Microbiology Flashcards – First Aid for the USMLE STEP 1


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  • Bacterial Structures: Peptidoglycan
    "Gives rigid support, protects against osmotic pressure; Sugar backbone w/ cross-linked peptide side chains. (function; chemical composition)"
  • Bacterial Structures: Cell wall / cell membrane (G+'s)
    Major surface Ag; Peptidoglycan for support. Teichoic acid induces TNF and IL-1.
  • Bacterial Structures: Outer membrane (G-)
    "Site of endotoxin (LPS), major surface Ag; Lipid A induces TNF and IL-1; Polysaccharide is the Ag"
  • Bacterial Structures: Plasma membrane
    Site of oxidative and transport enzymes; Lipoprotein bilayer
  • Bacterial Structures: Ribosome
    Protein synthesis; 50S and 30S subunits
  • Bacterial Structures: Periplasm
    "Space btw the cytoplasmic membrane and the peptidoglycan in G- bacteria; Contains may hydrolytic enzymes, including beta-lactamases"
  • Bacterial Structures: Capsule Function? Structure? (... and exception?)
    "Protects against phagocytosis; Polysaccharide (except in Bacillus anthracis , which contains D-glutamate)"
  • Bacterial Structures: Pilus/fimbria
    "Mediate adherence of bacteria to cell surface, sex pilus forms attachment btw 2 bacteria during conjugation; Glycoprotein"
  • Bacterial Structures: Flagellum
    Motility; Protein
  • Bacterial Structures: Spore
    "Provides resistance to dehydration, heat, and chemicals; Keratin-like coat, dipiclonic acid"
  • Bacterial Structures: Plasmid
    "Contains a variety of genes for ABX resistance, enzymes, toxins; DNA"
  • Bacterial Structures: Glycocalyx
    "Mediates adherence to surfaces, especially foreign surfaces (e.g. indwelling catheters); Polysaccharide"
  • Structures unique to gram (+) organisms
    Lipoteichoic acid Cell wall
  • Structures common to Gram +/- organisms
    "Flagellum, pilus, capsule, PDG, cytoplasmic membrane"
  • Features unique to G(-) organisms
    Endotoxin/LPS (outer membrane) Periplasmic space (location of many beta-lactamases)
  • Bacteria w/ unusual cell membranes/walls
    Mycoplasma: contain sterols and have no cell wall Mycobacteria: Contain mycolic acid. High lipid content.
  • G(+) cocci
    Staphylococcus Streptococcus
  • G(-) cocci
  • G(+) Rods
    My cobacterium (acid-fast) List eria B acillus C lostridium C orynebacterium What happened when you were sending that email to Gram + Rod ? My List B ecame CC 'd
  • G(-) Rods
    Haemophilus Yersinia Enterics (separate card) Legionella (silver stain) Bordatella Brucella Bartonella Francisella Pasteurella Gardnerella (gram variable)
  • Branching Filamentous bacteria (G+)
    Actinomyces Nocardia (weakly acid-fast)
  • Pleomorphic (G-) bacteria
    Rickettsiae Chlamydiae (Giemsa stain)
  • Spirochetes (G-)
    Leptospira Borrelia (Giemsa stain) Treponema
  • Neither G+ nor G- (b/c no cell wall)
  • Bugs that won't Gram stain
    Treponema (too thin) Rickettsia (intracellular) Mycobacteria (high-lipid-content cell wall requires acid-fast stain) Mycoplasma (no cell wall) Legionella pneumophilia (primarily intracellular) Chlamydia (intracellular)
  • Visualizing Treponemes
    Darkfield microscopy and fluorescent Ab staining
  • Visualizing Mycobacteria
    Acid-fast stain
  • Visualizing Legionella
    Silver stain
  • Giemsa's stain is used to visualize...?
