Lecture 3: Mycology 1

sterols/ergosterol

in the phospholipid bilayer membrane of fungi

Chitin and a form of glucan polymer

In the cell walls of fungi

Fungi are unaffected by

antibacterial pharmaceuticals

Fungi more closely related to

Animals than they to plants

Hyphae

Long, thread-like chains of cells that make thin filaments making up the fungus

Mycelium

mass of hyphae and grow at the tips and branch

septum

the wall that divides cells (internal cross- walls)

Function of ergosterol as the membrane sterol

provides a unique membrane surface, and a unique biosynthetic pathway

Azoles

Inhibit ergosterol biosynthesis

– Itraconazole, fluconazole, voriconazole, ketoconazole

Polyenes

a class of antifungal drugs used to treat fungal infections by binding to ergosterol in the fungal cell membrane which causes pores leading to fungi cell death

– Amphotericin B and Liposomal

Allylamines

Inhibit ergosterol biosynthesis (early)

– Terbinafine

Echinocandins

Disrupt cell wall glucan synthesis

– Caspofungin

Fungi reproduce

either asexually or by sexual reproduction

Chytridiomycota

Chytrids

Zygomycota

Common Molds

Ascomycota

Sac Fungi

Basidiomycota

Club Fungi

Deuteromycota

Imperfect Fungi (produces no sexual spores)

Microscopic Analysis based on:

Yeast cells, pseudohyphae, hyphae, and thermal dimorphism

Yeast cells

round or ovoid cells that produce daughters by budding

Pseudohyphae

chains of elongated yeast cells, have indentations in the wall where cells meet

Mycobiome

the fungi that are resident on the human body, can become opportunistic pathogens 

Dermatophyte Fungi

Keratinolytic and causes ringworm

-Species: microsporum spp, epidermophyton spp, trichophyton spp

Keratinolytic

Can utilize keratin as a nutrient source

ex: dermatophyte Fungi

Ringworm aka Tinea

Infections of keratinized tissues and named by location

Tinae examples

–Tinea capitis: Scalp

–Tinea corporis: Body

–Tinea cruris: Groin (jock itch)

–Tinea pedis: Foot (athlete’s foot)

Pityriasis Versicolor

superficial infection of the epidermis and caused by Malassezia spp and is treated by antifungals

Malassezia spp

causes Pityriasis Versicolor, dimorphic, lipophilic fungus, commensals on skin, and 90-100% of colonization rate

Onychomycosis

Fungal infection of the nails and is treated by nail lacquers (ciclopirox and amorolfine) or oral antifungals (terbinafine)

Onychomycosis Predisposing factors:

Tinea pedis, family history, age, male gender, trauma, diabetes, immunosuppression, poor peripheral circulation and smoking

Onychomycosis caused by 

Dermatophytes: Tinea Unguium. Mainly on toenalis like Trichophyton rubrum

Candida albicans, Candida parapsilosis – Mainly fingernails

Opportunistic Fungal Pathogens:

Candida sp., aspergillus fumigatus, and cryptococcus neoformans

Primary Fungal Pathogens

Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis

Why are fungi pathogens are emerging b/c

A new susceptible population b/c of HIV, transplantation, and cancer patients

Candida Species Morphology

Form yeast-like cells (blastoconidia), pseudohyphae and true hyphae in tissue

– Yeast cells form germ tubes in response to serum

Candida species are part of

the normal flora of most individuals of GI and GU

Candida is the cause of two major classes of disease:

Muco-cutaneous candidiasis and Disseminated candidiasis

Muco-cutaneous candidiasis

Superficial infection of overgrowth of normal flora limited to lining surfaces such as skin, oropharynx, GU tract, GI tract and respiratory tract

-Becomes invasive in sick people

Disseminated candidiasis

Occurs when Candida enters the bloodstream from the gut “leaky gut”, colonizes vein catheters and forms biofilms

Disseminated candidiasis Epidemiology

Candida bloodstream infections are the fourth most common behind coag-Staph, S. aureus and Enterococcus

Invasive candidiasis can occur

Disseminated candidiasis treatment

High risk patients will often be placed on antifungal prophylaxis and removal of contaminated indwelling catheters

Candida auris

emerging fungal pathogen thats multi drug resistant that causes systemic infections in hospitalized patients and nursing home residents