Candidiasis
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Direct answer
A germ-tube-positive, budding yeast with pseudohyphae in a clinical specimen is Candida albicans until proven otherwise — the germ tube (a lateral tube without a constriction, formed in serum at 37°C within about three hours) separates it from most other species, and chlamydospore formation on cornmeal agar completes the classical identification. The disease runs a spectrum from colonisation to thrush in neonates and inhaled-steroid users, vulvovaginitis with cottage-cheese discharge in pregnancy and diabetes, oesophagitis in advanced HIV, catheter-associated candiduria, and life-threatening candidaemia in the immunocompromised and intensive-care patient. Treatment scales with depth: topical clotrimazole or oral fluconazole for mucosal disease, intravenous fluconazole or an echinocandin for candidaemia, and source control — removing the central line — as the non-negotiable step; meanwhile Candida auris, the multidrug-resistant yeast that emerged in and spread through Indian intensive-care units, has made species identification and strict infection control simultaneous priorities.
What you must remember
- Bench card: oval budding yeast, pseudohyphae (true hyphae with parallel walls in tissue), germ tube positive for C. albicans; cornmeal agar with chlamydospores confirms; modern speciation rides on chromogenic (CHROMagar) and molecular platforms.
- Predisposing ladder for mucosal disease: antibiotics (flora loss), diabetes and pregnancy (glycogen and oestrogen), inhaled and systemic corticosteroids, advanced HIV with its CD4 decline, denture wear, and iron-deficiency anaemia with angular cheilitis completing the classical list.
- Oral candidiasis presentations: removable white pseudomembranes of thrush, erythematous patches, angular cheilitis, and denture stomatitis — the last needs denture hygiene, not just antifungals.
- Vulvovaginal candidiasis: thick, curdy, non-malodorous discharge with itching, pH normal (below 4.5), budding yeast on saline or potassium hydroxide mount — the pH point separates it from bacterial vaginosis and trichomoniasis.
- Recurrent disease (four or more episodes a year) prompts a diabetes screen and, in the Indian context, an HIV test; uncontrolled diabetes is the commonest correctable driver.
- Candidaemia risk: total parenteral nutrition, broad-spectrum antibiotics, central venous catheters, neutropenia and prolonged intensive care; endophthalmitis and hepatosplenic disease are sought before therapy is declared adequate.
- Candida auris: often multidrug resistant, with fluconazole resistance the rule; survives on skin and equipment for weeks; echinocandin first-line, amphotericin B for resistant strains, plus contact precautions and terminal room disinfection.
- Chronic mucocutaneous candidiasis points to T-cell immunodeficiency; oesophageal symptoms with oral thrush in HIV warrant empiric therapy.
From a swab to a blood culture bottle
A neutropenic patient on broad-spectrum antibiotics spikes a fever, and the blood culture flags yeast. The sequence: start an echinocandin (fluconazole only if the local map says susceptible), remove the central line, culture its tip, dilate both pupils and examine the fundi for candida endophthalmitis, and image for hepatosplenic disease if the fever lingers. The laboratory reports the species days later — and the species decides escalation: C. albicans usually yields to fluconazole, allowing a step-down once the patient is stable; C. auris demands echinocandin continuation, susceptibility testing and a ward-level outbreak response. Contrast the outpatient lanes: the diabetic woman with curdy discharge gets a potassium hydroxide mount and clotrimazole or single-dose fluconazole, plus glucose control; the asthma patient on inhaled steroids with thrush gets lozenges and mouth-rinsing after every steroid puff; the neonate with thrush gets topical therapy and a check of maternal hygiene — and each of them, if recurrent, gets a diabetes and HIV screen.
Where students slip
The germ tube is answered as if any Candida produces it — it is C. albicans (and the closely related C. dubliniensis), and a germ-tube-negative yeast is one of the others, which matters precisely in intensive care. Second, the pH of vaginal secretions is used backwards: candidiasis keeps the pH acidic, while bacterial vaginosis and trichomoniasis raise it — the exam pairs the pH number with the diagnosis and expects the match. Third, "candida in urine" triggers reflex antifungal prescribing, but asymptomatic candiduria in a catheterised patient is usually colonisation: remove or change the catheter and treat only symptomatic or high-risk patients. Fourth, the Candida auris stem — a yeast persisting on surfaces, resistant to fluconazole, spreading in an intensive-care unit — is asking for contact precautions and an echinocandin, not a stronger azole.
Frequently asked questions
What is the germ tube test?
Incubating the yeast in serum at 37°C for about two to three hours; a germ tube (a lateral appendage without a constriction at its base) identifies Candida albicans, the commonest pathogenic species.
How is vulvovaginal candidiasis distinguished from bacterial vaginosis?
Candidiasis gives a thick, curdy, itchy discharge with a normal acidic pH and budding yeast on microscopy; bacterial vaginosis gives a thin, malodorous discharge with pH above 4.5 and clue cells.
What is the first-line therapy for candidaemia?
An echinocandin such as caspofungin or micafungin initially, with step-down to fluconazole for susceptible species once stable — alongside central line removal and ophthalmological screening for endophthalmitis.
Why is Candida auris dangerous in hospitals?
It is frequently multidrug resistant (fluconazole resistance typical), persists for weeks on skin and surfaces, spreads in intensive-care units, and requires echinocandin therapy plus strict contact precautions and environmental disinfection.