Biological Agents - Bacteria
Bacteria are one-celled organisms that vary in shape and size from round cells (cocci) to long rod-shaped organisms (bacilli). The interior of the cell contains the nuclear material (DNA), cytoplasm, and cell membrane necessary for the life of the bacterium. Under special circumstances, some types of bacteria can transform into spores, which are more resistant to cold, heat, drying, chemicals and radiation than the bacterium itself. Like the seeds of a plant, spores lie dormant until conditions are favorable to germinate. Bacteria generally cause disease in humans and animals in one of two ways: by invading host tissues and/or by producing poisons (toxins). Many bacteria cause disease both ways.