A bacteria created hole in the hull of the Pagh
Bacteria were highly adaptable single-celled lifeforms. They were prokaryotic organisms that lacked a membrane-bound nucleus or membrane-bound organelles.
According to Captain Jonathan Archer, over seventy percent of the organisms on Earth were bacteria. (ENT: "The Andorian Incident")
Bacteria could be killed with antibiotics. (DS9: "Afterimage")
The Crystalline Entity left no trace of life behind on Melona IV, not even soil bacteria. (TNG: "Silicon Avatar")
Dr. Beverly Crusher first assumed that a bacterial infection was responsible for some VISOR malfunctions Geordi La Forge experienced in 2369. She later realized that tampering by solanogen-based lifeforms was responsible as she couldn't find any matching bacterial strain in the medical database. (TNG: "Schisms")
Upon his arrival in a village on Bajor in 2369, Dr. Julian Bashir ran a scan for bacteria in the water. (DS9: "The Storyteller")
In 2372, the USS Voyager's bio-neural gel packs were infected by bacteria from Neelix's brill cheese. (VOY: "Learning Curve")
In 2372, Bashir told Odo that an illness that made it difficult for him to hold his shape could be a bacterial infection. (DS9: "Broken Link")