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Foundations of Disease > Exam 1: Microbiology and Bacteriology > Flashcards

Exam 1: Microbiology and Bacteriology Flashcards

1
Q

Prokaryotes vs Eukaryotes

Major Characteristics

A
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2
Q

Bacterial Distinction

A
  • Bacteria grow in colonies
  • Sum of their characteristics provide distinguishing characteristics
    • Size
    • Color
    • Shape
    • Smell
    • Ability to resist abx
    • Sugar fermentation
    • Erythrocyte lysis
    • Lipid hydrolysis
  • Can be determined by using appropriate growth medium
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3
Q

Gram Stain

A

Allows differentiation between two major classes of bacteria.

Bacteria heat fixed/dried onto a slide then:

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4
Q

Bacterial Shape

A
  • Most common
    • Cocci
    • Baccilus ⇒ rod
    • Spiral
    • Curved
  • Rods & cocci can be individual cells or chains
  • Pure culture of a single species can have multiple morphologies ⇒ pleiomorphic rod
    • Depends on growth phase and conditions
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5
Q

Gram Positive

Unique Structures

A
  • Thick peptidoglycan cell wall
  • Teichoic acid
    • Lipotechoic acid
    • Wall techoic acid
  • Only gram + can form spores
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6
Q

Gram Negative

Unique Structures

A
  • Outer membrane
    • Lipopolysaccaride (LPS) ⇒ endotoxin
  • Periplasmic space
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7
Q

Gram Positive vs. Gram Negative

Characteristics

A
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8
Q

Cell Wall

A
  • Outermost component common to bacteria
    • Execpt Mycoplasma
  • Repetitive structure
  • Binds TLRs ⇒ activate innate immune responses
  • Composed mainly of peptidoglycan
  • Functions:
    • Protect cytoplasmic membrane from osmotic lysis
    • Maintains shape
    • Interacts with host and environment
  • Basis of gram + vs gram -
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9
Q

Peptidoglycan

(PG)

A
  • Only in bacterial cells
    • Good target for abx ⇒ Penicillin, Cephalosporins
  • Composed of layers of polysaccharide chains cross-liked by short peptides
    • Repeating disaccharides
      • N-acetylmuramic acid (NAM, MurNAc, M)
      • N-acetylglucosamine (NAG, GlcNAc, G)
  • Target for lysozyme
    • Cleaves β1-4 linkages between NAM & NAG
  • Gram +
    • PG forms multiple layers
    • Cross-linked into sheets by peptide bonds
      • Between 3rd AA (Lys) of one & 4th D-alanine of another
      • Terminal D-alanine lost during bond formation
  • Gram -
    • Small amount of PG
    • Usually only one layer thick with minimal cross-linking
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10
Q

Lysozyme cleaves ___ between ___ of ___.

A

β 1,4 linkages

NAM & NAG

bacterial cell walls

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11
Q

Peptidoglycan

Synthesis

A
  • Uses unusual D isomers
    • D-glucosamine
    • D-alanine
  • Does not use ribosomes
  • Crosslinking catalyzed by transpeptidase
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12
Q

Acid-Fast Bacteria

A
  • Do not gram stain
  • Cell wall rich in mysolic acid (lipid)
    • Resistance to drying, low pH, chemical agents
  • Visualized with acid-fast stains
    • Zeihl Neelson
    • Kinyon
  • Only 5 genera are medically important
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13
Q

Mycobacteria

A
  • Unusual cell wall w/ complex lipids
    • PG layer intertwined with arabinogalactan polymer
  • Surrounded by coat of mycolic acid, cord factor, wax D, and sufolipids
    • Responsible for virulence & antiphagocytic
  • Makes them unable to gram stain
  • Resists decolorization with acid-alcohol ⇒ acid-fast
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14
Q

Outer Membrane

A
  • Only in gram ⊖ bacteria
  • Asymmetric bilayer
    • Inner leaflet ⇒ normal PLs found in bacterial cytoplasmic membrane
    • Outer leaflet ⇒ mostly LPS
  • Periplasmic space
    • Between inner and outer membranes
    • Contains transport systems
    • Contains hydrolytic enzymes for metabolism
    • Many lytic virulence factors found here
  • Permeability barrier ⇒ limits movement of host enzymes and some Abx
  • Protective layer against environment
  • Limited variety of proteins in high concentration
    • Porins
    • Hydrophilic antimicrobials
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15
Q

