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Flashcards in Microbiology - Basic Bacteriology Deck (29):
1

Bacterial structures

  • For each
    • Function
    • Chemical Composition
  • Peptidoglycan
  • Cell wall/cell membrane (gram positives)
  • Outer membrane (gram negatives)
  • Plasma membrane
  • Ribosome
  • Periplasm
  • Capsule
  • Pilus/fimbria
  • Flagellum
  • Spore
  • Plasmid
  • Glycocalyx

  • Peptidoglycan
    • Gives rigid support, protects against osmotic pressure.
    • Sugar backbone with peptide side chains cross-linked by transpeptidase.
  • Cell wall/cell membrane (gram positives)
    • Major surface antigen.
    • Peptidoglycan for support. Lipoteichoic acid induces TNF and IL-1.
  • Outer membrane (gram negatives)
    • Site of endotoxin (lipopolysaccharide [LPS]); major surface antigen.
    • Lipid A induces TNF and IL-1; O polysaccharide is the antigen.
  • Plasma membrane
    • Site of oxidative and transport enzymes.
    • Phospholipid bilayer.
  • Ribosome
    • Protein synthesis.
    • 50S and 30S subunits.
  • Periplasm
    • Space between the cytoplasmic membrane and outer membrane in gram-negative bacteria.
    • Contains many hydrolytic enzymes, including β-lactamases.
  • Capsule
    • Protects against phagocytosis.
    • Polysaccharide (except Bacillus anthracis, which contains D-glutamate).
  • Pilus/fimbria
    • Mediate adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during conjugation.
    • Glycoprotein.
  • Flagellum
    • Motility.
    • Protein.
  • Spore
    • Resistant to dehydration, heat, and chemicals.
    • Keratin-like coat; dipicolinic acid; peptidoglycan.
  • Plasmid
    • Contains a variety of genes for antibiotic resistance, enzymes, and toxins.
    • DNA.
  • Glycocalyx
    • Mediates adherence to surfaces, especially foreign surfaces (e.g., indwelling catheters).
    • Polysaccharide.

2

Cell walls

  • Common to both
  • Unique to gram-positive organisms
  • Unique to gram-negative organisms

  • Common to both
    • Flagellum
    • Pilus
    • Capsule
    • Peptidoglycan
    • Cytoplasmic membrane
  • Unique to gram-positive organisms
    • Lipoteichoic acid
      • Combination of lipids and teichoic acids
    • Cell wall
  • Unique to gram-negative organisms
    • Endotoxin / LPS (outer membrane)
    • Periplasm

3

Bacterial taxonomy

  • Circular (coccus)
    • Gram-positive examples (2)
    • Gram-negative examples (1)
  • Rod (bacillus)
    • Gram-positive examples (6)
    • Gram-negative examples
      • Enterics (13)
      • Respiratory (3)
      • Zoonotic (4)
  • Branching filamentous
    • Gram-positive examples (2)
  • Pleomorphic
    • Gram-negative examples (2)
  • Spiral (spirochetes)
    • Gram-negative examples (3)
  • No cell wall
    • Gram-positive examples (1)

  • Circular (coccus)
    • Gram-positive examples
      • Staphylococcus
      • Streptococcus
    • Gram-negative examples
      • Neisseria
  • Rod (bacillus)
    • Gram-positive examples
      • Clostridium
      • Corynebacterium
      • Bacillus
      • Listeria
      • Mycobacterium (acid fast)
      • Gardnerella (gram variable)
    • Gram-negative examples
      • Enterics:
        • E. coli
        • Shigella
        • Salmonella
        • Yersinia
        • Klebsiella
        • Proteus
        • Enterobacter
        • Serratia
        • Vibrio
        • Campylobacter
        • elicobacter
        • Pseudomonas
        • Bacteroides
      • Respiratory:
        • ƒƒHaemophilus (pleomorphic)
        • Legionella (silver)
        • Bordetella
      • Zoonotic:
        • Francisella
        • Brucella
        • Pasteurella
        • Bartonella
  • Branching filamentous
    • Gram-positive examples
      • Actinomyces
      • Nocardia (weakly acid fast)
  • Pleomorphic
    • Gram-negative examples
      • Rickettsiae (Giemsa)
      • Chlamydiae (Giemsa)
  • Spiral (spirochetes)
    • Gram-negative examples
      • Borrelia (Giemsa)
      • Leptospira
      • Treponema
  • No cell wall
    • Gram-positive examples
      • Mycoplasma (does not Gram stain)

