This document discusses phage typing, which is a method used to characterize and detect differences between bacterial strains based on their susceptibility or resistance to various bacteriophages. Phage typing can be used to distinguish between strains that cause disease from harmless strains, and to trace the source of bacterial outbreaks. It involves observing the zones of clearing around spots of different bacteriophages to determine the susceptibility patterns and strain differences. Phage typing is commonly used in epidemiology to identify infectious agents like strains of Staphylococcus aureus, Listeria, or Bacillus anthracis.

1. Phage Typing
Dr. Mabel Merlen Jacob
Assistant Professor
Department of Microbiology
St. Mary’s College
Thrissur-680020
Kerala

2. Phage Typing,Dr.Mabel Merlen Jacob, St.Mary’s College
Identification of prokaryotes
•Identification of prokaryotes using phenotypic characteristics
• Identification of prokaryotes using genotypic characteristics
• Characterizing strain differences

3. Phage Typing,Dr.Mabel Merlen Jacob, St.Mary’s College

4. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
 Distinguish among different stains of bacteria -Especially when
only certain strains cause disease.
(Only certain strains of E. coli cause intestinal disease-
presence of virulence factors such as toxin production etc.)
 Detecting strains differences - helpful in tracing source of an
outbreak.
Characterizing strain differences

5. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College

6. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
Phage Typing
 Strains of a given species sometimes differ in their susceptibility to
various types of bacteriophages.
 The zone of clearing around the bacteriophage spot indicate the
susceptibility patterns of the test organism to different phages.
 Different patterns compared to determine strain differences

7. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College

8. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
Phage may be very specific
-infect only a few strains of a certain bacterial species
or
strains of two or more species of a particular genus-
http://microamaze.blogspot.com/2015/11/phage-typing-of-salmonella-typhimurium.html

9. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
 Phage typing - characterizing and detecting bacterial strains by their
reaction (susceptibility/ resistance) to various known strains of
phages.
 employed in epidemiology to identify an infectious agent.
 eg; 1) strains of Staphylococcus aureus/ Listeria involved in
outbreaks of food poisoning or other infections.
2) identification of Bacillus anthracis, the causative agent of
anthrax

10. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
 sterile, fairly dried agar plates pre-inoculated with the phage
suspensions -up to 25 phage preparations using a multi-syringe
applicator
 agar surface flooded with broth culture of the Listeria strains;
observed after overnight incubation
 The phage particles do not diffuse along the agar surface; remain in
the circular area coincident with the original phage drop.
Reversed phage typing procedure – Listeria

11. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
 prepared plates can be used directly or stored at 4°C until use
(two weeks)
 More than 100 ready-to-use phage typing plates from 1 ml of
each of the phage suspensions
 prepared, ready-to-use typing plates – no need of cloning and
titration of phages in each laboratory.
 a two-fold increase in efficiency than the conventional method.

12. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College
 Specificity of the phage employed
 Medium used for testing lytic activity of phage
 opaque media containing egg/ dense materials
to be avoided – visualization of plaques difficult.
 Media should have no inhibitory action on growth of
host bacterium
 on adsorption of phage
eg; Tween 80, malachite green – mycophages, presence of
bacteriocins or other inhibitory substances and/or proteins liberated by
the lysed host cells.
Important Considerations

13. Phage Typing,Dr.Mabel Merlen Jacob,St.Mary’s College