Lipopolysaccharide (LPS)

Overview

A

“Endotoxin”

  • Component of outer leaflet of outer membrane
  • Gram ⊖ bacteria only
  • Major mediator of fever and inflammation
  • Composed of 3 structurally and functionally distinct units
    • Lipid A
    • Core polysaccaride
    • O-antigen polysaccharide side chains
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16
Q

Lipid A

A

Responsible for toxic effects of LPS.

  • Essential for viability
  • Responsible for endotoxic activity
  • Phosphorylated glucosamine disaccharide backbone w/ FA attached
  • Anchors structure to outer membrane
  • Acts to connect LPS units into aggregates
  • Identical for related bacteria
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17
Q

Core Polysaccharide

A
  • Branched polysaccharide of 9-12 sugars
  • Essential for LPS structure
  • Essential for viability
  • Same for a species of bacteria
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18
Q

O Antigen

A
  • Attached to the core polysaccharide
  • Extends away from bacteria
  • Long linear polysacc. chain of 50-100 repeating units of 4-7 sugars each
  • Distinguishes serotypes/strains
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19
Q

Teichoic Acid

(TA)

A
  • Found in outer layer of cell wall of gram ⊕ bacteria only
  • Water soluble anionic polymers
    • Glycerol phosphate
    • Ribitol phosphate
  • Sugars, choline, or D-alanine can be attached ⇒ antigenic
    • Determined by Ab
    • May determine serotype
  • Two types of TA:
    • Wall teichoic acid (WTA)
      • Linked to PG
    • Membrane teichoic acid (lipoteichoic acid, LTA)
      • Linked to membrane glycolipid
      • Can be shed into host ⇒ immune response
  • Important virulence factor
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20
Q

Cytoplasmic Membrane

A
  • PL bilayer under PG cell wall
  • Lack sterols
    • Except for Mycoplasma
  • Functions:
    • Aids transport
    • Contains protein for ETC and metabolism
    • Aids secretion of enzymes/toxins
    • Contains enzymes for cell wall, DNA, and membrane lipid synthesis
    • Lined with actin-like protein filaments ⇒ maintains shape, site of septum formation during division
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21
Q

Flagella

A
  • Only on rods
  • Location and # varies
  • Used for movement
  • Structure:
    • Composed of flagellin
    • Achored to plasma membrane through hook and basal body
    • Powered by membrane potential
  • Flagellar antigens used to ID strains
    • H antigens
      • Ex. E. coli 0157:H7
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22
Q

Pili

A

“Fimbriae”

  • Composed of pilin
  • Used for attachment and adhesion
    • Adherence factor @ tip
  • Important for virulence
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23
Q

Sex Pilus

A

“F pili”

  • Attaches male to female during conjugation
  • Encoded for by plasmid F
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24
Q

Capsule

A
  • Gel layer encompasing entire bacteria
    • Loose polysaccharide or protein layers
    • Sugars vary w/ species
    • Small Ag differences distinguishes different serotypes or serogroups within species
  • Important for survival
  • Virulence factor that limits:
    • Phagocytosis
    • Susceptibility to complement
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25
Q

Spores

A

“Endospores”

  • Some gram ⊕ only
    • Bacillus, Clostridia
  • Stress ⇒ stop vegetative growth ⇒ produce spores (dormant state)
  • Spores resist drying, heat, radiation, chemicals
  • Return of good conditions ⇒ spores to vegetative state ⇒ germinate
  • Sometimes spores are the infectious form
    • Ex: B. antracis
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26
Q

Prokaryotic Metabolism

A
  • For rapid growth
  • More versatile in energy sources and oxidant use
  • More diverse nutritional requirements
  • More diverse biosynthetic pathways
  • PG, LPS, TA unique to bacteria
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27
Q

Bacteria divide by ___ process called ___.

