• saprobes- decompose organic matter
• symbionts- live with others for mutual benefit
• commensals- live with others without harm or benefit
• parasite- live with host to derive benefit and harms host

• study of fungi that cause human disease
  • yeasts (unicellular, spherical)
  • molds (filamentous w/ hyphae)

• single ovoid or spherical cell
• divide by budding, binary fission

• made of hyphae or fillaments
  • can be septated (divided by partitions)
  • can be coenocytic (multinuc. w/o partitions)
• hyphae can be
  • vegatitive- grow in or on culture
  • aerial- above medium (in envir.) and spread spores
• can be mycelium (mass of hyphae)

• fungi exist both as mold and yeast based on growth temperature
  • mould in envir. (25 C)
  • yeast as parasitic form within a host (37 C)

• Blastomyces dermatitidis
• Coccidioides immitis
• Histoplasma capsulatum
• Paracoccidioides brasiliensis
• Sporothrix schenckii

• cell membrane have ergosterol as major sterol (mammals have cholesterol)
• multilayerd cell wall made of chittin, glucans, mannoprotiens, other complex polysac. and polypeptides
• VF- some produce capsular polysaccharide that may enhance virulence and escape host defenses

• grow aerobically
• limited fermentation capacity
• fungi produce metabolites like:
  • ethalnol
  • penicillin
  • aflatoxin
• stain gram positive but are NOT acid fast
• polysac. on cell wall stain well with PAS (periodic acid stain) and methenamine silver

• generation time (hours as oppose to minutes for bacteria)
• all fungi reproduce asexually (anamorph)
  • clinics use asexual designation
• most can reproduce sexually under controlled culture conditions (teleomorph)

• cause superficial, localized, or systemic infections
• free living in nature and are usually acquired from envir.
• cause damage by:
  • eliciting inflammation
  • direct invasion of tissue

• aspergillus- decay vegetation
• Cryptococcus neoformans- pigeon droppings in the hood
• Histoplasma capsulatum- soil with bird and bat droppings from caving, spurlunking
• Sporothrix schenckii- rose, barbery thorns

fungi: endogenous habitat

• candida- skin and GI tract
• Malassezia furfur- human skin rich in sebaceous glands

• definition- can infect healthy people
• examples
  • Blastomyces dermatitidis
  • Coccidiodes immitis
  • Histoplasma capsulatum
  • Spororthrix schenckii

• definition- infect immunocompromised host
• examples
  • Candida
  • Aspergillus
  • Pneumocystis jirovecii

• normally, primary barriers (skin, mucosa) block entrance of fungi
• violation of these barriers allow entry of fungi
• bacterial flora of skin, mucosa compete with fungi and hinder unrestricted growth
• alteration in balance of normal flora by antibiotics allow certain fungi to prolif.

• Candida
• Aspergillus
• Mucor

• Cryptococcus neoformans
• Pneumocystitis jirovecii
• Blastomyces dermatitidis
• Coccidiodes immitis
• Histoplasma capsulatum

• 10% KOH wet mount- fungal cell walls remain in tact while tissues are destroyed
• India ink- see Cryptococcus neoformans capsule
• Calcofluor white stain- whitening agent binds to fungal chitin and fluoresces under UV
• PAS stain- fungal cell wall polysaccharides stain pink
• Gomori methenamine silver stain- fungal cell walls stain black
• Gridly stain- fungal cell walls stain purplish red (may look browtn
• Mucicamine stain- capsule of C. neoformans stains rose
• histopath important to see:
  • inflam. cells recruited
  • look for tissue invasion even if you cant visualize fungal elements

• culture at 25-30 C for up to four weeks on Sabouraud's agar
• yeast grow more rapidly than molds and can be suspended in broth media uniformly
  • can use chloramphenicol may be used to inhibit bacterial overgrowth
• if growth at 25 and 37 degrees, dimorphism
• ID
  • yeasts- biochemical and physiological properties
  • moulds- morphology of chlamydospores and hypahe

• serology- complement fixation Ab's helpful for Coccidioides immitis and Histoplasma capsulatum
• Ag- C neoformans (latex agglutination or ELISA) and Histoplasma Capsulatum (radioimmunoassay)
• investigation methods
  • metabolites
    • D arabinotol for invasive candidiasis
  • PCR- nucleic acid sequences

