Neutrophil engulfing bacteria. Coloured scanning electron micrograph (SEM) of a neutrophil engulfing Pseudomonas aeruginosa bacteria. P. aeruginosa is a non-invasive and opportunistic pathogen that rarely infects healthy individuals. It infects patients with compromised immune systems, and is a major cause of hospital-acquired (nosocomial) infections. Neutrophils are part of the body's immune response. They are highly motile, moving rapidly to areas of the body that are damaged or infected. They extrude extracellular traps to catch and engulf (phagocytose) and destroy pathogens such as bacteria and viruses, and foreign material that has entered the body.