A

asexual

binary fission

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28
Q

Time required for bacterial population to double called…

A

generation time

(Cell # after N generations = Initial # x 2N)

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29
Q

Growth Curve

A
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30
Q

Chemical Requirements

A
  1. Water
  2. Carbon
  3. Nitrogen
  4. Oxygen (some)
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31
Q

Carbon Sources

A
  • Most pathogenic bacteria need organic carbon ⇒ heterotrophs
    • Must be in a form that can be assimilated
    • Most common source from sugars
  • Some can use inorganic carbon like CO2 ⇒ autotrophs
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32
Q

Nitrogen Sources

A
  • Usually supplied by inorganic molecules
    • Ammonia (NH3) and Nitrate (NO3)
  • End-prod. for all paths is ammonia
  • Can use proteins if they have exoenzymes e.g. proteases
  • Nitrogen gas (N2) can be used by nitrogen-fixing bacteria
    • Add H to make ammonia
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33
Q

Oxygen Metabolism

A

O2 required for most human pathogens.

Used as a final electron acceptor in respiration.

Mechanisms for removal of toxic intermediates:

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34
Q

Oxygen Requirement

Classification

A
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35
Q

Intermediary metabolism includes…

A

catabolism ⇒ breakdown

anabolism ⇒ synthesis

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36
Q

The common universal intermediate is…

A

pyruvic acid

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37
Q

Pyruvate + NADH/NADPH produced via…

A

Embden-Myerhof glycolytic pathway

&

Pentose phosphate pathway

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38
Q

Embden-Meyerhof

Glycolytic Pathway

A
  • 1 glucose yields 2 ATP + 2 NADH
  • End product is pyruvate
    • Substrate for fermentation or respiration
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39
Q

Pentose Phosphate Pathway

A
  • Glucose ⇒ pentose phosphate ⇒ G-3-P ⇒ pyruvate
  • Releases CO2
  • Generates NADPH
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40
Q

Fermentation

A

Pyruvate reduced while NAPH re-oxidized

Lowers pH ⇒ growth often inhibited

  • Homolactic acid fermentation
    • Lactobacilli & strep
  • Mixed acid fermentation
    • Enteric bacteria
      • Most make H2 + CO2 via formic acid pathway
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41
Q

Shigella

Fermentation

A

Cannot make H2 or CO2

Negative for gas in “triple sugar iron” test

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42
Q

Clostridium

Fermentation

A

Anaerobe

Ferments sugars ⇒ acetone, isopropanolol, butanol, and butyric acid

Ferment proteins ⇒ amines

Gases build up in infected wounds ⇒ gas gangrene

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43
Q

Fermentation

Chart

A
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44
Q

Respiration

A

Electron transport + Oxidative phosphorylation

  • Pyruvate ⇒ TCA ⇒ NADH and FADH2
  • Oxygen is usually the final acceptor ⇒ aerobic
  • Certain bacteria can also use other compounds
    • Nitrogen ⇒ NO3
    • Sulfides ⇒ SO42+
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45
Q

Bacterial Genome

A
  • Chromosome
    • Haploid
    • Circular
    • Minimal size
    • Few to no introns
    • Little to no splicing
  • Extrachromosomal elements ⇒ plasmids
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46
Q

Operons

A
  • Short, continguous, linear group of related genes
  • Grouped into transcriptional units
  • Controlled by one promoter
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47
Q

Structural genes

A

Encodes enzymes and structural proteins.

E.g. ribosomal proteins

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48
Q

Regulatory Genes

A

Encode proteins that bind DNA regulatory sites

Repressors ⇒ operators

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49
Q

Operons make ___ which codes for ___ per mRNA.

A

polycistronic mRNAs

more than one gene

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50
Q

Insertion Sequences

(IS)

A

DNA sequence capable of replicating itself into a new site in the chromosome by non-homologous recombination.

Catalyzed by “transposase”

Encoded by IS.

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51
Q

Transposons

(Tn)

A

Insertional sequences (IS) that flank a structural gene.

Carries the genes with them to new chromosome sites.

Typically encodes abx resistance.

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52
Q

Base Substitutions

A

Silent, missense, or nonsense.

∆ abx resistence and virulence.

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53
Q

Additions & Deletions

A

Single base pair or string of bases added or deleted.

