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Microbiology
Unit 2
| Question | Answer |
|---|---|
| LD50 | Lethal Dose of a toxin for 50% of the test population. |
| ID50 | Infectious Dose of a toxin for 50% of the test population. |
| Common strategies pathogens use to enter a host | Adherence: after adhering, E. coli induces endocytosis to enter host cells & multiply within them. |
| Common portals of entry | Mucous membranes: respiratory tract, gastrointestinal tract, conjuctiva. Skin. Parenteral route (when skin or mucous membranes are penetrated or injured. Most enter through gastrointestinal & respiratory routes. |
| Adherence | Attaching to host tissues at their portal of entry. Adhesins/ligands bind to receptors on host cells. Receptors often made of sugars. |
| Adherence Examples | Glycocalyx (capsule): Streptococcus mutans. Fimbriae (pili): Escherichia coli. M protein: Streptococcus pyogenes. |
| Biofilms | Common mechanism for pathogenicity. Involved in 65% of human disease. Exopolymer production: bacteria excrete slime polymers onto the surface. This forms a barrier that is extremely resistant to chemicals, etc. & allows bacteria to concentrate nutrients. |
| How does a biofilm form? | Adsorption. Attachment of bacteria. Growth & division. Exopolymer production & biofilm formation. Attachment of other organisms to biofilm. |
| Common mechanisms for evading host defenses | Capsules, cell wall components, enzymes, antigenic variation, invasins, intracellular growth. |
| Capsules | Prevent phagocytosis. Streptococcus pneumoniae, Haemophilus influenzae, Bacillus anthracis, Yersinia pestis. |
| Cell Wall Components | M protein resists phagocytosis (streptococcus pyogenes). Fimbrae protein attaches to host cells and gets imported (E. coli). Mycolic acid resists digestion (Mycobacterium tuberculosis). Opa inhibits T helper immune cells (Neisseria gonorrhoeae). |
| Antigenic Variation | Surface proteins altered. Ex. the influenza virus. Varying types of HA & NA spikes. Genes mix & provide variation. |
| Antigenic shift | Trade genes (2 viruses affect cell at the same time). Changes in HA & NA spikes. Probably due to genetic recombination. |
| Antigenic drift | Slow evolutionary process. Point mutations in genes encoding HA or NA spikes. May involve only 1 amino acid. Allows virus to avoid mucosal IgA antibodies. |
| Enzymes | Coagulase coagulates fibrinogen into fibrin-prevents other blood from entering w/ immune cells. Kinases digest fibrin clots (streptokinase). Hyaluronidase hydrolyzes hyaluronic acid, a component of connective tissue (Clostridia) Microbes can move. |
| Enzymes Continued | Collagenase hydrolyzes collagen (Clostridia). IgA proteases destroy IgA antibodies (N. meningititidis, common from microbes that infect CNS) |
| Invasins | Use actin to move from one cell to the next (Listeria). Salmonella alters host actin to enter a host cell. Causes ruffling of cell. In cell, salmonella is protected from the immune system. |
| Intracellular Growth | Immune system can't get to the pathogen. |
| Common mechanisms for damaging host cells | Use host nutrients, disrupt host cell function, produce toxins waste products, produce endotoxin or exotoxin, produce siderophores. |
| Toxin | Substance that contributes to pathogenicity |
| Toxigenicity | Ability to produce a toxin |
| Toxemia | Inactivated toxin used in a vaccine |
| Antitoxin | Antibodies against a specific toxin |
| Exotoxin | Specific for a structure or function in host cell. (A-B, membrane disrupting or superantigen). Made in cell & secreted out. Gram +. By products of growing cell. Protein. No fever. Neutralized by antitoxin. LD50 small. B binding. A toxin. Lyse cell. |
| Endotoxin | LPS-Lipid A. Outer membrane. Gram -. Within cell envelope. Doesn't have to be excreted from cell. Causes fever. Not neutralized by antitoxin. Large LD50. |
| Superantigen Exotoxins | Cause intense immune response due to release of cytokines from immune cells (mostly T cells). Fever, nausea, vomiting, diarrhea, shock, & death. Ex. Scarlet fever, streptococcus pyogenes superantigens that damage the plasma membranes of blood capilaries). |
