Pathology 19

• Fungus are eukaryotes, non-motile, no chlorophyll, can be unicellular (yeast) or multicellular (mold), most are aerobes, others are facultative anaerobes, fungi reproduce sexually or asexually, fungi are heterotrophs (cannot make their own food), fungi are saprophytic (consume organic matter from dead tissue) or parasitic (obtain nutrients from living organisms) by using specific enzymes to breakdown extracellular substrates and absorb the product of digestion, fungi are good at taking advantage “opportunistic” but have important roles in nutrient cycling in an ecosystem, their natural habita
• Fungal classification is based on structure and method of reproduction, there are 4 main phyla: Zygomycota (common molds) which are sexual/asexual, Ascomycota (sac fungi) which are sexual/asexual, Basidiomycota (club fungi) which are sexual/asexual, Deuteromycota (imperfect fungi) which are asexual.
• Fungal classification can also be done on the basis of morphology, yeasts are a type of fungus.
• C.albicans can secrete hydrolases following adhesion to host cell surfaces and hyphal growth, facilitating active penetration into these cells and overcoming structural barriers that human host uses to prevent infection.
• Candida have virulence factors such as transition between yeast and hyphal forms, thigmotropism, expression of adhesins and invasins on the cell surface, secretion of hydrolytic enzymes, formation of biofilms, rapid adaptation to fluctuations in environmental pH, and powerful nutrient acquisition systems.
• C.albicans expresses 3 types of hydrolases: proteases, phospholipases, and lipases.
• C.albicans can turn or bend in response to a touch stimulus, a characteristic known as thigmotropism.
• Candida that colonize the gut invade through translocation or through anastomotic leakage after laparotomy.
• Suppression of bacterial gut flora will allow overgrowth of candida that colonize the gut and cause translocation of fungi to bloodstream, leading to candidemia.
• C.albicans can grow either as ovoid-shaped budding yeast, as pseudohyphae or as true hyphae (polymorphic fungus).
• Biofilms form in a sequential process, with mature biofilms being much more resistant to antimicrobial agents and host immune factors.
• Broad spectrum antibiotic kills normal flora of the gut including gram-positive and gram-negative bacteria.
• The hyphal form of C.albicans has been shown to be more invasive than the yeast form.
• Candida spp that colonize the skin will colonize intraluminal catheter and form biofilm.
• Fungi are subsequently released from the biofilm (microembolization), causing persistent candidemia.
• Systemic broad spectrum antibiotics disrupt the larger variety of bacterial normal human flora, leading to imbalance and relative overgrowth of candida.
• Parasilopsis, C.glabrata, C.krusei are species of Candida that cause blood stream infections, endocarditis, oropharangeal/oesophageal candidiasis, peritonitis, endophthalmitis, liver/spleen/brain/renal abscess.
• Candidal invasion of mucosa and blood stream is known as invasive candidiasis.
• C.albicans can form biofilms on catheters, dentures, and mucosal cell surfaces.
• Sinusitis, pulmonary infection, and disseminated disease are part of the spectrum of Aspergillus infections.
• Candidemia may originate from the gut or oral mucosa in poor immune state of ventilated/ICU patient.
• Invasive pulmonary aspergillosis (IPA) is a serious infection caused by Aspergillus species.
• Aspergillus spores are 8 µm in size.
• Fungal factors that contribute to the pathogenesis of IPA include the ability to grow in cavities within the lungs, high sporulating capacity, small spores, and airborne transmission.
• Infection can also be acquired from healthcare provider via contact.
• Aspergillosis is the most common fungal infection, caused by Aspergillus fumigatus, Aspergillus flavus, Aspergillus nidulan, Aspergillus niger, Aspergillus terreus.
• Host factors that increase the risk of IPA include long-term or repeated use of corticosteroids, structural changes in lung architecture, increasing rate of bacterial exacerbations, and malnutrition.
• Management of candidemia includes catheter management, antifungal therapy, and contact precaution (infection control).
• COVID-19 associated pulmonary aspergillosis (CAPA) is a condition where Aspergillus species invade the lungs due to prolonged mechanical ventilation and under sedation, high dose and long steroid therapy, and COVID infection.
• Candida albicans has powerful nutrient acquisition systems, including reductive system, siderophore uptake system, and heme-iron uptake system.
• Candida albicans can grow in acidic, neutral, and basic environments.
• Dermatophytosis can be caused by geophilic fungi, which inhabit soil where they decompose keratinaceous debris, or by anthropophilic fungi, which live on humans.
• Dermatophytes include Trichophyton, Microsporum, and Epidermophyton species.
• Muccocutaneous candidiasis is the most common species of Candida, with other species including C. tropicalis, C. glabrata, C. parapsilosis, and C. dubliniensis.
• Clinical manifestations of Candida infections can include cutaneous and nail infection, oropharyngeal candidiasis, vulvovaginitis, and intertriginous candidiasis.
• Tinea pedis, Tinea unguium, and Tinea capitis can be caused by anthropophilic fungi.
• Chromoblastomycosis is a chronic, localized disease of the skin and subcutaneous tissues caused by dematiaceous (darkly pigmented) fungi that form sclerotic bodies in tissue, progressing very slowly (1 - 2mm/year).
• Candida albicans and related species are common causes of Candidiasis.
• Epidermophyton is a common cause of Candidiasis, which can affect the skin, mucous membrane, and nail.
• Subcutaneous mycosis is caused by fungi that inhabit soil or plants, and can spread via implantation or injury.