Dormant Forms of Food-Contaminating Pathogenic Bacteria

Abstract— Decreasing the vital risk of microbial contamination of foodstuffs and food production facilities requires more efficient determination of microbial load, including enumeration of the dormant, ametabolic forms of food-contaminating pathogens. Under starvation stress, the life cycle of food-contaminating pathogenic and opportunistic bacteria of the genera Salmonella, Pseudomonas, Listeria, etc. ends in emergence of a small subpopulation of cystlike dormant forms (cDF), which are ametabolic, stress-resistant (heat-resistant), retain the colony-forming ability for up to 3 months, and differ from the vegetative dells in their ultrastructural organization. Investigation of the cDF heat resistance revealed heterogeneity of their subpopulations. Heating of the Salmonella cDF revealed the previously unknown phenomenon: in the region of compacted nucleoid, numerous vesicles were formed, which were surrounded by an envelope probably formed by a lipid membrane (l = 75 Å) encrusted with globules of the Dps (a DNA-binding protein of dormant cells) dodecamer and containing the fragments of segmented nucleoid DNA as a form of lateral gene transfer. Long-term (3 months survival of Listeria as heat-resistant L-forms, reverting to the cell-wall morphotype (with formation of regular colonies) upon plating under standard conditions, was another unexpected finding. Heterogeneity of surviving anabiotic cells in morphotypes (cDF and L-forms), heat resistance, and dormancy depth indicate the need for pretreatment of food-contaminating microflora samples in order to activate the dormant form germination for higher efficiency of microbiological monitoring.