1. Characterizing and Classifying Fungus
Chapter 12
Characterizing and Classifying Fungus

2. Mycology: The Study of Fungi

3. Appearance of Fungi Yeast – unicellular grow at 37oC Mold –
Microscopic
Macroscopic
Yeast –
unicellular
grow at 37oC
Mold –
multicellular
grow at 25oC

4. Dimorphic nature of true fungal pathogens
Figure 22.2

5. Yeasts Round to oval shape; 5-10X larger than bacteria
Reproduce by budding, form a blastospore
Figure 12.3

6. Molds Composed of hyphae - multicellular branching filaments
- mass of hypae = mycelium
Hyphae are septate (with crosswalls) or nonseptate (coenocytic)

7. Molds Hyphae are vegetative or aerial
Reproduce by sexual and asexual sporulation
Figure 12.2

8. Classification by Sexual Sporulation
Zygomycete- produce Zygospores
examples: Rhizopus (bread mold)
Ascomycete – produce Ascospores
examples: Penicillium, Saccharomyces
Basidiomycete – produce Basidiospores
examples: mushrooms, Cryptococcus
Deuteromycete (anamorphs)– asexual spores
examples: Stachybotrys, Pneumocystis
rRNA analysis revealed that most deuteromycetes belong in the division Ascomycota

9. Zygomycete Life Cycle
Figure 12.6

10. Ascomycete Life Cycle
Figure 12.7

11. Basidiomycete Life Cycle
Figure 12.8

12. Asexual sporulation by mitosis
Three basic types of asexual spores:
Sporangiospores - form in sac called sporangium
Conidiospores – no sac; form at tip or side of hyphae
Chlamydospore – thickened cell wall inside hyphae
Spore type is used in medical labs to identify pathogenic fungi

13. Representative asexual spores of molds
Figure 12.18

14. Representative asexual spores of molds

15. Benefits of Fungus Major role in decomposition
Major role as producers of:
antibiotics
alcohols
organic acids
vitamins
foods: blue cheese, soy sauce, breads

16. Medical Mycology Medical mycology-
Diagnosis, management, and prevention of mycoses (fungal diseases)
Mycoses
among the most difficult diseases to diagnose and treat
Signs of mycoses are often missed or misinterpreted
Fungi are often resistant to antifungal agents

17. Epidemiology of Mycoses
Fungi and their spores are almost everywhere in the environment
most people will experience a fungal infection at some time
Typically acquired via inhalation, trauma, or ingestion
Most mycoses are not contagious
Dermatophytes, fungi found on the skin, are the major exception

18. Classification of Fungal Diseases
Systemic mycoses Deep within body
Subcutaneous mycoses Beneath the skin
Cutaneous mycoses Affect hair, skin, nails (Dermatophytosis)
Superficial mycoses Localized on outermost skin layers /hair shaft
Opportunistic mycoses Caused by normal microbiota or fungi that are normally nonpathogenic

19. Systemic Mycoses Caused by True Pathogenic Fungi
Acquired through inhalation
Begin as a generalized pulmonary infection that disseminates via the blood to the rest of the body
Have the ability to actively attack and invade tissues
Exhibit dimorphism
Endemic to certain regions, primarily in the Americas

20. Systemic Mycoses Caused by True Pathogenic Fungi
Coccidioidomycosis (San Juaquin Valley Fever)
Caused by Coccidioides immitis
Histoplasmosis (Ohio Valley Fever)
Caused by Histoplasma capsulatum
Blastomycosis (North American Blastomycosis)
Caused by Blastomyces dermatitidis
Paracoccidomycosis (South American Blastomycosis)
Caused by Paracoccidioides brasiliensis

