general bacteriology

• All bacteria are generally unicellular with a simple structure.
• Bacteria are Prokaryotes, meaning their cell lacks a membrane-bound nucleus and lacks clearly defined sub-cellular organelles.
• Bacteria have an enormous range of metabolic capacities and can be found in some of the most extreme environments on earth.
• Only a small minority of bacteria causes disease.
• All cells are Eukaryotes, Prokaryotes, Unicellular, and Multicellular.
• Bacteria have no cell wall, while Eukaryotes and Prokaryotes have a cell wall.
• The cell wall is unique to prokaryotes and serves various functions such as giving shape, protecting the cell from external stresses, contributing to virulence, and targeting for antimicrobials.
• The bacterial cell consists of protoplasm, the body of the bacteria, and include the cytoplasmic membrane, cell wall, capsule, fimbriae/pili, and flagella.
• The bacterial cell nucleoid contains a single chromosome and is a circular double-stranded DNA molecule (~1mm).
• The cytoplasmic membrane of bacteria is a phospholipids and protein bilayer, multifunctional compared to Eukaryotes, with functions such as protein synthesis, electron transport, and oxidative phosphorylation.
• The cell wall is rigid and surrounds the cell membrane, is semi-permeable, and functions to prevent osmotic lysis, protect the cell from external stresses, contribute to virulence, and target for antimicrobials.
• The cell wall lies outside the cell membrane and bacteria have a cell wall containing a polymer called peptidoglycan, unique to prokaryotes, which is rigid and important in defining the shape of the cell and giving the cell mechanical strength.
• Gram-negative cells have a thin layer of peptidoglycan in the periplasmic space.
• The outer surface of the outer membrane of Gram-negative cells contains a unique lipid component, lipopolysaccharide (LPS), which is extremely important in pathogenesis.
• Gram-negative cells have a second lipid bilayer called the outer membrane that enables diffusion across the outer membrane.
• Gram-positive cells form a crystal violet-iodine complex.
• Lugols Iodine is applied as a mordant or fixative in Gram stain.
• Gram-negative bacteria undergoes decolorizing.
• Gram-positive cells have a thick peptidoglycan layer that resists lysis by complement, but can still be opsonized.
• The thickness of the peptidoglycan layer determines the Gram stain characteristic, which is used in the identification of bacteria.
• Gram-positive cells contain Teichoic acids and lipoteichoic acids, which are polymers of ribitol or glycerol phosphates, and are interspersed within the peptidoglycan layer.
• Gram-positive cells are joined by short peptides that attach to the N-acetyl muramic acid.
• Primary stain for Gram stain is Ammonium oxalate crystal violet, which the cell wall absorbs.
• Decolorizing agent for Gram stain is acetone or alcohol, which Gram-positive bacteria resists due to its thick peptidoglycan layer.
• Gram-negative cells have a periplasmic space between the inner (cytoplasmic) and outer membrane.
• Gram-positive cells have anchored Teichoic acids and lipoteichoic acids in the cell membrane.
• The cell wall is essential for survival, as rupture of the cell wall leads to cell lysis.
• Primary Stain: Gram positive bacteria.
• Acid fast bacteria cannot be stained by Gram stain and are most similar to gram-positive bacteria.
• Sex pili initiate conjugation.
• Fimbriae and pili are short thin filaments around the bacteria, with fimbriae used for adhesion to host cells and pili by attaching to other bacteria can transfer DNA.
• Reactivation, or "germination", is the process of reactivating dormant bacteria.
• Gram positive bacteria are stained with a primary stain.
• The cell wall of acid fast bacteria is composed of fatty acids which contribute to virulence.
• Dormant or stationary phase bacteria, such as Bacillus species and Clostridia species, form spores.
• Mycoplasma are very labile, have a small genome, and are the simplest free-living organisms.
• Bacillus anthracis capsule is made of lipoproteins.
• Bacteria may have flagella used in locomotion, which are long thin filaments (0.02 µm) that can be polar or peritrichous.
• Mycolic acid, arabinogalactans, and sulfolipids are mycobacterial virulence factors.
• Counter stain: dilute carbol fuchsin.