| Lysogenic Conversion | Exotoxins can be shared by lysogenic conversion. |
| Sideropores | Bacteria excrete sideropores which bind iron. Bacteria take them back up. Use host's iron. Iron chelated. |
| Cytopathic effects of viruses | Cease in cell function. Release of lysozomal compartment into cell. Inclusion bodies. Fusion of infected cells (clumping). Release of immune-suppressign substances. Produce interferons (protection). Antigenic changes to signal host immune system. |
| More cytopathic effects of viruses | Chromosomal changes in host cell (provirus). Cancer-causing (repress contact inhibition & apoptosis). |
| Actions of Interferons (IFNs) | IFN-alpha & IFN-beta cause cells to produce antiviral proteins that inhibit viral replication. Gamma-IFN causes neutrophils & macrophages to phagocytize bacteria. |
| Pathogenic Properties of Fungi | Fungal wastte products may cause symptoms. Chronic infections provoke an allergic response. Tichothecene toxins inhibit protein synthesis: Fusarium. Proteases digest protein-Candida, Trichophyton. Capsule prevents phagocytosis-Cryptococcus. |
| How do pathogens exit their hosts? | Respiratory tract-coughing & sneezing. Gastrointestinal tract-feces & saliva. Genitourinary tract-urine & vaginal secretions. Skin. Blood-biting arthropods & needles or syringes. |
| The Pyrogenic Response | The origin of fevers. Bacterium carrying an endotoxin enters a macrophage. Endotoxin released. Cell makes & secretes cytokines that travel to the hypothalamus. Hypothalamus secretes prostaglandins which cause fever. Septic shock. 1/2 pts. die. |
| Lysogenic conversion can spread pathogenic genes | Temperate phages carrying toxic genes enter the lysogenic cycle & include those genes in another bacterium. |
| The First Line of Defense | Physical barriers microbes face when colonizing human hosts. |
| Skin | Epidermis consists of tightly packed cells w/ keratin-a protective protein. Lysozyme, high salt, fatty acid in sebum, & low pH (3-5) inhibit bacterial growth. |
| Mucous membranes | Mucous traps microbes (glycoprotein produced by goblet cells). Ciliary escalator-microbes trapped in mucous are transported away from the lungs. Whooping cough destroys goblet cells & ruins ciliary escalator. |
| Lacrimal Apparatus | Washes eye |
| Saliva | Washes microbes off |
| Urine | Low pH 1.2-3, lysozyme, urea; defecation,k vomiting: flushes out. |
| Vaginal Secretions | Low pH, flows out |
| Normal Microbiota | Microbial antagonism/competitive exclusion: normal microbiota compete w/ pathogens or alter the environment. Commensal mircobiota: Microbe benefits & host is unharmed-may be opportunistic pathogens. |
| Lysozyme | Breaks down bacterial cell walls |
| Antibacterial peptides | Potent, broad spectrum antibiotics. |
| Transferrin & lactoferrin | Iron-binding blood plasma glycoproteins. Keeps host iron away from microbes. Lactoferrin is a type of transferrin that provides antimicrobial activity to infants. |
| Second Line of Defense | Part of innate immunity. Toll-like Receptors, Cytokines, Formed Elements, Inflammation, Phagocytosis, Lymphatic system, Fever, The Complement System |
| Toll-like Receptors (TLRs) Recognize pathogens & alert body. | TLRs attach to Pathogen-associated molecular patterns (PAMPs). TLRs induce defensive cells to release cytokines that regulate the intensity & duration of immune responses. Recruit macrophages as well as other defensive cells, isolate & destroy microbes. |
| Cytokines | "To move cells." Protein produced by all cells of the immune system in response to a stimulus. |
| Interleukins | Between leukocytes (WBCs). IL-1, IL-2, etc. Communicate between WBCs. |
| Chemokines | Induce migration to areas of infection/tissue damage. Draw immune cells to an area. |
| TNF-alfa | Inflammatory reactions of autoimmune diseases |
| Interferons | Protect cells from viral infections |
| Red Blood Cells | Transport O2 & CO2 & store iron so microbes can't use it. |
| White Blood Cells (Leukocytes) | Neutrophils (polymorphs), Basophils, Eosinophils, Monocytes, Dendritic Cells, Natural Killer Cells |
