Method to Isolate Escherichia coli O157:H7 from Food

Area of Science:

• Food microbiology
• Microbial diagnostics
• Bacteriology

Background:

• Escherichia coli (E. coli) is a common bacterium, with certain strains causing hemorrhagic colitis (HC).
• Accurate and rapid detection of HC E. coli in food is crucial for public health.
• Existing methods for isolating HC E. coli can be time-consuming and complex.

Purpose of the Study:

• To develop a novel direct plating medium for the efficient overnight isolation of hemorrhagic colitis (HC) strains of Escherichia coli from food samples.
• To provide a reliable diagnostic tool for identifying specific HC E. coli in food matrices.

Main Methods:

• A new selective medium was formulated incorporating tryptone, sorbitol, an indicator dye, and a fluorogenic substrate.
• The medium utilizes a specific bile salt concentration and an elevated incubation temperature (44.5°C) for selective growth.
• Colony color (blue) and subsequent indole staining (red) differentiate HC strains, with serological confirmation.

Main Results:

• The developed medium allows for direct overnight isolation of HC E. coli strains from food.
• HC E. coli colonies appear blue on the medium and turn red after indole staining.
• Non-HC E. coli (Type I) colonies appear yellow with negative indole reactions.
• Recovery rates of HC E. coli from artificially contaminated ground beef reached ≥90%.

Conclusions:

• The new medium provides a sensitive and specific method for the direct isolation and presumptive identification of HC E. coli in foods.
• This diagnostic tool can significantly improve the speed and efficiency of foodborne pathogen detection.
• The method offers a valuable advancement for food safety monitoring and surveillance programs.