The commitment-to-infection step of phage adsorption that involves strong attachment to the bacterial surface and/or conformational changes in virion proteins.
Under normal circumstances, such as given phage irreversible adsorption of a phage-sensitive bacterium, this irreversible adsorption is followed by phage-genome translocation into the bacterial cytoplasm. Also can be described as irreversible attachment. Contrast with reversible adsorption.
The transition from reversible adsorption to irreversible adsorption is not instantaneous and at sufficiently high bacterial densities this transition step can both limit and define overall phage adsorption rates to bacteria (which is to say that adsorption kinetics are saturable given sufficient bacterial availability with the reversible to irreversible transition defining the "turnover rate" in the overall phage-adsorption "reaction").
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