Medical Microbiology Test Questions – Flashcards
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| Medical Microbiology |
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| human-microbe interactions: parasites, pathogens, virulence, host resistance, infection, disease, normal flora |
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| Parasites |
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| organism living in or on host & causes damage; diagnostic micro: parasitic worms & protozoa (stool samples) |
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| Infection |
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| such a rare process - amazing occurs at all |
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| Normal flora |
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| necessary to keep pathogens or competing bacteria away; intimately intertwined in physiology; w/o it, we wouldn't last a week |
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| Skin |
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| dry ; acidic (from amino acids on surface ; need water) - tough place to live; most w/I sweat glands ; hair follicles, Gram (+) because more resistant to UV light |
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| Transient Flora |
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| never stays in same place - transiently colonizing; can cause pathogenicity |
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| Resident Flora |
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| always stays in same place |
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| Oral Cavity - Saliva |
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| Saliva is hard place to live because lack of nutrients ; lysozymes/lactoperoxidase destroy bacteria; |
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| Oral Cavity - Teeth |
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| Teeth ; gumline have most flora; most anaerobic or strict anaerobes; plaque buildup is biofilm ; traps oral strep or bacilli; when eating, sugars attach ; ferment acid on biofilm, eventually eroding teeth; not as diverse as other biofilms but not monotypic |
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| Intestinal Tract |
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| gradient of pH increases ; O2 decrease moving down tract; very complicated ecosystem; organisms stretch out on flora based on physiology (anaerobic bacteria closer to colon; more aerobic closer to esophagus); archaea bacteria in GIT; gas production (H2, CO2, CH4) |
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| IT Flora |
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| B12 ; K production, steroid mods; they create vitamins we can't but need; they modify basal compound steroids we made; process carbs first that we can't; they metabolize first then we absorb to digest; detoxify foreign chemicals |
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| Sloughing epithelial cells |
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| Gram (-) help to slough epithelial cells to inhibit growth of pathogens |
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| Disruption of normal flora |
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| antimicrobials disrupt normal flora, especially in lower tract, which affects chemostat; need to limit antimicrobials |
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| Upper respiratory tract |
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| mucous membranes - do most work, keep inhaled particles from entering lower tract |
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| Lower respiratory tract |
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| lungs have normal flora; ciliated epi cells keep out particles; 15% have pneumocystis controlled by macrophages but can cause disease; normal flora can cause disease if immune system defective |
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| Urogenital Tract - Bladder |
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| Bladder is sterile - urine great medium for culturing; can get cystitis |
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| Urethra |
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| facultative (-) rods ; (+) cocci; can become opportunistic pathogens; nosocomial is infection from hospital from catheter |
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| Vagina |
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| Pre-puberty ; post-menopause: no glycogen ; alkalinic, Gram (-); Adults have glycogen ; acidic, Gram (+) |
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| Pathogenesis |
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| creation of disease; bacteria has to enter, adhere, invade tissues, colonize ; have virulence factors; w/o adherence, nothing will occur |
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| Adherence |
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| Bacteria can adhere ; not cause problems but must adhere if they are going to become pathogenic |
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| Colonization |
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| bacteria can colonize w/o causing problems; just growth doesn't mean pathogenic yet; mycobacteria can off and on colonize but not cause harm |
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| Harmful interactions |
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| exposure, adherence, invasion of tissues, further exposure, colonization/growth, production of virulence factors = pathogen; either toxicosis or invasiveness causes pathogenicity |
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| invasiveness |
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| spreads all over to cause tissue damage; ability to gain access to & invade, colonize & become pathogenic |
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| toxicity |
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| release of toxins to local or systemic areas to damage tissues |
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| Host entry - specific |
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| breaks in skin or mucous membranes (wounds, trauma) allow easy entry but some can implant w/o aggressive entry (gonorrhea) |
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| Specific adherence |
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| glycocalyx (capsule, slime layer), fimbrae (many small rods) & pili (few) allow bacteria to adhere like glue to tissues or cells; E. coli mainly causes pathogenicity from fimbrae in upper UT; pili are like grappling hooks |
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| Fimbrae & antibiotics |
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| some antibiotics can strip pathogenic flora of its fimbrae, making it inactive & losing pathogenic status |
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| Host entry - invasion |
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| penetration of epithelium, initiation of pathogenicity, growth on altered normal surfaces (burned skin, cuts); need plenty of bacterial cells to invade; can leave local sites & grow distantly (blood, lymph) |
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| Immune system & invasion |
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| immune system tries to keep bacterial infection local so it does not become systemic |
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| Growth limitations |
