Gram Positive and Gram Negative Bacteria I and II Flashcards Preview

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Flashcards in Gram Positive and Gram Negative Bacteria I and II Deck (34)
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describe the equation for CFU/mL


describe the 4 stages of bacterial growth


describe how turbidity can be used to assess bacterial growth


smaller size = better ___ to ___ ratio

smaller size = better surface area to volume ratio

substances enter and diffuse quickly


describe the association between arrangement and cell shape


describe cellular features unique to bacteria

  • flagella for motility
  • peptidoglycan cell wall
  • capsule
  • lipopolysaccharide (G-ve)
  • type of communication


name features that are common to both G+ve and G-ve bacteria

  • cytoplasmic membrane that lacks cholesterol
  • cell wall made of peptidoglycan
    • structurally slightly different in G+ve vs G-ve
      • basis of the Gram stain for differentiation
  • external features: capsules and cell walls
  • flagella for motility (not all species and not all the time)
    • eukaryotes use cilia: structurally and functionally different


describe the cytoplasmic membrane in bacteria

structurally similar to that of eukaryotes

  • lacks sterols (cholesterols)
    • hence need for cell wall (provides rigidity; gives cells their shape)
  • bacterial membrane is functionally varied
  • main roles:
    • selective permeability and transport
    • electron transport and oxidate phosphorylation (aerobes)
    • excretion
    • biosynthetic functions
    • chemotactic systems


summarize the features and roles of the bacterial cytoplasmic membrane


describe the peptidoglycan composition of the bacterial cell wall

  • encloses cytoplasmic membrane and cytoplasmic contents
  • defines cell shape
  • high intracellular osmotic pressure would otherwise burst cell (lacks stabilizing sterols)


name the 2 features that define gram staining character by cell wall composition

  1. thickness of layers of peptidoglycan
  2. cross-linking (type and extent)




which 2 acidic polysaccharides are found only in gram positive cell walls?

  • teichoic acid
  • lipoteichoic acid


describe the composition of the cell walls among the groups (bacteria, algae, protozoa, fungi)


describe the steps of Gram staining 


gram positive bacteria have a ___ PG 


gram negative bacteria have a ____ PG


summarize the characteristic features based on Gram stain between Gram positive and Gram negative


describe the linkage found in Gram positive 


describe the catalase test

  • look for immediate oxygen bubbles; "fizzing"
    • bubbles = positive result
  • useful for differentiation between Gram positive cocci:
    • + staphylococcus
    • - streptococcus


list the medically important Gram positive pathogens

  • catalase-positive
    • Staphylococcus aureus
    • S. epidermidis
    • S. saprophyticus
  • catalase-negative
    • E. faecalis
    • E. faecium
  • Lactococcus
  • Streptococcus sp.
    • Streptococcus pneumoniae
    • S. pyogenes
    • S. agalactiae
  • Viridans Streptococci


describe features of the Gram negative outer membrane

  • structurally and functionally different to cytoplasmic membrane
  • chemically distinct
    • inner leaflet: similar to cell cytoplasmic membrane
    • distinctive outer leaflet
      • lipopolysaccharide (LPS)
      • outer membrane proteins
        • porins: enable passive diffusion of specific low molecular weight hydrophillic compounds
      • key control point for prevention of access by antibiotics 


name significant features of the lipopolysaccharide (LPS) layer

  • role as physical barrier between G-ve bacteria and immediate environment
  • recognized by the immune system: used to indicate presence of bacteria
  • triggers inflammatory response
    • severe reponse to high levels of LPS: endotoxic shock
    • contributes to pathogenesis and associated clinical symptoms


describe the structure of lipopolysaccharide (LPS)


describe the function of porins in G-ve bacteria

  • water-filled open channels that span outer membrane that allow passive diffusion of small hydrophilic molecules into cell
  • important contributor to antibiotic resistance 
    • changes or modifications to OMPs (outer membrane proteins)


summarize difference between G+ve and G-ve based on cell wall


describe mycoplasma sp. and mycobacteria

​exceptions to the G+ve and G-ve principles

  • mycoplasma sp.
    • e.g. mycoplasma pneumoniae
    • lacks cell wall
    • has cellular membrane that contains sterols to provide rigidity
  • mycobacteria
    • e.g. mycobaterium tuberculosis
    • waxy outer coat with high % lipids


describe the linkage found in G-ve bacteria


describe endospores 

endospores are structures located inside the bacterial cell that are extremely resistant


describe what is seen


name 2 bacteria that can form endospores 

bacteria that can form endospores include Bacillus and Clostridium


summarize the components of an endospore