4

Bacteria with unusual cell membranes/walls

  • Mycoplasma
    • Contain sterols.
    • Have no cell wall.
  • Mycobacteria
    • Contain mycolic acid.
    • High lipid content.

5

Gram stain limitations:
Bugs that don't Gram stain well

  • These Microbes May Lack Real Color.
  • Treponema (too thin to be visualized).
    • Treponemes—dark-field microscopy and fluorescent antibody staining.
  • Mycobacteria (high lipid content in cell wall detected by carbolfuchsin in acid-fast stain).
  • Mycoplasma (no cell wall).
  • Legionella pneumophila (primarily intracellular).
    • Legionella—silver stain.
  • Rickettsia (intracellular parasite).
  • Chlamydia (intracellular parasite; lacks muramic acid in cell wall).

6

Stains

  • Giemsa
  • PAS (periodic acid–Schiff)
  • Ziehl-Neelsen (carbol fuchsin)
  • India ink 
  • Silver stain 

  • Giemsa
    • Chlamydia, Borrelia, Rickettsiae, Trypanosomes, Plasmodium.
    • Certain Bugs Really Try my Patience.
  • PAS (periodic acid–Schiff)
    • Stains glycogen, mucopolysaccharides; used to diagnose Whipple disease (Tropheryma whipplei).
    • PASs the sugar.
  • Ziehl-Neelsen (carbol fuchsin)
    • Acid-fast organisms (Nocardia, Mycobacterium).
  • India ink
    • Cryptococcus neoformans (mucicarmine can also be used to stain thick polysaccharide capsule red).
  • Silver stain
    • Fungi (e.g., Pneumocystis), Legionella, Helicobacter pylori.

7

Special culture requirements

  • H. influenzae
  • N. gonorrhoeae, N. meningitidis
  • B. pertussis
  • C. diphtheriae
  • M. tuberculosis
  • M. pneumoniae
  • Lactose-fermenting enterics
  • Legionella
  • Fungi

  • H. influenzae
    • Chocolate agar with factors V (NAD+) and X (hematin)
  • N. gonorrhoeae, N. meningitidis
    • Thayer-Martin (or VPN) media
      • Vancomycin (inhibits gram-positive organisms)
      • Polymyxin (inhibits gram-negative organisms except Neisseria)
      • Nystatin (inhibits fungi)
    • “to connect to Neisseria, please use your VPN client”
  • B. pertussis
    • Bordet-Gengou (potato) agar
    • Bordet for Bordetella
  • C. diphtheriae
    • Tellurite agar, Löffler medium
  • M. tuberculosis
    • Löwenstein-Jensen agar
  • M. pneumoniae
    • Eaton agar, requires cholesterol
  • Lactose-fermenting enterics
    • Pink colonies on MacConkey agar (fermentation produces acid, turning colony pink)
    • E. coli is also grown on eosin–methylene blue (EMB) agar as colonies with green metallic sheen
  • Legionella
    • Charcoal yeast extract agar buffered with cysteine and iron
  • Fungi
    • Sabouraud agar.
    • Sab’s a fun guy!”

8

Obligate aerobes

  • Definition
  • Examples

  • Definition
    • Use an O2-dependent system to generate ATP.
  • Examples
    • Include Nocardia, Pseudomonas aeruginosa, and MycoBacterium tuberculosis.
      • Nagging Pests Must Breathe.
    • Reactivation of M. tuberculosis (e.g., after immune compromise or TNF-α inhibitor use) has a predilection for the apices of the lung, which have the highest Po2.
    • P. aeruginosa is an aerobe seen in burn wounds, complications of diabetes, nosocomial pneumonia, and pneumonias in cystic fibrosis patients.