| Neutrophils (polymorphs) | 1st Responders. Phagocytosis, motile (leave blood). |
| Basophils | Histamine (inflammation and allergic responses) |
| Eosinophils | Kill parasites (helminths). Phagocytosis, leave blood, produce toxins to kill pathogens. |
| Monocytes | Phagocytosis (after leaving blood). Longer lived than neutrophils, but take longer to develop. |
| Dendritic Cells | Phagocytosis. Initiate adaptive immunity (TLR). Abundant in epidermis, mucous, thymus, lymph. |
| Natural Killer Cells (T cells & B cells) | Adaptive immunity. Destroy larger target cells, not bacteria (cytolysis, granzymes). Cancer cells, protozoa, helminths, etc. |
| Platelets | Blood Clotting |
| The Process of Inflammation (Purpose: destroy injurious agent, limit damage, repair/replace damage). | Chemicals: histamine, kinins, prostaglandins, leukotrienes, & cytokines released by damaged cells. Blood clot. Abscess. Vasodilation. Margination-phagocytes stick to endothelium. Diapedesis-phagocytes squeeze between endothelial cells. Phagocytosis. |
| Role of HISTAMINE in inflammatory response | Vasodilation, increased permeability of blood vessels. |
| Role of KININS in inflammatory response | Vasodilation, increased permeability of blood vessels. |
| Role of PROSTAGLANDINS in inflammatory response | Intensify histamine & kinin effect. |
| Role of LEUKOTRIENES in inflammatory response | Increased permeability of blood vessels, phagocytic attachment. |
| Pathway of Phagocytosis | 1 Chemotaxis & Adherence 2 Ingestion 3 Formation of phagosome 4 Fusion of phagosome w/ lysosome to form phagolysosome 5 Digestion of microbe by enzymes 6 Formation of residual body containing indigestible material 7 Discharge of waste |
| Microbial Evasion of Phagocytosis | Inhibit adherence: M protein, capsules. Kill phagocytes: Leukocidins, Streptolysin-release lysosome into cytoplasm. Lyse phagocytes: Membrane attack complex. Escape phagosome. Prevent phagosome-lysosome fusion. Survive in phagolysosome. |
| Neutrophils in phagocytosis | 1st Response. Lots in blood. |
| Macrophages in phagocytosis | Monocytes that leave blood to become macrophages are 2nd response. Fixed macrophages reside in tissues & organs. Wandering macrophages gather at infection. |
| Dendritic Cells in phagocytosis | Phagocytosis; Initiate adaptive immunity-have TLRs. Abundant in epidermis, mucous, thymus, & lymph. |
| Advantages of Fever | Increases transferrins (bind iron in blood to keep infection down). Increases IL-1 activity. Produces interferon. |
| Disadvantages of Fever | Tachycardia (arrythmia). Acidosis. Dehydration. 44-46C fatal (112-114F). |
| Why do virally infected cells produce interferons? | IFN-alpha & beta cause cells to produce antiviral proteins that inhibit viral replication. Gamma IFN causes neutrophils & macrophages to phagocytize bacteria. |
| Antiviral Actions of Interferons | Infecting virus induces host cell to produce IFN-mRNA which is translated into alpha & beta IFNs. These released by host & bind to plasma membrane or nuclear membrane receptors on uninfected cells, inducing them to synthesize antiviral proteins (AVPs). |
| The Complement System | Defensive system composed of over 30 proteins produced in the liver. Destroys invading microbes. Not adaptable. Destroy by cell lysis, inflammation, & enhanced phagocytosis. Act as a cascade. |
| Three Functions of Complement Activation | Opsonization or immune adherence: Enhanced phagocytosis by coating microbe. Cytolysis by Membrane Attack Complex. Inflammation: attract phagocytes. |
| Functions of C3 convertase, C3a & C3b | Inactive C3 splits. C3b binds to a microbe enhancing phagocytosis. C3b also splits C5. Along w/ C5a, C3a binds to mast cells & causes them to release histamine & other chemicals to help w/ inflammation. |
| Convertase Definition | An enzyme that cleaves inactive protein precursors into smaller biologically active molecules. |
| Functions of C5 convertase, C5a & C5b | C5 split by C3b. C5b, C6, C7 & C8 bind & insert into plasma membrane of microbe. These attract C9-forms MAC. Along w/ C3a, C5a binds to mast cells allowing release of inflammatory chemicals. C5a is a powerful chemotactic factor that attracts phagocytes. |
