Detection and characterization of Escherichia coli O157:H7 in drinking water from Baghdad city using phenotypic, immunological, and molecular methods

Document Type : Research Paper

Authors

1 Market Research and Consumer Protection Center, University of Baghdad, Baghdad, Iraq

2 Market Research and Consumer Protection Center, University of Baghdad, Baghdad, Iraq.

Abstract

Objective
The aim of this study was to isolate and identify Escherichia coli O157:H7 from drinking water intended for human consumption in Baghdad City. The isolates were characterized using conventional phenotypic and biochemical methods. Then, their ability to produce Shiga toxin (Stx) was determined using ELISA. In addition, molecular identification and genotyping were performed. For detecting the presence of stx1 and stx2 genes, multiplex polymerase chain reaction (MPCR) was used. Another goal was to compare these genes as diagnostic and epidemiological indicators with traditional diagnostic methods.
Material and methods
Thirty drinking water samples were collected from both sides of Baghdad City (Karkh and Rusafa) between July and August 2023. Samples were collected in sterile 250-mL glass bottles containing 3% sodium thiosulfate. Cefixime-tellurite sorbitol MacConkey agar (CT-SMAC) was used to isolate E. coli O157:H7. Biochemical identification was performed using the API 20E system. Moreover, ELISA was used to determine the production of Shiga toxin. Molecular detection of stx1 and stx2 genes was conducted using the PCR technique.

Results
Out of the 30 drinking water samples analyzed, 25 E. coli isolates were obtained. Biochemical tests identified 10 isolates as E. coli. While, the API 20E system confirmed 6 isolates. Serological examination using the rapid latex agglutination test confirmed that four isolates belonged to the E. coli O157:H7 serotype. ELISA results demonstrated that all four isolates produced Shiga toxin. MPCR analysis revealed that one isolate carried the stx1 gene (180 bp), while all four isolates carried the stx2 gene (255 bp).
Conclusion
Shiga toxin (Stx), also known as verotoxin, is an AB₅ toxin produced by certain strains of E. coli, particularly E. coli O157:H7. Furthermore, it is closely related to the toxin produced by Shigella dysenteriae. The presence of stx1 and stx2 genes in drinking water isolates can highlight the potential public health risk. It also can support the use of molecular methods as reliable tools for the detection and surveillance of pathogenic E. coli in drinking water.

Keywords

References

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Agricultural Biotechnology Journal
Volume 18, Issue 2
February 2026
Pages 239-254

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