Dodecylamine rapidly kills of spores of multiple Firmicute species: properties of the killed spores and the mechanism of the killing.

AIMS: Previous work showed that Bacillus subtilis dormant spore killing and germination by dodecylamine take place by different mechanisms. This new work aimed to optimize killing of B. subtilis and other Firmicutes spores and to determine the mechanism of the killing. METHODS AND RESULTS: Spores of seven Firmicute species were killed rapidly by dodecylamine under optimal conditions and more slowly by decylamine or tetradecylamine. The killed spores were not recovered by additions to recovery media, and some of the killed spores subsequently germinated, all indicating that dodecylamine-killed spores truly are dead. Spores of two species treated with dodecylamine were more sensitive to killing by a subsequent heat treatment, and spore killing of at least one species was faster with chemically decoated spores. The cores of dodecylamine-killed spores were stained by the nucleic acid stain propidium iodide, and dodecylamine-killed wild-type and germination-deficient spores released their stores of phosphate-containing small molecules. CONCLUSIONS: This work indicates that dodecylamine is likely a universal sporicide for Firmicute species, and it kills spores by damaging their inner membrane, with attendant loss of this membrane as a permeability barrier. SIGNIFICANCE AND IMPACT OF THE STUDY: There is a significant need for agents that can effectively kill spores of a number of Firmicute species, especially in wide area decontamination. Dodecylamine appears to be a universal sporicide with a novel mechanism of action, and this or some comparable molecule could be useful in wide area spore decontamination.

Killing of bacterial spores by dodecylamine and its effects on spore inner membrane properties.

AIMS: The objective of this study was to determine the effects of Ca-dipicolinic acid (CaDPA), cortex-lytic enzymes (CLEs), the inner membrane (IM) CaDPA channel and coat on spore killing by dodecylamine. METHODS AND RESULTS: Bacillus subtilis spores, wild-type, CaDPA-less due to the absence of DPA synthase or the IM CaDPA channel, or lacking CLEs, were dodecylamine-treated and spore viability and vital staining were all determined. Dodecylamine killed intact wild-type and CaDPA-less B. subtilis spores similarly, and also killed intact Clostridiodes difficile spores ± CaDPA, with up to 99% killing with 1 mol l-1 dodecylamine in 4 h at 45°C with spores at ~108  ml-1 . Dodecylamine killing of decoated wild type and CLE-less B. subtilis spores was similar, but ~twofold faster than for intact spores, and much faster for decoated CaDPA-less spores, with ≥99% killing in 5 min. Propidium iodide stained intact spores ± CaDPA minimally, decoated CaDPA-replete spores or dodecylamine-killed CLE-less spores peripherally, and cores of decoated CaDPA-less spores and dodecylamine-killed intact spores with CLEs. The IM of some decoated CaDPA-less spores was greatly reorganized. CONCLUSIONS: Dodecylamine spore killing does not require CaDPA channels, CaDPA or CLEs. The lack of CaDPA in decoated spores allowed strong PI staining of the spore core, indicating loss of these spores IM permeability barrier. SIGNIFICANCE AND IMPACT OF THE STUDY: This work gives new information on killing bacterial spores by dodecylamine, and how spore IM's relative impermeability is maintained.