Global impact of antibiotic-resistant strains of Staphylococcus aureus on patients’ health is not mitigated by newly developed antibiotics. The phage therapy is an effective approach employing natural enemies of bacteria – bacteriophages – to battle the infection [1]. It is currently of limited availability and should be made accessible to patients with multi-resistant bacterial infections. However, current knowledgebase on Staphylococcus phages, which serves authorities to approve wider use of phage therapy, is incomplete [2]. To investigate ultrastructure of phage infection mechanism, we employed a cryo electron tomography on a single cell thinned by focused ion beam milling. Here we present a snapshot of intracellular environment during lytic cycle stages of polyvalent Myoviridae phage phi 812 [3, 4] in planktonic Staphylococcus aureus cell. We show, that within 15 minutes of infection new phage capsids are apparent on the inner surface of cellular membrane. After 30 minutes infection, the empty, filling, and full phage capsids with or without connected tail are assembled in cytosol. In contrast to a widely accepted assumption on precise timing of a phage life cycle, we show that a considerable amount of newly formed phage particles is incomplete upon lysis.
Increased resistance to treatment in Staphylococci caused by a biofilm formation can be addressed by use of a combined phage-antibiotic therapy [5, 6]. Research on the behaviour of phages in biofilm will provide kinetic frameworks for application of a combined therapy to minimize inhibition of a phage component. Here we show, that with super resolution fluorescence microscopy, we can track phage particles during infection of native S. aureus biofilm. To track overall phage movement and determine the time frame for application of antibiotic, we will use a light sheet fluorescence microscopy. The native biofilm in a flow-cell setting will be recorded during infection by labelled phages. In order to minimize background autofluorescence of growth media with casein component, we developed transparent defined minimal media with comparable growth capacities. Characterization of phage infection dynamics can facilitate progress in phage therapy approval and availability to patients with urgent need of alternative therapy.