Topic 4 Eukaryotic microorganisms.pdf

Foundations of Pharmacology PHRM2005 Dr. Ricky R Lareu Eukaryotic Microorganisms 2 Key Concepts Fungus structure, growth and replication Protozoa structure and life cycle Protozoa transmission Learning Outcomes Describe the dimorphic nature of fungi structure and types of infection Describe the gene...

Foundations of Pharmacology PHRM2005 Dr. Ricky R Lareu Eukaryotic Microorganisms 2 Key Concepts Fungus structure, growth and replication Protozoa structure and life cycle Protozoa transmission Learning Outcomes Describe the dimorphic nature of fungi structure and types of infection Describe the general structure of protozoa and their characteristic two-stage life cycle Reading and reference material Mim’s Medical Microbiology 5th Ed., Chapters 4-7 3 The Fungi: Overview Fungi consist of eukaryotic cells Mycology is the study of fungi Wikimedia Commons ▪ Fungal diseases are called mycoses Only moulds and yeasts are microbes ▪ Mushrooms, toadstools, bracket fungi, puffballs are fruiting bodies (fleshy fungi) Fungi are important environmental organisms – major decomposers of organic matter (saprophytes) Most are harmless to humans: ▪ Of 70,000+ species only about 300 can cause disease e.g. Candida albicans Fungi are commensal organisms, used in biotechnology: wine, beer, soy sauce, bread production; drug production: cyclosporine, penicillin Fungi commonly cause skin and hair infections ▪ More serious opportunistic infections in immunocompromised individuals 4 Structure of Fungi: 2 forms Moulds – Filamentous, multicellular ▪ made up of microscopic filaments called hyphae which form a branched structure – mycelium ▪ Multicellular/multinucleate Yeasts – single-celled (unicellular), usually larger than bacteria, oval-shaped Mouldy bread Figure 5-9 from Burton’s Micro. for the Health Sciences Dimorphic – some species are capable of both filamentous and unicellular growth Depends on environmental conditions: ▪ 25°C (room temp.) → filamentous structure, growth in mould form on culture media ▪ 37°C (body temp.) → unicellular, grow in colony form on culture media Figure 4.1 from MMM 5 Fungal Growth and Reproduction Filamentous forms grow by extension of the ends of the hyphae and production of spores (called conidia) Sporulation on aerial hyphae: sexual and/or asexual, many different structural forms Spores: ▪ Important for dispersal – easily carried by wind ▪ Dormant survival structure ▪ Spore are very resistant to heat, chemicals, standard autoclaving Yeasts can grow by budding or binary fission: Images: http://www.fungionline.org.uk 6 Fungi Wall Structure Fungal cell wall has unique composition ▪ Possess different molecules to bacteria and mammalian cells – drug targets Ergosterol – cell membrane, high content Not found in mammalian cell membrane Equivalent to cholesterol in mammals Target for antifungals e.g. amphotericin B Chitin (polysaccharide) found on exoskeleton of arthropods Antifungal – nikkomycin β-glucan – cellulose Cross-linked and provide rigidity to wall Echinocandins block synthesis Glycosylated proteins Cellulose layer Ergosterol in cell membrane Nature Reviews - Microbiology 7 The Protozoa Single celled animals – eukaryotes Generally free-living found in soil and water Most protozoa are harmless Some are pathogens well adapted to live parasitically in humans and animals ▪ e.g. giardia, malaria Do not have a cell well – a few have a structure called a pellicle which provides similar protection Many protozoa are capable of movement: ▪ Ciliates, use cilia; Amoeba, use pseudopodia; Flagellates, use flagella ▪ Sporozoa are non-motile i.e. Plasmodium sp., causing malaria ▪ Both intracellular (e.g. toxoplasmosis) and extracellular (e.g. amoeba, malaria) types exist Entamoeba histolytica, CDC, USA 8 Protozoa Life Cycle Typically consists of 2 stages – e.g. Giardia spp. Trophozoite ▪ Motile, feeding and dividing stage Cyst ▪ Non-motile, dormant, survival stage ▪ Usually the infective stage Some protozoa are more complex than this ▪ Plasmodium (malaria) 9 Protozoan sites of infection Transmission is most common from food/water contamination or insect vectors Protozoan pathogens have various strategies including intracellular and extracellular modes (depends on organism) Have evolved various strategies to survive immune responses Symptoms of protozoan infections often due to immune reactions 10 Summary Eukaryotic parasites includes the fungi and the unicellular protozoa. Most fungi can exist in two forms – unicellular and filamentous, which depend on environmental conditions. Most fungi can undergo both asexual (budding, spores) and sexual reproduction (spores) Protozoa are unicellular and many are motile and most have a two-step life cycle (trophozoite, cyst). 11