Rhodotorula mucilaginosa

Associated infections

• Catheter-related fungaemia and bloodstream infection
• Endocarditis, rarely
• Meningitis in immunocompromised hosts, rarely
• Peritonitis in peritoneal dialysis patients
• Endophthalmitis
• Skin and soft tissue infection
• Ventriculoperitoneal shunt infection, reported rarely
• Colonisation of respiratory specimens without infection

Transmission route

Acquisition is environmental rather than person-to-person, and the principal route to clinical infection is contamination of an indwelling device. Rhodotorula species have a strong affinity for plastic surfaces and are efficient biofilm formers, and they have been recovered from central venous catheter tips and from flexible endoscope channels. This affinity for polymeric surfaces makes the organism relevant to reprocessing in a way that many environmental yeasts are not.

Within a healthcare building, the reservoirs are the wet, low-flow parts of the system rather than the treated water itself: tap outlets and aerators, flexible hoses, spray arms, seals and gaskets, drain traps, condensate trays, humidifier reservoirs and any vessel where water stands between uses. Movement from these reservoirs onto equipment occurs through splash, through direct contact at the point of use, and through the final rinse if a contaminated fitting sits downstream of the treatment train. Airborne dispersal from drains and from wet cleaning activity contributes at short range and is one reason samples taken close to a sink can be positive when the water itself is not.

In a water-quality context, Rhodotorula is genuinely water-associated and can colonise wet points downstream of treatment: taps, hoses, spray arms, storage vessels, connectors and inadequately dried endoscope channels or storage cabinets. A single isolation may reflect sampling or airborne contamination, but repeated recovery from final rinse water or from channel samples should prompt investigation of residual moisture, drying protocols, point-of-use filtration and biofilm in distribution pipework and fittings rather than being dismissed. Because the organism grows in nutrient-poor water, remediation that addresses only organic loading without addressing stagnation and biofilm is unlikely to be durable.

Relevance in endoscopy and reprocessing

Rhodotorula has a specific and well-documented place in endoscope reprocessing. Hagan and colleagues reported a pseudoepidemic in which Rhodotorula rubra was recovered from bronchoscopy specimens from eleven patients; investigation identified contamination of the bronchoscope suction channel with the yeast together with potentially pathogenic bacteria. Isolates ceased after the scope was reprocessed appropriately and an alcohol and air flush was introduced through the suction channel to ensure complete drying between patients. The episode is instructive on two counts. First, it produced no infections but a substantial burden of false-positive results, with the attendant risk of unnecessary antimicrobial treatment and diagnostic confusion, which is the characteristic harm of a pseudo-outbreak. Second, the intervention that resolved it was a drying intervention, not a change of disinfectant, which locates the fault precisely.

That is the general lesson for this organism. Rhodotorula is not notably resistant to high-level disinfection; as a vegetative yeast it is inactivated by peracetic acid, glutaraldehyde and ortho-phthalaldehyde delivered correctly, and by thermal disinfection in a washer-disinfector. What it exploits is the interval after disinfection. A channel that retains moisture, a connector that is not purged, an elevator recess that holds a droplet, or a storage cabinet whose air supply is inadequate or unfiltered all provide the conditions this organism needs, and it will grow on the trace organic carbon present in rinse water without any additional nutrient input. Once established as biofilm on the channel lining, it becomes markedly harder to eliminate with a standard cycle and tends to recur after apparently successful remediation.

The practical implications for endoscopy, CSD and dental water are consistent. Verified channel drying, whether by forced medical-grade air, an alcohol flush where the manufacturer permits it, or a validated drying cabinet with a demonstrated air change rate, is the primary control. Storage cabinets require documented performance and periodic internal cleaning rather than assumed function. In CSD, wet load carriers, spray arms and standing water in chamber sumps warrant attention. In dental settings, waterlines that sit idle overnight and over weekends are a classic niche, and visible pink staining at a line outlet or in a bottle reservoir should be treated as a finding requiring line disinfection rather than a cosmetic issue.

Interpreting a detection

Rhodotorula is one of the organisms for which a positive water result is genuinely plausible. Unlike Candida albicans or Candidozyma auris, this yeast is a legitimate resident of wet points in built water systems, so a detection should not be assumed to be a handling artefact. That said, the organism is also common in air and on wet surfaces generally, so a single low-count isolate remains consistent with airborne or contact contamination during sampling, particularly where the sample was taken adjacent to a sink or drain.

The first checks focus on where water stands. Establish where in the system the sample was taken and what lies between the treatment train and that point: hose length, fittings, aerators, filters and their change dates. Ask how frequently the outlet is used and whether it had been standing idle. Inspect the accessible wet components for visible pink or orange staining, which for this organism is a genuinely useful field indicator. Confirm that samples taken at the treatment plant outlet were negative, since a positive at the point of use with a negative upstream localises the problem to the distribution tail and changes the remediation entirely. Review the drying and storage stages of the reprocessing cycle in parallel, because a Rhodotorula finding in a channel sample points there first.

A single isolate with no repeat and no clinical linkage is reasonably managed by remediating the implicated fitting, flushing the outlet, reviewing filter change intervals and repeating the sample. A trend carries considerably more weight. Repeated recovery from the same outlet, from successive final-rinse samples, or from multiple scopes indicates an established biofilm rather than transient contamination, and remediation should target the physical niche: replacement rather than disinfection of hoses and flexible tubing, service of aerators and spray arms, elimination of dead legs and low-flow branches, and verification of drying cabinet performance. Escalation to the facility infection-prevention service is warranted where detection persists after remediation, where counts are rising, where the same organism is recovered from both water and reprocessed devices, or where any immunocompromised patient has a Rhodotorula isolate temporally linked to the implicated equipment. Because the organism is intrinsically resistant to the antifungals used empirically for candidaemia, a clinical isolate in such a patient is a matter of some urgency and the environmental link should be communicated promptly.

Antimicrobial resistance

Rhodotorula species show intrinsically reduced susceptibility to the azole antifungals, including fluconazole and voriconazole, and are intrinsically resistant to the echinocandins because their cell wall composition and target enzyme differ from those of Candida species. Amphotericin B, alone or with flucytosine, is the agent most consistently active in vitro and is the usual basis of treatment. Management of catheter-related Rhodotorula fungaemia normally requires removal of the implicated line in addition to antifungal therapy. Because empirical antifungal regimens directed at candidaemia commonly use fluconazole or an echinocandin, correct species identification materially changes clinical management, and a laboratory report of a pink or pigmented yeast should prompt definitive identification rather than being treated as a presumptive Candida.

With respect to disinfection, the organism has no notable chemical resistance in planktonic form. It is inactivated by the high-level disinfectants used in endoscope reprocessing, by thermal disinfection, and by free chlorine at concentrations used in water treatment and in dental waterline shock protocols. The tolerance that matters is biofilm-associated. Growing within an extracellular matrix on the interior of a hose, a channel lining or a storage vessel, the organism withstands short-contact disinfection and routine flushing, and the effect is compounded where biofilm is mixed and includes bacterial partners contributing additional matrix.

The operational conclusion is that chemical intervention alone is an unreliable remedy for a persistent Rhodotorula problem. Durable control comes from removing the conditions that sustain it: eliminating stagnation and dead legs, replacing rather than repeatedly disinfecting flexible components that have become colonised, maintaining point-of-use filtration where specified, and above all achieving verified drying of channels and storage environments. Facilities that respond to a repeat detection with an additional disinfection cycle and no change to drying practice should expect the organism to return.