Serratia
Summary
Serratia marcescens is a motile, non-lactose-fermenting gram-negative rod of the Enterobacteriaceae that produces a red pigment, prodigiosin. It is an opportunistic nosocomial pathogen causing pneumonia, urinary tract infection, and bacteraemia, and is often multidrug resistant.
Detail
Serratia is one of the classic hospital-acquired gram-negatives, thriving in moist environments such as ventilators, catheters, intravenous fluids, and soap dispensers, and it has caused outbreaks traced to contaminated infusions and to injection drug use. It is a member of the SPACE or SPICE group — Serratia, Pseudomonas, Acinetobacter, Citrobacter, Enterobacter — which carry inducible chromosomal AmpC beta-lactamase; this is examinable because these organisms may appear susceptible to third-generation cephalosporins in vitro yet develop resistance during treatment, so cefepime or a carbapenem is preferred. Serratia is also catalase-positive, which matters in chronic granulomatous disease, where NADPH oxidase deficiency leaves patients susceptible to catalase-positive organisms including Staphylococcus aureus, Serratia, Nocardia, Burkholderia cepacia, and Aspergillus, diagnosed by an abnormal dihydrorhodamine flow cytometry test. The red pigment is a helpful visual clue but is produced by only some strains and mainly at room temperature.
Sources
- Levinson Medical Microbiology and Immunology
- First Aid for the USMLE Step 1
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.