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35 Cards in this Set

  • Front
  • Back
List the microorganisms and toxins we need to know
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"
What are the major groups of parasites?
1. PROTOZOA: single celled; microscopic
2. METAZOA: mutlicellular; macroscopic; helminthes (worms) and arthropods
Describe Protozoa
 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
Give 4 Classes of Protozoa
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)
Describe Protozoan morphology and life cycle
 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
Describe morphology and classes of Helminths/Metazoa
 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
Nematodes/Roundworms
 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
Give an example of a parasitic infection
Dracunculus medinensis
Cestodes/Tapeworms
 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
Trematodes/Flukes
 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
Helminths Routes of Transmission
 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
Strategies used by parasites to avoid the immune defenses
 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
General pathologic mechanisms in parasitic diseases
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
Characteristics of Fungi
 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
Describe fungal structure
 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)
Describe fungal morphology
 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)
Describe yeast reproduction
 Unicellular
 Reproduce asexually by budding or fission
 elongation of daughter cell = pseudohyphae
 germ tube formation = characteristic of Candida albicans
 Colonies on agar
What is a hyphae?
 Multicellular
 Long filaments
septate – transverse walls
aseptate – no transverse walls, multinucleated
 Reproduce asexually and/or sexually
 Mycelium on agar – can be hairy, woolly, pigmented
Describe fungal reproduction
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
What class of Fungi are common human pathogens?
Deuteromycetes: reproduce asexually; have septate hyphae
Includes candida, crytococcus, coccidiodes
What are the classifications of Mycoses?
1. superficial
2. opportunistic
3. systemic
4. subcutaneous
5. cutaneous
Fungal Pathogenesis
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
What is dimorphic systemic mycoses?
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
What are the major targets for antifungal drugs?
1. DNA/RNA synthesis: antimetabolites
2. B-glucan synthase: echinocandins
3. Ergosterol (in cell membrane): polyenes
4. ergosterol synthesis pathway: azoles, allyamines, morpholine
What are the drugs of the two classes we need to know?
1. Polyenes:
Amphotericin B
Nystatin
2. Azoles:
a. Triazoles
Fluconazole
Itraconazole
Voriconazole
b. Imidazoles
Ketoconazole
Clotrimazole
Miconazole
Amphotericin B
• 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
Nystatin
• Given in units
• Less toxic
• Not absorbed from the gut
• Used to treat oral or GI fungal infections
What are the Azole Antifungals?
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
MOA of Azoles
• 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
Side effects of Azoles
• 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
Ketoconazole
• 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
Clotrimazole & Miconazole
• Administered topically (OTC available)
• Often used for treatment of vulvovaginal candidiasis
Fluconazole
• Orally or intravenously
• Good CSF penetration
• Treat candidemia or cryptococcal meningitis
Itraconazole
• Oral
• Treat cryptococcosis, and certain aspergillosis
• Dose-related inotropic effects (potential CHF)**
• Avoid use with calcium channel blockers**
Voriconazole
2nd generation triazole
• Extremely broad spectrum
• Used for the treatment of invasive aspergillosis and resistant candidiasis