Plasma effects on bacterial spores in a wet environment

An arc-seed microwave plasma torch, which can run stably at low airflow rate (e.g., 0.3931s^-1) and produces an abundance of reactive atomic oxygen in its plasma effluent, is applied for studying the effects of atomic oxygen on bacterial spores in solution. Bacillus cereus was chosen as the biological agent. The experimental results show that the plasma effluent can penetrate into water to kill B. cereus spores. The kill time (i.e., 10-fold reduction time) is about 10s at an exposure distance of 3 cm, 24 s at 4 cm, and 31 s at 5 cm. Morphological studies are performed via scanning electron and atomic force microscopes, which take two- and three-dimensional images of spores to record the changes in their morphological structures and shapes caused by the plasma effluent. The loss of appendages and exosporium in the structure as well as flattened cell shapes are observed.