Ecological as well as physiological perspective on bacterial resistance to phages as seen following phage adsorption. Specifically, there exist gradations in bacterial interference with phage productivity ranging from (i) no interference (“normal lytic infection”) to (ii) partial blocks on phage productivity and/or extension of the phage infection cycle that can slow down phage population growth (“reduced infection vigor” [17] as seen with “reduced burst size” or “extended latent period”) to (iii) bacterial self-sacrifice for the sake of phage elimination (“abortive infection”; see also [225]) to (iv) bacteria simply inactivating infecting phages but without loss of bacterial viability (“restriction, exclusion, or immunity”; hosts in any case are shown as green ovals). These various mechanisms are reviewed by Hyman and Abedon [17] and also Labrie et al. [164]. Not shown, bacteria can also block phage infection by resisting phage attachment following phage encounter, though generally this does not result in phage metabolism in either a physiological or pharmacological sense. For comparison of mechanisms of bacterial resistance to phages to the immunity displayed especially by animals against pathogens, see Abedon [227]. Note also that analogies exist between mechanisms of bacterial resistance to phages and mechanisms of bacterial resistance to antibiotics. These include as mediated by compound destruction or avoidance of interaction through changes in target structures, though notably absent is a phage-resistance equivalent to “efflux off the antibiotic from the cell” (p. 1451) [160].
