A-049. Inhibitory Effects of Nisin against Bacillus anthracis Spores

I. M. Gut, A. M. Prouty, W. A. van der Donk, S. R. Blanke;
Univ. of Illinois, Urbana, IL.

During inhalational anthrax, the in vivo development of Bacillus anthracis from dormant spores into vegetative bacilli is an important step in the progression of disease. However, there are no current therapeutic strategies for disrupting B. anthracis development in vivo. Pursuant to this objective, we report that nisin, a well-studied lantibiotic, inhibits the in vitro outgrowth of germinated spores prepared from B. anthracis Sterne 7702. The minimum inhibitory concentration of nisin against B. anthracis spores was determined to be 0.6 μM, while the minimal bactericidal concentration was 40 μM. Interestingly, significantly higher nisin concentrations of 1 µM and 10 µM were demonstrated to inhibit vegetative bacilli and endospore growth in liquid culture, respectively, for 18 h, and consistent with previous studies, nisin prevented outgrowth of endospores. Although outgrowth was prevented, nisin did not inhibit the loss of refractility or heat resistance that accompanies the initiation of germination. This irreversible inhibition of spore outgrowth occurred only in the presence of a germinant. Following germination initiation, nisin prevented the establishment of a membrane potential and oxidative metabolism, but allowed the release of dipicolinic acid. Transmission electron microscopy demonstrated that even in the presence of nisin, the endospore core is freed from the exosporium, sporecoat, and cortex once germination is initiated. Collectively, these data suggest that nisin prevents the outgrowth of endospores through the modulation of the endospore membrane, while at the same time allowing the endospore core to become vulnerable to antimicrobial treatments.