Viability Measurements and the Survival of Microbes Under Minimum Stress

Increased production of colicin E1 in stationary phase

“…Thus, expression of the cea-kil operon might be induced in a subpopulation of the producing cells that are most severely affected, causing their death and lysis and increasing the chances of survival for the rest of the population. This apparent suicide would serve the purpose of eliminating cells in the moribund state (44) with no hope for survival but which might be effectively competing with cells more suited for survival for the few nutrients available. This is similar to the theory we have proposed for the role of regulation by the SOS response (51).…”

Dormancy in non-sporulating bacteria

“…The term viability as used here is not correct (since some of the cells obviously had lost the ability to form colonies). However, it is plausible that the loss of the viability that does occur under conditions of prolonged cultivation in chemostats can be related to the shock of sudden nutrient abundance in the plat-275 ing medium [56,57]. Such a phenomenon, known as substrate-accelerated death, can occur when the substrate that limited the growth of a population accelerated its death when added to starved cells [57].…”

“…The question arises, however, as to whether bacteria are really dying in the 'death' phase. When viability is measured by plating, it may be rapidly decreased to a few percent from an initially high level, a number which is then typically maintained for many days more [57]. Notwithstanding, it is often unclear as to whether this viability is calculated on the basis of the total counts at the beginning of the death phase or for each measurement point during the death phase.…”

“…Notwithstanding, it is often unclear as to whether this viability is calculated on the basis of the total counts at the beginning of the death phase or for each measurement point during the death phase. It has been known for many years that some morphological changes occur in old bacterial cultures [57]; just as during the production of VBNC, cells in stationary phase become much smaller and almost spherical [65].…”

“…Whilst population effects (i.e. favourable cell-cell interactions) on survival during starvation have been known for a long time [57], it was argued in this case that cells that had been in stationary phase for a long time possessed a 'killer phenotype', dramatically decreasing the survival of young cells [66]. This phenomenon presumably reflects the synthesis and excretion of some specific compounds by old cells which are able to decrease the apparent viability of young cells; as in many other studies in which viability was estimated simply by plate counts, it was not excluded that such compounds actually served to induce dormancy in the 'young' population.…”