FIG 7.

Viability and wet heat sensitivity of C. perfringens spores exposed to HP. Spores of C. perfringens were exposed to an HP of either 150 MPa (A and B) or 550 MPa (C and D) for various times, either without (A and C) or with (B and D) prior heat activation, and spores that retained DPA, phase-bright spores, spore viability, and spore viability after exposure to 89°C in water for 30 min were measured, all as described in Materials and Methods. Symbols: ○, spores that retained DPA (100 individual spores examined); ●, phase-bright spores (100 individual spores examined); △, spore viability determined in duplicate; and ▲, spore viability after heat treatment determined in duplicate. Values for spores that retained DPA and were phase bright are expressed relative to the average values in untreated spores; values for viability with and without a heat treatment are expressed relative to the viability of spores that were neither HP nor heat treated. Standard deviations for viability values were between ±30 and 50% in panels A and B. An experiment identical to that for this figure gave very similar results (data not shown).