Candidiasis

Intro & Species - Yeastie Beasties 101

• Candida: Opportunistic yeast, part of normal flora (skin, GIT, GU).
• Dimorphic: Exists as budding yeast (commensal) & pseudohyphae/hyphae (invasive).
  • C. albicans forms true hyphae (germ tubes).
• Species:
  • C. albicans: Most common.
  • Non-albicans Candida (NAC): C. tropicalis, C. parapsilosis, C. glabrata (often reduced azole susceptibility), C. krusei (intrinsic fluconazole resistance).

⭐ Candida albicans is the most common species and is germ tube positive.

Pathogenesis & Virulence - Candida's Crafty Conquests

• Adherence: Mediated by Als proteins (Agglutinin-like sequence) & Hwp1 (Hyphal wall protein 1); crucial first step.
• Biofilms: Structured communities on surfaces (e.g., catheters, implants); ↑ drug resistance, protects from host defenses.

  ⭐ Biofilm formation by Candida species, especially on indwelling medical devices, is a major virulence factor contributing to drug resistance.

• Phenotypic Switching: Yeast-to-hyphae transition (dimorphism) is key for invasion. Hyphae penetrate tissues.
• Hydrolytic Enzymes: Secreted aspartyl proteases (SAPs), phospholipases, lipases; damage host tissues, facilitate invasion.

Clinical: Mucocutaneous - Surface Skirmishes

• Oral Thrush: White, removable plaques (pseudomembranes) on oral mucosa. Risk: Infants, immunocompromised, steroid inhalers.
• Esophagitis: Dysphagia, odynophagia, especially in HIV/AIDS.
• Vulvovaginitis (VVC): Intense itching, burning; thick, white "cottage cheese" discharge. Risk: Diabetes, antibiotics, pregnancy.

  ⭐ Recurrent vulvovaginal candidiasis (RVVC) is defined as ≥4 symptomatic episodes in 12 months.

• Intertrigo: Erythematous rash with satellite lesions in moist skin folds (axillae, groin, inframammary).
• Diaper Rash: Confluent erythematous rash with satellite pustules in diaper area.
• Onychomycosis: Fungal infection of nails; thickened, discolored.

Clinical: Invasive - Deep Dive Dangers

Invasive candidiasis: severe, life-threatening infections, often in immunocompromised.

• Key Risk Factors: Central lines (CVCs), TPN, neutropenia, broad-spectrum antibiotics, major surgery, immunosuppression, prolonged ICU stay.
• Major Syndromes:
  • Candidemia: Candida in blood; most common.
  • Disseminated: Hematogenous spread.
    • Endophthalmitis (eye; risk of blindness).
    • Endocarditis (heart valves).
    • CNS infection (meningitis, abscesses).
    • Hepatosplenic, osteoarticular.
  • Candida UTI: Often catheter-related, esp. in high-risk.

⭐ In patients with candidemia, an ophthalmologic exam is mandatory to rule out Candida endophthalmitis, even in asymptomatic patients.

Lab Diagnosis - Unmasking the Yeast

• Microscopy: KOH mount (budding yeasts, pseudohyphae; true hyphae - C. albicans). Gram stain (Gram-positive).
• Culture: Sabouraud Dextrose Agar (SDA).
• Identification: Germ Tube Test (C. albicans/dubliniensis). Chromogenic agar (species differentiation).
• Advanced: (1,3)-β-D-glucan assay, PNA-FISH, MALDI-TOF MS.

⭐ The germ tube test is a rapid, simple, and inexpensive test for the presumptive identification of Candida albicans and Candida dubliniensis.

Treatment - Candida Combat Plan

High‑Yield Points - ⚡ Biggest Takeaways

• Candida albicans: Most common, dimorphic (yeast & pseudohyphae). Germ tube test positive.
• Clinical forms: Oral thrush, vulvovaginitis (cottage cheese), esophagitis, cutaneous, systemic (immunocompromised).
• Risk factors: Immunosuppression, diabetes, antibiotics, corticosteroids, catheters.
• Diagnosis: KOH mount (yeast, pseudohyphae), culture on SDA; Chromogenic agar for speciation.
• Treatment: Topical azoles; oral fluconazole; echinocandins or Amphotericin B for severe/invasive disease.
• Chronic Mucocutaneous Candidiasis (CMC) linked to T-cell defects (e.g., AIRE).