9

Obligate anaerobes

  • Definition
  • Examples

  • Definition
    • They lack catalase and/or superoxide dismutase and are thus susceptible to oxidative damage.
    • Generally foul smelling (short-chain fatty acids), are difficult to culture, and produce gas in tissue (CO2 and H2).
    • Anaerobes are normal flora in GI tract, pathogenic elsewhere.
    • AminO2glycosides are ineffective against anaerobes because these antibiotics require O2 to enter into bacterial cell.
  • Examples
    • Include Clostridium, Bacteroides, and Actinomyces.
    • Anaerobes Can’t Breathe Air.

10

Intracellular bugs

  • Obligate intracellular 
  • Facultative intracellular

  • Obligate intracellular
    • Rickettsia, Chlamydia.
      • Stay inside (cells) when it is Really Cold.
    • Can't make own ATP.
  • Facultative intracellular
    • Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis.
    • Some Nasty Bugs May Live FacultativeLY.

11

Encapsulated bacteria

  • Definition
  • Examples

  • Definition
    • Their capsules serve as an antiphagocytic virulence factor.
      • Capsule + protein conjugate serves as an antigen in vaccines.
    • Are opsonized, and then cleared by spleen.
      • Asplenics have decreased opsonizing ability and are at risk for severe infections.
      • Give S. pneumoniae, H. influenzae, N. meningitidis vaccines.
  • Examples
    • Streptococcus pneumoniae, Haemophilus influenzae type B, Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, and group B Strep.
    • SHiNE SKiS.

12

Catalase-positive organisms

  • Definition
  • Examples

  • Definition
    • Catalase degrades H2O2 before it can be converted to microbicidal products by the enzyme myeloperoxidase.
    • People with chronic granulomatous disease (NADPH oxidase deficiency) have recurrent infections with catalase (+) organisms.
  • Examples
    • Pseudomonas, Listeria, Aspergillus, Candida, E. coli, S. aureus, Serratia.
    • You need PLACESS for your cats.

13

Encapsulated bacteria vaccines

  • Definition
  • Examples

  • Definition
    • Some vaccines containing polysaccharide capsule antigens are conjugated to a carrier protein, enhancing immunogenicity by promoting T-cell activation and subsequent class switching.
    • A polysaccharide antigen alone cannot be presented to T cells.
  • Examples
    • Pneumococcal vaccine
      • PCV (pneumococcal conjugate vaccine, i.e., Prevnar)
      • PPSV (pneumococcal polysaccharide vaccine with no conjugated protein, i.e., Pneumovax)
    • H. influenzae type B (conjugate vaccine)
    • Meningococcal vaccine (conjugate vaccine)

14

Urease-positive bugs (examples)

  • Cryptococcus, H. pylori, Proteus, Ureaplasma, Nocardia, Klebsiella, S. epidermidis, S. saprophyticus.
  • CHuck norris hates PUNKSS.

15

Pigment-producing bacteria (examples)

  • Actinomyces israeliiyellow “sulfur” granules, which are composed of filaments of bacteria.
    • Israel has yellow sand.
  • S. aureusyellow pigment.
    • aureus (Latin) = gold.
  • Pseudomonas aeruginosa—blue-green pigment.
    • Aerugula is green.
  • Serratia marcescensred pigment.
    • Think red maraschino cherries.

16

Bacterial virulence factors

  • Definition
  • Protein A
  • IgA protease
  • M protein

  • Definition
    • These promote evasion of host immune response.
  • Protein A
    • Binds Fc region of IgG.
    • Prevents opsonization and phagocytosis.
    • Expressed by S. aureus.
  • IgA protease
    • Enzyme that cleaves IgA.
    • Secreted by S. pneumoniae, H. influenzae type B, and Neisseria (SHiN) in order to colonize respiratory mucosa.
  • M protein
    • Helps prevent phagocytosis.
    • Expressed by group A streptococci.

