Similar to sperm, bacteria can represent attraction, where you can become 'infected' or transformed by allowing your biological drives free reign within you. At the same time, infection or ‘getting something from others’ carries the message of how you are being influenced by those around you.
To dream of watching bacteria in a Petri dish denotes your sense of gaining insight into how you feel about your biological drives. Germs can appear ‘unclean’ and threatening, or they can portray the sense of how things happen to your body that are beyond your control. It can symbolize sexual feelings, where ideas take hold and simply grow. A virus shows the power of thought and its connection to what unfolds in experience. The fever that is connected to illness shows feelings (possibly anger) that needs to be released.