Inhibition of Bacillus anthracis and potential surrogate bacilli growth from spore inocula by nisin and other antimicrobial peptides.

The ability of nisin, synthetic temporin analogs, magainins, defensins, and cecropins to inhibit Bacillus anthracis, Bacillus cereus, Bacillus thuringiensis, Bacillus mycoides, and Bacillus subtilis growth from spore inocula was determined using well diffusion assays. Nisin, magainin II amide, and defensins were inhibitory in screening against B. anthracis Sterne or B. cereus ATCC 7004, but only nisin inhibited virulent B. anthracis strains. The MICs of nisin against the 10 Bacillus strains examined were 0.70 to 13.51 microg/ml. Synthetic temporin analogs also inhibited B. anthracis but were not as potent as nisin. None of the strains examined were appropriate B. anthracis surrogates for testing sensitivity to antimicrobial peptides.

Growth characteristics of virulent Bacillus anthracis and potential surrogate strains.

The objectives of this study were to compare generation and lag times of virulent Bacillus anthracis strains with those of other Bacillus strains, to identify possible surrogates for growth studies, and to determine if the B. cereus module of the U.S. Department of Agriculture Pathogen Modeling Program (PMP) had predictive value for B. anthracis. Growth characteristics of B. anthracis, B. cereus, B. mycoides, and B. subtilis strains in brain heart infusion broth at pH 6.5, 6.0, and 5.5 were determined by absorbance measurements. Growth curves of B. anthracis Sterne and B. cereus strains appeared similar, and the generation times for strain Sterne fell within the PMP's 95% confidence interval for B. cereus. However, the virulent B. anthracis strains Vollum and Pasteur had shorter generation times than the avirulent Sterne strain and most other surrogates and were lower than the PMP's 95% confidence interval for B. cereus. Growth curves of B. cereus ATCC 9818 and B. subtilis ATCC 6633 were more similar to those of virulent B. anthracis strains, but all potential surrogates had significantly different generation times and lag times under some conditions.

Thermal resistance of spores from virulent strains of Bacillus anthracis and potential surrogates.

The objective of this study was to determine the thermal resistance of spores of Bacillus anthracis and potential surrogates. The heat resistance of spores suspended in buffer (pH 7.0 or 4.5), milk, or orange juice was determined at 70, 80, and 90 degrees C. D-values for B. anthracis strains Sterne, Vollum, and Pasteur ranged from < 1 min at 90 degrees C to approximately 200 min at 70 degrees C and were lower under acidic than under neutral conditions. The D-values for B. anthracis spores fell within the range obtained for spores from eight strains of Bacillus cereus, Bacillus thuringiensis, Bacillus mycoides, and Bacillus subtilis. However, there were significant differences (P < 0.001) among the D-values of the strains. The z-values in pH 7.0 buffer and milk averaged approximately 10.5 degrees C and were not significantly different among strains (P < 0.05). The z-values in pH 4.5 buffer and orange juice averaged 12.9 and 13.9 degrees C, respectively, significantly (P < 0.05) higher than those obtained in milk or in pH 7.0 buffer. The significance of this difference was driven by large differences among a few strains. The z-values for B. anthracis strain Pasteur were twice as high in the acid media than in the neutral media. This study confirms that B. anthracis spores are not unusually heat resistant and that spores from validated Bacillus species are appropriate surrogates for thermal resistance studies.