Concepts in microbiology - fungi Flashcards
What does mycology mean?
study of fungi
What are medical mycologists?
scientists who study pathogenic fungi
What is mycotoxicology?
the study of fungal toxins and their effects
What are mycoses (s. mycosis)?
diseases caused by fungi
Which domain are fungi a part of?
eukaryota
What is the variation in size and complexity of fungi?
Can be microscopic single cell yeasts, macroscopic mushrooms, humungous fungus
Beneficial impacts of mycology
fungi are decomposers, used as industrial fermenters (foods, beverages, and steroids, antibiotics, drugs), used to model eukaryotes in research
Detrimental impact of fungi
cause of many animal and plant diseases
How is DNA in fungi arranged?
fungi is eukaryotic so DNA is arranged into chromosomes
Example of fungi having different morphological states
hyphae (can be 100s times the biovolume of a different fungi)
Examples of eukaryotic microbes
yeasts and molds
Are yeasts multi or unicellular?
unicellular
How do yeasts reproduce?
Budding (a form of asexual reproduction in which nucleus divides by mitosis)
What colour do yeasts appear in a gram stain?
Blue/purple because they are gram positive (due to cell wall)
How do fungi gain their nutrients?
they are heterotrophs
Use of yeasts
ferment beer, wine, bread
How are yeasts grown in vitro?
25-37C, acidic conditions, enriched with Sabouraud’s dextrose, potato dextrose, nutrients
Are molds uni or multicellular?
multicellular
How can molds reproduce?
Sexual or asexual (sporulation) reproduction
Usual habitat for molds
dark/moist conditions
How do molds grow?
grow in multicellular, fibre-like structures called hyphae
Components of the cell wall of fungi
chitin, glucans, glycoproteins
What is the most abundant component of the fungi cell wall?
Glucans
Components of fungi cell membrane
phospholipids and ergosterol (equivalent to cholesterol)
Which component of the fungi cell membrane is a target for some antifungals?
ergosterol
Why is the fungi cell wall a key virulence factor?
Cell wall can be reorganised
Dimorphic meaning
ability to have different shape/phenotype/morphism
Examples of single cell fungi demonstrating dimorphism
spores, yeasts, pseudohyphae, hyphae, filaments
How many people do fungal infections kill annually?
2 - 3.75 million
Examples of fungi on WHO’s priority list
invasive candidiasis, invasive aspergillosis, cryptococcosis, cryptococcal meningitis, crytococcaemia, azole and multidrug resistance fungi (Candida auris)
Scale of fungal infection severity
superficial, cutaneous, subcutaneous, opportunistic, invasive
Name of group of fungi that affect hair, skin and nails (superficial / cutaneous)
dermatophytes (require keratin)
What are subcutaneous fungal infections?
Fungal infections beneath the skin caused by ubiquitous organisms entering (found in environment)
What are opportunistic fungal infections?
When common commensals become pathogenic if the host is vulnerable
When may a patient be vulnerable to opportunistic fungal infections?
on immunosuppressants, antibiotics, suffering from disease, diabetes
Example of fungus that has multidrug resistance
Candida auris
What is a mycobiome?
Total composition of fungal species in a community
Which part of the body has the most diverse fungi ecosystem?
oral cavity
What is candidiasis?
group of infections affecting different tissues of the oral cavity
What fraction of the world’s population has a fungal infection?
1/3 rd
What type of eukaryotic microbes are Candida?
yeasts
Name of imbalance of common commensals
dysbiosis
Name of most commonly isolated yeast
Candida albicans
Why is Candida albicans problematic?
It has multidrug resistance (not a common commensal)
What stage of fungal infection severity do Candidiasis infections fall into?
Opportunistic (common commensals that become pathogenic in immunocompromised individuals)
Why did Hippocrates call Candidiasis “a disease of the diseased”?
Candidiasis is usually a second infection to other diseases and disorders
Examples of risk factors for oral candidiasis
HIV, diabetes, dentures, antibiotics and corticosteroids, smoking, cancer
How may HIV lead to Candidiasis infection?
HIV immunosuppressant reduces T cells, enabling proliferation of Candida
How may diabetes lead to Candidiasis?
High glucose allows proliferation of Candida
How many corticosteroids lead to Candidiasis?
The reducing in inflammation in tissues reduces number of immune cells.
How may antibiotics lead to Candidiasis?
Wipes out normal bacterial flora allowing proliferation of Candida
What is denture stomatitis?
Candida oral infection caused by combination of poor oral hygiene, ill fitting dentures (inflammation) and Candida plaque.
Example of Candida virulence factor
mycotoxins
Which is the most common and most virulent type of Candidiasis (can be over 70%)?
Candida albicans (one of only a few Candida pathogens)
Why is Candida albicans the most common Candida?
C. albicans has a large number of virulence factors allowing it to evade and persist in the environment.
Examples of C. albicans virulence factors
adhesion, biofilm formation, phenotypic switching, thigmotropism (tissue penetration)
Example of polymorphic switching of Candida
Budding to produce unicellular yeast form, or can switch to hyphal /pseudo hyphal states (polymorphic)
How can the morphology of Candida act as a mechanical force?
Formation of hyphae can physically damage and invade host tissues by exerting pressure.
Factors that may trigger change in Candida morphology
temperature, serum, pH, nutrient starvation, osmolarity, stress
Biofilm definition
matrix-enclosed microbial (bacterial + fungal) populations that are adherent to each other and/or surfaces.
Stages in biofilm formation
adhesion, initiation (proliferation), maturation, dispersal
How does the biofilm aid bacterial and fungal communities?
provides protection from immune system, antifungals, detergent and antiseptics. Allows sharing of nutrients and resources.
Examples of proteins that are virulence factors of Candida
ALS (agglutinin-like sequence), HWP1 (hyphal cell wall protein), SAP’s (secreted aspartyl proteinases)
What are ALS?
Agglutinin-like sequence. Gene for glycoprotein that helps Candida adhesion
What is HWP1?
Gene that encodes a surface mannoprotein (Hyphal cell wall protein) which aids covalent binding to buccal cells.
What are SAP’s?
Secreted Aspartyl Proteinases which are involved in phenotypic switching, adhesion, cavitation, invasion and nutrient acquisition from the host.
Which antifungals do SDCEP and NICE guidelines indicate should be used for oral candidiasis?
Azole and Polyenes
Which common antiseptic has a high efficacy against Candida species?
CHX
What is the most commonly used antifungal class of drug?
Azoles including Fluconazole
What do the antifungals echinocandins target?
Inhibits beta-glucan synthesis in cell wall of fungi
What do the antifungals azoles target?
inhibit the synthesis of ergosterol which reduces membrane integrity
What do the antifungals polyenes target?
Bind to ergosterol and reduce pores causing membrane disruption
Changes that can cause antifungal resistance
overexpression of cellular components (e.g. ergosterol), mutations of target, changes in drug transporter expression
What are High Biofilm Formers (HBF)?
Some strains of the same Candida species that are more readily able to form a biofilm due to heterogeneity.
What is heterogeneity?
genetic and metabolic differences. Heterogeneity of Candida species plays a large role in biofilm formation.
Why do HBFs confer a higher drug resistance?
Because these strains from a thicker biofilm. Biofilm reduces the permeability of antimicrobials.
What does polymicrobial refer to?
Fungi associating with commensal and pathogenic bacteria (more than one infectious agent)
Examples of infections that are polymicrobial
denture stomatitis, endodontic infections, caries, periodontal disease, angular cheilitis
