Chapter 22

Question 1

General Fungi Info

Answer 1

• Severe caries and tooth decay in children due to relationship between fungus and bacteria
  
  • S. Mutans and Candida
• Fungi are eukaryotic, almost always aerobic, and have same organelles associated with it as other eukaryotes.
  
  • Also have CELL WALLS that are different from those of bacteria or plants
• Kingdoms: Plants, Animals, Fungi, Bacteria

Question 2

Fungi Cell Walls

Answer 2

• Components of Fungi cell walls
  
  • Chitin - polymer of glucose
    
    • Also found in exoskeletons of arthropods
    • Used as fat magnets to attract fat for consumption, but is indiscriminant which fat molecules it picks-up so can be related to obesity (but then, it is more about the amount of carb. consumption)
  • Glucans - polymer of glucose
  • Proteins
• As opposed to cholesterols in humans, fungus have ergosterol in their membrane; signify something fungal
  
  • Clinically, it can be used as target for certain medications

Question 3

Types of Fungi

Answer 3

• Fungus come in two different forms:
  
  • Molds - multicellular, have mycelium (and filament, etc.); when COLD (sexual or asexual)
  • Yeast - unicellular; when NOT cold
    
    • Asexual reproduction = binary fission
• Dimorphous fungus have both of those forms at the same time; depending on the temperature
  
  • “Cold Mold, Yeastie Beastie”
• Dematiaceous fungi: pigmented due to melanin (same as humans)
  
  • Reproduce sexually and asexually
  • Usually cause subcutaneous infection

Question 4

Mycosis Introduction

Answer 4

• Mycosis = fungal infection
  
  • Often when your barrier is broken down e.g. skin, flora
  • Also due to diet, poor health,
  • Common during immunosuppression
    
    • Transplant of organs, cancer treatment
    • Stop of folic acid production to kill cancer but also adverse effect on person - not enough DNA
    • Gut flora is also affected;
    • Acute depression during chemotherapy
  • Loss of CD4 T cells

Question 5

Types of Mycosis: Superficial Mycosis

Answer 5

• Superficial
  
  • Toenails and fingernails, skin and hair –> Integument
  • Outermost part of the skin = epidermis; contain keratin

Question 6

Types of Mycosis: Cutaneous Mycosis

Answer 6

• Cutaneous
  
  • Further down in the skin layers; alive part
  • Still keratin is present in this layer
  • Examples:
    
    • Ring worm - a fungus
    • Tinea _____ (refers to a skin infection with a dermatophyte (ringworm) fungus. )
      
      • Tinea Capitis = scalp fungus
      • Tinea Cruris = jock itch
      • Tinea Pedis = athlete’s foot
      • Tinea Unguium = nails
    • Needed to be treated promptly to prevent further problems

Question 7

Types of Mycosis: Subcutaneous Mycosis

Answer 7

• Subcutaneous
  
  • Dermis of the skin; include muscle and connective tissue
  • Dematiaceous (dark-colored ) fungi
    
    • Produce melanin in their cell walls
  • Usually caused by deep cuts or deep lesions in skin
  • May even lead to amputation of the limbs

Question 8

Types of Mycosis: Systemic Mycosis

Answer 8

• Systemic - Whole body
  
  • Usually start with respiratory tract; lung and disseminate from there
  • Again can be common among immunosuppressed people
  • Usually asymptomatic among healthy people
  • Example:
    
    • Histoplasmosis (by histoplasma)
      
      • Found internally; growth in lungs
      • Granuloma - a growth in the lungs
      • Ohio River valley (disease)
      • Mississippi river valley (disease)
      • Histoplasmosis is common among AIDS patients because of their suppressed immunity (wiki)

Question 9

Types of Mycosis: Opportunistic Mycosis

Answer 9

• Opportunistic
  
  • Only in patients who are already severely immunocompromised
  • e.g. AIDS patients, etc.
  • Examples:
  • Candida albicans - oral thrush
    
    • Part of the normal flora but when found in oral cavity - NOT normal
    • NOT a normal occurrences
    • Patients who take medications, AIDS patients, antibiotics, steroids, diabetics
  • Pmeumocystitics Jivoveci - found in AIDS patients
    
    • Associated with lungs of patients with AIDS

Question 10

Opportunistic vs Systemic Mycosis

Answer 10

Question 11

Culturing and Testing Fungus

Answer 11

• Right after taking sample from a patient, it is cultured - may take up to 30 days
• Grown on Sabouraud agar - agar used to grow fungus; pH altered to select for fungus and no other species
  
  • Also antibiotics can be added to even further select for fungus
  • Some stains can be also utilized
• Sugar Utilization test - biochemical test to see how sugars are utilized specific to different fungus
• Serological Test - use of antibody to look for fungal antigens in the sample

Question 12

Classes of Antifungal Medication

Answer 12

• Polyenes - The polyenes bind to ergosterol in the fungal cell membrane and thus weakens it, causing leakage of K+ and Na+ ions, which may contribute to fungal cell death (wiki).
  
  • Amphotericin B (“amphoteric”)
    
    • Binds to ergastrol in fungal membrane thus NO major effect on human membranes
    • NOT completely safe however.
    • Given in Liposome form - minimize the toxicity by not having to give as much; allow the drugs to be released at the right target for a longer period of time.
  • Nystatin - topical medication
    
    • Also target and bind to ergastrol
• Azole Derivatives
  
  • Inhibit synthesis of ergosterol and other fungal sterols
• Nucleoside analogues
  
  • Stop replication of DNA and RNA
  • Of course there is side effect but still used
• Griseofulvin
  
  • Interact with fungal microtubules
  • Inhibits fungal mitosis by binding to microtubules
• Candins
  
  • Inhibit formation of cell wall
  • Depress synthesis of glycans needed for cell wall of fungus