Effect of pressure waves on bacteria suspended in water

Shock pressure waves with a frequency of 50/sec. and a maximal pressure of 60–70 kg./cm.2 greatly reduced the viability of E. coli. A similar effect was obtained also on staphylococci, enterococci, Salmonella Zanzibar, and coliphages T2. On the contrary no effect on spores of B. subtilis was found. The effect was practically independent of the maximal pressure within the range from 30–80 kg./cm.2, the highest pressure tested. The effect decreased with increasing cell density of the bacterial suspension. Bacteria surviving shock treatment died considerably more rapidly when stored at 4°C. than bacteria treated in the same way except for exposure to pressure waves. Morphological examinations with the aid of ordinary light microscopy as well as electron microscopy suggest that the effect was due to mechanical action on the bacterial cell walls.