Fungal Infections

• What are fungi?

  They are eukaryote heterotrophs (obtain nutrition from their environment) that have cell walls
• What is the difference between yeasts and moulds?

  
• What are pseudohyphae produced by and what do they look like?

  Bud elongation, and can resemble a string of sausages

  
• What are hyphae produced by and what do they look like?

  Apical extension from the protrusion out of a cell and these tend to have even and parallel sides at all times

  
• What kind of colonies does yeast produce?

  Moist looking ones

  
• What kind of colonies do mould hyphae produce?

  They'd form a colony on solid media that is round

  Sub-surface growth occurs & special spore structures may be on the surface

  
• How can you distinguish mould and yeast infections in tissue by microscopy?

  Compare the hyphae

  
• Are any fungi commensal to humans?

  Yeast:Candida albicans- GI tract/oralOtherCandidaspecies may be found in the GIMalasezzia- skin

  Moulds:No commensal moulds
• What factors can predispose to candidiasis?

  Age- infancy, elderly

  Endocrine disorders

  Defects in cell mediated immunity

  Cancer

  Drug addiction

  Drug therapy- antibiotics, corticosteroids, immunosuppression

  Surgery

  IV catheters
• What are the commonestCandida species?

  Candida albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei
• How do mostCandida infections arise?

  The species is commensal to GI tract, so usually infections arise from the endogenous flora but occasionally exogenous sources are implicated

  e.g. hospital outbreaks and the commonest cause of these areC. albicans
• What is the latest nosocomial (hospital acquired)problem?

  Candida auris

  Colonises readily, persists in environment, highly resistant to antifungals
• Give some examples of oral manifestations of candidiasis.

  
• What does oral candidiasis look like in children?

  
• What are predisposing factors for intertrigo?

  Obesity

  
  

  Diabetes

  
  

  Anything that increases your risk of skin folds because it's brought on by occlusion, so the increase in moistness and colonisation of the skin eventually leads to infection

  
• What is chronic mucocutaneous candidiasis?

  Inherited

  Recurrent oral, skin, nail infection

  
  

  Skin lesions on the face and scalp = candida Granuloma

  
• CanCandida cause systemic infection?

  Yes
• What do we mean by systemic infections?

  Infection you find in the blood, lungs & internal organs, skin

  
• How doesCandida albicanscause infection (1)?

  1. Ability to adapt to changes in environment

  2.Ability it adhere to different surfaces

  3.Production of destructive enzymes

  
• How doesCandida albicanscause infection (2)?

  4. Changes in cellular morphology.

  5. Production of biofilms

  6.Evasion of host defence

  7. Toxin production.

  
• What is cryptococcosis?

  A chronic, subacute to acute pulmonary infection resulting from inhalation of cryptococcus yeasts

  
  

  On dissemination the yeast shows a predilection for the CNS & cryptococcal meningitis occurs

  
• What can systemic spread of cryptococcosis result in?

  Skin lesions

  Infection of bone and internal organs may also occur
• What is cryptococcosis associated with?

  Pigeon droppings
• What is the causative organism of cryptococcosis?

  Cryptococcus neoformans
• Is cryptococcosis particularly dangerous?

  Only if you have HIV/AIDS or anything that makes your immune system extremely weak
• How does cryptococcus exist?

  Only in the yeast form, no hyphae produced
• What is the major virulence factor of cryptococcus?

  Capsule is protective, prevents phagocytosis

  Melanin is immunomodulatory
• What kind of infections do dermatophytes cause and what is the source?

  Ringworm fungi

  
  

  Common, superficial infection

  Sources include human, animal & soil
• What kind of infections do aspergillus cause and what is the source?

  Uncommon, systemic infection

  Environmental source

  Can often infect immunocompromised hosts
• What factors predispose to mould infections?

  1. History of trauma to site of infection

  2.Host immune status

  3.Underlying disease

  4.Exposure to a source

  5.Portal of entry

  
• What do dermatophytes use as substrates?

  Keratin (so species infect hair, skin, nails)
• What is the commonest cause of skin & nail dermatophyte infection?

  Trichophyton rubrum
• What is tinea?

  Medical term for ringworm (a clinical dermatophyte infection)
• What is tinea capitis?

  A fungal infection of the scalp characterised by red papules or spots at the opening of the hair follicle
• What are the risk factors for tinea capitis?

  
• What do clinical presentations of tinea capitis look like?

  Often fine scaling, mild erythema, patchy alopecia

  Hairs break at skin level: black-dot alopecia

  
• What are the pathogenicity mechanisms for tinea (1)?

  1. Adhesion (e.g by adhesins, enzymes)

  
  

  2.Invasion ( produce hyphae, complex process regulated by protein content and pH)

  
  

  3.Utilise keratin (breaking disulphide bridges)

  
• What are the pathogenicity mechanisms for tinea (2)?

  4. Manipulation of the immune response

  
  

  5.Host adaptation (species associated with humans cause low grade chronic infections compared to animals)

  
• What can aspergillosis cause?

  - environmental moulds (decay in leaves + compost)

  
  

  -Allergic aspergillosis - temporary presence of aspergillosis in respiratory tract, healthy host, usually caught by agricultural workers.

  
  

  -Aspergilloma - Colonisation of pre-existing cavities in lung, fungal ball formed, otherwise healthy.

  
  

  -Invasive aspergillosis - Pulmonary focus, dissemination possible, immune compromised host

  
  

  -Systemic aspergillosis - in lungs, brain, other organs and usually a immune compromised host

  
  

  -Cutaneous aspergillosis - primary infection due to skin damage (healthy or immune compromised host)

  
• Summary 1