains. This study implied that the STEC strains harboring eae gene had high pathogenic potential. Key words: Non-O157 Shiga toxin-producing Escherichia coli; eae gene; Multilocus sequence typing; Subtying