1 opportunistic fungal infections candida susan richardson january 11, 2010
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Opportunistic Fungal Infections
Candida
Susan RichardsonJanuary 11, 2010
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Opportunistic Fungal Infections Require impairment of host immunity to cause serious infection Clinical infection - localized to severe systemic infection Yeasts:
– Candida spp. (albicans, tropicalis, parapsilosis, krusei, glabrata, lusitaniae, kefyr, guilliermondii etc.)
– Cryptococcus neoformans Filamentous fungi:
– Aspergillus spp. (fumigatus, niger, flavus)– Zygomycetes (Rhizopus, Mucor, Rhizomucor, Absidia)– Fusarium spp.– Penicillium spp. (marneffei)– Pseudallescheria boydii (Scedosporium apiospermium)– Curvularia spp.
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Predisposing Factors (Immunologic)
Cancer (esp. hematological malignancy)– Key defect: Neutropenia
Organ Transplantation (bone marrow, liver, lung, kidney)– Key defect: Neutropenia, Impaired T cell function
Cellular Immune Dysfunction (AIDS, lymphoma, CMC)– Key defect: Impaired T cell function
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Predisposing Factors (Non-Immunologic)
Chemotherapy (cytotoxic) - mucosal damage of GI, respiratory, GU tracts
Antibiotics - Broad spectrum; loss of normal flora, esp. anaerobic
Invasive devices - breach skin/mucosal defences, i.e. intravenous lines, urinary catheters, tracheostomies
Invasive procedures - surgery, diagnostic biopsies
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Transmission of Opportunistic Fungi
Candida, Trichosporon, Malassezia– ENDOGENOUS
» unique strain
» colonization precedes infection
» antibiotic suppression of normal flora, fungal overgrowth
– EXOGENOUS» hand carriage health care worker
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Transmission of Opportunistic Fungi
Aspergillus, Zygomycetes, other filamentous fungi, Cryptococcus– EXOGENOUS
» inhaled conidia
» ventilation systems, construction, heliports, plants, environment
» direct contact - dressings, arm boards, burns, wounds
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Candida MOST COMMON invasive fungal infection in
immunocompromised patients 4th most common cause of nosocomial blood stream
infection Species implicated in human disease most often:
– C. albicans
– C. tropicalis
– C. parapsilosis
– C. krusei (fluconazole resistant)
– C. glabrata
– C. lusitaniae (amphotericin B resistant)
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Candida
Thick cell wall of mannan and glucan polysaccharides
Unicellular, budding (asexual) reproduction (blastospores)
– Filament formation» Pseudohyphae (buds stay attached, constricted,
chains of elongated blastospores)» Hyphae (buds germinate)
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Cell wall Candida albicans
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Candida - Pathogenicity / Virulence Factors
C. albicans >>> virulent than other Candida species
Rapid switching of expressed phenotype– Enhanced ability to reassort and regulate genetic
expression by chromosomal rearrangement and recombination
» phenotypic - nutrient stress produces different colony forms
» virulence factors (including antifungal resistance, e.g. C. lusitaniae vs. amphotericin B)
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Candida - Pathogenicity / Virulence Factors
Hyphal formation– Hyphal formation is associated with tissue invasion (
yeast forms associated with epithelial colonization)» spontaneous C.albicans non-hyphae-forming mutant
shows decreased pathogenicity in a rat Candida vaginitis model
» Experimental renal infection - yeast and hyphae initiate renal lesions, but hyphae are essential for invasion of the renal pelvis.
Hyphae adhere more readily to host epithelial surfaces than do yeast cells (50x more adherent)
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Candida - Pathogenicity / Virulence Factors
Contact sensing - growth of hyphae on filters or membranes (thigmotropism)– When placed on agar medium grow through pores and
along grooves. Tissue penetration may be aided by following surface discontinuities and microscopic breaks
Surface hydrophobicity– Hydrophobic C. albicans at 25 C >>virulent than more
hydrophilic C. albicans at 37 C
– Hydrophobic CA show increased adherence and more rapid hyphal germ tube formation
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Candida - Pathogenicity / Virulence Factors
Surface virulence molecules (receptors, adhesins, pyrogens, and immunomodulators)– Candida adhere to:
» epithelial cells (buccal, cervical, corneal, urinary, gastrointestinal mucosa), vascular endothelial cells, spermatozoa, plastics
– Candida form ligands to host components - C3d, iC3b, fibrinogen, laminin, fibronectin, fucose receptors, N-acetylglucosamine receptors
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Candida Pathogenicity / Virulence Factors
Molecular mimicry– Surface coat of molecules that mimics host components
(decreases recognizability)» C. albicans cells in the bloodstream become rapidly coated with
host platelets via the fibrinogen-binding ligand.
Lytic enzymes– Hydrolases with broad substrate specificities (proteinase,
phospholipase(s), lipase(s), acid phosphomonoesterase). – Aspartyl proteinase - most potent or thoroughly studied.