21. San Joaquin Valley Fever
Coccicioides immitis

22. Coccidioidomycosis- San Joaquin Valley Fever
Epidemiology
thrives in areas with sandy alkaline soils, very high temperatures, low rainfall, and low elevation
Symptoms
Most often result in pulmonary conditions
Many patients show no or few symptoms but some may develop severe or chronic pulmonary disease
Dissemination to other sites occurs mostly in immunocompromised individuals
Treatment
Infections in healthy individuals resolve on their and require no treatment
Amphotericin B is the preferred drug for those who require treatment

23. Coccidioidomycosis
Subcutaneous tissue lesions due to dissemination from the lungs
Figure 22.4
Spherules in lung tissue
Figure 22.5

24. Histoplasmosis – Ohio Valley Fever
Epidemiology
Found mostly in the eastern United States but also in Africa and Asia
Fungi found in moist soils containing high levels of nitrogen from bat and bird droppings
Route of infection
Inhalation of spores into the lungs is the most common
H. capsulatum first attacks alveolar macrophages and is then dispersed beyond the lungs via the blood and lymph
Usually asymptomatic and resolve without damage
Treatment
Amphotericin B is preferred drug if required

25. Histoplasma capsulatum

26. Blastomycosis Epidemiology Route of Transmission Symptoms
Endemic in the southeastern United States north to Canada
Fungi found in soils rich in organic matter
Route of Transmission
Inhalation of dust can carry fungal spores or hyphal pieces into the lungs
Symptoms
Pulmonary blastomycosis is the most common manifestation in humans
Initial pulmonary lesions are mostly asymptomatic and symptoms, when they develop, are often vague; resolves in most people but in others it may be chronic

27. Blastomyces dermatitidis
Yeast in lung
Mold in soil
Cutaneous Blastomycosis

28. Paracoccidioidomycosis
Epidemiology
Found in southern Mexico and regions of South America
Relatively rare disease found most in farm workers in endemic areas
Symptoms
Similar to blastomycosis and coccidiodomycosis
Infection begins as a pulmonary condition
Dissemination almost always follows
Produces a chronic inflammatory disease of mucous membranes- gums, lips, tongue
Treatment
Amphotericin B or Ketoconazole

29. Paracoccidiodes brasiliensis
Figure 22.8
Characteristic “steering wheel” formation seen in tissue samples
Ulcerative lesions on mucous membranes
Figure 22.7

30. Subcutaneous Mycoses Characteristics
Fungi are commonly found in the soil
Infections are rare
Requires traumatic introduction of the fungal elements beneath the outer, dead layers of skin
Most lesions remain localized to the subepidermal tissues in the skin
Example: Sporotrichosis (Rose thorn disease)

31. Subcutaneous Mycoses Sporotrichosis (Rose thorn disease)
Sporothrix schenckii is the causative agent
Subcutaneous infection usually limited to the arms and legs
Those who work with plant material at highest risk for infection
Cutaneous sporotrichosis
Produces nodular lesions around the infection site
Lymphocutaneous sporotrichosis
Secondary lesions occur on the skin along the course of lymphatic vessels
Effectively treated with topical agents

32. Sporotrichosis – Rose thorn disease
Rose thorn disease or
Gardener’s disease
Sporothrix schenkii
Mold
Yeast

33. Cutaneous Mycosis- Dermatophytoses
Dermatophytes
Caused by Trichophyton, Epidermophyton, Microsporum
Ringworm or “Tinea”
Fungal infections of the skin hair, nails
Result from fungi that use keratin as a nutrient source and thus colonize only dead tissues
Symptoms
Infections were previously called ringworm because they resemble a worm lying below the surface of the skin
Can provoke cell-mediated immune response that damages living tissues

34. Common Dermatophytoses
Tinea pedis “Athletes foot”
Tinea cruris “Jock itch”
Tinea corporis “Ringworm”

35. Superficial mycoses – Pityriasis versicolor
Fungi interfere with melanin production
Characterized by depigmented or hyperpigmented patches of scaly skin
Relapses are common
Malassezia furfur
Causative agent
fluoresces pale green providing a rapid diagnostic method
Grows in oil

