Monitoring Bacteriophage Infection on Bacterial Cells Using FISH

The possibility of visualizing bacteriophage-host interactions through fluorescence in situ hybridization (FISH)-derived methods is gaining relevance in the last few years. These methods allow the possibility of discriminating between phage-infected and noninfected cells and the assessment of the different infection stages at the single cell level. In opposition to bacterial cells, the detection of phages is more challenging due to the low number of nucleic acid copies. However, by using a conserved region of the phage genome that is highly expressed during transcription, a FISH signal targeting phage DNA copies and mRNA transcripts can be easily visible inside the bacterial host cells.In this book chapter, we will cover both the design of locked nucleic acid (LNA) probes for phages and a FISH method for the detection of phages inside bacterial cells.