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Candida Pathogenicity / Virulence Factors
Growth rate and undemanding nutrient requirements– Virulent strains have shorter doubling times than
attenuated strains
– C. albicans not fastidious, but nutritionally deprived mutants (auxotrophs for adenine, lysine, serine, uracil and heme) show decreased virulence
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Candida
Human commensal (endogenous)– skin, gastrointestinal, genitourinary tracts– 5 - 15% carriage rate in normal people– increased carriage with use of antibiotics
Environmental (exogenous)– much less common– food, animals, soil hospital environment– outbreaks have occurred
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Candida - Clinical
Mucous membrane infections– Thrush (oropharyngeal)– Esophagitis– Vaginitis
Cutaneous infections– Paronychia (skin around nail bed)– Onychomycosis (nails)– Diaper rash– Balanitis– Chronic mucotaneous candidiasis
» children with T-cell abnormality
Mucosal candidiasis
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Oral thrush
Vaginal candidiasis
Cutaneous candidiasis
19BalanitisDiaper dermatitis
Cutaneous candidiasis
20Onychomycosis and paronychia Chronic mucocutaneous candidiasis
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Candida - Clinical Urinary tract infection Fungemia
Disseminated (systemic, invasive) infection– Immunocompromised patients
» Cancer/chemotherapy
» Neonatal candidiasis
– Endophthalmitis (eye)– Liver and spleen– Kidneys– Skin– Brain– Lungs– Bone
Clinical profile
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Central catheter
Parenteral nutrition
Broad-spectrum antibiotics
Neutropenia
Very low birth weight
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Disseminated candidiasis
Endophthalmitis Disseminated skin lesion
Disseminated candidiasis
24Hypo-echoic splenic lesions
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Candida - Laboratory Diagnosis 1
Specimens - Blood, tissue (biopsy or autopsy), sterile fluid, urine, CSF, skin, respiratory secretions
Microscopy (direct on specimen - except blood and urine)– Gram stain, Calcofluor
Histopathology (tissues)– H & E - stain poorly
– GMS, PMS - stain well
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Candida species
Top: Calcofluor White x400: Yeast and
pseudohyphae
Bottom: Gram stain x1000: Yeast and
pseudohyphae
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Pathology of disseminated candidiasis
Yeast-like cells and septate hyphaeGMS
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Pathology of disseminated candidiasis
Esophagus, vascular invasion, blastoconidia and pseudohyphae, PAS
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Pathology of disseminated candidiasis
Hematogenous renal candidiasis. Disseminated miliary abscesses, cortex and medulla. Necrotic papillae.
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Candida - Laboratory Diagnosis 2 Culture (all specimens)
– Colony morphology
» White, smooth, creamy, sometimes wrinkled
– Laboratory identification
» Unique color on chromagar
» Chlamydospore production (terminal vesicle)
» Germ tube production (in horse serum) beginning of true hypha (no constriction)
– C. albicans - Germ tube positive
– Other Candida - Germ tube negative
» Carbohydrate assimilation and fermentation (API 20C, Vitek2, RapID and reference)
» Urea and nitrate
» Microscopic morphology on Cornmeal Tween 80
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Yeast Identification
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Candida species
Candida albicansSabouraud Agar
Morphology: Creamy white yeast,
may be dull, dry irregular and
heaped up, glabrous and tough
Chromagar
producing green pigmented colonies
on specially designed medium to
speciate certain yeasts based on
color they produce
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Candida species
Germ tube: inoculation of yeast in horse serum incubated at 370C for 2 to 3 hours
Germ Tube: Positive
Germ tube is a continuous filament
germinating from the yeast cell without constriction at the point of attachment.
e.g. C. albicans, C. dubliniensis
Germ Tube: Negative
Shows constriction at the attachment site
e.g. other Candida species, esp. C. tropicalis
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Candida species
Candida albicans
Oxgall Agar
large round and thick
walled chlamydospores
Cornmeal Agar
clusters of
blastospores along
pseudohyphae at regular
intervals
x400 x1000
x400
x1000
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Yeast identification
C. parapsilosisShort, curved pseudohyphae
C. lusitaniaeSlender, branched, curved pseudohyphaeshort chains of blastoconidia
C. guilliermondiiFew, short pseudohyphaeClusters of blastoconidia at septae
C. lipolyticaElongated blastoconidia in short chainsarthroconidia
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Yeast identification
C. dubliniensisTerminal chlamydospores
C. tropicalisGraceful long pseudohyphaeSingle/small groups blastoconidia along pseudohyphae
C. kruseiElongate blastoconidiaCross-matchsticks, tree-like
C. glabrataNo pseudohyphae, small blastoconidia
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Candida - Laboratory Diagnosis 3
Candida antigen, antibody and metabolite detection– NOT useful in routine practice
– Low sensitivity and specificity Polymerase chain reaction
» No more sensitive than blood culture in studies to date
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Candida - Treatment
Remove infected intravenous lines Antifungal therapy for systemic infection
– Amphotericin B IV– Azoles (fluconazole, itraconazole,
voriconazole, posaconazole) orally, intravenous– Flucytosine (only with Ampho B because of
resistance)– Echinocandins (caspofungin, micafungin)
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Candida antifungal resistance
Primary (inherent) resistance– C. lusitaniae (amphotericin B)– C. glabrata (fluconazole)– C. krusei (fluconazole)
Secondary (acquired) resistance– Fluconazole, other azoles– Amphotericin B– 5-FC
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Candida antifungal susceptibility testing
Testing methodology– Reference broth microdilution (CLSI)– Commercial broth microdilution with alamar
blue (Sensititre, YeastOne)– E-test– Disk diffusion (CLSI– Vitek 2
Candida antifungal susceptibility testing
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Candida antifungal susceptibility testing
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