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35 Cards in this Set
- Front
- Back
List the microorganisms and toxins we need to know
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Mycoplasma– no cell wall, not seen on a gram stain
Spirochetes – too thin to be seen on a gram stain; endoflagella for motility Mycobacterium – specific cell wall; acid fast; not seen on gram stain Staphylococci – gram positive cocci in clusters Streptococci – gram positive cocci in chains Enterobacteriaceae– gram negative rods Bacillus and Clostridium – gram positive rods; spore forming Example of toxins and their mode of action: Diphtheria toxin – inhibition of protein synthesis Cholera toxin – hyperactivation Tetanus toxin – blocks release of inhibitory neurotransmitters Botulinumtoxin – blocks release of acetylcholine from peripheral nerves Toxic Shock Syndrome Toxin - superantigens" |
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What are the major groups of parasites?
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1. PROTOZOA: single celled; microscopic
2. METAZOA: mutlicellular; macroscopic; helminthes (worms) and arthropods |
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Describe Protozoa
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Free-living or parasites or both
Can be intra- or extra-cellular parasites Disease may be caused directly (e.g. rupture of red cells in malaria) but in general damage caused by host’s response Transmission: ingestion of contaminated food or water, insect vectors, sexual contact, in-utero from mother |
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Give 4 Classes of Protozoa
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1. Ameoba
binary fission pseudopods e.g. Entamoeba histolytica (Amebiasis) 2. Flagellate binary fission whiplike flagella e.g. Trypanosoma (trypanosomiasis), Giardia (Giardiasis) 3. Ciliate binary fission hairlike structures = cilia rarely cause human disease 4. Sporozoa often intracellular parasites schizogony (multiple fission) and sporogony (sexual or asexual division of a spore ) no organelle of locomotion e.g. Plasmodium (malaria), Toxoplasma (toxoplasmosis) |
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Describe Protozoan morphology and life cycle
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Morphology & Life Cycle – important for identification
cyst: dormant stage in the life cycle of protozoan parasites; thick-walled structure; resistant form trophozoite: active feeding stage in the life cycle of protozoan parasites oocysts: encysted from of a zygote spores: single-celled asexual or sexual reproductive body; resistant form sporozoites active bodies into which sporozoans divide in one stage of their life cycle formed by sporogony Infective stage vs. diagnostic stage |
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Describe morphology and classes of Helminths/Metazoa
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Large organisms – complex body organization
External surface covered with a cuticle Primary nervous & excretory system – no circulatory system Well developed reproductive system – generally oviparous (excrete eggs) Attachment structures: anterior hooks or suckers Primarily anaerobic but larvae need O2 Classification based upon morphology, reproduction, alimentary tract, and host 3 important classes of helminths Roundworms – Nematodes Tapeworms – Cestodes Flukes – Trematodes |
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Nematodes/Roundworms
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Long cylindrical body and generally no attachment organs
Separate sexes Tubular alimentary tract Feed on host tissues or on intestinal contents e.g. intestinal nematodes - dwell within human GI tract e.g. tissue nematodes – infect tissues & lymphohematogenous syst. (e.g. Toxocara canis) Life cycle – from simple and direct to complex requiring one intermediate host |
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Give an example of a parasitic infection
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Dracunculus medinensis
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Cestodes/Tapeworms
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Flat ribbonlike segmented bodies
Head = scolex; equipped with organs of attachment (muscular suckers and/or hooks) Hermaphroditic reproductive elements called proglottids (form chain of segments behind head) No digestive system; absorb pre-digested nutrients Life cycle: from simple and direct to complex requiring one intermediate host |
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Trematodes/Flukes
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Leaf-shaped bodies*
Oral and ventral suckers for attachment to host Hermaphroditic Incomplete digestive system - feed on host tissues or on intestinal contents Complex life cycle - two or more intermediate hosts |
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Helminths Routes of Transmission
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found in regions where climate is good for infective form survival
frequent in poor and low hygiene conditions 1. via intermediate host (accidental ingestion of larvae in tissue of another host 2. fecal-oral route 3. active skin penetration 4. injection by blood-sucking insect |
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Strategies used by parasites to avoid the immune defenses
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Surface antigenic variation
e.g. Plasmodium, Giardia… Molecular mimicry e.g. Schistosomes, Plasmodium, Trypanosomes Masking of antigenic sites acquisition of coating of host molecules – e.g. Filaria, Schistosomes, Trypanosomes Intracellular location Immunosuppression suppression of parasite-specific B- and T-cell responses; degradation of immunoglobulins |
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General pathologic mechanisms in parasitic diseases
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1. Toxic parasite products
lytic enzymes: proteinases, collagenase, elastase amebic ionophore catabolites 2. Mechanical tissue damage blockage of internal organs migration through tissue (helminth larva)… 3. Immunopathology hypersensitivity autoimmunity |
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Characteristics of Fungi
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Ubiquitous as free-living organisms
nonphotosynthetic heterotrophes usually obligate aerobes grow optimally at 25 - 30°C Mostly beneficial: food, health industry, degradation of waste products… Only a small portion cause human diseases fungal infections = mycoses Most fungal infections acquired from environment or via normal flora |
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Describe fungal structure
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Eukaryotes
Uni- or multicellular organisms CELL WALL: determines shape, attachment to host cell, and induces inflammatory response; composed of cell membrane covered by a cell wall composed of (1) chitin; (2) B-glucans; (3) mannoproteins Cytosol: nuclear membrane, mitochondria, golgi bodies, endoplasmic reticulum; at least one nucleus (often multinucleate) |
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Describe fungal morphology
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Complex structural features used in speciation
2 basic morphological forms Yeast – unicellular Hyphae (molds or moulds) - multicellular Dimorphic fungi can exist either as yeasts or as molds, depending on growth conditions e.g. temperature: molds in cold environment vs. yeasts in warm host (candida does the opposite) |
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Describe yeast reproduction
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Unicellular
Reproduce asexually by budding or fission elongation of daughter cell = pseudohyphae germ tube formation = characteristic of Candida albicans Colonies on agar |
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What is a hyphae?
