Bacteriophage Typing
Different strains of a serologically or otherwise identical species
of bacteria are susceptible to one or more different bacterio-phages. When a
suspension of phages is deposited on the lawn culture of a susceptible
bacterium, an area of clearing occurs after incubation due to lysis of the
susceptible bacteria by the phages. These zones of lysis are called plaques. The shape, size, and nature of
plaques are characteristic for different phages. Since a single phage particle
is capable of producing one plaque, plaque assay can be used for titrating the
number of viable phages in preparation. On the basis of this phenomenon, many
bacterial species can be divided into various phage types. Phage typing has
been used in epidemiological study of infec-tions or outbreaks caused by Staphylococcus aureus, Salmonella spp., Vibrio cholerae, and many other bacteria.
Different phages are available, which show difference in their
specificity for genus, species, or strains. Examples are (i) genus-specific bacteriophages for Salmonella, (ii) specific
bacteriophages for all members or strains of
Bacillus anthracis, and (iii) for all members of V.
cholerae bio-type classical (e.g., Mukherjee’s phage IV). Mukherjee’s phage
IV lyses all strains of V. cholerae
biotype classical, but not V. cholerae biotype
Eltor.
Phage typing of S. aureus
is a pattern method in which a set of standard phages is employed for
intraspecies typing of staphylococci. A strain of Staphylococcus may be lysed by a num-ber of phages. Hence, the
phage type of a strain is designated by the number of the different phages that
lyse it. Phage typing of Salmonella
Typhi is carried out by using prophage, which is active against only fresh
isolates of S. Typhi possessing the
Vi antigen.
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