36. Factors that Predispose Individuals to Opportunistic Mycoses
Table 22.1

37. Opportunistic Mycoses
Usually limited to people with poor immunity
Immunocompromised individuals
Mycoses account for most deaths associated with AIDS and used to define end-stage disease
Can be difficult to identify because their symptoms are often atypical
Opportunisitic mycoses:
Candidiasis –Localized infections in mouth (thrush), vagina, skin. Systemic in HIV infections.
Pneumocystis pneumonia (PCP) - HIV associated pneumonia. Rare prior to AIDS epidemic
Cryptococcoses – causes meningitis when fungus spreads to CNS. Systemic in HIV infections
Aspergillosis – causes pulmonary disease; allergies

38. Candidiasis Candida albicans - most common causative agent Yeast
Normal flora of skin and mucous membranes
Can be transmitted between individuals
Always an opportunist infection producing wide range of diseases

39. Thrush - Oropharyngeal Candidiasis
Candidiasis Clinical Manifestations
Diaper Rash
Thrush - Oropharyngeal Candidiasis
Onychomycosis
Ocular candidiasis
Figure Overview

40. Cryptococcosis Cryptococcus neoformans Yeast
Resists phagocytosis by producing capsules
Has affinity for the central nervous system where blood/brain barrier protects it from immune response
Route of Transmission
Infections can result from the inhalation of airborne spores found in bird droppings
Negative stain of
Encapsulated yeast
in cerebral spinal fluid

41. Cryptococcosis Cryptococcal meningitis
Most common clinical form of cryptococcal infection
Follows dissemination of the fungus to the CNS
Symptoms: headache, stiff neck, nausea, photophobia, hallucinations, fever
Primary pulmonary cryptococcosis
Asymptomatic or mild pneumonia
Invasive cryptococcosis sometimes occurs, resulting in chronic pneumonia
Cutaneous cryptococcosis
Skin lesions or inflamed subcutaneous

42. Aspergillosis Due to Aspergillus fumigatus and other species
Clinical Manifestations
Hypersensitivity aspergillosis
Manifests as asthma or other allergic symptoms
Noninvasive aspergillomas (mycetoma)
Masses of fungal hyphae form in the cavities after a case of pulmonary tuberculosis
Acute invasive pulmonary aspergillosis
May present as mild pneumonia
Necrosis of lung tissue can lead to significant respiratory impairment
Nonpulmonary diseases can also result
Includes cutaneous and systemic aspergillosis

43. Mycetoma caused by Aspergillus

44. Fungal Intoxications and Allergies
Some fungi cause allergies
Fungal allergens can elicit a hypersensitivity response in sensitive individuals seen as hay fever or eczema
Result from inhalation, ingestion, or other contact
Sick Building Syndrome caused by Stachybotrys
Some fungi produce toxins
Mycotoxicosis
Caused by eating foods contaminated with fungal toxins
Mycetismus
Mushroom poisoning from eating a fungus

45. Mycotoxicoses- Fungal Toxins
Mycotoxins
normal byproducts of metabolic activities but are poisonous to animals and humans
Aflatoxins –produced by Aspergillus flavus
consumed in contaminated food crops; prevalent in the tropics
can cause liver and kidney damage, gastrointestinal or gynecological disturbances, or cancers
carcinogenic at low levels when consumed continually
Ergot alkaloids- used to make drugs
Ergotamine – treatment for migraine headaches
Ergometrine – constricts blood vessels; stimulates labor contractions

46. Mold on food
Yeah, but…Can I cut off the moldy part of the cheese (or bread) and eat the rest?

47. Mycetismus- Fungal Toxins
Mushroom Poisoning
Most mushrooms are not toxic
Poisonous varieties called toadstools
Poisons cause neurological dysfunction or hallucinations, organ damage, or even death
Amanita phalloides - “death cap” mushroom; produces deadliest mushroom toxin

48. Psilocybin mushrooms –
Have psychoactive compound causing hallucinations
“shrooming”