Most bacteria do not cause human disease

Most bacteria are not human disease-causing pathogens; many live in the environment or as part of normal microbial communities. But the exact “1%” depends on what is counted: described species, strains, all bacteria on Earth, or those that can interact with humans. Some bacteria can be harmless in one body site or host but cause infection under different conditions. “Only a minority are pathogenic” is a sound generalization; exactly one percent is a rough estimate, not a fixed proportion.