Transcript Candida - Infectious Diseases

Opportunistic Fungal Infections
Candida
Susan Richardson
January 11, 2010
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Opportunistic Fungal Infections
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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:
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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
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Mucosal candidiasis
Oral thrush
Vaginal candidiasis
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Cutaneous candidiasis
Diaper dermatitis
Balanitis
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Cutaneous candidiasis
Onychomycosis 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
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Endophthalmitis (eye)
Liver and spleen
Kidneys
Skin
Brain
Lungs
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Clinical profile
Central catheter
Parenteral nutrition
Broad-spectrum
antibiotics
Neutropenia
Very low birth weight22
Disseminated candidiasis
Endophthalmitis
Disseminated skin lesion
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Disseminated candidiasis
Hypo-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 hyphae
GMS
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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
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» Microscopic morphology on Cornmeal Tween 80
Yeast Identification
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Candida species
Candida albicans
Sabouraud 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
x400
Cornmeal Agar
clusters of
blastospores along
pseudohyphae at regular
intervals
x1000
x400
x1000
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Yeast identification
C. parapsilosis
Short, curved pseudohyphae
C. guilliermondii
Few, short pseudohyphae
Clusters of blastoconidia at septae
C. lusitaniae
Slender, branched, curved pseudohyphae
short chains of blastoconidia
C. lipolytica
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Elongated blastoconidia in short chains
arthroconidia
Yeast identification
C. dubliniensis
C. tropicalis
Terminal chlamydospores
Graceful long pseudohyphae
Single/small groups blastoconidia along pseudohyphae
C. krusei
Elongate blastoconidia
Cross-matchsticks, tree-like
C. glabrata
No 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
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Candida antifungal susceptibility
testing
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Candida antifungal susceptibility
testing
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