Antibiotics and Bacteria

Gram (-) vs. Gram (+)

• Gram-negative bacteria
  • Thin layer of peptidoglycan
  • Outer membrane is composed of endotoxins
  • Outer membrane contains porins that allow certain substances to pass
  • Periplasm is the space between the plasma and outer membrane
  • Gram-negative cells show up as pink in Gram stains
• Gram-positive bacteria
  • Thick layer of peptidoglycan
  • No outer membrane
  • No porins
  • Gram-positive bacteria show up as purple in Gram stains

Bacteria Structures

• Nucleoid: region in the cytoplasm that contains the bacteria’s DNA molecule
  • The bacterial chromosomal DNA is supercoiled
• Plasmid: Circular and double-stranded DNA molecules
  • Plasmids can be transferred and typically contain genetic material for antibiotic resistance
• Ribosomes: facilitate bonding of amino acids for protein synthesis
• Cell Wall: Rigid wall that prevents lysis
  • Peptidoglycan contributes to the rigidity of the cell wall
• Capsule (glycocalyx): allows attachment to surfaces and protection
• Flagella: Protein appendages that move the bacteria
• Pili: Filamentous appendages that allow for attachment
  • Involved in conjugation
• Endotoxins: LPS molecules

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