Phagentyp

Phagentyp, or phage type, is a classification of bacterial strains based on their susceptibility to a standardized panel of bacteriophages. In this method, a bacterial isolate is exposed to a set of lytic phages, typically on a plate in which phages are applied to a lawn of bacteria. The pattern of lysis—clear zones where the bacteria have been killed—across the phage panel defines the phagotype. Phagentyp schemes are defined by reference laboratories and can vary between regions or institutions.

Applications: Phage typing was widely used for epidemiological typing of outbreaks, notably in Salmonella enterica serovars, Staphylococcus aureus, and other species. It allowed discrimination of closely related strains when genetic differences were small and helped trace transmission pathways.

Advantages and limitations: The method is relatively inexpensive and fast when a preset panel exists. However, it is labor-intensive and relies on viable, well-characterized phages. Results can be influenced by growth conditions, phage preparation, and bacterial receptor changes. Reproducibility between laboratories is limited due to different phage panels and interpretation criteria. In many settings, phage typing has lower discriminatory power than modern molecular methods such as pulsed-field gel electrophoresis, multilocus sequence typing, or whole-genome sequencing.

Current status: Phage typing has largely declined in routine use and has been largely supplanted by sequence-based typing, but it remains of historical importance and is still used in some reference laboratories and research contexts.