Many extracellular pathogenic bacteria colonize human or animal bodies through evasion of the host immune system, a process called host-pathogen interaction. What happens when other intruders try to invade the same host and try to establish themselves in the same niche is largely unknown. In one well-studied case, Pseudomonas aeruginosa is known to secrete the protein azurin as a weapon against such invaders as cancers, parasites and viruses. The production of such weapons by pathogenic bacteria could provide important insights into how a pathogen responds in the post-colonization state to impede other intruders for its own survival. Moreover, these molecules might find use in the pharmaceutical industry as next-generation therapeutics.