The alternative explanations for persisters are legion. They might be completely dormant, or normal cells caught in a protected part of the cell cycle when the antibiotic arrives, or a state induced in response to antibiotic treatment. Balaban and colleagues looked at the behavior of single cells immobilized in a microfluidic device and saw that the few cells surviving antibiotic treatment were growing slowly even before the drug was added.
Extrapolating from the behavior of two mutants that produce an excess of persisters, the team deduced that wild-type cells make persisters both in response to time spent in stationary phase and at a constant rate during normal growth. Persisters escape their sluggish state at a slow but appreciable rate.
For basic researchers, the persistence pathway offers a bacterial example of an alternative phenotypic state, and one that is somehow generated at a low, constant frequency. For clinicians,the pathway may present a target for drugs that would get rid of the few bacteria left after conventional antibiotic treatments. ▪