micro 9 Flashcards
Candida albicans
alba = white. Dimorphic; forms pseudohyphae and budding yeasts at 20°C A, germ tubes at 37°C B .
Systemic or superficial fungal infection. Causes oral C and esophageal thrush in immunocompromised (neonates, steroids, diabetes, AIDS), vulvovaginitis (diabetes, use of antibiotics), diaper rash, endocarditis (IV drug users), disseminated candidiasis (especially in neutropenic patients), chronic mucocutaneous candidiasis.
Treatment: oral fluconazole/topical azole for vaginal; nystatin, fluconazole, or echinocandins for oral/esophageal; fluconazole, echinocandins, or amphotericin B for systemic.
Aspergillus fumigatus
Monomorphic septate hyphae that branch at 45° Acute Angle D E . Causes invasive aspergillosis in immunocompromised patients, neutrophil dysfunction (eg, chronic granulomatous disease).
Can cause aspergillomas in pre-existing lung cavities, especially after TB infection. Some species of Aspergillus produce Aflatoxins (associated with hepatocellular carcinoma).
Allergic bronchopulmonary aspergillosis (ABPA) F—hypersensitivity response associated with asthma and cystic fibrosis; may cause bronchiectasis and eosinophilia.
Cryptococcus neoformans
5–10 μm with narrow budding. Heavily encapsulated yeast. Not dimorphic. Found in soil, pigeon droppings. Acquired through inhalation with hematogenous dissemination to meninges. Culture on Sabouraud agar. Highlighted with India ink (clear halo G) and mucicarmine (red inner capsule H). Latex agglutination test detects polysaccharide capsular antigen and is more specific.
Causes cryptococcosis, cryptococcal meningitis, cryptococcal encephalitis (“soap bubble” lesions in brain), primarily in immunocompromised.
Treatment: amphotericin B + flucytosine followed by fluconazole for cryptococcal meningitis.
Mucor and Rhizopus spp.
Irregular, broad, nonseptate hyphae branching at wide angles I .
Causes mucormycosis, mostly in ketoacidotic diabetic and/or neutropenic patients (eg, leukemia). Inhalation of spores fungi proliferate in blood vessel walls, penetrate cribriform plate, and enter brain. Rhinocerebral, frontal lobe abscess; cavernous sinus thrombosis. Headache, facial pain, black necrotic eschar on face; may have cranial nerve involvement. Treatment: surgical debridement, amphotericin B or isavuconazole.
Pneumocystis jirovecii
Causes Pneumocystis pneumonia (PCP), a diffuse interstitial pneumonia A. Yeast-like fungus (originally classified as protozoan). Most infections are asymptomatic. Immunosuppression (eg, AIDS) predisposes to disease. Diffuse, bilateral ground-glass opacities on CXR/CT, with pneumatoceles B. Diagnosed by lung biopsy or lavage. Disc-shaped yeast seen on methenamine silver stain of lung tissue C .
Treatment/prophylaxis: TMP-SMX, pentamidine, dapsone (prophylaxis only), atovaquone. Start prophylaxis when CD4+ count drops to < 200 cells/mm3 in HIV patients.
Sporothrix schenckii
Sporotrichosis. Dimorphic, cigar-shaped budding yeast that grows in branching hyphae with rosettes of conidia; lives on vegetation. When spores are traumatically introduced into the skin, typically by a thorn (“rose gardener’s disease”), causes local pustule or ulcer with nodules along draining lymphatics (ascending lymphangitis A ). Disseminated disease possible in immunocompromised host.
Treatment: itraconazole or potassium iodide.
Think of a rose gardener who smokes a cigar and pot.
Giardia lamblia
Protozoa—gastrointestinal infections
Giardiasis—bloating, flatulence, foul-smelling, fatty diarrhea (often seen in campers/hikers)— think fat-rich Ghirardelli chocolates for fatty stools of Giardia
* that colonizes and reproduces in the small intestine
*Cysts in water DiagNosis
Multinucleated trophozoites A or cysts B in stool, antigen detection
*treatmeNt Metronidazole
Entamoeba histolytica
Amebiasis—bloody diarrhea (dysentery), liver abscess (“anchovy paste” exudate), RUQ pain; histology of colon biopsy shows flask-shaped ulcers
- transmission by cyst
- Once the trophozoites are excysted they colonize the large bowel
- TXOnce the trophozoites are excysted they colonize the large bowel
- Metronidazole; paromomycin or iodoquinol for asymptomatic cyst passer
Cryptosporidium
Severe diarrhea in AIDS Mild disease (watery diarrhea) in immunocompetent hosts
Oocysts in water Oocysts on acid-fast stain E , antigen detection
Prevention (by filtering city water supplies); nitazoxanide in immunocompetent hosts
