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79 Cards in this Set
- Front
- Back
Bacterial Growth Curve
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Growth Requirements
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1. Oxygen requirements 2. Nutrient requirements 3. Temperature requirements
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Growth Requirements: Oxygen
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1. Obligate aerobes 2. Anaerobes 3. Facultative anaerobes
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Obligate Aerobes
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Require oxygen
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Anaerobes
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Do not require oxygen: 1. Obligate anaerobes: damaged by oxygen 2. Aerotolerant anaerobes (microaerophilic): tolerate small amounts of oxygen 3. Facultative anaerobes: grow under aerobic/anaerobic conditions
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Growth Requirements: Nutrient Requirements
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1. Undemanding: simple media 2. Demanding (fastidious): complex media
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Growth Requirements: Nutrient Requirements-Common Undemanding Species
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E. coli, Salmonella, and other gram-negative enteric bacteria
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Growth Requirements: Nutrient Requirements-Common Demanding (Fastidious) Species
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Haemophilus and Neisseria spp.
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Temperature Requirements
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Most pathogenic spp. near normal body temperatures (35ºC to 37ºC)
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Cell Division
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Binary fission; simpler process than mitosis 1. Chromosome duplication 2. New cell envelope synthesis
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Chromosomal Duplication: Initiation
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1. At specific sequence (replication origin) in DNA 2. Once it starts, it won't stop (even under unsuitable conditions, e.g. starvation)
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Chromosomal Duplication: Nutrients Available
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1. Synthesis of new chromosome begins before previous chromosome synthesis is complete (born pregnant)
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Cell Envelope Synthesis
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New membrane and cell wall in center of cell, forming a septum that eventually divides cytoplasm into two daughter cells
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Spore Formation (Sporogenesis)
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1. Variant of cell division 2. Induced by depletion of essential nutrients 3. Often produces and releases antibiotics and toxins 4. Gram-positive only (some spp.)
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Spore Germination
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1. Produce vegetative (normal) cells 2. Initiated by damage to spore coat, due to: A) Trauma B) Water C) Aging 3. Requires specific nutrients 3.
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Spore Resistance
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1. Resistant to heat, drying, chemicals (e.g. disinfectants) 2. Can survive for long periods of time
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Spore Vulnerability
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1. Once germination has begun and coat is disrupted, spore is vulnerable to same agents as vegetative cells 2. Autoclaving for 15 minutes 3. Aldehyde disinfectants
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Most Important Spore Formers
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1. Bacillus spp. 2. Clostridium spp.
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Bacterial Genetic Elements
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1. Chromosome 2. Plasmids 3. Bacteriophages 4. Transposons
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Bacterial Genetic Elements: Chromosome
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1. Single, double-stranded, circular DNA molecule 2. ~5 million base pairs
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Bacterial Genetic Elements: Gene Structure
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1. Cistron 2. Operator 3. Operon 4. Promoter 5. Replicon
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Bacterial Genetic Elements: Gene Structure-Cistron
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Region of DNA that codes for a single protein; a complementation unit
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Bacterial Genetic Elements: Gene Structure-Operator
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Nucleotide sequence, located between promoter and first structural gene of an operon, that binds a repressor protein
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Bacterial Genetic Elements: Gene Structure-Operon
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Bacterial transcription unit comprising a promoter, operator, and one or more structural genes
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Bacterial Genetic Elements: Gene Structure-Promoter
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Nucleotide sequence in an operon that is recognized by RNA polymerase
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Bacterial Genetic Elements: Gene Structure-Replicon
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Replication unit, consisting of a replication origin, a replication terminus, and the intervening coding sequence
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Lac Operon
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Bacterial Genetic Elements: Bacteriophages
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Viruses that infect bacteria
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Bacterial Genetic Elements: Bacteriophages-Types
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1. Lytic phage 2. Lysogenic phage
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Lytic Phage
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Replicates independently of host chromosome and kills bacterial host cell
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Lysogenic Phage
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1. Can integrate genome into host bacteria without killing it 2. Toxin genes are carried by some 3. May become lytic under unsuitable living conditions
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Common Lysogenic Phages
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1. E. coli lambda phage 2. Corynephage Beta; carries diptheria toxin
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Bacterial Genetic Elements: Transposons
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1. Move from one position in chromosome or between different molecules of DNA 2. Lack replication origin
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Bacterial Genetic Elements: Transposons-Types