17

Main features of exotoxins and endotoxins

  • Source
  • Secreted from cell?
  • Chemistry
  • Location of genes
  • Toxicity (high/low)
  • Clinical effects
  • Mode of action
  • Antigenicity
  • Vaccines
  • Heat stability
  • Typical diseases

  • Source
    • Ex: Certain species of some gram-positive and gram-negative bacteria
    • En: Outer cell membrane of most gram-negative bacteria
  • Secreted from cell?
    • Ex: Yes
    • En: No
  • Chemistry
    • Ex: Polypeptide
    • En: Lipopolysaccharide (structural part of bacteria; released when lysed)
  • Location of genes
    • Ex: Plasmid or bacteriophage
    • En: Bacterial chromosome
  • Toxicity
    • Ex: High (fatal dose on the order of 1 μg)
    • En: Low (fatal dose on the order of hundreds of micrograms)
  • Clinical effects
    • Ex: Various effects
    • En: Fever, shock (hypotension), DIC
  • Mode of action
    • Ex: Various modes
    • En: Induces TNF, IL-1, and IL-6
  • Antigenicity
    • Ex: Induces high-titer antibodies called antitoxins
    • En: Poorly antigenic
  • Vaccines
    • Ex: Toxoids used as vaccines
    • En: No toxoids formed and no vaccine available
  • Heat stability
    • Ex: Destroyed rapidly at 60°C (except staphylococcal enterotoxin)
    • En: Stable at 100°C for 1 hr
  • Typical diseases
    • Ex: Tetanus, botulism, diphtheria
    • En: Meningococcemia; sepsis by gram-negative rods

18

Bugs with exotoxins

  • Inhibit protein synthesis (4)
  • Increase fluid secretion (3)
  • Inhibit phagocytic ability (1)
  • Inhibit release of neurotransmitter (2)
  • Lyse cell membranes (2)
  • Superantigens causing shock (2)

  • Inhibit protein synthesis
    • Corynebacterium diphtheriae
    • Pseudomonas aeruginosa
    • Shigella spp.
    • Enterohemorrhagic E. coli (EHEC), including O157:H7 strain
  • Increase fluid secretion
    • Enterotoxigenic E. coli (ETEC)
    • Bacillus anthracis
    • Vibrio cholerae
  • Inhibit phagocytic ability
    • Bordetella pertussis
  • Inhibit release of neurotransmitter
    • Clostridium tetani
    • Clostridium botulinum
  • Lyse cell membranes
    • Clostridium perfringens
    • Streptococcus pyogenes
  • Superantigens causing shock
    • Staphylococcus aureus
    • Streptococcus pyogenes

19

Bugs with exotoxins:
Inhibit protein synthesis

  • For each
    • Toxin
    • Mechanism
    • Manifestation
  • Corynebacterium diphtheriae
  • Pseudomonas aeruginosa
  • Shigella spp.
  • Enterohemorrhagic E. coli (EHEC), including O157:H7 strain

  • Corynebacterium diphtheriae
    • Toxin: Diphtheria toxin*
    • Mechanism: Inactivates elongation factor (EF-2)
    • Manifestation: Pharyngitis with pseudomembranes in throat and severe lymphadenopathy (bull neck)
  • Pseudomonas aeruginosa
    • Toxin: Exotoxin A*
    • Mechanism: Inactivates elongation factor (EF-2)
    • Manifestation: Host cell death
  • Shigella spp.
    • Toxin: Shiga toxin (ST)*
    • Mechanism: Inactivates 60S ribosome by removing adenine from rRNA
    • Manifestation: GI mucosal damage Ž--> dysentery; ST also enhances cytokine release, causing hemolytic-uremic syndrome (HUS)
  • Enterohemorrhagic E. coli (EHEC), including O157:H7 strain
    • Toxin: Shiga-like toxin (SLT)*
    • Mechanism: Inactivates 60S ribosome by removing adenine from rRNA
    • Manifestation: SLT enhances cytokine release, causing HUS; unlike Shigella, EHEC does not invade host cells
  • *Toxin is an ADP ribosylating A-B toxin
    • B (binding) component binds to host cell surface receptor, enabling endocytosis
    • A (active) component attaches ADP-ribosyl to disrupt host cell proteins.

