Bacteriophage Ecology Group

Bacteriophage Ecology Group Bacteriophage Ecology Group

Residual Fraction


A subpopulation within a phage stock that displays slower adsorption rates than the majority of the stock.

Often this residual fraction is present as a few percent, or at lower frequencies, and as a phage population that remains free following prolonged (many hours) of adsorption. The residual fraction is problematic in practical terms because it can result in inaccurate determinations of adsorption rate constants if determined via end-point – i.e., two time points, start and finish – rather than kinetic means (> 2 time points).

The concept of a residual fraction is somewhat generic and here is being defined according the usage of Delbrück (1942), p. 17, who noted that "a given suspension of virus is inhomogeneous with respect to its affinity to the bacteria."


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