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1. Simple transposons 2. Complex transposons
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Bacterial Genetic Elements: Transposons-Simple
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Encode only the proteins needed to move (insertion sequences)
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Bacterial Genetic Elements: Transposons-Complex
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Carry other genes: 1 Antibiotic resistance 2. Pathogenicity Island
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Pathogenicity Islands
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1. Large, complex transposons that contain all the genes needed for a pathogenic mechanism 2. May contain several operons
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Pathogenicity Islands Control
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Coordinately controlled by environmental (temperature), metabolic, and other triggers
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Mechanisms of Genetic Transfer
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Recombination: Types
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1. Homologous 2. Nonhomologous
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Recombination: Types-Homologous
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Between closely related DNA sequences 2. Generally results in substitution of one sequence for another 3. Basis for periodic shifts in Salmonella flagella and Neisseria gonorrhoeae pilus antigens
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Recombination: Types-Nonhomologous
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1. Occurs between dissimilar DNA sequences 2. Generally results in insertions or deletions 3. Basis for integration of phages into host chromosome and movement of transposons
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Mechanisms of Bacterial Virulence
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1. Adherence 2. Invasion 3. Tissue Damage 4. Bacteremia 5. PAMPs 6. Toxins 7. Antibiotic Resistance 8. Evasion of host immune system
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Mechanisms of Bacterial Virulence: Adherence
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1. Prevents bacteria from being washed away and allows colonization 2. Accomplished via adhesin molecules
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Mechanisms of Bacterial Virulence: Adherence-Adhesin Molecules
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1. Interact with host cell receptors to attach bacteria to host 2. Most commonly associated with fimbriae (common pili) of enteric bacteria and N. gonorrhoeae, but present elsewhere as well
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Mechanisms of Bacterial Virulence: Invasion
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Breaking through tissue barriers into sterile sites and colonizing tissue
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Sterile Sites
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1. Blood 2. CSF 3. Brain 4. Organ parenchyma 5. Lower lung airways 6. Joint spaces 7. Bone
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Mechanisms of Bacterial Virulence: Tissue Damage
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1. Damaging metabolites 2. Degradative enzymes 3. Exotoxins 4. Intracellular growth 5. Ectopic bacterial growth
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Mechanisms of Bacterial Virulence: Tissue Damage-Metabolites
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Acids, gases, and other byproducts formed during bacterial growth
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Mechanisms of Bacterial Virulence: Bacteremia
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Primary mechanism for spreading bacteria throughout body
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Mechanisms of Bacterial Virulence: PAMPs
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Repetitive microbial structures that bind TLRs, activate macrophages and promote cytokine release
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Examples of PAMPs
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1. Peptiodoglycan 2. LPS 3. Lipotechoic acid 4. Techoic acid 5. Flagellin 6. CpG oligodeoxynucleotides
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Mechanisms of Bacterial Virulence: Toxins
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1. Endotoxin 2. Exotoxin
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Mechanisms of Bacterial Virulence: Toxins-Endotoxin
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1. Lipid A component of LPS 2. Outer membrane of gram-negatives 3. Released during early stages of infection 4. Initiates complement and clotting pathways
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Mechanisms of Bacterial Virulence: Toxins-Exotoxins (Types)
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1. Cytolytic 2. A-B 3. Superantigen
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Mechanisms of Bacterial Virulence: Toxins-Exotoxins (Cytolytic)
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Tissue-degrading enzymes
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Mechanisms of Bacterial Virulence: Toxins-Exotoxins (A-B)
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Composed of one or more B subunits, which bind to cell surface, and an A subunit, which enters the cell and acts on it
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Mechanisms of Bacterial Virulence: Toxins-Exotoxins (Superantigens)
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1. Activate T cells in the absence of antigen by cross-linking the T cell receptor and class II major histocompatibility complex on antigen-presenting cells 2. Cause inappropriate release of cytokins, with possible life-threatening autoimmune response and T cell death 3. e.g. TSST
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System
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1. Encapsulation 2. Biofilms 3. Intracellular growth 4. Reduction of phagocytic cell function 5. Inactivation of antibody 6. Inhibition of complement action 7. Antigenic variation
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Encapsulation
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1. Polysaccharide (slime) layer 2. Poorly antigenic 3. Deter phagocytosis because they are slippery and tear way 4. Protect against degradation in phagolysosomes
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Biofilms
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1. Sticky webs of polysaccharide that protect against host defenses and antimicrobials 2. Require quorum sensing
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Intracellular Growth
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1. Escape host immune detection 2. Can be obligate or facultative 3. Chronic stimulation of immune response may result in granuloma formation (e.g. facultatives)
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Intracellular Growth (Obligate Intracellular Species)
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1. Rickettsia spp. 2. Chlamydia spp. 3. Coxiella spp.
