Candida Species and Candidiasis
On this page
Direct answer
Candida species are yeasts that live harmlessly on the skin and mucosa, and they cause candidiasis when host defences or anatomical barriers fail. Candida albicans is the commonest species and the one that forms a germ tube in serum at 37 °C. Invasive candidiasis in ICU or neutropenic patients is the high-yield form, and an echinocandin is the first-line treatment while the species and its susceptibility are still unknown.
What you must remember
- Germ tube test: Candida albicans forms germ tubes within about two to three hours in serum at 37 °C, and Candida dubliniensis is the only other common species that does so.
- Chlamydospores: thick-walled resting spores on cornmeal agar are a feature of Candida albicans and Candida dubliniensis.
- Candida glabrata: germ tube negative, a small budding yeast without pseudohyphae, with reduced fluconazole susceptibility.
- Candida krusei: intrinsically resistant to fluconazole, so it is treated with an echinocandin or amphotericin B.
- Candida auris: an emerging multidrug-resistant yeast that spreads in hospitals and colonises skin, and some older commercial systems misidentify it.
- Candidaemia management: an echinocandin such as micafungin or caspofungin first-line, early removal of the central venous catheter and step-down to fluconazole once the isolate is susceptible.
- Ocular involvement: dilated fundoscopy is essential in every patient with candidaemia, because chorioretinitis and endophthalmitis can be silent.
A fever with yeast in the blood
A patient in the medical ICU has a central venous catheter, has received broad-spectrum antibiotics for a week and develops persistent fever. Blood cultures grow budding yeasts.
- Confirm the yeast: a Gram stain of the positive bottle shows budding yeast, and the species is identified by a rapid method such as MALDI-TOF or a germ tube test where available.
- Remove the source: the central catheter is removed early, because the biofilm on it harbours the yeast, and a new line is placed only after blood cultures clear.
- Start an echinocandin: micafungin, caspofungin or anidulafungin is first-line in the unstable or neutropenic patient, without waiting for the species result.
- Examine the eyes: a dilated fundus examination looks for chorioretinitis, and ophthalmology review is needed if lesions are seen.
- Step down by species: fluconazole is used once the patient is stable and the isolate is susceptible, while Candida krusei and resistant isolates stay on an echinocandin or amphotericin B.
Each step is driven by the host and the laboratory result, so the empirical drug is changed as soon as the species and susceptibility are known.
Where the exam tries to catch you
Candida questions reward precise knowledge of species differences and first-line drugs.
- Trap: treating Candida auris like ordinary albicans candidaemia Correct: Candida auris is often resistant to several drug classes and spreads in hospitals, so screening, contact precautions and environmental cleaning come first.
- Trap: giving fluconazole first to a critically ill patient with unknown species Correct: an echinocandin is first-line until susceptibilities return, because fluconazole fails against Candida krusei and some Candida glabrata isolates.
- Trap: calling a germ tube negative yeast Candida albicans Correct: only Candida albicans and Candida dubliniensis form germ tubes, and Candida glabrata is a germ tube negative yeast that needs further identification.
Frequently asked questions
What does a positive germ tube test indicate in Candida?
A positive germ tube test indicates Candida albicans or Candida dubliniensis, because germ tubes form within hours in serum at 37 °C. Other species, including Candida glabrata, are germ tube negative and need further identification. The test is quick and inexpensive, so it is a common first step in laboratories.
Why is Candida auris a concern in hospitals?
Candida auris is a multidrug-resistant yeast that colonises skin, spreads between patients and survives on hospital surfaces for prolonged periods. Some older commercial identification systems misidentified it, which delayed recognition. Control depends on screening, contact precautions and environmental disinfection.
Which antifungal is first-line for candidaemia in a critically ill patient?
An echinocandin such as micafungin or caspofungin is first-line for candidaemia in critically ill or neutropenic patients. Fluconazole is reserved for stable patients with susceptible isolates, and amphotericin B is used in some settings. The choice is revised once susceptibility results are available.
Why must the eyes be examined in candidaemia?
Candidaemia can seed the eye and cause chorioretinitis or endophthalmitis, which may be painless in the early stages. A dilated fundus examination is therefore performed in every patient with candidaemia. Ophthalmology review is needed whenever lesions are found.