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Multicellular
Long filaments septate – transverse walls aseptate – no transverse walls, multinucleated Reproduce asexually and/or sexually Mycelium on agar – can be hairy, woolly, pigmented |
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Describe fungal reproduction
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1. Sexual reproduction
sexual spores; involves meiosis 2. Asexual reproduction asexual spores; involves mitosis only – progeny genetically identical Conidia - formed by budding or hyphal separation Sporangiospores – within a sac named sporangium **spores or conidia are important for ID; often the infective form |
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What class of Fungi are common human pathogens?
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Deuteromycetes: reproduce asexually; have septate hyphae
Includes candida, crytococcus, coccidiodes |
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What are the classifications of Mycoses?
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1. superficial
2. opportunistic 3. systemic 4. subcutaneous 5. cutaneous |
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Fungal Pathogenesis
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1. Infectious process
trauma or inhalation transfer from person-to-person - only in case of superficial mycoses (e.g. sharing cloths) normal flora – opportunistic mycoses 2. Survival inside the host interference with complement function – e.g. Candida albicans antiphagocytic capsule – e.g. Cryptococcus neoformans survive phagocytosis + then replicate – e.g. Histoplasma capsulatum 3. Tissue damage mostly caused by host immune + inflammatory responses |
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What is dimorphic systemic mycoses?
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Fungal infections of the body caused by fungal pathogens which can overcome the physiological and cellular defenses of the normal human host by changing their morphological form
Geographically restricted and the primary site of infection is usually pulmonary, following the inhalation of conidia |
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What are the major targets for antifungal drugs?
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1. DNA/RNA synthesis: antimetabolites
2. B-glucan synthase: echinocandins 3. Ergosterol (in cell membrane): polyenes 4. ergosterol synthesis pathway: azoles, allyamines, morpholine |
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What are the drugs of the two classes we need to know?
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1. Polyenes:
Amphotericin B Nystatin 2. Azoles: a. Triazoles Fluconazole Itraconazole Voriconazole b. Imidazoles Ketoconazole Clotrimazole Miconazole |
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Amphotericin B
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• Broad spectrum (A ‘Gold’ Standard)
• MOA: binds to ergosterol and forms a transmembrane channel, causing K+ leakage e.g. Coccidioides immitis, Histoplasma capsulatum, Blastomyces dermatitidis, and Paracoccidioides brasiliensis • The drug of choice in treating most opportunistic mycoses caused by fungi (e.g., Candida species, Cryptococcus neoformans, Aspergillus species, and the Zygomycetes) • Reduced side effects in liposomal formulation |
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Nystatin
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• Given in units
• Less toxic • Not absorbed from the gut • Used to treat oral or GI fungal infections |
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What are the Azole Antifungals?
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Five-membered organic rings that contain either two or three nitrogen molecules (the imidazoles and the triazoles respectively)
• Imidazoles • Clotrimazole, miconazole, ketoconazole • Triazoles • Itraconazole, fluconazole, voriconazole |
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MOA of Azoles
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• Inhibit cytochrome P450 14a-demethylase (P45014DM) involved in the biosynthesis of
ergosterol Acetate → Lanosterol → (CYP450 14α-demethylase) → 14-demethylanosterol → Ergosterol for fungal cell membrane synthesis ****INHIBITS CYP450 14α-demethylase |
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Side effects of Azoles
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• Side effects
• Life-threatening liver toxicity (long-term use, esp ketoconazole)*** • less problematic with the triazoles • Nausea and vomiting • Drug interactions E.g., cyclosporin, certain antihistamines, anticoagulants (warfarin), antiseizure, oral hypoglycemic and other medications that are metabolized via similar pathways in the liver |
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Ketoconazole
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• Administered both orally and topically
• Active against mucosal candidiasis and a variety of cutaneous mycoses • Also used to treat Cushing’s syndrome and prostate cancer |
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Clotrimazole & Miconazole
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• Administered topically (OTC available)
• Often used for treatment of vulvovaginal candidiasis |
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Fluconazole
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• Orally or intravenously
• Good CSF penetration • Treat candidemia or cryptococcal meningitis |
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Itraconazole
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• Oral
• Treat cryptococcosis, and certain aspergillosis • Dose-related inotropic effects (potential CHF)** • Avoid use with calcium channel blockers** |
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Voriconazole
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2nd generation triazole
• Extremely broad spectrum • Used for the treatment of invasive aspergillosis and resistant candidiasis |