the immune system attacks bacteria once they have invaded the body
bacteria_can_cause_disease is pathogen. bacteria is not one_cause_of_illness. bacterial_agent is bacterium. plague_bacterium is bacterial_agent. swarming_bacterium is bacterium. bacteria is one_cause_of_illness. bacterial_pneumonia is bacterial_infection. pathogen is infectious_agent. bacterial_agent is not bacterium. salmonella_bacterium is bacterial_agent.