• location- outermost layers of hair, skin
• dx- wet mount of hair or skin with 10% KOH
• pathogenesis- dont elicit a host response, so mild infections with no or minimal inflammation

• black piedra- hard, grity brown-black concretions on scalp hair due to Piedraia hortae
• white piedra- soft, white granules on hair shafts of genital and beard areas due to Trichosporon beigelli
• tinea nigra- brown black macules on palms ore soles due to Exophiala werneckii
• tinae/pityriasis versicolor- hyper and hypopigmented confluent scaly macules on torso due to Malessezia furfur

• black and wite piedra- shave all hair (dont recur)
• tinea nigra- topical keratolytic agent or azole
• tinae/pityriasis versicolor- selenium sulfide 2.5% solution or other keralytic agents, topical azole for recurrence

• grow on Sabouraud's agar with 1% olive oil

• infect keratinized tissues and may elicit cellular response
• dermatophytes belong to three genera
  • Microsporum
  • Trichophyton
  • Epidermophyton
• dx
  • wet mount on 10% KOH skin, hair, or nail scraping
  • culture in media with cycloheximide and chloramphenicol to inhibit overgrowth of saprobic fungi and bacteria

• clinical diseases
  • tinea capitis (head)
  • tinea corporis (body)
  • tinea pedis (feet)
  • tinea barbae (beard)
  • tinea cruris (perineum)
  • tinea ungulum (nails)
• tx
  • tinea capitis has a different tx than the other tinea

• involves dermis, subQ tissue
• usually involves trauma for entry
• tx- some infections may not respond to antifungal therapy and require surgery
• clinical disease
  • lymphocutaneous sporotrichosis
  • chromoblastomycosis
  • phaeohyphomycosis
  • eumycetoma mycetoma

• cause- Sporothrix schenckii (dimorphic)
• entry- implanted into skin by trauma (ex: gardening and caught on thorns, exposed)
• clinical manifestation- nodule at site of entry ulcerate and form other nodules along lymphatic drainage channels
• dx- culture
  • white mold will darken into brown-black w/prolonged incubation at 25 C
  • cigar shaped yeast on biopsy
• tx
  • saturated solution of KI

• cause- Fonsecaea or Cladosporium species
• manifestation- warty, vegitative, cauliflower like lesions
• dx- histopath with epithelial cell hyperplasia and copper colored spherical fungi, sclerotic or Mediar bodies (dark colored bodies)
• tx- surgical excision or cryosurger

• cause- Pseudaliescheria boydii and Madurella grisea (can be also actinomyces, bacteria)
• manifestation- purulent drainage (creamy, granular) from sinus tract
• dx- histopath of grains from sinus tracts show fungal elements (culture) with dead debri
• tx- surgical excision or amputation for extensive disease w/ wide margin to prevent recurrence

• acquired from endogenous or environmental sources
• may invade organs of entire body
• enter bloodstream for dissemination
• examples
  • primary
    • Blastomyces dermatitidis
    • Coccidioides immitis
    • Histoplasma capsulatum
  • opportunisitc
    • Aspergillus
    • Candida
    • Cryptococcus neoformans

• entry- inhaled spores enter lung
• dogs may develop similar diseases
• dimorphic
• epidemiology- localized to easter pt of US with hot spots in Carolinas, Mississippi delta, and Great Lakes

• clinical manifestations (slow healing lesion)
  • primary lung infection may be inapparent
  • chronic pneumonia with cavity
  • dissimenate in skin, bone, UG tract
• pathology- broad based budding yeast within microabscesses and granuloma
  • looks like TB, so you would need a culture to dx properly

• dimorphic fungus
• entry- inhaled spores enter lung
• clinical manifestation
  • symptomatic lung infection in 40%
  • chronic infection may cause lung cavity
  • disseminate to CNS, bone, skin

• predisposition for dissemination:
  • AIDS
  • darked skinned individuals
  • pregnancy
• dx
  • culture (lab handling can result in acquisition)
  • biopsy
  • complement fixation Ab for disseminated disease and relapse
• pathology- endospores within spherules seen in pyogenic and granulomatous reaction