Morphological and Physiological Changes Induced by High Hydrostatic Pressure in Exponential- and Stationary-Phase Cells of Escherichia coli : Relationship with Cell Death

Abstract

The relationship between a loss of viability and several morphological and physiological changes was examined with Escherichia coli strain J1 subjected to high-pressure treatment. The pressure resistance of stationary-phase cells was much higher than that of exponential-phase cells, but in both types of cell, aggregation of cytoplasmic proteins and condensation of the nucleoid occurred after treatment at 200 MPa for 8 min. Although gross changes were detected in these cellular structures, they were not related to cell death, at least for stationary-phase cells. In addition to these events, exponential-phase cells showed changes in their cell envelopes that were not seen for stationary-phase cells, namely physical perturbations of the cell envelope structure, a loss of osmotic responsiveness, and a loss of protein and RNA to the extracellular medium. Based on these observations, we propose that exponential-phase cells are inactivated under high pressure by irreversible damage to the cell membrane. In contrast, stationary-phase cells have a cytoplasmic membrane that is robust enough to withstand pressurization up to very intense treatments. The retention of an intact membrane appears to allow the stationary-phase cell to repair gross changes in other cellular structures and to remain viable at pressures that are lethal to exponential-phase cells.

Genes of Escherichia coli O157:H7 That Are Involved in High-Pressure Resistance

“…Krzyzaniak et al (36) reported DNA conformational changes in low-salt buffer when the solution was treated with high pressure at 600 MPa. Other researchers observed a condensation of E. coli nucleoids in response to high pressure at 200 MPa for 8 min (38). Reducing the transcription of dps in response to pressure may allow the chromosomal DNA to renature to its protective state without interruption by abundant DNA-binding proteins.…”

Importance of Considering Injured Microorganisms in Sterilization Validation

“…It is interesting that the mechanism of DNA damage by heat was different for the spore and vegetative cell of B. subtilis (Uchida and Kadota, 1979). Cells in the log phase are more susceptible to injury than spores or cells in the stationary phase (Mackey, 1984;Mossel and van Betten, 1984;Manas and Mackey, 2004). Important properties of the substrate include the water content, the concentration and type of ions and pH, the oxidation-reduction potential, the gas atmosphere, the presence of protective agents, and contamination with other microorganisms.…”

Damage in Escherichia coli Cells Treated with a Combination of High Hydrostatic Pressure and Subzero Temperature

“…Condensation of nucleoids was also reported for L. monocytogenes (21) and L. plantarum (41). More recently, Mañas and Mackey (22) observed nucleoid condensation of E. coli cells in both exponential-and stationary-phase cells stained with DAPI. In addition, our TEM micrographs showed the appearance of dense clusters that correspond to aggregated cytosolic proteins and ribosomes.…”

“…In addition, our TEM micrographs showed the appearance of dense clusters that correspond to aggregated cytosolic proteins and ribosomes. Such clumps have been reported for S. enterica (21), E. coli (22), and Leuconostoc mesenteroides (14). Table 1 presents an attempt to examine nucleoid condensation and protein aggregation in conjunction with microbial inactivation after different pressure treatments for 10 min.…”

“…The cell membrane has been suggested to be one of the major targets (8,22,25,39,40). Loss of physical integrity of E. coli outer and inner membranes has been demonstrated by the increased uptake of fluorescent probes such as propidium iodide (PI), a DNA binding dye that does not penetrate intact cytoplasmic membranes (1,8,25), and the hydrophobic dye 1-N-phenylnaphtylamine, which is excluded from access to outer and cytoplasmic phospholipids by an intact outer membrane (8, 13).…”