Fluorogenic assays for immediate confirmation of Escherichia coli

Area of Science:

• Microbiology
• Analytical Chemistry
• Food Safety

Background:

• Escherichia coli (E. coli) is a key indicator of fecal contamination in various matrices.
• Traditional methods for E. coli detection can be time-consuming and may not effectively identify stressed or injured cells.

Purpose of the Study:

• To develop and validate a rapid, sensitive assay for the detection and confirmation of E. coli.
• To improve upon existing methods for identifying heat- and chlorine-injured E. coli cells.

Main Methods:

• Incorporation of 4-methylumbelliferone glucuronide (MUG) into lauryl tryptose broth for a most-probable-number (MPN) assay.
• Utilizing the fluorogenic product of glucuronidase hydrolysis by E. coli for detection.
• Employing microtitration plates for an automated, rapid confirmatory test.

Main Results:

• The MUG-based assay provided presumptive (gas production) and confirmed (fluorescence) results for E. coli within 24 hours at 35°C.
• The assay demonstrated high accuracy, with approximately 90% of fluorescent tubes containing fecal coliforms.
• The method showed superior performance in detecting heat- and chlorine-injured E. coli cells compared to violet red bile agar.
• Sensitivity was high, detecting a single viable E. coli cell within 20 hours, and automated microtitration assays yielded results in 4-24 hours.

Conclusions:

• The fluorogenic MUG assay offers a rapid, sensitive, and reliable method for E. coli detection in food, water, and milk.
• This assay is advantageous for identifying injured E. coli cells and can be adapted for automation.
• The MUG assay enhances the efficiency of E. coli monitoring in various sample types.