Characterization of non-O157 enterohemorrhagic Escherichia coli isolated from different sources in Egypt

Abstract

Background: Enterohemorrhagic Escherichia coli (EHEC) O157 is implicated in serious food and water-borne diseases as hemorrhagic colitis (HC), and the potentially fatal hemolytic uremic syndrome (HUS). However, new players of non-O157 EHEC have been implicated in serious infections worldwide. This work aims at analyzing serotype and genotypic-based virulence profile of EHEC local isolates.

Methods: A total of 335 samples were collected from different sources in Egypt. E. coli was isolated and subjected to serotyping. Non-O157 EHEC isolates were tested for virulence genes using PCR, phenotypic examination, phylogenetic typing, and molecular investigation by ERIC typing and MLST to disclose genetic relatedness of isolates. A heat map was used to identify potential associations between the origin of the isolates, their phenotypic and genotypic characteristics.

Results: A total of 105 out of 335 isolates were identified as E. coli. Surprisingly, 49.5% of these isolates were EHEC, where O111, O91, O26 and O55 were the most prevalent serotypes including 38.46% from stool, 21.15% urine, 23.1% cheese, 9.62% meat products, 3.85% from both yogurt and sewage water. Screening 15 different virulence genes revealed that sheA, stx2 and eae were the most prevalent with abundance rates of 85%, 75% and 36%, respectively. Fifteen profiles of virulence gene association were identified, where the most abundant one was stx2/sheA (19%) followed by stx2/stx2g/sheA/eae (11.5%). Both stx2/sheA/eae and stx2/stx2g/sheA were equally distributed in 9.6% of total isolates. Phylogenetic typing revealed that pathogenic phylogroups B2 and D were detected among clinical isolates only. Forty-six different patterns were detected by ERIC genotyping. MLST resolved three sequence types of ST70, ST120 and ST394. The heat map showed that 21 isolates were of 70% similarity, 9 groups were of 100% clonality.

Conclusions: The prevalence of non-O157 EHEC pathotype was marginally higher among the food isolates compared to the clinical ones. The endemic ST120 was detected in cheese, necessitating crucial measures to prevent the spread of this clone. Clinical EHEC isolates exhibited a higher score, and combination of virulence genes compared to food and sewage water isolates, thereby posing a significant public health concern.

Keywords: Biofilm; Intimin; Non O157 EHEC- ERIC; Serum resistance; Shiga toxin.

Fig. 1

Molecular typing of EHEC isolates collected from various sources. Similarity of clustering analysis was performed using ERIC-PCR analysis. Dendrogram representing UPGMA and Dice coefficient for E. coli. CU: urine, CS: stool, EC: cheese, EM: meat, EW: sewage water, EY: yogurt and EB: beef burger isolates

Fig. 2

Heat map with hierarchical clustering of EHEC isolates collected from various sources based on their phenotypic and virulence genes reflecting differences between isolates. Blue represents negative, red represents positive result of phenotypic and genotypic characters. Hierarchical clustering was performed using UPGMA and Jaccard coefficient. CU: urine, CS: stool, EC: cheese, EM: meat, EW: sewage water, EY: yogurt and EB: beef burger isolates