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| physical (37oC), nutritional & trace elements (iron) needed; iron can be drawn in by acidophores from bacteria, allowing them to become pathogenic |
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| Dissemination |
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| swollen lymph nodes signalling infection sites, inflammation causes sentinels to be called in to respond (WBC's, etc) |
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| Bacteremia |
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| viable or living bacterial cells in blood, but not growing |
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| Septicemia |
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| pathogenic bacterial cells from blood that have invaded ; grown - can cause death |
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| Virulence |
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| measure of how pathogenic a bacteria is or relative ability of parasite to cause disease; physiological factors allow them to be competitive in their environments helps to dominate body |
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| Virulence factors |
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| extracellular proteins help establish ; maintain disease; enzymes aid colonization ; growth; fibrin clots allow pathogens to live in body and not get attacked; have to be effective because of energy cost or will be cut lose |
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| Attenuation |
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| continuous re-growth of pathogen eventually loses pathogenicity |
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| VF - toxicity |
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| how much toxins are needed to cause pathogenicity |
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| Exotoxins |
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| extracellular proteins; cause damage far from infection site; botulinum loose - most virulent toxin; tetanus toxin clenched |
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| Enterotoxins |
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| intestines; organ system failure; from food poisoning; massive secretion of fluid; E. coli and Shigella are same bug phylogenetically (shig has 4 diff species derived from non-pathogenic E. coli); shiga toxin causes more severe Shigellosis |
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| Endotoxin |
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| Gram (-) lipopolysaccharide; release of endogenous pyrenogens; usually have low levels in circulation; causes fever, diarrhea, decrease in lymphocytes ; leukocytes ; platelets, inflammation; severe is septic shock; test levels with Limulus (horseshoe crabs) |
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| Host defense mechanisms |
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| nonspecific, specific, natural resistance; amplitude of reaction for response rate: nonspecific attack anything (weak rate), specific only attacks one kind (strong rate) |
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| Nonspecific mechanism |
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| always turned on, no prior stimulus from particular pathogen; can react towards anything (primary immune response) |
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| Specific mechanism |
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| prior infection, body already built-up immune response for specific pathogen to be turned on (needs priming from repeated exposure to be more efficient) (secondary immune response) |
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| Natural host resistance |
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| certain populations have resistance to diseases because they lack receptors for those pathogenic cells (bacteria, virus) |
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| Stress |
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| can allow normal flora to become pathogenic, it harms immune system if too high |
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| Physical ; Chemical defenses |
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| these are independent of immune system; secretions, blood, cilia, mucous, normal flora, skin, acidity, flushing, pH |
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| Inflammation ; fever |
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| body's response to infection - low amounts can be good to rid bacteria; high or chronic amounts are bad; swollen, red & warm when fluid released & blood (RBC, WBC) at site of infection; fever either kills or stimulates blood to kill pathogen (pyrogenic compounds) |
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| Cytokines |
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| chemical messengers produces by leukocytes to send signals & bring in reinforcement |
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| Clinical Microbiology |
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| detection & ID of pathogens, antimicrobial susceptibility testing - determine if pathogen suspectible to what antibiotic; more important to figure out antimicrobial susceptibility than the ID of pathogen; can start broad spectrum AB's ; switch once ID determined |
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| Clinical Micro Routes |
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| microbiological route is classical: collect specimen; Conventional: culture ; isolate specimen; Molecular: immunological or molecular; Immunological |
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| Molecular route |
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| detect genetics, molecules or Ag's specific to that bug; can also do Ag-Ab test (PCR most common); amplification of nucleic acids |
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| Conventional Micro route |
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| enrich, select or differentiate culture & isolate to identify & determine AB susceptibility |
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| Molecular micro route |
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| search for genome of pathogen (nucleic acid hybridization or PCR) |
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| Molecular immuno route |
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| search for pathogen's microbial cells or virus particles using fluorescent Ab test or ELISA |
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| Immuno route |
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| blood sample - search for Ab against suspected pathogens Ag; Ab assay (agglutination, RIA, ELISA, etc) |
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| Specimen collection |
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| most important step in clinical micro; asceptic collection; can get contamination or not enough of sample; transport |
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| culture media |
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| general purpose (NA), enriched (BA), selective (EMB Gm -) or differential (EMB Lac +) |
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| Blood cultures |
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| rule out bacteremia vs. septicemia; aerobic ; anaerobic vials; amt/vol of sample VERY important (can increase or decrease sensitivity) incubate 5 days |
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| UTI's |
