Serratia marcescens: A colourful microbe

VOL. 9 NO. 1 JANUARY 2008 British Journal of Infection Control 25 Newsom’, said the professor,’ I want you to test this surgeon’s mask’. ‘Go to the roof garden, gargle with a broth culture of Chromobacterium prodigiosum, put the mask on and read aloud for ten minutes holding an agar plate in front of your mouth’. I thoroughly enjoyed escaping from the laboratory to the Westminster Medical School roof garden with its view of the Houses of Parliament. Today I would think twice about swallowing that culture, as we recognise Serratia marcescens as an antibiotic-resistant pathogen, capable of causing nosocomial infections. However its ability to produce a red pigment (prodigiosin) makes it a good marker germ (Figure 1), and growth on starchy foods means its effects have been recognised since medieval times. Today we call it a ‘coliform’ and link it with klebsiellas and enterobacters. Pigment is not produced by all strains, and laboratory subcultures may lose the ability to make it, so that colonies resemble those of other coliforms. It has been isolated from water, soil, sewerage, foodstuffs and animals. There are two excellent historical reviews one from Gaughren in 1969 and the other by Yu in 1979, from which I have quoted extensively.