| Function of Membrane Attack Complex (MAC) | Holes of MAC result in cytolysis |
| Three ways to activate Complement | Classical pathway, Alternative pathway, & Lectin pathway. |
| Classical Pathway | C1 activated by binding to antigen-antibody complexes. Activated C1 splits C2 and C4. C2a & C4b combine & activate C3. |
| Alternative Pathway | C3 combines with factors B, D, & P on the surface of a microbe. Causes C3 to split. B, D, & P are PAMPS. Direct activation w/o presence of antibodies. Important in novel infections. |
| Lectin Pathway | Lectin binds to an invading cell. Bound lectin splits C2 & C4. C2a & C4b combine & activate C3. Lectin is a protein that binds carbohydrates on outside of microbe. |
| Complement System Summary | Serum proteins activated in a cascade. Activated by antigen-antibody rxn. Proteins, C3, B, D, P & a pathogen. C3b causes opsonization. C3a + C5a cause inflammation. C5b+C6+C7+C8+C9 cause cell lysis. |
| Ways Bacteria Evade Complement | Capsules prevent C activation. Surface lipid-carbohydrate prevent MAC formation. Enzymatic digestion of C5a. Ex. Group A Beta-Hemolytic Streptococci (GAS)-M protein helps evade complement & adhere to mucous membranes. |
| Basic Structure of Antibodies | Globular proteins-immunoglobulins (Ig). The # of antigen-binding sites determines valence (most have 2 sites: bivalent). V=variable region-binds antigen. C=constant for an Ig type. Fc=binds complement or to a cell. Fc stem, hinge, heavy & light chains. |
| Five Results of Ag-Ab Binding | Agglutination, Opsonization, Complement Fixation, Neutralization, & Antibody-Dependent Cell-Mediated Immunity |
| Agglutination | Reduces the number of infectious units to be dealt with. First primary reaction: pull invader out of solution. |
| Opsonization | Coating antigen with antibody enhances phagocytosis. Helps phagocytes recognize bacteria. |
| Complement Fixation | Causes inflammation & cell lysis. Either IgG or IgM antibodies activate complement. |
| Neutralization | Blocks adhesion of bacteria & viruses to mucosa. Blocks attachment of toxin. Inactivated so microbe can't bind to a cell. |
| Antibody-Dependent Cell-Mediated Immunity | Large organisms must be attacked externally. 1 Target cell coated w/ antibodies 2 Cells of innate immune sys (eosinophils, macrophages, NK cells) bind to Fc regions of antibodies 3 Target cell is lysed |
| Five Types of Fc Regions | IgG, IgM, IgA, IgE, IgD |
| IgG Antibodies | Monomer. In blood, lymph, & intestine. Cross placenta to protect fetus/newborn. Most abundant in serum: 80%. Fix complement. Cross Blood vessels to site of inflammation, enhance phagocytosis, neutralize toxins & viruses. 23 day half-life. |
| IgM Antibodies | Pentamer-large size restricts movement. In blood, lymph, & on B cells. 5-10% of serum antibodies. Fix complement. Agglutinates microbes, 1st Ab produced in response to infection. 10 binding sites. Predominant in response to blood type. 5 day half-life. |
| IgA Antibodies | Dimer. In secretions, so most abundant antibody in human body! 10-15% of serum Abs. Mucosal protection (prevents attachment of microbes). 6 day half-life |
| IgE Antibodies | Monomer. On mast cells, on basophils, & in blood. 0.002% of serum Abs. When antigen binds they release histamine. Allergic reactions; lysis of parasitic worms. 2 day half-life. |
| IgD Antibodies | Monomer. B cells surface, blood, lymph. 0.2% of serum Abs. Serum function unknown. Presence on B-cells initiates immune response. 3 day half-life. |
| Activation of B Cells | HumoralImmnune 1 Major Histocompatibility complex (MHC) expressed on mammalian cells. 2 T-dependent antigens-Ag presented w/ (self) MHC to TH cell. TH cell produces cytokines that activate B cell. 3 T-independent antigens stimulate the B cell to make Abs. |
| MHC | Types 1 and 2 reveal two types of disease. |
| MHC 1 | Displays internal proteins (such as from viral infection) on all nucleated cells. |
