Study of phage typing

Phage typing is a method of bacterial typing based on the sensitivity of a strain to a set of specific bacteriophages . Each phage, or bacterial virus, selectively infects certain strains of bacteria, resulting in a unique fingerprint of sensitivity specific to each isolate.

This technique is used to differentiate strains belonging to the same bacterial species , identify cross-contaminations and trace the origin of contaminations in industrial, agri-food, environmental or pharmaceutical environments.

Phage typing represents a powerful microbiological traceability tool , particularly for monitoring persistent contamination in production lines, industrial surfaces or finished products.

Methods and protocols used

Phage typing relies on the specific interaction between bacteriophages and host bacteria .

Main steps of the analysis:

1. Culture of the bacterial strain to be typed on nutrient medium.
2. Application of different specific bacteriophages on the bacterial surface.
3. Observation of lysis plaques (clear areas formed by bacterial destruction by the phage).
4. strain's sensitivity profile
5. Comparison with reference profiles to identify or differentiate the strain.

Modern methods combine classical phage typing with molecular tools such as:

• PCR genetic identification of strains or phages.
• sequencing (NGS) for detailed characterization of the bacterial and phage genome.
• Bioinformatics analysis for phylogenetic classification and comparison between isolated strains.

Affected matrices

The study of phage typing is applied to many matrices:

• Agri-food products : milk, meat, fermented products, ready-to-eat foods.
• Industrial surfaces : production lines, tanks, packaging, equipment.
• Water and effluents : environmental microbiological control.
• Bioproducts and probiotic formulations : verification of strain purity and stability.
• Materials and packaging : search for bacterial contamination linked to packaging.

Industrial and regulatory applications

The study of phage typing is particularly used for:

• Trace cross-contamination within a production site.
• Identify the source of recurring contamination (e.g., Listeria monocytogenes , Staphylococcus aureus , Salmonella enterica ).
• Monitor the effectiveness of cleaning and disinfection protocols.
• Ensure microbiological compliance of finished products.
• Establish a bacterial risk profile as part of a quality audit or regulatory expertise.

In the agri-food sector, this method complements the approaches of surface microbiological control and microbiota analysis (NGS) .

Related analyses

For an integrated approach to microbiological safety, YesWeLab recommends coupling phage typing with other complementary analyses:

• Gene expression analysis to link phage sensitivity profiles to strain genetic activity.
• Study of alpha and beta diversity to characterize the overall microbial composition.
• Sterility test to verify the absence of microbial contamination in finished products.
• Ecotoxicological test (Microtox) to assess the biological effects of contamination.

YesWeLab expertise

YesWeLab relies on a network of ISO 17025 and COFRAC accredited laboratories , specializing in industrial microbiology and molecular biology .

Thanks to the YesWeLab digital platform , it is possible to:

• Order and track your analyses online,
• Centralize your microbiological data,
• Access comprehensive and comparative reports,
• Benefit from personalized scientific support.