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| very common & from normal flora, most common is nosocomial infection (from hospital); (-) rods or (+) cocci |
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| Urine specimens |
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| bacturia - infection 105; culture on blood agar or MacConkey agar; MA selective gram (-) & differential for Lac (+); Blood is both Gram (+) & Gram (-) Also blood specimen for nitrite production, or high WBC; dipstick |
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| Fecal specimens |
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| preservation necessary; Selective & Differential media required; Campylobacter most common cause of GTI's; H10157 big outbreak from variation of Enterohemorrhagic E. coli (cause shiga toxins); Parasites (worms, protozoa) |
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| Fecal Parasites |
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| worms like tapeworms or protozoa like nematodes |
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| Wound/Abscess cultures |
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| wound - superficial, deep; specimens - tissue, fluid aspirate, swab; anaerobes tissue sample or fluid aspirate from outside of wound (not swab of tissue); "jelly donut story"; most likely polymicrobic infection (do anaerobic ; aerobic cultures) |
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| Abscess treatment |
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| antimicrobials hard to disseminate abscesses so masses have to be excised |
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| Genital cultures |
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| STD's; some hard to culture, Neisseria, Chlamydia, Treponema pallidum (syphillis) & HIV |
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| Neisseria |
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| enriched, selective agar w/ increased CO2 & humidity |
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| Chlamydia |
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| very hard to culture; cell culture & Ag detection or nucleic acid sequencing tests (can also determine if other infections) ***for sexually abused - cannot run nucleic test bcz false (+); only cell culture for legal purposes |
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| Polymorphonuclear cells |
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| Gram (-) diplococci Neisseria - can see only one form for males but different morphology for females |
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| Growth-dependent ID methods |
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| selective & differential media; conventional biochemical tests; rapid biochemical tests; automated biochemical tests |
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| Antimicrobial susceptibility testing |
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| disk diffusion methods & liquid dilution methods |
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| Disk diffusion methods |
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| Kirby-Bauer, Zones of inhibition, interpretation: sensitive, intermediate |
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| Liquid dilution methods |
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| minimum inhibitory concentration (MIC) |
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| Immunological ID methods |
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| serology: Ag-Ab reactions, IgM, IgG, agglutination, fluorescent Ab's, ELISA (enzyme-linked immunosorbant assay) |
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| IgM, IgG |
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| IgM key because it's quickly increased during infection (current or recent infection); IgG harder to test for |
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| Agglutination |
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| Ag-Ab binding to form lattice = + result |
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| Fluorescent Ab's |
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| tag Ab's w/ fluorescent dye & wash; see binding with color |
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| ELISA (don't focus on - might not be on test) |
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| direct enzyme-linked immunosorbant assay; Ab's to virus on plate; add patient sample (serum, etc) which possible virus particles or Ag's; Add antivirus Ab with conjugated enzyme; wash w/ buffer; add substrate for enzyme; + results are colored; quantitation proportional to Ag |
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| Molecular diagnostic methods* |
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| based on analysis of pathogen-specific nucleic acid (NA); can use PCR's or other technology to amplify sequences; because complimentary DNA is stable |
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| Benefits of molecular diagnostic methods |
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| readily extracted, visualized & detected; sequences unique to each pathogen & can be amplified; DNA stable |
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| Mol diagnostic methods: NA (nucleic acid) probes & PCR* |
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| NA probes: ssDNA, specific to particular pathogen, hybridization reactions PCR: amplify NA targets, increasity sensitivity, qualitative PCR, quantitative PCR (viral load), reverse transcriptase PCR (RT-PCR); PCR uses two NA primers, one is cell & one is ssDNA |
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| NA probes - Detection* |
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| place specimen cells on filter; lyse cells & generate ss target DNA; add reporter-labeled probe; allow for reannealing to target; measure hybridization directly if reporter radioactive or fluorescent; add enzyme substrate if reporter enzyme; detect using radioactive detector, fluorimeter or colorimeter/visual inspection |
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| NA probes - Measure Reporter* |
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| lyse & denature sample in NaOH; region complementary to target DNA with reporter probe & capture probe; hybridize sample DNA to probes in solution; nucleases destroy unhybridized probe; target DNA against complementary DNA - capture w/ dipstick; measure reporter. |
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| Qualitative PCR |
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| Used for mycobacterium TB |
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| RT-PCR* |
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| HIV is RNA virus so RT needed, then do PCR |
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| clinical micro - diagnostic virology* |
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| cytopathogenic effect on cell lines; electron microscopy; ELISA, virus-specific PCR |
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| clinical micro - diagnostic virology* |
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| selective media, non-selective media, direct microscopic observation |
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| Exotoxins - Gram (+) or (-)? |
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| Gram (+) |
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| Endotoxins - Gram (+) or (-)? |
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| Gram (-) |
