Rhodotorula mucilaginosa is a species of yeast that produces colonies with a distinct pink, orange, or red appearance. This coloration comes from carotenoid pigments, which are thought to protect the organism from ultraviolet light. This yeast is a basidiomycete, a group of fungi that includes mushrooms and smuts, and it reproduces by budding.
Common Environmental Presence
Rhodotorula mucilaginosa is widespread in environments from soil and lakes to ocean water, and its adaptability allows it to thrive in diverse temperatures. It is frequently found in households, causing the pink or orange film on shower curtains, tile grout, and sink drains. Its ability to survive with very little nitrogen allows it to colonize these nutrient-poor surfaces.
Beyond the home, R. mucilaginosa is present in natural ecosystems and on food products like fruit juices and cheeses. It has been isolated from plant surfaces and even crustaceans. This yeast’s resilience allows it to be found in extreme environments, including the soils of Antarctica.
The pinkish residue in bathrooms can also be caused by the bacterium Serratia marcescens, which is often mistaken for R. mucilaginosa. While both produce a similar pigment, R. mucilaginosa is a yeast (fungus) and S. marcescens is a bacterium. S. marcescens prefers wetter locations like the toilet bowl, while the yeast is more common on surfaces like shower grout.
Role as an Opportunistic Pathogen
Rhodotorula mucilaginosa is considered an opportunistic pathogen, a microorganism that does not cause illness in healthy people. Its presence on the skin or in the environment is harmless for most individuals, as it exists as a saprophyte living on decaying organic matter.
An opportunistic pathogen can cause an infection when a person’s immune system is compromised or when it enters sterile parts of the body. For R. mucilaginosa, this means it can become an agent of infection under specific circumstances. These infections are uncommon in the general population but are seen more frequently in healthcare settings.
Associated Human Infections and Risk Factors
The most common infection caused by Rhodotorula mucilaginosa is fungemia, the presence of fungi in the bloodstream. These infections are frequently linked to indwelling medical devices like central venous catheters (CVCs). The yeast can form biofilms, which are microbial communities that adhere to surfaces like catheters and are difficult to eradicate.
Less common infections include meningitis, eye infections (endophthalmitis), and peritonitis, an inflammation of the abdominal lining. Fungemia accounts for the vast majority of infections, with one review showing it comprised 79% of cases. The mortality rate for Rhodotorula infections is reported to be between 12% and 20%.
Individuals most at risk for a Rhodotorula infection are those with weakened immune systems. Risk factors include:
- Cancer, particularly hematologic malignancies
- Chemotherapy or corticosteroid treatments
- HIV/AIDS
- The presence of a central venous catheter (CVC)
- Recent surgery or use of broad-spectrum antibiotics
- Being a premature infant
Management and Treatment
In a household, managing Rhodotorula mucilaginosa requires regular cleaning and moisture control. The pink film can be removed from surfaces with household cleaners containing bleach. Keeping these areas clean and dry prevents the yeast from growing, as it thrives in damp conditions.
In a clinical setting, treating an infection is complex. The primary step in managing a bloodstream infection is removing the contaminated medical device, like a CVC, which often serves as the source of the infection. This action alone can sometimes be sufficient to resolve the fungemia.
Medical treatment for invasive infections involves antifungal medications. The yeast is resistant to certain antifungals like echinocandins and fluconazole, so treatment relies on other agents such as amphotericin B. Antifungal susceptibility testing helps guide the selection of the most effective medication.