    use for: Borrelia Plasmodium Trypanosomes Chlamydia
  • PAS (periodic acid-Schiff) stain
    "stains glycogen, mucopolysaccharides; Used to diagnose Whipple's dz (PASs the sugar)"
  • Ziehl-Neelsen stain
    Use to stain Acid-fast bacteria
  • India ink
    used to visualize Cryptococcus neoformans (mucicarmine also could be used)
  • Silver stain
    "used to visualize: fungi, Legionella"
  • Media/Special culture requirements for: H. influenzae
    Chocolate agar w/ factors V (NAD) and X (hematin) (Media used for isolation)
  • Media/Special culture requirements for: N. gonorrheae
    Thayer-Martin media (or VPN media)
  • Media/Special culture requirements for: B. pertussis
    Bordet-Gengou (potato) agar (Media used for isolation)
  • Media/Special culture requirements for: C. diphtheriae
    "Tellurite plate, Loffler's media (Media used for isolation)"
  • Media/Special culture requirements for: M. tuberculosis
    Lowenstein-Jensen agar (Media used for isolation)
  • Eaton's agar
    M. pneumoniae
  • Media/Special culture requirements for: E. coli
    Eosin-methylene Blue (EMB) agar (blue-black colonies w/ metallic sheen) (Media used for isolation)
  • Eosin-methylene Blue (EMB) agar (blue-black colonies w/ metallic sheen)
    E. coli
  • Media/Special culture requirements for: Lactose-fermenting enterics
    Pink colonies on MacConkey's agar (Media used for isolation)
  • Media/Special culture requirements for: Legionella
    Charcoal yeast extract agar buffered w/ increased iron and cysteine (Media used for isolation)
  • Media/Special culture requirements for: Fungi
    Sabouraud's agar (Media used for isolation)
  • G(-) Enterics (rod-shaped)
    E. coli Shigella Salmonella Yersinia Klebsiella Proteus Enterobacter Serratia Vibrio Campylobacter Helicobacter Pseudomonas Bacteroides
  • Obligate aerobes
    "Use an O2-dependent system to generate ATP Examples: (Nagging Pests Must Breathe) Nocardia Pseudomonas Mycobacterium, Bacillus Also: to help remember Pseudomonas aeruginosa - AERuginosa is an AERobe"
  • Pseudomonas aeruginosa O2 tolerance? Where does it show up?
    "P. AERuginosa is an AERobe seen in burn wounds, nosocomial pneumonia, and pneumonias in cystic fibrosis pts."
  • Obligate Anaerobes
    (Anaerobes Can't Breathe Air) Clostridium Bacteroides Actinomyces
  • Aminoglycosides and anaerobes
    AminO2 glycosides are ineffective against anaerobes b/c these ABX require O2 to enter into the bacterial cell.
  • Obligate intracellular bugs
    "Rickettsia, Chlamydia (Stay inside [cells] when it's R eally C old) *Can't make their own ATP"
  • Facultatively intracellular bugs
    Some Nasty Bugs May Live FacultativeLY Salmonella Neisseria Brucella Mycobacterium Listeria Francisella Legionella Yersinia
  • Quellung Reaction
    "Postive quellung: If encapsulated bug is present, the capsule swells when specific anti-capsular antisera are added (Quellung = capsular swellung)"
  • Urease (+) bugs
    (PUNCH-K); Proteus Klebsiella H. pylori Ureaplasma Nocardia Cryptococcus
    "you need SSPACE for your CATs. S.aureus, Serratia, Pseudomonas, Actinomyces, Candida, E.coli"
  • Important virulence factors in S. aureus
    "protein A: Binds Fc region of Ig, disrupts opsonization and phagocytosis."
  • IgA protease Who secretes it?