20

Bugs with exotoxins:
Increase fluid secretion

  • For each
    • Toxin
    • Mechanism
    • Manifestation
  • Enterotoxigenic E. coli (ETEC)
  • Bacillus anthracis
  • Vibrio cholerae

  • Enterotoxigenic E. coli (ETEC)
    • Toxin:
      • Heat-labile toxin (LT)*
      • Heat-stable toxin (ST)
    • Mechanism:
      • Overactivates adenylate cyclase (increases cAMP) Ž--> increased Cl- secretion in gut and H2O efflux
        • Labile in the Air (Adenylate cyclase)
      • Overactivates guanylate cyclase (increases cGMP) --> decreased resorption of NaCl and H2O in gut
        • Stable on the Ground (Guanylate cyclase)
    • Manifestation: Watery diarrhea
  • Bacillus anthracis
    • Toxin: Edema factor
    • Mechanism: Mimics the adenylate cyclase enzyme (increases cAMP)
      Manifestation: Likely responsible for characteristic edematous borders of black eschar in cutaneous anthrax
  • Vibrio cholerae
    • Toxin: Cholera toxin*
    • Mechanism: Overactivates adenylate cyclase (increases cAMP) by permanently activating Gs --> increased Cl- secretion in gut and H2O efflux
    • Manifestation: Voluminous “rice-water” diarrhea
  • *Toxin is an ADP ribosylating A-B toxin:
    • B (binding) component binds to host cell surface receptor, enabling endocytosis;
    • A (active) component attaches ADP-ribosyl to disrupt host cell proteins.

21

Bugs with exotoxins:
Inhibit phagocytic ability

  • For each
    • Toxin
    • Mechanism
    • Manifestation
  • Bordetella pertussis

  • Bordetella pertussis
    • Toxin: Pertussis toxin*
    • Mechanism: Overactivates adenylate cyclase (increases cAMP) by disabling Gi, impairing phagocytosis to permit survival of microbe
    • Manifestation
      • Whooping cough: child coughs on expiration and “whoops” on inspiration
      • Toxin may not actually be a cause of cough
      • Can cause “100-day cough” in adults
  • *Toxin is an ADP ribosylating A-B toxin:
    • B (binding) component binds to host cell surface receptor, enabling endocytosis;
    • A (active) component attaches ADP-ribosyl to disrupt host cell proteins.

22

Bugs with exotoxins:
Inhibit release of neurotransmitter

  • For each
    • Toxin
    • Mechanism
    • Manifestation
  • Clostridium tetani
  • Clostridium botulinum

  • Clostridium tetani
    • Toxin: Tetanospasmin
    • Mechanism: Protease cleaves SNARE proteins required for neurotransmitter release
    • Manifestation
      • Spasticity, risus sardonicus, and “lockjaw”
      • Toxin prevents release of inhibitory (GABA and glycine) neurotransmitters from Renshaw cells in spinal cord
  • Clostridium botulinum
    • Toxin: Botulinum toxin
    • Mechanism: Protease cleaves SNARE proteins required for neurotransmitter release
    • Manifestation:
      • Flaccid paralysis, floppy baby
      • Toxin prevents release of stimulatory (ACh) signals at neuromuscular junctions -->Ž flaccid paralysis

23

Bugs with exotoxins:
Lyse cell membranes

  • For each
    • Toxin
    • Mechanism
    • Manifestation
  • Clostridium perfringens
  • Streptococcus pyogenes

