[Pathogenic Listeria in the soil and in association with algae: a reversible transition into a nonculturable state]

The analysis of the dynamics of the amount of L. monocytogenes in soil extract in association with green algae and in their absence, carried out in parallel by the bacteriological method and in polymerase chain reaction (PCR), revealed the mass transition of L. monocytogenes into the nonculturable state. The proportion of vegetative (bacteriologically detected) forms in the bacterial population rapidly decreased, while its total amount remained unchanged due to the formation of inactive (nonculturable) L. monocytogenes forms. Algae or their metabolites considerable accelerated this process: by day 26 L. monocytogenes could not be isolated, but in PCR they could be registered at their initial concentration: 10(6) microbial cells/ml. Inactive L. monocytogenes forms were shown to revert into the vegetative (culturable) state under the action of fetal serum, live and killed infusoria, auxin. The concentration of revertants grown on a solid culture medium was high: 10(4)-10(5) colony-forming units/ml.