A bacteriologist is a scientist whose work is the scientific study of bacteria — those tiny living things that can help us or make us ill. They grow bacteria in labs, look at them under a microscope, and try to learn how they live, how they spread, and which medicines can stop the harmful ones. Some work in hospitals, some in universities, some in food or water safety. The word is formal and belongs to science; it is the name of a job, not the name of the subject. Though actually, in everyday English people sometimes just say “a lab scientist,” but bacteriologist is the exact title for this work.