Color enhanced SEM of human macrophage ingesting pseudomonas. Macrophages are white blood cells (leukocytes) or mononuclear phagocytes that ingest bacteria as part of the immune response to infection. Pseudomonas is a widespread soil bacterium which acts as an opportunic pathogen. This bacteria is pathogenic in humans, but mainly restricted to opportunistic infections in compromised hospital patients. Original 9l0452.