1. What diseases do yeasts and molds cause?
Mycology
What diseases do yeasts and molds cause?

2. Mycology Mycology is the study of fungi which includes yeast and molds
They are eukaryotic and are chemo-heterotrophs (require organic compounds for energy and a carbon source)
Most have a cell wall of chitin
Molds are made of long filaments called hyphae
If there are cross walls that divide the hyphae into uninucleate units the hyphae are septate hyphae
If there are no cross walls, the hyphae are called non-septate or coenocytic hyphae
When the hyphae grow and intertwine to form a mass, they are called mycelium

3. Mycology
The portion of mycelium concerned with obtaining nutrients is called the vegetative mycelium
The portion concerned with reproduction is called aerial mycelium because it usually projects above the surface of the vegetative mycelium
Yeasts are non-filamentous, unicellular fungi that are oval or spherical in shape.
Yeasts reproduce by the process of budding

4. Mycology Dimorphic fungi
When the buds fail to detach from each other, pseudohyphae are seen
Dimorphic fungi
Some fungi, including most of the pathogenic fungi, exhibit two forms of growth. This is known as dimorphism and the organisms can grow either as a yeast-like form or a mold-like form.
Frequently the form that the organism grows as is temperature dependent and at 370 C the organism grows as a yeast-like form and at RT it grows in a mold-like form. CO2 concentration or the presence of serum may also be a determining factor
How is the dimorphism of Candida albicans different from that described above?

5. Mycology How do we identify molds in the lab?
Based on type of hyphae (septate versus non-septate)
Based on color of mycelium
Based on reproductive structures
Molds may form either sexual or asexual spores
Sexual spores are formed from the fusion of nuclei from two opposite mating strains of the same species. They are only formed under special conditions, but they are used to classify fungi (more on this later)
Asexual spores, which are most commonly used in identification, are formed by the aerial mycelium of a single organism by mitosis and cell division

6. Arthrospores
Arthrospores are formed by the fragmentation of septate hyphae

7. Mycology
Chlamydospores are thick walled spores formed within a hyphae

8. Mycology
Sporangiospores are formed within a sac (sporangium) at the end of an aerial hyphae called a sporangiophore

9. Sporangiospores

10. Mycology
Conidiospores are produced in a chain at the end of a conidiophore. Unicellular conidiospores are called microconidia

11. Microconidia

12. Mycology
Multicelled conidiospores are called macroconidia

13. Macroconidia

14. Mycology
Blastospores consist of a bud coming off the parental cell

15. Mycology
Fungi are classified based on the type of sexual spore that they form
Zygomycota
Have non-septate hyphea
Have asexual sporangiospores
Form sexual zygospores. They are large spores enclosed in a thick wall and formed from the fusion of two cells

16. Zygospores

17. Mycology Ascomycota Have septate hyphae Have asexual conidiospores
Have sexual ascospores. Ascospores result from the fusion of nuclei of two cells. They are produced in a sac-like structure called an ascus.

18. Ascospores inside an ascus

19. Mycology Basidiomycota Have septate hyphae Have asexual conidiospores
Have sexual basidiospores. Basidiospores are formed externally on a base pedestal called a basidium

20. Basidiospores

21. Mycology
Fungal diseases – any fungal infection is called a mycosis. Mycoses are classified into five groups based on the mode of entry and the level of infective tissue:
Systemic mycosis – is a fungal infection deep within the patient
Can involve a number of tissues and organs
Usually caused by saprophytic fungi that live in the soil
The route of transmission is via inhalation of spores. Therefore the infection usually begins in the lungs and then spreads to other tissues
The diseases often resemble tuberculosis
The infections are not contagious

22. Mycology
Examples of systemic mycoses include
Coccidioidomycosis (San Joaquin Valley Fever)– caused by Coccidiodes immitis
Histoplasmosis – caused by Histoplasma capsulatum
Blastomycosis – caused by Blastomyces dermatitidis
Subcutaneous mycoses (mycetoma) - are fungal infections beneath the skin
They are caused by fungi that live in soil and vegetation
Infection occurs when spores or hyphae are planted directly into a puncture wound
The infections are not contagious
Examples of subcutaneous mycoses include
Chromomycosis – caused by Phialophora or Fonsecae
Maduramycosis – caused by Allescheria boydii

23. Mycetoma

24. Mycology
Cutaneous mycoses (ringworm) – are fungal infections of the hair, epidermis, and nails
Are caused by fungi known as dermatophytes (dermatomycosis) which secrete the enzyme keratinase which digests keratin, a protein found in hair, skin, and nails.
Infection is from person to person or animal to person by contact with infected hair or epidermis.
Tinea capitis is a scalp and hair infection
Tinea pedis is a foot infection infection (athlete’s foot)
Tinea unguium is an infection of the nails
Microsporum, Trichophyton, and Epidermophyton are the causative agents

25. Cutaneous mycoses

26. Mycology
Superficial mycoses – are fungal infections localized to the hair shafts and superficial epidermal cells
Is spread by direct contact with infected hair or skin
Examples are
White piedra in which white balls are found on the hair shafts is caused by Trichosporon
Black piedra is caused by Piedra ishortae
Tinea nigra in white black spots are seen on the skin is caused by Cladosporium werneckii

27. Black piedra

28. Mycology
Opportunistic mycoses – caused by a pathogen that is generally harmless in its normal habitat (includes normal flora), but can become pathogenic in a debilitated or traumatized host
Mucormycosis – caused by Rhizopus or Mucor in patients with ketoacidosis
Aspergillosis – caused after inhalation of Aspergillus spores in those with lung disease or cancer
Candidiasis – caused by Candida albicans.
Vulvovaginal candidiasis often occurs following antibiotic therapy
Thrush is an infection of the mouth and throat

29. Thrush