Serratia marcescens is a gram-negative, rod-shaped opportunistic bacteria belonging to the family Yersiniaceae. Immunocompromised or debilitated birds are more at risk of secondary infection with S. marcescens. S. marcescens tends to invade their host via the respiratory tract, and is responsible for causing a wide range of infections involving the respiratory tract, urinary tract, bloodstream, skin, brain, and heart.
Where found: S. marcescens is found throughout the environment, especially in areas with damp conditions. The pathogen commonly grows in bathrooms, particularly on tile grout, shower corners, toilet water lines, and basins. It is identifiable as a pink, pink-orange, or orange discoloration and slimy film feeding off phosphorus-containing materials or fatty substances such as soap and shampoo residue.