∆ surface components ⇒ ∆ virulence

Antigenic variation vs phase variation

54
Q

Antigenic Variations

A

Expression of different variants of surface molecules which vary in chemical composition.

Ex. Pilin proteins (S1, S2,…) of Neisseria gonorrhoeae

55
Q

Phase Variations

A

Presence or absence of surface molecules due to regulated expression.

Ex. Flagella proteins (H1 and H2) of Salmonellae typhimurium

56
Q

Slipped-Stranded Mispairing

A
  • During DNA replication or transcription
  • In regions w/ contiguous short nucleotide repeats
  • DNA polymerase stutters or slips
  • Results in amplification or deletion
  • Ex. Bordetlla pertussis & Neisseria gonorroeae
    • Mispairing in promoters of several genes ∆ or eliminates expression of pili
57
Q

Gene Rearrangements

A

Reversible, genotypic adaptations that occur at relatively high rates (10-3),

Occurs through site-specific recombination.

Examples:

E. coli type I fimbriae

Salmonella expression of hagA or hagB, encodes flagellin proteins, controlled by recombinational inversion of a promotor.

58
Q

Plasmids

A
  • Circular supercoiled DS-DNA
  • Self-replicating extrachromosomal DNA
    • Large plasmids replicate like host chromosomes
      • Usually a single or few copies
    • Small plasmids replicate independently
  • One or more copies per cell
  • May insert into chromosome (episome)
  • Introduces novel enzymes and pathways
59
Q

Conjugative Plasmids

A

Have tra genes which encode transfer enzyme and sex pili.

60
Q

Nonconjugative Plasmid

A

Lack tra genes.

Can be transferred by other mechanisms

(Like tagging along behind a conjugative plasmid)

61
Q

R plasmid

A

Transmission of multiple abx resistance:

RTF (resistance transfer factor) ⇒ conjugative plasmid

+

R determinants ⇒ transposons carrying abx resistance genes

62
Q

Virulence Factors

Transmission

A

Ex:

  • Toxin and fibriae of enterotoxigenic E. coli (ETEC)
  • Toxins of Staphyloccous, Bacillus anthracis, and Clostridium tetani
  • “Invasion” genes of Yersinia an dShigella
  • Iron siderophores of E. coli
63
Q

Bacteriophage

A
  • Bacterial viruses
  • Specific for different bacteria
  • Structure:
    • Capsid ⇒ protein subunits
      • Icosahedral, helical, or combo
    • Genome
      • DNA or RNA
      • SS or DS
      • Linear or circular
      • 3,000-105 BP
  • Can be lytic or lysogenic
64
Q

Lytic Bacteriophage

A
  • Rapid replication
  • 20 minutes from infection to bacterial lysis
65
Q

Lysogenic Bacteriophage

A

Slower replication:

  • Integration
    • Infection
    • Lytic pathway repressed
    • DNA integrates into host chromosomes
    • Replicates along with bacteria
  • Induction
    • Adverse conditions ⇒ induction (de-repression) of lytic genes
    • DNA excised
    • Enters lytic cycle
  • Lytic cycle
    • Rapid replication
    • Cell lysis
66
Q

Lysogenic Bacteriophage

Clinically Important Examples

A

Can transfer genes between bacteria:

  • Salmonella ⇒ mod. of surface Ag
  • Corynebacterium diphtheriae ⇒ encodes endotoxin
  • EHEC (Enterohemorrhagic E. coli) ⇒ encodes exotoxin
  • Clostridium botulinum ⇒ encodes exotoxin
  • Staphylococcus ⇒ abx resistance, toxins
  • S. aureus phage typing ⇒ lysogenic strains immune to infection by related phage
    • Pattern of immunity with phage panel provides a typing system
67
Q

Transfer of chromosomal DNA requires ___ between donor and recipient DNA.

A

homologous recombination

68
Q

Transformation

A

Free donor DNA taken up by recipient bacterium.

  • Derived from lysed cells or free plasmids
  • Occurs naturally in vivo
  • Depends on competence of recipient
    • Ability to take up DNA and be transformed
    • Varies for different bacterium and growth conditions
    • S. pneumoniae & Neisseria gonorrhoeae naturally competent
    • E. coli can be made competent
69
Q

Transfection

A

Donor DNA from bacteriophage DNA

(Transformation and infection)

Can carry along bacterial genes within viral genome

70
Q

Transduction

A

Donor DNA carried to recipient within bacteriophage capsid.

