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18 Cards in this Set
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What are Fungi? |
Fungi: • eukaryotic microbes, uni or multicellular. • Structural features: 1. typicalinternal eukaryotic ‘compartments’ 2. cellenvelope • plasma membrane (phospholipid bilayer); containsergosterol (bacteria do not contain sterols). • Cell “wall”; rigid, multi-layered consisting ofchitin (polymer of linked n-acterlyglucosamine). |
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What are the two fungal morphological types? |
Fungi morphological types: 1. Yeasts: • Single-celled fungi. • 5-15 uM diameter • Most reproduce by budding. 2. Molds: • Multi-cellular fungi. • Filamentous structure (hyphae) • Branched, cylindrical tubes. • Form mycelium during growth. • Reproduce via a ‘spore’ stage (not same asbacteria spores. |
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What is a dimorphic fungi? |
“dimorphic Fungi” can switch from yeast to mold form. • Environment dependent (temperature, nutrients,etc.) • Eg; histoplasma àmycelial growth at 25°C, yeast growth at 38°C. |
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What are the three types of fungal mycoses? |
Types of Mycoses: 1. Cutaneous (Superficial) • Outermost layers of skin (epidermis), hair,nails, etc. • Usually transmitted by the direct contract. • Caused by “dermatophytes” (use keratin asnutrient source) • Eg; trichophyton àathlete’s foot. • Microsporum àringworm
2.Subcutaneous: • Infections of dermis of skin and subcutaneoustissues. • Usually associated with traumatic injury.
3. Systemic(deep) • Infections of internal organs. • Usually start in lunges (airborne) then spreadsfurther. • Can be very severe |
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Describe what occurs during a Candidiasis infection. |
Candidiasis (candida albicans) • A fungal infection. • A yeast often found asymptomatically as part ofthe normal human flora (skin, mouth, vagina, intestinal tract). • Can multiply and cause disease if: o A change in immune status. o A change in “balance” of normal flora socompetition is eliminated. o Normal body defenses are breached (eg; cuts,abrasions, burns). Eg. Vulvovaginitis (“yeast infections”) • Cutaneous candidiasis – hardening and distortionof fingernails. • Intestinal candidiasis – ulcerative lesions inintestinal tract. • Oral candidiasis (thrush) – soft, crumbly, whileflecks in oral cavity. |
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Describe a coccidiodomycosis infection. |
coccidiodides immitis • A Fungal infection. • A dimorphic fungus found in the soil in warm,dry areas· • Mycelium growth in environment releasesfragments of hyphae.· • Dust particles carry hyphae frags. Inhaled byhumans. · •Develop into “spherules” in lungs causingrespiratory distress (cough, chest pains, fever). •Self-limiting, but may spread to other organs ifimmunocompromised. |
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How would we diagnose a fungal infection? |
Laboratory Diagnosis of Fungal Infections. 1. Direct microscopic examination. a. Collect patietient specimen from affected area(ef. Skin, tissue, etc.) b. Stain the specimen, examine microscopically andidentify the fungal species based on appearance of spores or hyphae. 2. Growthon culture media + biochemical identification. (similar to culture methods usedfor bacteria). o Inoculate patient specimen ontoselective/differential media. o Identify fungal species based on growth andbiochemical properties. |
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Describe the MOA of Polyenes. |
polyenes • amphotericin B, nystatin • Antifungal • Bind to ergosterol, creating pores in fungalplasma membrane. • Good for oral or vaginal candida infections(Nystatin) or for severe systemic infections (Ampho. B), • some toxicity and sideeffects (nausea, anemia, kidney damage). |
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Describe the MOA of Azoles |
Azoles • antifungal • Family of synthetic chemicals which block ergosterol synthesis: defective membranes lead to leakage of cytoplasmiccontents. Eg; • Imidazoles (eg. Miconazole, clotrimazole);non-prescription creams for topical applications. • Triazoles (eg veroconazole, fluconazole); lesstoxic àgiven orally for system infections. o Note: the number of other (non-azole compoundsalso inhibit ergosterol synthesis and are effective vs various dermatophytes. |
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Describe the MOA of Nucleotide Analogues. |
Nucleotide Analogues - Antifungal • Nucleic acid analogue which acts as NA synthesisinhibitor. •Transported into fungal cells by a membranetransport protein. •Metabolized to 5-FU by fungal enzymes; blocksDNA, RNA synthesis. •Less toxic vs other anti-fungals because humancells have less ability to transport and metabolize flucytosine. |
