Electrochemical investigation of the dynamics of Mycobacterium smegmatis cells' transformation to dormant, nonculturable form.

Dynamics of transformation of Mycobacterium smegmatis cells by cultivation under nonoptimal conditions (partial starvation) to dormant, nonculturable form has been studied. For this aim, an electrochemical method was developed to detect both viable and 'viable but nonculturable' (VBNC) cells. The current produced by bacteria placed at the electrode surface was measured in the presence of 2,6-dichlorophenol indophenol (DCIP) at the applied potential of 350 mV. It has been established that electrochemical activity changes parallel with the growth of biomass. The transition of M. smegmatis to a dormant, nonculturable state goes along with the decrease of the detection current up to 20% of the maximum level. This means that nonculturable cells have rather high rest metabolic activity. The course of the CFU values has a complicated character during bacterial growth. The placement of the bacterial culture on the solid medium appears to cause a new stress that stops proliferation and stimulates aggregation. Both processes distort CFU measurement results. The quantitative estimation of the viable but nonculturable cells by counting colonies, measuring optical density and current produced by bacteria has been discussed.