  • Packaged DNA contains random fragments ⇒ generalized transduction
  • Packaged DNA contains specific sequences located adjacent to lysogenic phage site ⇒ specialized transduction
71
Q

Conjugation

A

Transfer of DNA via conjugative (F or R) plasmid.

  • Tra genes
    • Encode sex pilus & special replication enzymes
  • Sex pilus
    • Mediates contact
    • Cells drawn together & fuse at one point
    • Donor DNA passed through
      • Rolling circle DNA replication
72
Q

An organism that is able to evade normal host defenses to cause infection is called a…

A

pathogen

73
Q

Damage or loss of tissue/organ function due to infection or host inflammatory responses is called…

A

disease

74
Q

Opportunistic Pathogens

A
  • Rarely cause disease in healthy hosts
  • Regularly cause disease in compromised hosts
  • Normal flora
    • Staphylococcus epidermis
      • Post-surgical
      • Catheter-related
    • E. Coli
  • Environmental organisms
    • Pseudomonas aeruginosa
      • Burn victims
      • CF patients
75
Q

Primary Pathogens

A

Rarely associated with host except for in the case of disease

76
Q

The relative ability of organisms to cause infection and disease is called…

A

virulence

77
Q

Virulence Determinants

A

Traits that promote colonization and survival of infecting bacteria:

  • Structural
    • Capsule
    • LPS
    • Pili
  • Biochemical
    • Exotoxins
    • Proteases
    • Siderophores
  • Genetic
    • Variation of surface Ag
78
Q

Toxins that lyse RBC and other cells…

A

Hemolysins / Cytotoxins

79
Q

Enzyme that helps wall bacteria off from attack…

A

coagulase

80
Q

Enzymes that help bacterial break down clots and spread locally and systemically includes…

A

Fibrinolysin

Hyaluronidase

Collagenase

81
Q

Enzyme that inactivates IgA….

A

IgA proteases

(important with mucosal pathogens)

82
Q

Traits that render bacteria pathogenic are called…

A

virulence factors

83
Q

Bacterial

Virulence Mechanisms

A
  • Adherence
  • Invasion
  • Growth byproducts (gas, acid)
  • Toxins
  • Degradative enzymes
  • Endotoxin
  • Superantigen
  • Induction of excess inflammation
  • Evasion of phagocytic and immune clearance
  • Capsule
  • Abx resistance
  • Intracellular growth
84
Q

Regions in the chromosome or on plasmids that contain sets of genes for virulence factors are called…

A

pathogenicity islands

(May require coordinated expression)

85
Q

Koch’s Postulates

A

How to show an organism causes a particular disease:

  1. Must be present in every case of the disease
  2. Must be isolated from host and grown in lab dish
  3. Disease must be reproduced when pure culture of agent inoculated into healthy susceptible host
  4. Same agent must be recovered again from experimentally infected host
86
Q

Molecular Koch’s Postulates

A

How to show that a particular virulence factor is involved in a specific disease:

  1. Trait associated more often with pathogenic strains than non-pathogenic ones
  2. Inactivation of gene(s) associated with trait decreases or eliminates virulence
  3. Virulence restored when mutated gene replaced with wild-type gene
87
Q

Factors Affecting Disease Development

A
  • Pathogenicity (virulence) of pathogen
  • Immune & nutritional state of host
  • Route of entry
  • Number of bacteria
88
Q

Stages of Infection

A
  1. Encounter
  2. Entry
  3. Colonization
  4. Multiplication
  5. Invasion/Dissemination
89
Q

Encounter

A
  • Human-to-human
    • Fecal-oral
    • Respiratory or salivary
    • Venereal
  • Animal-to-animal ⇒ zoonoses
    • Vector ⇒ biting arthropod (mosquitos, ticks)
    • Vertebrate reservoir
    • Vector-vertebrate reservoir
90
Q

Transmission

A

Exit and entry of organisms from:

  • Mucosal surfaces
    • Respiratory tract
    • Urinary tract
    • Genital tract
    • GI tract
    • Conjunctiva
  • Skin
    • Trauma
    • Surgery
    • Eczema
    • Others
91
Q

Pathogens must evade or compromise ___ & ___ in order to invade the host.

