Inactivation of Bacterial Spores by Hydrostatic Pressure

TLDR

Pressure inactivates spores by first triggering germination and then killing the germinated forms, as indicated by chemical, phase‑contrast, and electron‑microscopic changes. Hydrostatic pressure up to 8000 atm inactivated Bacillus and Clostridium spores, with inactivation depending on pressure‑holding time, temperature (rapid at high temperatures, optimum pressure below 50 °C), pH, and ionic strength; extreme pH or high ionic strength reduced inactivation, and some spores became heat‑sensitive after pressurization.

Abstract

SUMMARY: Spores of various species of the genera Bacillus and Clostridium were inactivated by hydrostatic pressures up to 8000 atmospheres. Inactivation was a function of holding time at pressure rather than of the compression and decompression stages. Inactivation generally proceeded more rapidly at high than at low temperatures; below about 50° there was a well defined optimum pressure for inactivation, but above about 50° an increase in pressure up to 8000 atmospheres caused progressively more inactivation. Inactivation was decreased at extremes of pH value and by high ionic strength solutions. A proportion of the spores pressurized under certain conditions became heat-sensitive. These observations, and the chemical, phase-contrast, and electron-microscopic changes seen in pressurized spores, suggested that pressure caused inactivation of spores by first initiating germination and then inactivating the germinated forms.