the immune system attacks bacteria once they have invaded the body
bacterial_infection is infection. pathogen is infectious_agent. bacteria is one_cause_of_illness. bacterial_agent is bacterium. plague_bacterium is bacterial_agent. bacterial_pneumonia is bacterial_infection. bacteria_can_cause_disease is pathogen. salmonella_bacterium is bacterial_agent. tuberculosis is bacterial_infection. swarming_bacterium is bacterium.