Phage-based forensic tool for spatial visualization of bacterial contaminants in cheese

Area of Science:

• Microbiology
• Food Science
• Biotechnology

Background:

• Traditional microbial testing lacks spatial information, hindering source identification of contamination.
• Visualizing bacterial contaminant location is crucial for troubleshooting in food processing environments.

Purpose of the Study:

• To evaluate a genetically engineered phage for visualizing bacterial contaminants on cheese without magnification.
• To demonstrate the potential of reporter phages as a forensic tool in food safety.

Main Methods:

• A T7 bacteriophage engineered with NanoLuc luciferase was used to detect Escherichia coli.
• Two application methods were tested: topical application in soft agar and incorporation within agar/cheese.
• Bioluminescent signals were captured using a digital camera after substrate addition.

Main Results:

• The reporter phage successfully visualized the spatial location of E. coli on both lysogeny broth (LB) agar and queso fresco (QF).
• Detection limits varied across the four tested scenarios, with the lowest inoculum levels ranging from 1.18 × 10^1 to 5.48 × 10^1 cfu/well.
• Blue bioluminescent spots accurately indicated the location of bacterial colonies.

Conclusions:

• The proof-of-concept demonstrates that reporter phages can serve as a forensic tool for visualizing bacterial contaminants in food matrices.
• This method provides spatial data, unlike traditional homogenizing techniques.
• Future research will focus on applying this concept to dairy-relevant phage-pathogen systems.