    "Secreted by S. pneumoniae, H. influenzae type B, and Neisseria to prevent phagocytosis"
  • Group A streptococcus (pyogenes) virulence factors
    M protein: Helps prevent phagocytosis
  • Exotoxin vs. Endotoxin: Chemistry
    Exo: Polypeptide; Endo: Lipopolysaccharide (structural part of the bacteria. Released when lysed)
  • Exotoxin vs. Endotoxin: Location of genes
    Plasmid or bacteriophage; bacterial chromosome (Exo ; Endo)
  • Exotoxin vs. Endotoxin: Toxicity
    High (fatal dose on the order of 1 microgram); Low (fatal dose on the order of hundreds of micrograms) (Exo ; Endo)
  • Exotoxin vs. Endotoxin: Clinical effects
    "Various; Fever, shock (Exo ; Endo)"
  • Exotoxin vs. Endotoxin: Mode of action
    Various; Includes TNF and IL-1 (Exo ; Endo)
  • Exotoxin vs. Endotoxin: Antigenicity
    Induces high-titer Abs called antitoxins ; Poorly antigenic (Exo ; Endo)
  • Exotoxin vs. Endotoxin: Vaccines
    Toxoids useful as vaccines; No toxoids formed and no vaccine available (Exo ; Endo)
  • Exotoxin vs. Endotoxin: Heat stability
    Destroyed rapidly at 60C (except staphylococcal enterotoxin); Stable at 100C for 1 hour (Exo ; Endo)
  • Exotoxin vs. Endotoxin: Typical diseases
    "Tetanus, botulism, diphtheria; Meningococcemia, sepsis by G(-) rods (Exo ; Endo)"
  • Superantigens
    "Bind directly to MHCII and T-cell receptor simultaneously, activating large numbers of T-cells to stimulate release of IFN-gamma and IL-2"
  • Toxins: TSST-1
    "Organism, toxin function: S. aureus, SuperAg that causes toxic shock syndrome (fever, rash, shock)."
  • Toxins: Exfoliatin
    "Organism, toxin function: S. aureus, Causes staphylococcal scalded skin syndrome"
  • Toxins: Enterotoxins
    "Organism, toxin function: S. aureus (and others) Cause food poisoning"
  • ADP ribosylating exotoxins
    "Diphteria toxin, Exotoxin A (P.aureginosa), Heat-Labile Toxin (ETEC), Cholera Toxin, Pertussis Toxin,"
  • Toxins: Diphtheria exotoxin
    "Organism, toxin function: Corynebacterium diphtheriae, ADP-ribosylating A-B exotoxin that inactivates EF-2 (similar to Psudomonas exotoxin A) Causes pharyngitis and pseudomembrane in throat."
  • Toxins: Cholera toxin
    "Organism, toxin function: Vibrio Cholerae ADP ribosylation of G-protein stimulates adenylyl cyclase Increased pumping of Cl- into gut and decreased Na+ absorption Water moves into gut lumen Causes voluminous rice-water diarrhea"
  • "Toxins: Heat-labile toxin, Heat-stabile toxin"
    "Organism, toxin function: E. coli ADP-ribosylating A-B toxins Heat-labile: stimulates Adenylyl cyclase (nc cAMP-inc Cl and h2o secretion to the gut) Heat-stabile: stimulates Guanylate cyclase (inc cGMP- dec reabsorption of NaCl and h2o."
  • Toxins: Pertussis toxin (PT)
    "Organism, toxin function: Bordetella pertussis. ADP-ribosylating A-B toxin that increases cAMP by inhibiting Gi. Causes whooping cough Inhibits chemokine receptor --> causes lymphocytosis"
  • Toxins: alpha toxin
    "Organism, toxin function: Clostridium perfringens, Causes gas gangrene (phospholipase degrades tissue and cell membranes). Get double zone of hemolysis on blood agar"
  • Toxins: Tetanus toxin (tetanospasmin)
    "Organism, toxin function: C. tetani Blocks the release of inhibitory neurotransmitters GABA and glycine Causes lockjaw"
  • Toxins: Botulinum toxin (aka Botox)
    "Organism, toxin function: C. botulinum Blocks release of ACh Causes anticholinergic symptoms, CNS paralysis (especially cranial nerves) Spores found in canned food, honey (causes floppy baby)"
  • Toxins: Edema factor
    "Organism, toxin function: Bacillus anthracis, mimics adenylate cyclase"
  • Toxins: Shiga toxin
    "Organism, toxin function: Shigella, and E. coli O157:H7 Cleaves host cell rRNA (inactivates 60S ribosome) Enhances cytokine release, causing HUS"
  • Toxins: Streptolysin O
    "Organism, toxin function: S. pyogenes, a hemolysin. Ag for ASO Ab, which is used in Dx of rheumatic fever"
  • cAMP inducers (list)
    "Vibrio cholerae, B. pertussis, E. coli, Bacillus anthracis, *Cholera, pertussis, and E. coli toxins act via ADP ribosylation to permanently activate endogenous adenylate cyclase (increasing cAMP), While anthrax edema factor is itself an adenylate cyclase"
  • Vibrio Cholerae toxin and cAMP
    "Toxin permanently activates Gs, Causing rice-water diarrhea (Cholera turns the on on)"
  • B. pertussis and cAMP
    "Pertussis toxin permanently disables Gi, causing whooping cough (Pertussis toxin turns the off off) *Pertussis toxin also promotes lymphocytosis by inhibiting chemokine receptors."
