BMS2052 Lecture Notes - Lecture 15: Tinea Capitis, Griseofulvin, Nucleolus
30 May 2018
School
Department
Course
Professor
Week 5. Fungi and Fungal Infections
• Overview of fungal structure and function:
o Spore bearing
o Absorptive nutrition
o Lack chlorophyll
o Both sexual and asexual
o Cell usually encased in chitin
o Free living in nature
o Functions as decomposers in energy cycle
o Most are aerobes or facultative anaerobes
o Over 100,000 known species with around 200 reported to cause disease in humans –
mycoses
o Increasing in immunocompromised patients
• Environmental distribution:
o Primarily terrestrial
o Few aquatic
o Many are parasitic and pathogenic in plants, animals and other fungi
o Some form symbiotic associates
• Fungal cultures are classified by presence of sexual reproduction structures
• Yeast and moulds:
Yeast
Moulds
o Single celled yeast
o Larger than bacteria
o Fission: divide evenly to produce 2 new cells
o Budding: divide unevenly by budding
o Colonies resemble similar to bacteria
o Are facultative anaerobes which allows
them to grow in a variety of environments
o Ferment carbohydrates to produce ethanol
and CO2 if O2 is not available
o Multicellular, filamentous
o Identified by physical appearance, colony
characteristics and reproductive spores
o Thallus: body of mould or fleshy fungus
o Hyphae: long filaments
Septate: divided by cross walls (septa)
Coenocytic (aseptate): not divided by
septa
Vegetative: portion that obtains
nutrients
Reproductive/aerial: portion connected
with reproduction
o Mycelium: large, visible, filamentous mass
made up of many hyphae
find more resources at oneclass.com
find more resources at oneclass.com
• Dimorphism:
o Can exist as both multicellular fungi (moulds) and yeast
o Many pathogenic species
Mould dorms aerial and vegetative hyphae
Yeast form reproduces by budding
o Dimorphism in pathogenic fungi typically depends on temperature:
37 degrees = yeast
25 degrees = mould
o Dimorphism in non-pathogenic fungi may depend on other factors such as CO2
concentration
o Is reversible
• Structure of fungi:
o Typical eukaryote features
o Nucleus
Nucleolus, membrane and linear chromosomes
Cytoplasm
Usually in haploid state
Diploid nucleus is formed in sexual reproduction
o Cytoskeleton
o Ribosomes
o Organelles
o “oe do’t hae a ell all
• Fungal spores vs bacteria spores:
Fungal spores
Bacterial spores
o 1 spore gives rise to a mycelium
o Can be part of their asexual/sexual
reproduction
o 1 spore=1 bacterial cell
o Formed during unfavourable conditions
• Lab diagnosis:
o Direct examination
-> size, morphological features
-> some yeast stain gram positive
o Culturing: enriched media, longer incubation time
o Ag and Ab detection
-> some Ab directed against a variety of fungal Ag
• Fungi as infectious agents :
o Moulds and yeast are widely distributed in air, dust and formites
o Some form part of normal flora
o Relatively non-pathogenic
o Only around 200 are linked to disease
o Humans are relatively resistant
find more resources at oneclass.com
find more resources at oneclass.com
o Immunocompromised patients are at high risk – primary fungal pathogen can invade
and grow
o Fungi are most common pathogen in plants – destroys crops
o Key adaptation to survival and grow in humans is ability to switch from hyphal cells to
yeast
o Thermal dimorphism
o There are 5 groups depending on route of infection
Direct contact: superficial, cutaneous, subcutaneous
Systemic infections
Opportunistic mycoses
o Emerging fungal pathogens:
Opportunistic pathogen has little or no virulence, host defences must be
impaired
Account for 10% of nosocomial infections
Dermatophytes may be undergoing transformation into true pathogens
• Epidemiology of mycoses:
o Most fungal pathogens do not require a host to complete life cycles and infections are
ot ouiale does’t oe uh fro perso to perso
o Dermatophytes and candida spp. Naturally inhabit human body and are transmissible
o Dermatophytes most prevalent
o Cases go undiagnosed or misdiagnosed
o Can get systemic, subcutaneous, cutaneous or superficial infections
• Pathogenesis of fungi:
o Portal of entry:
Primary mycoses – respiratory/inhale
Subcutaneous – inoculated skin due to trauma
Cutaneous and superficial – skin surface
o Virulence factors:
Thermal dimorphism
Toxin production
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Increasing in immunocompromised patients: environmental distribution, primarily terrestrial, few aquatic, many are parasitic and pathogenic in plants, animals and other fungi, some form symbiotic associates, fungal cultures are classified by presence of sexual reproduction structures, yeast and moulds: Identified by physical appearance, colony characteristics and reproductive spores: thallus: body of mould or fleshy fungus, hyphae: long filaments. Coenocytic (aseptate): not divided by septa and co2 if o2 is not available. Reproductive/aerial: portion connected with reproduction: mycelium: large, visible, filamentous mass made up of many hyphae, dimorphism, can exist as both multicellular fungi (moulds) and yeast, many pathogenic species. Yeast form reproduces by budding: dimorphism in pathogenic fungi typically depends on temperature: 25 degrees = mould: dimorphism in non-pathogenic fungi may depend on other factors such as co2 concentration. Is reversible: structure of fungi, typical eukaryote features, nucleus. Diploid nucleus is formed in sexual reproduction: cytoskeleton, ribosomes, organelles, o(cid:373)e do(cid:374)"t ha(cid:448)e a (cid:272)ell (cid:449)all, fungal spores vs bacteria spores:
