Bacterial structures play essential roles in survival, pathogenicity, and cellular function.
Major structures include the cell wall, capsule, plasmid, ribosomes, cell membrane, and flagella.
Chromosome: Carries genetic information, typically found in a single, circular form.
Pilus (Fimbriae): Hair-like appendages used for attachment and conjugation.
Ribosomes: Sites of protein synthesis, smaller than eukaryotic ribosomes (70S vs 80S).
Inclusion Bodies: Storage sites for nutrients and other material in the cytoplasm.
Flagellum: Structures used for motility, capable of rotation and movement towards stimuli.
Capsule or Slime Layer: A gelatinous layer that protects bacteria and aids in adherence.
Cell Wall: Provides structure and protection, composed mainly of peptidoglycan.
Plasmid: Small, circular DNA molecules that can confer antibiotic resistance.
Cell Membrane: A phospholipid bilayer that regulates material entering and exiting the cell.
Outer layer composed primarily of peptidoglycan, providing shape and rigidity.
Contains both D- and L-amino acids, critical for its structure.
Composed of alternating units of N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM).
Cross-linked by oligopeptides, contributing to overall strength.
Bacteria categorized as Gram-positive or Gram-negative based on their ability to retain the dye during the Gram stain process.
Gram-positive: Thick peptidoglycan layer, retains crystal violet dye (appears purple).
Gram-negative: Thin peptidoglycan layer, cannot retain dye (appears red after counterstaining).
Capsule: A well-defined, dense layer that protects against phagocytosis and aids in adherence.
Slime Layer: A loose, unorganized layer that helps prevent desiccation and aids in biofilm formation.
Capsules are determinants of virulence, enhancing bacterial survival against immune responses.
Example: Streptococcus mutans uses its capsule for adherence to tooth enamel, contributing to caries formation.
Flagella are long, whiplike appendages used for locomotion via chemotaxis.
Comprised of the protein flagellin, enabling rotary motion powered by ion movement across the membrane.
Monotrichous: A single flagellum at one end.
Lophotrichous: Multiple flagella at one end.
Amphitrichous: One flagellum at each end.
Peritrichous: Flagella distributed all around the bacterium.
Dormant structures formed under stress conditions.
Highly resistant to heat, radiation, and chemical disinfectants.
Nutrient depletion triggers spore formation.
DNA and cytoplasm are isolated and surrounded by a thick protective coat.
Endospores can remain dormant for years, activating upon nutrient availability.
Thin appendages made of pilin protein, longer than fimbriae but shorter than flagella.
Primarily found on Gram-negative bacteria.
Mediates bacterial adherence to host tissues.
Involved in the process of conjugation for DNA transfer.
Composed of a lipid and polysaccharide; major component of the outer membrane.
O-antigen: Polysaccharide side chains varying among strains.
Core polysaccharide: Attached to lipid A, necessary for structure and function.
Lipid A: Anchors LPS in the membrane and is responsible for toxicity.
LPS acts as an endotoxin, triggering strong immune responses in hosts.
Important in bacterial identification and pathogenic mechanisms.
Genera like Mycobacterium have an unusual, lipid-rich cell wall that cannot be Gram stained.
Acid-fast due to resistance to decolorization after staining, commonly tested using Ziehl-Neelsen stain.
High lipid content including mycolic acids, which contribute to the bacterium's virulence.
A genus that lacks a cell wall; resistant to antibiotics targeting cell wall synthesis.
Can cause various human diseases, including atypical pneumonia.