Dermal tissue is to a plant as epithelialtissue is to an animal.
Dermal tissue on a plant is basically like the plant's skin, while epithelial tissue is the animal's skin. They're both very similar, and both serve to protect the plant/animal.
Water would move out of the cells of the microorganisms by osmosis and the cytoplasm would become dehydrated, killing the cells. The brine is a hypertonic solution, thereby "pulling" the water out of the bacterial cells.
