Tests on intracellular pH (pHi) in the resistant
sub-population showed that the pHwasmuch lower, ~ pH 5.6, than in the sensitive bulk population. The hypothesis
is proposed that extreme resistance toweak-acid preservatives in Z. bailii is due to population heterogeneity,
with a small proportion of cells having a lower intracellular pH. This reduces the level of accumulation of any
weak acid in the cytoplasm, thus conferring resistance to all weak acids, but not to other inhibitors.