Acetic acid stress induces resistance and growth adaptation of Bacillus weihenstephanensis KBAB4.

Abstract

Aims: Bacillus weihenstephanensis KBAB4 is a Gram-positive bacterial strain belonging to the group Bacillus cereus. In this study, the impact of the physiological state on acetic acid resistance and on growth limits was investigated.

Methods and results: Strain KBAB4 was cultivated in BHI medium to produce reference cells (BHI, pH 7.2), HCl-adapted cells (BHI, pH 5.5), or acetic acid-adapted cells (BHI, pH 5.5+14 mM of acetic acid). The bacterial resistance of these cells was measured by inactivation, monitoring the reduction of the bacterial concentration in BHI, pH 5.5 + 150 mM of acetic acid. The growth limits of reference or acid-adapted cells were assessed on 96-well plates with BHI medium supplemented with HCl (pH 4.6 to 5.2) or acetic acid (from 14 mM to 150 mM). The acid resistance (δ, i.e. the first decimal decrease) during inactivation increased almost 3-fold for the HCl-adapted cells and 5-fold for the acetic acid-adapted cells, compared to the reference cells. The pH growth limits and the minimal inhibitory concentration of acetic acid were not affected by HCl adaptation, whereas they were modified for acetic acid-adapted cells.

Conclusions: For strain KBAB4, within an isogenic population, the bacterial life history influences the inactivation time during lethal acetic acid exposure, as well as the growth limits. This raises the question of whether this factor should be considered in the assessment of microbiological risks in food safety models for other B. cereus strains, since variability in the physiological state could be a decisive factor influencing food safety.