We must consider:
Phage Host range(a mathematical criterion is required for selecting an useful phage among a lot of phages)
A selected Phage must have a Wide Host Range.
A bacteriophage with a wide host range is a phage capable of killing the highest number of different isolated cultures belonging to a given bacterial species ( example: Staphylococcus aureus from various sources).
For this reason it is indispensable to apply a mathematical criterion for selecting a phage among a lot of phages capable of effectively killing bacteria of a targeted bacterial species from various sources.
Virulence
A bacteriophage is selected as “Virulent “ when this phage is capable of effectively killing bacteria from various sources compared to capacity of the non selected phages.
For selecting a phage, by this property, we use the criterion of the lower concentration capable of killing bacteria compared to concentrations of the non selected phages.
Example:
two Phages with the same Host range
Phage A is effective in killing bacteria at 10^7 dilution
Phage B is effective in killing bacteria at 10^9 dilution
Phage B is the selected phage.
Mutant Phages
Selection of a Mutant Phage by Mutagenization:
a) phages must be always lytic phages
b) mutant phages, if compared to wild-type phage ( non mutaginezed phage or Parental Phage), may have both host range and virulence increased.
