Bacterial Structure and Function 1: Structure Flashcards Preview

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Flashcards in Bacterial Structure and Function 1: Structure Deck (11)
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1
Q

How small are bacteria

A
  • plant 10^-4
  • animal 10^-5
  • bacteria 10^-6, 1 um
  • need to use at least a light microscope, and then electron microscope
2
Q

Structural characteristics of bacteria

A
  • genome: DNA, no introns, single circular chromosome, nucleoid- like a eukaroytic nucleus, concentrates the genome in one intracellular position, unlike a eukayotic nucleus, no membrane-bound compartment
  • 70S ribosomes
  • peptideoglycan cell wall
  • reproduction by binary fission
3
Q

Microscopic Appearance

A
  • 10-100X smaller than eukaryotes
  • 500-1000X larger than viruses
  • visible by light microscopy with phase contrast or staining
4
Q

Bacterial shape

A
  • cocci (round): staph, strep, neisseria
  • bacilli (oval): bacillus, salmonella
  • spirochetes (corkscrew): Borrelia, Treponema

Some bacteria have characteristic clumping patterns:

1) Cocci in clumps: staph
2) Cocci in chains: strep
3) Diplococci: Neisseria

5
Q

Gram- stain procedure

A

1) Fix bacteria to microscope slide with heat
2) Stain with crystal violet (all bacteria turn purple)
3) Iodine treatment (Gram (+)s become permanently purple)
4) Decolorize with alcohol (leaches purple from Gram(-)s)
5) Counterstain (safrinin re-stains Gram(-)s so they’re visible)

6
Q

Basis of gram-stain

A
  • Gram+ and Gram- cell walls are significantly differnet
  • Gram+ has 3 layers of peptidoglycan, no exterior membrane
  • Gram- has 1 layer of peptidoglycan and does have an exterior membrane
  • other differences include LPS in Gram- and more frequent genetic transfer by plasmid exchange among Gram-: creates major problem with antibiotic resistance
7
Q

Acid-fast (mycobacteria)

A
  • third category of cell wall type
  • they do not stain Gram + but are structurally different from other Gram -
  • mycloic acid layer of Acid-fast bacteria resists both CV and counterstain
  • includes mycobacterium tuberculosis
8
Q

Clinical significance of gram-stain

A
  • fast and cheap: THE most commonly ordered lab test
  • cuts the differential in half by quickly eliminating a large category of candidate pathogens
  • can occasionally make the diagnosis: gram - diplocci in cervical smear= gonorrhea
9
Q

LPS

A
  • component of Gram- cell walls
  • have O-antigen segment on the outside helps with lab ID
  • have Lipid A near the outer membrane which is toxic
  • can cause septic shock either during sepsis or after antibiotic treatment when LPS is released from dead bacteria into blood
  • teichoic acids are the nearest equivalent in Gram+ much less likely to cause shock
10
Q

Glycocalyx

A
  • slime layer: loose coating of polysaccharide helps bacteria attach to host cells, form biofilms (hard to clean, specially since antibiotic resistance can be easily shared)
  • capsule: firm enclosure helps with attachment, resists phagocytosis, can be clinically useful for serologic testing or vaccine target, often a virulence factor
11
Q

Pili/Fimbrae

A
  • used for attachment, often a virulence factor
  • gram+ pili are recently-discovered covalently linked pili subunits
  • gram- pili come in many types, incorporate many different molecules, some have evolved into propulsion systems or secretion systems that are virulence factors in their own right
  • Type IV pili- locomotion
  • Type III and IV secretion pili