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Intracellular Growth (Facultative Intracellular Species)
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1. Mycobacterium spp. 2. Salmonella spp. 3. Listeria spp. 4. Brucella spp. 5. Francisella spp. 6. Yersinia spp. 7. Legionella spp.
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Intracellular Growth (Mechanisms)
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1. Inhibition of phagolysosome fusion (M. tuberculosis) 2. Protective outer layers (M. tuberculosis) 3. Lysosomal enzyme resistance
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Reduction of Phagocytic Cell Function
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1. Inhibition of phagocytosis: A) Capsule B) Certain cell surface proteins (e.g. M protein) 2. Reduction of phagolysosomal killing: A) Inhibition of phagolysosome fusion B) Capsule C) Catalase detoxification 3. Killing phagocytes via exotoxins
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Reduction of Phagocytic Cell Function (Killing of Phagocytes)
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1. Streptolysins of S. pyogenes 2. Lethal toxin of anthrax 3. Alpha toxin of C. perfringens
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Inactivation of Antibody
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1. Immunoglobulin A (IgA)-degrading proteases 2. IgG-binding surface proteins
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Inactivation of Antibody (IgA-degrading Proteases)
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1. Permit mucosal surface colonization 2. e.g. A) N. gonorrhoeae B) N. meningitidis C) S. pneumoniae D) H. influenzae
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Inactivation of Antibody (IgG-Binding Surface Proteins)
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1. Protect bacterial cells from antibody action 2. e.g. Protein A of S. aureus
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Inhibition of Complement Action
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Antigen in LPS may protect cells from complement-mediated lysis by preventing access to membrane
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Mechanisms of Bacterial Virulence: Evasion of Host Immune System-Antigenic Variation
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DNA rearrangement involving homologous recombination
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Antibacterial Immunopathogenesis
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1. Inflammation 2. Tissue-damageing immune responses 3. Cross-reacting antibacterial antibodies 4. Deposition of immune complexes 5. Sepsis 6. Superantigens
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Antibacterial Immunopathogenesis: Inflammation
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1. Complement, neutrophils, macrophages, and other responses to bacteria lead to inflammation 2. Cell-mediated immune responses induced by intracellular infections may lead to granulomas
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Antibacterial Immunopathogenesis: Tissue Damaging Immune Responses
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1. More common in viruses 2. Bacterial examples: A) Chlamydia spp. (LGV) B) Treponem spp. (syphilis) C) Borrelia spp. (Lyme disease)
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Antibacterial Immunopathogenesis: Cross-Reacting Antibacterial Antibodies
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Rheumatic fever, a sequela to streptococcal infections, is caused by antibodies to M protein that cross-react with and initiate damage to heart
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Antibacterial Immunopathogenesis: Deposition of Immune Complexes
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Poststreptococcal glomerulonephritis results from accumulation of antigen-antibody complexes in glomeruli of kidneys
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Antibacterial Immunopathogenesis: Sepsis
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Bacterial cell wall components activate TLRs and induce systemic release of tumor necrosis factor-alpha, IL-1, and IL-6, which activate phase responses
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Antibacterial Immunopathogenesis: Superantigens
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Activate T cells to release large amounts of cytokines (cytokine storm) to cause sepsis-like pathogenesis
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