Funghi

• Common characteristics of fungi:

  • Fungi are eukaryotic organisms, unlike prokaryotic bacteria
  • Their cell wall is formed by polysaccharides, with a different composition than that of G+ bacteria, but stains purple/violet ("gram-positive")
  • Fungi have a slower cell cycle than bacteria, leading to prolonged infections
  • Majority of antibacterial agents are not effective, so special drugs called antimycotics are used
• In the practical, we will focus on microscopic fungi, but macroscopical fungi with fruits like Amanita phalloides, Inocybe patouillardi, Amanita panterina, and Entoloma eulividum can cause diseases and even death
• Mycoses caused by microscopic fungi in the human body include fungal inflammations, toxic actions, allergies to fungi, and fungi present in the body acting as pressure to surrounding tissues
• Dermatophytes, common agents of skin mycoses, include genera Trichophyton, Epidermophyton, and Microsporum. They can be anthropophilic (person-to-person), zoophilic (from animals), or geophilic (from the environment)
• Aspergillus niger is a causative agent of aspergillosis, often seen in persons working in wet, dusty places. Aspergillosis is an example of organ or systemic mycoses.

  Attacks both diseased and sometimes healthy people.
• Systemic mycoses affect multiple organs and the whole body, often following a primary disease like diabetes mellitus, immunity defects, or in transplanted patients. They are caused by Candida, Penicillium, Aspergillus, Histoplasma, Pneumocystis, and others, and are treated with strong, broad-spectrum antimycotics
• Zygomycetes are true molds with non-septate hyphae that can cause rare but severe infections, especially in diabetics. They can grow quickly and may lead to serious complications like living thrombus or rapid brain invasion.

  Live on saprophytes (fruit) and the most important genera are: Rhizopus and Mucor.
• Candida albicans is a common causative agent of vaginal mycoses, which can be multifactorial and influenced by dietary, hormonal, and other factors.

  Reservoir is in intestine.

  Recurrent infections should be treated with a combination of local and systemic treatments
• Candidosis may be both surface (skin, mucosal) and systemic.

  • Mucosal candidoses, beside vaginal mycoses also oral mycosis is seen (in sucklings and people with diseased immunity)
  • Skin candidoses are common, too (for example „diaper dermatitis“ in sucklings)
  • Systemic infections are present mostly in immunodefficient persons and persons treated by combination of broad- spectre antibiotics

  The most common is Candida albicans, also C. tropicalis, C. glabrata, C. krusei, C. parapsillosis etc.

  In some of them, we can see natural resistances (e. g. C. krusei for fluconazole)
• Cryptococcus neoformans is very dangerous and may cause pneumonia, meningitis, and sepsis in immunodeficient persons
• Pneumocystis jirovecii was once thought to be a protozoon and can cause infections
• Saccharomyces contains wine and beer yeasts and may cause vaginal mycoses in 8% of cases
• Morphology of fungi:

  • Blastospores are oval or round cells characteristic of yeasts
  • Hyphae are fibers that may be branched, septate or notseptate
  • Mycelium is a sample of hyphae that may be vegetative or generative
• Fungi can multiply sexually or asexually, with spores for sexual multiplication and conidia for asexual multiplication
• Physiology of micromycetes:

  • Fungi grow slower than bacteria
  • Majority of medically important fungi grow well at lower temperatures
  • Fungi have rich biochemical activity, especially in yeasts
• Diagnostics of mycoses:

  • Sampling includes particles of skin, nails, hairs, etc.
  • Proper diagnostics involve microscopic and culture methods
  • Sampling for dermatomycoses should avoid contamination, don't send only swab but several skin particles and sample from active infection sites.
• Diagnostics of systemic mycoses:

  • Proper diagnostics are essential to find the primary cause of the disease
  • Direct diagnostics involve relevant materials like blood for culture and modern methods for direct antigen detection
  • Indirect detection includes serum antibodies
• Diagnostics of candidoses:

  • Culture is basic for identification of Candida
  • Microscopic examination shows oval cells, budding, and pseudomyelia
  • In vitro susceptibility testing is possible but less reliable than in bacteria

  In skin and mucosal form we use swabs mostly in transport medium FungiQuick or (in genital swabs only) C. A. T.

  In systemic form swabs, too, or blood, punctate.
• Biochemical identification of yeasts can be done using tests like Auxacolor but not fot filamentous fungi.
• Diffusion tablet test of susceptibility to antimycotics involves testing with fluconazole
• Microscopy of filamentous fungi is different from yeasts and is more important for observation
• Indirect diagnostics of fungi can be done through microprecipitation in agar
• Differentiation between colonies of Candida and staphylococci on bacteriological media can be difficult
• Selective medium for yeasts like Sabouraud agar is used with antibiotics to prevent bacterial growth
• Chromogenic media contain colorless chromogenes that become colored in the presence of specific reactions
• Chromogenic medium can differentiate Candida species based on color reactions.

  • C. albican is green.
  • C. trobicalis is blue.
  • C. glabrata and krusei is pink.
• Fungi can grow easily even on poor media and majority of medically important fungi grow well at lower temperatures
• Fungi are cultured on Sabouraud agar with methylene blue for susceptibility testing to antimycotics
• Filamentous funghi.

  Microscopy is different than that of yeasts and we can observe various types of spores and conidiae.

  We observe without immersion, objective multiplying 4× or 10×, eventually 40 ×.

  Culture are different from yeast, both on Sabouraud agar and eventually blood agar.

  Biochemical differentiation is usually not performed here, unlike the situation in yeasts.

  
  

  
  

  
  
• Example of indirect diagnostics of fungi includes microprecipitation in agar to detect antigen-antibody reactions
• Dimorph fungi cause mycoses in immunodeficient patients.

  Coccidioides immitis grows more quickly than the others. Usually is asymptomatic or with small symptoms only. It is worse in persons with a developed AIDS, where you can see primary lung infections.

  Histoplasma capsulatum is seen mostly in the USA, but also in Africa.

  More genera: Blastomyces, Paracoccidiodioides, Sporothrix and other