Persister cells

Persister cells are subpopulations of cells that resist treatment, and become antimicrobial tolerant by changing to a state of dormancy or quiescence. Persister cells in their dormancy do not divide. The tolerance shown in persister cells differs from antimicrobial resistance in that the tolerance is not inherited and is reversible. When treatment has stopped the state of dormancy can be reversed and the cells can reactivate and multiply. Most persister cells are bacterial, and there are also fungal persister cells, yeast persister cells, and cancer persister cells that show tolerance for cancer drugs. Recognition of bacterial persister cells dates back to 1944 when Joseph Warwick Bigger, an Irish physician working in England, was experimenting with the recently discovered penicillin. Bigger used penicillin to lyse a suspension of bacteria and then inoculate a culture medium with the penicillin-treated liquid. Colonies of bacteria were able to grow after antibiotic exposure. The important observation that Bigger made was that this new population could again be almost eliminated by the use of penicillin except for a small residual population. Hence the residual organisms were not antibiotic resistant mutants but rather a subpopulation of what he called ‘persisters’. The formation of bacterial persisters is now known to be a common phenomenon that can occur by the formation of persister cells prior to the antibiotic treatment or in response to a variety of antibiotics. Antimicrobial tolerance is achieved by a small subpopulation of microbial cells termed persisters. Persisters are not mutants, but rather are dormant cells that can survive the antimicrobials that effectively eliminate their much greater number. Persister cells have entered a non-growing, or extremely slow-growing physiological state which makes them tolerant (insensitive or refractory) to the action of antimicrobials. When such persisting pathogenic microbes cannot be eliminated by the immune system, they become a reservoir from which recurrence of infection will develop.