  • E. coli and cAMP
    Heat-labile toxin stimulates adenylyl cyclase
  • Bacillus anthracis and cAMP
    "Anthrax toxin includes edema factor, a bacterial adenylate cyclase (increases cAMP)"
  • Endotoxin
    A Lipopolysaccharide found in the cell wall of G(-) bacteria N-dotoxin is an integral part of the gram-Negative cell wall *Endotoxin is heat stable
  • Endotoxin and Macrophages
    "Activates Macs: IL-1 causes fever; TNF causes fever, hemorrhagic tissue necrosis; NO causes hypotension (shock) "
  • Endotoxin and complement
    "Activates the complement (alternative pathway): C3a causes hypotension, edema C5a causes PMN chemotaxis "
  • Endotoxin and Hageman factor (factor XII)
    "Activates Hageman factor This activates coagulation cascade, causing DIC "
  • Bacterial growth curve
    Lag phase: metabolic activity w/o division Log phase: rapid cell division Stationary phase: nutrient depletion slows growth. Spore formation in some bacteria. Death phase: prolonged nutrient depletion and buildup of waste products leads to death.
  • Transformation
    DNA taken up directly from environment by competent prokaryotic and eukaryotic cells. Any DNA can be used
  • F+ x F- Conjugation
    "F+ plasmid contains genes for conjugation process. Bacteria w/o this are termed F-. Plasmid is replicated and transferred through pilus from the F+ cell. Plasmid DNA only, no transfer of chromosomal genes."
  • Hfr x F- Conjugation
    "F+ plasmid can become incorporated into bacterial chromosomal DNA, now termed Hfr cell. Replication of incoporated plasmid DNA may include some flanking chromosomal DNA. Transfer of plasmid and chromosomal genes."
  • Generalized transduction
    "Lytic phage infects bacterium, leading to cleavage of bacterial DNA and synthesis of viral proteins. Parts of bacterial chromosomal DNA may become packaged in viral capsid. Phage infects another bacterium, transferring these genes."
  • Specialized transduction
    "Lysogenic phage infects bacterium; viral DNA incorporated into bacterial chromosome. When phage DNA is excised, flanking bacterial gnees may be excised w/ it. DNA is packaged into phage viral capsid and can infect another bacterium."
  • Transposition (transposons)
    "Segment of DNA can jump (excision and reincorporation) from one location to another, can transfer genes from plasmid to choromosome and vice versa. "
  • 5 bacterial toxins encoded in a lysogenic phage
    ABCDE ShigA -like toxin B otulinum toxin (certain strains) C holera toxin D iphtheria toxin E rythrogenic toxin of Streptococcus pyogenes
  • Gram (+) | Rods | ?
    "Clostridium (anaerobe), Corynebacterium, Listeria, Bacillus"
  • "Gram (+) | Cocci | Catalase (+), in clusters (Staphylococcus) | Coagulase (+) | ?"
    Staphylococcus aureus
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