Serratia marcescens is a bacterium commonly found in various environments, often drawing attention due to its distinctive red or pink coloration. This widespread microorganism can appear in unexpected places, leading many to wonder about the source of its vibrant hue.
The Red Pigment
The characteristic red color of Serratia marcescens stems from a specific pigment known as prodigiosin. This compound is a secondary metabolite, meaning it is not directly involved in the bacterium’s primary growth or metabolism. Prodigiosin is chemically classified as a tripyrrole pigment, characterized by its structure containing three pyrrole rings.
Not all strains of Serratia marcescens produce this pigment; some are non-pigmented. Even among strains that do produce prodigiosin, the intensity of the color can vary widely, ranging from light pink to a deep, dark red. This variability contributes to the different appearances of Serratia marcescens growth observed in various settings.
Conditions for Color Production
Several environmental factors significantly influence the production of prodigiosin by Serratia marcescens. Temperature is a primary determinant, with optimal pigment production occurring within a range of 20°C to 30°C. Temperatures above this range can inhibit or prevent pigment formation, resulting in colorless bacterial growth.
Nutrient availability also plays a role in prodigiosin synthesis. For instance, phosphate limitation can enhance pigment production. The presence of specific amino acids or certain carbon sources can also impact the amount of pigment produced. These variable conditions explain why a red stain might be visible one day but absent or less intense another, even in the same location.
Common Habitats
Serratia marcescens is highly adaptable and commonly thrives in moist environments. It is frequently found in domestic settings, often responsible for the pink or orange-red slimy film seen in bathrooms on shower grout, toilet bowls, sinks, and drains. This bacterium feeds on fatty residues from soap and shampoo, contributing to its prevalence in these areas.
Beyond the household, it naturally inhabits soil, water, and can be found on some foods. Serratia marcescens forms biofilms, which are protective layers that allow bacteria to adhere to surfaces and resist removal. This characteristic enables it to persist in damp conditions.
Health Considerations
While Serratia marcescens is considered a low-virulence organism for healthy individuals, it can act as an opportunistic pathogen, particularly in healthcare settings. It is a cause of hospital-acquired infections. Patients with weakened immune systems or those with medical devices are at higher risk of infection.
This bacterium can be associated with various infections, including:
- Urinary tract infections
- Respiratory tract infections like pneumonia
- Wound infections
- Bloodstream infections
- Meningitis
- Eye infections
To minimize exposure in the home, regular cleaning of moist surfaces with household cleansers and disinfectants is recommended. Good hand hygiene practices are also important in preventing its spread.