A

natural defense mechanisms & barriers

92
Q

Transmission/invasion depends on…

A
  1. Site
  2. Dose
    • Each organism has a threshold number required to cause disease
  3. Route
    • Some cause disease only when entering at certain sites
    • Some cause different diseases at different sites
93
Q

Colonization

A

Establishment of a pathogen at its portal of entry.

  • Most often receptor mediated
  • Colonization of sterile site implies defect in natural defense mech. or new portal of entry
  • Use specific mech. to adhere to and colonize different body surface
94
Q

Receptor Mediated Adhesion

A
  • Mediated by adhesins
    • e.g. pili or surface proteins
  • Binds to specific carbs or protein receptors on surface of host cell
  • Can be host-specific or tissue specific
95
Q

Non-specific Adherence

A

Mediated by carbohydrate or lipid adhesins

  • Ex.
    • Alginate capsule of Pseudomonas aeruginosa
      • Promotes adherence in lungs of CF patients
    • Polysacc. slime of Strep. epidermis
      • Promotes biofilm formation
96
Q

Intracellular Bacteria

A
  • Invades host cells
  • Often mediated by invasins
    • Protein that recognizes host integrins
  • Protected from immune response
  • Ready supply of nutrients
  • More likely to disseminate throughout obdy
97
Q

Quorum Sensing

A

Ability of baceria to respond as a community by sensing and communicating with each other when density reaches a threshold.

  • Via small secreted metabolites
  • When bacteria sense a quorum has developed, they can respond in many ways:
    • Express virulence factors
    • Become resistant to abx
    • Forming a biofilm
98
Q

Biofilms

A

Organized communities of sessile bacteria.

  • Sessile ⇒ anchored cells attached to a surface
  • Planktonic ⇒ free-living cells
  • Biofilms have complex physical and metabolic structure
  • More resistant than planktonic bacteria to:
    • Abx
    • Serum abx-complement mediated killng
    • phagocytosis
  • Issue for indwelling catheters
99
Q

Bacterial products that directly harm tissue or trigger destructive biologic activity are called…

A

toxins

100
Q

Endotoxin

Mechanism

A

“Lipopolysaccharide (LPS)”

  • On outer leaflet of outer membrane of gram ⊖ bacteria
  • LPS ↔︎ LPS-binding protein (LBP)
  • LPS-LBP complex ↔︎ CD14 receptors on monocytes, macrophages, endothelial cells
  • LPS-CD14 ↔︎ Toll-like receptor 4 (TLR4)
    • Cell activation ⇒ cytokine production & release
  • Acts on complement, fibrinolytic, coagulation, temp regulation, and circulatory systems
101
Q

Endotoxin

Effects

A

Acts on complement, fibrinolytic, coagulation, temp regulation, and circulatory systems:

  • Fever
  • Hypoglycemia
  • Enhanced glycolysis
  • Triggers release of vasoactive substances
    • Serotonin, Kallikrein, Kinins
  • Hypotension and shock
  • Activate C3 & complement cascade via alternative pathway
  • Impaired perfusion of organs
    • Accumulation of organic acids and metabolic acidosis
  • Disseminated intravascular coagulation (DIC)
    • Activation of factor XII (Hageman factor)
    • Intrinsic coagulation cascade
    • Activation of plasminogen
    • Inc. platelet adherence to endothelium
    • Occlusion of small vessels
  • Death
102
Q

Endotoxin Table

A
103
Q

Exotoxins

Overview

A
  • Both gram ⊕ and gram ⊖
  • Generally secreted or surface proteins
  • Several broad classes, most notably:
    • Pore-forming toxins
      • Form lethal holes in host cell membranes
    • Enzymatic toxins
      • Gain entry into host cells and alter intracellular signaling or other cell processes
        • Leads to pathology and cell death
  • Targets limited and well defined
    • Ribosomes
    • Transport mechanisms
    • Intracellular signaling (cAMP, GPCR)
104
Q

Exotoxin

Structure

A

Most exotoxins are dimeric (A-B) toxins:

