Killing the spores of Bacillus species by molecular iodine.

AIMS: To determine the responses of spores of Bacillus subtilis and Bacillus anthracis surrogate Bacillus thuringiensis Al Hakam to I2 treatment.

METHODS AND RESULTS: Spores of B. subtilis and B. thuringiensis killed by aqueous 30°C-I2 could germinate, and their inner membrane (IM) was intact. Spore coats were important in I2 resistance, DNA-protective proteins were not important, and survivors of I2 treatment were not mutagenized. Viabilities of I2 -treated, 90-98% killed spores were much lower on high-salinity media, and the treated spores were more heat sensitive than the untreated spores. Germinated I2 -killed spores were dead as determined by staining with nucleic acid dyes, and many appeared to have been lysed.

CONCLUSIONS: Aqueous I2 appeared to kill B. subtilis and B. thuringiensis spores such that spores lyse soon after they germinate, and not by causing DNA damage or rupture of spores' IM. I2 treatment also generated many damaged spores that could only be recovered under nonstressful conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY: This work shows that spores of the model organism B. subtilis, and B. thuringiensis, a surrogate for B. anthracis spores, exhibit similar mechanisms of resistance to and killing by I2 . Generation by I2 treatment of conditionally dead spores indicates that appropriate media are essential to efficiently enumerate viable I2 -treated spores.