A measure of the rate at which free phages become attached to bacteria.
Technically the adsorption constant is the probability of adsorption of a single phage to a single bacterium, both suspended in a single unit volume of fluid over a single unit of time. Typically adsorption constants are also determinations of rates of irreversible rather than reversible adsorption to bacteria. The adsorption constant is often presented in volume per time units, such as ml/min, where a typical value is in the range of 10-8 to 10-9 ml min-1. Units of ml/hr are also commonly used such that 60*X ml/min = Y ml/hr.
The phage adsorption constant represents a complicated parameter combining phage diffusion rates, bacterial target size, and phage affinity for bacteria. Increases in any of these parameters will result in increases in the phage adsorption constant. The constant is independent, however, of both phage and bacterial densities though at very high bacterial densities delays in transitions from reversible to irreversible adsorption may occur more slowly than rates of phage adsorption, resulting in an inability to calculate the latter from adsorption-rate information.
Determinations of adsorption rates and thereby adsorption constants ideally involves kinetic measurements of either phage removal from the free phage state or phage gain of the adsorbed state. The former can be misleading, however, when working with poorly defined systems such that free phage loss can occur for reasons other than phage adsorption.
References:
Abedon, S. T. (2011). Envisaging Bacteria as Phage Targets. Bacteriophage 1:228-230.
Kropinski, A. M. (2010) Measurement of the Rate of Attachment of Bacteriophage to Cells. Methods in Molecular Biology 501:151-155.
Hyman, P., Abedon, S. T. (2010) Practical Methods for Determining Phage Growth Parameters. Methods in Molecular Biology 501:175-202.
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