  • B portion ⇒ binding
    • Binds to specific cell surface receptors
  • A portion ⇒ action
    • Transferred into cell interior
    • Acts to promote cell injury
105
Q

Exotoxin

Examples

A
  • Corynebacterium diptheriae ⇒ diptheria toxin / Pseudomonas aeruginosa ⇒ exotoxin A
    • one A subunit, one B subunit
    • ADP-ribosylase ⇒ transfer ADP-ribose from NAD to target protein elongation factor EF2 ⇒ inhibits protein synthesis
  • Vibrio cholerae ⇒ cholera toxin
    • one A subunit, five B subunits
    • ADP-ribosylase ⇒ activates adenylate cyclase ⇒ overproduction of cAMP
  • Bacillus anthracis ⇒ anthrax toxin
    • one B subunit (Protective Antigen, PA) + different A subunits with distinct enzyme activities
    • One A subunit ⇒ Edema factor ⇒ calmodulin-dependent adenylate cyclase
106
Q

Exotoxin

Table

A
107
Q

Exotoxin

Expression

A
  • Genetics
    • Encoded on bacterial chromosome, plasmids, or lysogenic bacteriophage
  • Regulation
    • Expression governed by environmental conditions
      • pH, temperature, ionic concentrations (Fe2+, Ca2+)
    • Toxin may not be produced under normal environmental niche under normal conditions
    • Under stress, toxin produced in attempt to enhance survival
108
Q

Superantigens

A
  • Activates CD4+ T-cells
  • Binds simultaneously to TCR & MHC II on APCs without Ag
    • Not Ag specific
    • Occurs outside of the MHC & TCR binding domains
  • Results in polyclonal T-cell activation ⇒ cytokine storm
    • IL-1, TNF, IL-6, IFN, IL-2, and other cytokines
  • Causes life-threatening autoimmune-like responses
  • Examples:
    • Staphylococcus auresus ⇒ Toxic shock syndrome toxin (TSST-1)
    • Staphylococcus ⇒ enterotoxins
    • Streptococcus pyogens ⇒ pyrogenic toxins
109
Q

Iron Requirement

A
  • All pathogens, except Strep, require iron for growth
  • Almost no free iron in human body
    • Bound by transferrin, lactoferrin, Hb, etc
  • Developed ways to get iron from hosts
    • Siderophores
    • Lactoferrin or transferrin binding proteins
110
Q

Siderophores

A

Small soluble molecules that bind free iron or take iron from transferrin and/or lactoferrin and bring it back to the organism.

111
Q

Lactoferrin/Transferrin

Binding Proteins

A

Allows bacterial to bind to and acquire iron directly from iron-preloaded host molecules.

112
Q

Hyaluronidase

A
  • Found in Strep and Staph
  • Degrades hyaluronic acid ⇒ carbon source
  • Speculated to act as virulence factor that destroys polysaccharide that holds animal cells together ⇒ aids local dissemination
113
Q

Collagenase

A
  • Found in Clostridium perfringens
  • Breaks peptide bonds in collagen
  • Assist in destroying ECM structures ⇒ aids dissemination
114
Q

Neuraminidase

A
  • Found in Shigella dysenteriae
  • Cleaves glycosidic linkages of neuraminic acids
  • Functions to cleave a sialic acid residue off glanglioside GM1 ⇒ asialo-GM1
    • Can preferentially bind type 4 pili
115
Q

Lecithinases

A
  • Found in many bacteria
  • Phospholipase that acts on lecithin
116
Q

Normal Flora

A
  • Collection of microorganisms found in normal healthy individuals
  • Inhibits the establishment of pathogens
  • Provides host with vitamins
  • Can become pathogenic:
    • In immunosuppressed or immunocompromised individuals
    • Removed from usual anatomic niche
      • Ex. E. coli and Strep. faecalis
        • Normal in GI
        • Pathogenic in GU
117
Q

Bacterial

Chromosomal DNA

A
  • Generally circular
  • One origin for bidirectional replication
  • One terminus halfway around chromosome
118
Q

Prokaryotic

DNA Polymerases

A

DNA Polymerase I, II & III

119
Q

Eukaryotic

DNA Polymerases

A

DNA Polymerase δ, α & ε

120
Q

Prokaryotes have ___ and ___ that break and rejoin DNA strands to prevent supercoiling.

