The Surata IV Microbes are a species of microscopic life forms from the planet Surata IV, which have developed a symbiotic relationship with the local predatory vines.
The mobile vines provide hollow thorns where the microbial spores can be stored. When the vine detects the approach of a warm-blooded organism, it intentionally stabs them with its thorns in order to infect them with the microbes; which then proceed to attack the victims' nervous system and kill it. The vine benefits by feeding on the victim's corpse afterwards.
According to Dr. Pulaski, these microbes can't be considered bacteria or viruses, but instead have elements of both. When they infect a victim, they fuse themselves to the surrounding nervous tissue at a molecular level, resulting in that a transporter's bio-filter isn't capable of removing them.
- Star Trek: The Next Generation, s02e22, "Shades of Grey" (1989)