Insertion element IS3-based PCR method for subtyping Escherichia coli O157:H7

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Escherichia coli O157:H7 is a significant foodborne pathogen.
• Accurate subtyping is crucial for tracking outbreaks and understanding transmission.
• Pulsed-field gel electrophoresis (PFGE) is a common but complex subtyping method.

Purpose of the Study:

• To develop a simple and rapid subtyping method for Escherichia coli O157:H7.
• To evaluate the efficacy of a novel PCR-based approach targeting the IS3 repetitive element.
• To compare the performance of the new method with PFGE.

Main Methods:

• Developed a PCR subtyping method using variable DNA sequences flanking the IS3 element.
• Prepared template DNA by boiling bacterial cells in Chelex.
• Performed two separate IS3 PCR amplifications: single primer (IS3A) and dual primers (IS3A and IS3B).
• Applied the method to 35 E. coli O157:H7 isolates previously characterized by PFGE.

Main Results:

• PFGE identified 25 distinct subtypes among the isolates.
• Single IS3A PCR identified 6 subtypes; IS3A-IS3B PCR identified 14 subtypes.
• Combined IS3 PCR amplifications yielded 15 distinct subtypes.
• The IS3 PCR method successfully grouped all outbreak-related isolates.
• PCR banding patterns demonstrated reproducibility.

Conclusions:

• IS3 PCR subtyping is a simple, rapid, and reproducible method for E. coli O157:H7.
• While less sensitive than PFGE, it effectively screens for unrelated isolates and identifies outbreak clusters.
• This PCR-based approach offers a valuable alternative for routine subtyping in diagnostic laboratories.