A

DNA topoisomerases & DNA gyrases

121
Q

Prokaryotic DNA Replication

Mechanism

A
  1. Helicase unwinds DNA double helix ⇒ melting
  2. DNA gyrase nicks and seals DNA strands as meling occurs
    • Allows DNA to spin & prevents supercoiling
  3. DNA binding proteins coats strands to prevent reassociation
  4. Primase places RNA primer
  5. DNA polymerase III replicates DNA starting at the 3’-OH primer
    • Leading strand continuous
    • Lagging strand in Okazaki fragments
  6. Gaps on lagging strand closed by DNA polymerase I
    • Exonuclease activity excises RNA
    • Polymerase activity replaces RNA with DNA
  7. DNA ligase joins sections
122
Q

Speed of DNA replication

A
  • DNA Pol III ⇒ 800 nuc/sec
  • E. coli has 4 million BP w/ 1 origin of replication
    • Would take 40 minutes for replication ⇒ too slow by factor of 2
  • Able to replicate faster because a new round of DNA replication started before cell division complete
123
Q

Relatively few ___ target replicationn due to ___.

A

abx

large number of proteins involved

124
Q

Prokaryotic RNA Polymerase

A

Bacterial have only one RNA polymerase for all classes of genes (mRNA, rRNA, tRNA)

  • 4-5 subunits
    • two identical α
    • one β
    • one β’
    • one σ ⇒ for initiation
125
Q

Prokaryotic RNA Synthesis

(Transcription)

A
  • Occurs 5’ ⇒ 3’
  • Promoters
    • Conserved sequences at -10 and -35 upstream
    • Binds RNA polymerase
    • Sigma factor lost when transcription begins
  • Termination
    • “Hairpin” secondary structures followed by string of U’s
  • RNA may be processed by endonucleases and exonucleases
    • No 5’ cap, 3’ poly-A tail, or splicing
126
Q

Prokaryotic Ribosomes

A
  • 70S Ribosomes
    • 30S ⇒ small subunit
      • 16S ribosomal RNA
    • 50s ⇒ large subunit
      • 23S and 5S ribosomal RNA
  • 20-30 ribosomal proteins
127
Q

Prokaryotic tRNAs

A

Amino-acylated tRNA:

  • Adapter RNA molecules
  • AA linked to 3’ terminal base of tRNA
    • Catalyzed by amino acyl-tRNA synthetase
128
Q

Bacterial mRNAs are usually ___ coding for multiple genes and have a ___ half-life.

A

polycistronic

shorter ⇒ degraded in minutes

129
Q

Prokaryotic

Genetic Code

A
  • 20 AA
  • Triplet codons
  • Degenerate
  • 3 stop codons
  • AUG start codon ⇒ methionine
130
Q

Prokaryotic Translation

Initiation

A
  • Occurs at 1 or more internal AUGs within mRNA ⇒ polycistronic
  • Shine-Dalgarno sequence pairs with 16S ribosomal RNA
  • Starts with formylmethionine (fMET)
  • First, 30S initation complex forms
    • mRNA +fMET-tRNA + 30S subunit
    • Also GTP + Initiation factors IF 1, 2, and 3
  • Then, 70S initiation complex forms
    • 30S complex + 50S subunit
      • GTP ⇒ GDP
    • fMET-tRNA now in P (peptidyl) site of 50S subunit
131
Q

Prokaryotic Translation

Elongation

A
  • Second paired amino acyl-tRNA bind to A (aminoacyl) site on 50S subunit
    • Delivered by elongation factor EF-Tu
      • GTP ⇒ GDP
  • Peptidyl transferase activity of 50S subunit catalyzes peptide bond formation
  • Translocation occurs
    • Peptidyl-tRNA moves from A ⇒ P site
    • Elongation factor EF-G involved
      • GTP ⇒ GDP
  • Process repeats
132
Q

Prokaryotic Translation

Termination

A
  • Release factor required
  • Final peptidyl-tRNA bond hydrolyzed
  • 70S sibosome dissociates

Foundations of Disease (46 decks)

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