HIGH-PRESSURE TRANSIENT SENSITIZATION OF ESCHERICHIA-COLI TO LYSOZYMEAND NISIN BY DISRUPTION OF OUTER-MEMBRANE PERMEABILITY

Escherichia coli MG1655 suspensions in 10 mM phosphate buffer (pH 7.0) were subjected to high pressures in the range of 180 to 320 MPa for 1 5 min. Cell death war evident at 220 MPa and increased exponentially w ith pressure. Surviving populations were sublethally injured, as demon strated by their reduced ability to form colonies on violet red bile g lucose agar, a selective growth medium containing crystal violet and b ile salts. During exposure to high pressure (>180 MPa), cells were sen sitive to lysozyme, nisin, and ethylenediaminetetraacetic acid (EDTA), as was apparent from an increased lethality of pressure in the presen ce of these agents. Sublethal injury in the surviving population was l ower in the presence of nisin and lysozyme, but higher in the presence of EDTA. Combinations of EDTA with nisin or lysozyme present during p ressure treatment increased lethality in an additive manner. However, the addition of lysozyme, nisin and/or EDTA to pressurized cell suspen sions immediately after pressure treatment did not cause any viable co unt reduction. Finally, we observed leakage of the periplasmic enzyme p-lactamase from an ampicillin-resistant recombinant E. coli MG1655 un der high pressure. These results suggest that high pressure transientl y disrupts the permeability of the E. coli outer membrane for water-so luble proteins.