Determination Of Cross-Infectivity of E. Coli Phages

The bacteriophages are host-specific i.e. they infect their respective hosts. However, some of the bacteriophages may infect the other host also, and the bacteriophages of other hosts may infect the first one. If this type of situation arises, it is called cross infectivity of the bacteriophages.


  • Plaques in E. coli lawns
  • Culture of Pseudomonas or any other sewage bacteria
  • Nutrient agar
  • Sterile Petri dishes
  • Sterile culture tubes
  • Flasks


  1. Procure the plates showing phages in E. coli lawns
  2. Meanwhile prepare a freshly double agar layer plate seeded with sewage bacteria (other than E. coli) as described in previous experiment.
  3. Transfer the plaque (phage) by stabbing with the help of a flamed and cooled needle.
  4. Mark on the back of the plate where the phage was placed.
  5. Incubate the plate at 35ºC overnight and record the plaques.
  6. Record the host range of the phage with other bacteria.


Appearance of plaques shows cross infection of the bacteriophages

Host range of e.coli phage


Dr. R. C. Dubey – Practical Microbiology

Gaurav Singh

Editor in Chief Medical Microbiology & Recombinant DNA Technology (RDT) Labs - RDT Labs Magazine

Leave a Reply