  • Clostridium perfringens
    • Toxin: Alpha toxin
    • Mechanism: Phospholipase (lecithinase) that degrades tissue and cell membranes
    • Manifestation: Degradation of phospholipids Ž--> myonecrosis (“gas gangrene”) and hemolysis (“double zone” of hemolysis on blood agar)
  • Streptococcus pyogenes
    • Toxin: Streptolysin O
    • Mechanism: Protein that degrades cell membrane
    • Manifestation
      • Lyses RBCs
      • Contributes to β-hemolysis
      • Host antibodies against toxin (ASO) used to diagnose rheumatic fever (do not confuse with immune complexes of poststreptococcal glomerulonephritis)

24

Bugs with exotoxins:
Superantigens causing shock

  • For each
    • Toxin
    • Mechanism
    • Manifestation
  • Staphylococcus aureus
  • Streptococcus pyogenes

  • Staphylococcus aureus
    • Toxin: Toxic shock syndrome toxin (TSST-1)
    • Mechanism: Bring MHC II and TCR in proximity to outside of antigen binding site to cause overwhelming release of IFN-γ and IL-2 -->Ž shock
    • Manifestation
      • Toxic shock syndrome: fever, rash, shock
      • Other toxins cause scalded skin syndrome (exfoliative toxin) and food poisoning (enterotoxin)
  • Streptococcus pyogenes
    • Toxin: Exotoxin A
    • Mechanism: Bring MHC II and TCR in proximity to outside of antigen binding site to cause overwhelming release of IFN-γ and IL-2 -->Ž shock
    • Manifestation: Toxic shock syndrome: fever, rash, shock

25

Endotoxin

  • Definition
  • Associations

  • An LPS found in outer membrane of gramnegative bacteria (both cocci and rods).
  • Associations: ENDOTOXIN
    • C3a --> hypotension & Edema
    • Nitric oxide --> hypotension
    • Coagulation cascade --> DIC/Death
    • Outer membrane
    • TNF-α --> fever & hypotension
    • O-antigen
    • eXtremely heat stable
    • IL-1 --> fever
    • C5a --> Neutrophil chemotaxis

26

Transformation

  • Ability to take up naked DNA (i.e., from cell lysis) from environment
    • Also known as “competence”
  • A feature of many bacteria, especially S. pneumoniae, H. influenzae type B, and Neisseria (SHiN).
  • Any DNA can be used.
  • Adding deoxyribonuclease to environment will degrade naked DNA in medium Ž--> no transformation seen.

27

Conjugation

  • F+ × F– 
  • Hfr × F– 

  • F+ × F–
    • F+ plasmid contains genes required for sex pilus and conjugation.
      • Bacteria without this plasmid are termed F–.
    • Plasmid (dsDNA) is replicated and transferred through pilus from F+ cell.
      • No transfer of chromosomal genes.
  • Hfr × F–
    • F+ plasmid can become incorporated into bacterial chromosomal DNA, termed high-frequency recombination (Hfr) cell.
    • Replication of incorporated plasmid DNA may include some flanking chromosomal DNA.
      • Transfer of plasmid and chromosomal genes.

28

Transposition

  • Segment of DNA (e.g., transposon) that can “jump” (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa.
  • When excision occurs, may include some flanking chromosomal DNA, which can be incorporated into a plasmid and transferred to another bacterium.
  • Examples include antibiotic resistance genes on R plasmid.

29

Transduction

  • Generalized 
  • Specialized 
    • Definition
    • Encoded genes

  • Generalized
    • A “packaging” event.
    • Lytic phage infects bacterium, leading to cleavage of bacterial DNA.
    • Parts of bacterial chromosomal DNA may become packaged in viral capsid.
    • Phage infects another bacterium, transferring these genes.
  • Specialized
    • An “excision” event.
      • Lysogenic phage infects bacterium
      • Viral DNA incorporates into bacterial chromosome.
      • When phage DNA is excised, flanking bacterial genes may be excised with it.
      • DNA is packaged into phage viral capsid and can infect another bacterium.
    • Genes for the following 5 bacterial toxins are encoded in a lysogenic phage (ABCDE):
      • ShigA-like toxin
      • Botulinum toxin (certain strains)
      • ƒƒCholera toxin
      • ƒƒDiphtheria toxin
      • Erythrogenic toxin of Streptococcus pyogenes

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