| MHC 2 | Displays external proteins on Antigen Presenting Cells (APC). Antigen Presenting Cells digest antigens & show fragments on surface. |
| Cells that display MHC 2 molecules | B cells, Dendritic cells (skin, genital tract, lymph, blood, various tissues), Activated macrophages migrate to lymph (activated by ingestion of antigenic material or by cytokines). |
| Two roles of B cells when activated | B cells clonally expand into antibody-producing plasma cells and memory cells. Plasma cells secrete antibodies into the blood stream. |
| T-dependent activation of B Cells | Ig receptors on B cell are the same. Bind antigen, internalize & process it & display fragment on MHC 2. T helper cell (TH) receptors produce B-cell activating cytokines. B-cell clones. |
| T-independent activation of B Cells | Weaker immune response. Not as many memory cells made. T-independent antigen delivers both signals. Repetitive, can bind may B-cell receptors at once to activate. |
| How do our bodies produce antibodies so much faster the 2nd time we are exposed to an antigen? | Memory Cells |
| T Cells | Mature in thymus. Thymic selection eliminates immature self-recognizing ones. T-cell receptors (TCRs) to respond to antigens. Require Antigen Presenting Cells. Characterized by clusters of differentiation, CD. Cell-mediated Immunity. |
| Cytotoxic T Cell TC (CD8+) | Detects MHC 1. Detect endogenous pathogens & cancer cells. Activated into Cytotoxic T Lymphocytes. Induce Apoptosis by released cytokines. Clonally expand producing more CTLs & memory cells. CTL releases perforin & granzymes to kill targets. |
| Helper T Cell TH (CD4+) | Detects MHC 2. Activated by APCs. TH1 stimulates cellular immunity, macrophages, phagocytosis, & complement. TH2 stimulates antibody production (especially IgE in allergies) & eosinophils. |
| T Regulatory Cells (Treg) | 5-10% of T cells. Have CD4+ & CD25 molecules. Combat autoimmunity & protect good intestinal bacteria & fetus. |
| HIV Human Immunodeficiency Virus | Etiologic agent that causes aids. HIV-1 is more virulent and infective than HIV-2. Infects primarily Helper T-cells & is sheltered by host cell. |
| AIDS Acquired Immunodeficiency Syndrome | CD4+ T cell counts <200/mm3. Presence of AIDS-defining illness (Kaposi's sarcoma, Pneumocystis pneumonia, primary CNS lymphoma). |
| AIDS Prevalence/Incidence Rates. What do we expect in subsequent years? | 25 mil have died from aids. 100 mil infected. 5 mil infected/yr. Leading cause of death in sub-Saharan Africa. As disease spreads through China & India, it is expected to increase. They have much larger populations than Africa. |
| HIV Structure | Polyhedral. Retrovirus. Has reverse transcriptase. Lipid membrane. gp 120 docking glycoprotein. gp 41 transmembrane glycoprotein. RNA inside capsid inside matrix. |
| HIV Life Cycle | gp 120 spike attaches to receptor & coreceptor on cell. gp 41 participates in fusion of HIV w/ cell. Entry pore created. HIV uncoats releasing RNA core. Some form proviruses-latent. Making new viruses-active. |
| Why are there 1-100 million different HIV variants in one infected human? | Reverse transcriptase is very error prone so a mutation is probably introduced at every position in the HIV genome many times each day (100bil generated/day) |
| Normal course for HIV infection | Memory cell holds HIV dormant as provirus for decades resistant to antivirals. TH cells are depleted,& B cells fail to propogate. This leads to depleted antibodies. Antibodies can't do 5 mechanisms. Classical pathway of complement dependent on antibodies. |
| Current Treatments for HIV | Chemotherapy: reverse transcriptase inhibitors, protease inhibitors, fusion inhibitors (targets gp41), integrase inhibitors. Given in a cocktail (hightly active antiretroviral therapy (HAART). |
| Transmission of HIV (25% of HIV-positive African American’s don’t know they have this disease)! | 85% heterosexual. 1/3 infections in Europe from injected drugs. Blood 1000-100,000viruses/mL, semen 10-50vir/mL, breast milk. 20% transmission rate mother to child. Needlestick injury risk .3%. Transfusions tested. No saliva, tears, urine, or mosquito. |
