Container material dictates stability of bacteriophage suspensions: Light scattering and infectivity measurements reveal mechanisms of infectious titre decay

Aims: To measure the infectious titre (IT) decay rate for various bacteriophages as a function of storage container material. Additionally, parallel light scattering and infectious titre measurements reveal distinct mechanisms for IT loss, depending on phage.

Methods and results: Suspensions of bacteriophages 44AHJD, P68 and gh-1 were stored in various labware. IT of each suspension was repeatedly measured over the course of 2 weeks. Large variability in IT decay was observed, with >4 log₁₀ loss in glass and low-binding polypropylene. Incubation of polymer containers with Bovine Serum Albumin (BSA) resulted in a consistent reduction in IT decay. Aggregation state of phage suspensions was studied by nanoparticle tracking analysis (NTA), revealing highest aggregation in glass-stored suspensions and lowest after storage in BSA-treated containers.

Conclusions: Glass and 'low-binding' containers may aggravate IT decay while BSA treatment may present an easy mitigation strategy. IT versus NTA titre diagrams highlight the importance of phage inactivation in combination with aggregation.

Significance and impact of the study: Container material is a significant determinant of bacteriophage IT decay. It is therefore essential to confirm IT following storage and tailor choice of phage storage containers accordingly. Aggregation of phages and adsorption onto labware surfaces are not only the mechanisms accounting for IT loss but also biological instability.