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What is different for antifungals than for antibiotics? |
Antifungals: • Because fungi are eukaryotic, achieving“selective toxicity” is sometimes difficult. •Potential host toxicity means that some agentscan only be used topically for external (cutaneous) infections. •Relatively small number of agents (as comparedto antibiotics). •Increased use of “species-specific” agents makesaccurate laboratory identification of fungi more important. •various modes of action, but most target thefungal cell envelope or interfere with DNA/RNA synthesis. |
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What is a parasite? |
Parasites: General term to describe an organisms that, as part oftits life cycle, resides in or on a mammalian host. Two Taxonomic groups (both eukaryotic). Protozoa and Helminths Bothgroups are responsible for significant human disease. |
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Describe the protozoa. |
Protozoa •Microscopic, single celled •Similar to yeast in size and internalcomplexity. •Many different taxonomic groups distinguished byappearance, type of motility, etc. •Some protozoa can alternate between twomorphological forms, depending on their environment: eg gardia Trophozoite vs cyst form (eg. Giardia) Trophozoite; metabolically active and replicating form found inside the host. Cyst: dormant, non-replicating form with thickened wall structure to help survival in the environment (resists drying, stress, etc.) Form which is transmitted from host to host. |
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Describe the Helminth. |
Helminths (metazoan) •Micro or macroscopic •Multicellular worms •Differentiated organs/tissues. •Includes all worms that have parasiticlifestyle, but only three groups of human importance. - Nematodes, tapeworms, and flukes. • Usually macroscopic with complex bodyorganization. - Attachment structures (hooks, suckers) - Primitive nervous, reproductive, excretorysystems. •Many reproduce sexually via eggs which formlarvae. - Eggs and/or larvae are transit forms (inenvironment). - Adults worms replicate in host and give diseasepathology.· • By physical obstruction/displacement of tissues. •By producing various tissue-degrading enzymes.· •By interfering with intestinal absorption offoods. |
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What occurs during a giardiasis infection? |
giardiasis (Giardia Lamblia) • Most common protozoan intestinal disease innorth America. •Abdominal cramping, belching, nausea,flatulence. • Foul-smelling, greasy, watery diarrhea. • Resolves in 1-4 weeks, but may persist formonths (kids).· • Cyst (environmental) and trophozoite (in vivo)forms· • Can have both human and animal (beaver, dog)hosts. • Transmission via fecal-oral route. • Ingestion of water contaminated with cysts • Direct contact with fecal material from infectedperson. • Cyst form isingested; stomach digestive enzymes degrade cyst wall, which triggersconversion to trophozoite form in the intestinal tract. •Trophozoites multiply & attach to intestinal villi via suckers. • Dehydrationof stool during passage through large intestine triggers conversion back tocyst form & excretion to environment. |
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What occurs during a Pinworm infection. |
Parasitic Infection: Pinworms (enterobius) • Nematode Group.· •Most common helminth parasitic infection inNorth America • Mild diarrhea, intense perianal itching are usuallyonly symptoms· • Eggs swallowed, hatch in duodenum & mature in large intestine •Adultworms attach to intestinal wall • migrate at night to peri-anal area and depositeggs. •Scratchingcontaminates hands, bed linens with eggs. • Re-infectionvia hand to mouth contact, contaminated food, or if eggs released into air byhandling bed linens, etc. •2 week life cycle, infectionresolves if re-infection is prevented. •Since eggs are not released in feces, diagnosisrequires finding eggs in the perianal area with ‘pinworm paddles’. |
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Discuss anti-parasitic agents. |
Anti-ParasiticAgents • Relatively few in number • Most interfere with a protozoan biosynthetic pathway or with helminthneuromuscular functions eg. Metronidazole (Giardia) - electron transport inhibitor eg. Pyrantel pamoate (pinworms) - blocks neuromuscular activity ® paralysis 5 |
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What is special about Giardia |
Can switch between a trophozoite and cyst form. • Trophozoite vs cyst form (eg. Giardia) Trophozoite; metabolically active and replicating form found inside the host. Cyst: dormant, non-replicating form with thickened wall structure to help survival in the environment (resists drying, stress, etc.) Form which is transmitted from host to host. |