| Genetic Factors that affect HIV infection | No immune system has ever eradicated HIV. 1% of pop has a major deletion in CCR5 (mostly Europeans). Some African prostitutes remain HIV neg. due to unusually effective CTLs (Cytotoxic T cells). Other factors: blocks in efficient binding for HIV to CCR5. |
| CCR5 | gp120 receptor |
| Sources of difficulties in developing an HIV vaccine | If T cell is a longed-lived memory cell than HIV can lay dormant for decades (resistant to antivirals and challenges vaccines). Reverse transcriptase is super error prone. |
| How can vaccination result in immunological memory & immunity from subsequent infection? | Memory B cells. Faster immune response when the real deal is introduced. IgG Antibodies produced faster on 2nd exposure. Vaccination creates a herd community. |
| Types of Naturally Acquired Immunization | Active: recovery from infection. Passive: maternal antibodies-placental, breast milk transfer. |
| Types of Artificially Acquired Immunization | Active: vaccination. Passive: injection of preformed antibodies. |
| Attenuated whole-agent vaccines | Live attenuated-long term cultivation selects for non-virulent strains. Exs. Vaccinia (smallpox), BCG (tuberculosis). Genetically engineered-removed virulent genes Ex. FluMist Sometimes dangerous: w/ influenza, another strain could mix & make new. |
| Inactivated whole-agent vaccines | Kill microbe. Salk polio, rabies, influenza, chlolera, pneumococcal pneumonia. |
| Subunit vaccines | Most common type of vaccine. Use pieces. Exs. Acellular pertussis, hepatitis B. |
| Toxoid vaccines | Look like a toxin. Neutralize. Don't last. Require boosters. Exs. Tetanus, diphtheria, botulism. |
| Conjugated vaccines | Peptide or polysaccharide, linked to protein. Exs. Streptococcus pneumoniae Haemophilus influenzae. |
| Nucleic acid (DNA) vaccines | DNA injected and transcribed/translated. Ex. West Nile (for horses). |
| Function of adjuvants in stimulating innate immunity & directing adaptive immune response to antigens contained in vaccines. | Adjuvants such as Alum induce local inflammation & bring immune system cells to the site where the vaccine was injected. |
| Vaccine advantages. | Eradicated many bacterial & viral diseases. |
| The Anti-vaccine movement | Started w/ hypothesis that measles vaccine caused a leaky gut, sending toxic substances into the blood & brain causing autism. Correlation. Retraction by 10 of the 13 authors. Called a deliberate fraud by one author. |
| Monoclonal Antibodies (MABs) | Highly specific antibodies produced in large quantity by clones of a single hybrid cell formed in the laboratory by the fusion of a B cell with a tumor cell. Goal to make fully human ones. Now made from mice. In lab, select B cell & let it mass produce. |
| Antibody Precipitation Reactions | Reaction of soluble antigens with antibodies. Get a precipitate band. |
| Antibody Agglutination Reactions | Particulate antigens & antibodies. Antigens on a cell (direct agglutination). |
| Antibody Titers | Concentration of antibodies against a particular antigen. You can visualize what concentration of antibodies is needed for agglutination. |
| Direct fluorescent-antibody tests | Fluorescent antibodies connect to microbe isolated from patient & fluoresce. Direct tests detect antigens from pt sample. |
| Indirect tests | Detect antibodies in patient's serum. Primary antibody binds antigen. Secondary antibody binds 1st and fluoresces. |
| Direct Enzyme-Linked Immuosorbent Assay (ELISA) | Antibody adsorbed to well. Pt. sample added, antigen binds to antibody. Enzyme-linked antibody specific for test antigen added & binds to antigen forming sandwich. Add enzyme substrate. Rxn produces product that causes color change. West Nile, food indus. |
| Indirect Enzyme-Linked Immuosorbent Assay (ELISA) | Antigen adsorbed to well. Pt. serum added. Antigen binds to antibody. Enzyme-linked anti-HISG is added & binds to bound antibody. Enzyme's substrate added & rxn produces product that causes color change. HIV. Cheap & routinely run. |
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