BACTE: BACTERIAL STRUCTURE, FUNCTION, GROWTH AND NUTRITION

• Only about 3% - 5% of known microbes can cause disease.
• Vast majority of known microbes are nonpathogens.
• Some microbes can be found as normal inhabitants of the human also known as normal flora.
• Pathogenic (disease-causing) bacteria are prokaryotic cells that infect eukaryotic hosts (humans).
• Antibiotic action - Inhibits bacterial growth without harming eukaryotic host cells.
• Cell wall is a rigid structure that maintains the shape of the cell.
• The two major types of cell walls are gram positive and gram-negative.
• Mycobacteria (gram positive) have a modified cell wall called an acid-fast cell wall.
• Mycoplasmas have no cell wall.
• Cell wall prevents bursting of  the cell from the high osmotic pressure inside it.
• The principal component of the gram-positive cell wall is a very thick protective peptidoglycan (murein) layer.
• Gram-positive cell wall consists of glycan (polysaccharide) chains of alternating N-acetyl-d-glucosamine (NAG) and N-acetyl-d-muramic acid (NAM)
• Gram-positive cell wall has short peptides, each consisting of four amino acid residues, are attached to a carboxyl group on each NAM residue.
• Gram-positive cell wall has a negatively charged teichoic acid (anchored to the peptidoglycan and contribute to the charge of the cell wall)
• The inner peptidoglycan layer of gram-negative cell wall is much thinner than in gram-positive cell walls.
• The additional outer membrane unique to the gram negative cell wall are proteins, phospholipids, and lipopolysaccharide (LPS).
• Porins are add in the permeability of the cell wall in gram-negative cell wall.
• Gram-negative cell wall lipopolysaccharide conains three regions: antigenic O–specific polysaccharide, core polysaccharide, and inner lipid A also called endotoxin that produces fever and shock conditions in patients.
• Gram-negative cell wall outer membrane acts as a barrier to hydrophobic compounds and harmful substances.
• Gram-negative cell wall outer membrane acts as a sieve, allowing water-soluble molecules to enter through protein-lined channels called porins and provides attachment sites that enhance attachment to host cells.
• Gram-negative cell wall periplasmic space is a gel-like matrix containing nutrient-binding proteins and degradative and detoxifying enzymes. It is also involve in peptidoglycan synthesis.
• The location of gram-negative cell wall periplasmic space is in between peptidoglycan and cytoplasmic memberane.
• Acid-fast cell wall is a gram-positive cell wall structure but also contain a waxy layer of glycolipids and fatty acids (mycolic acid) bound to the exterior of the cell wall.
• Acid-fast cell wall - More than 60% of the cell wall is lipid - mycolic acid.
• Acid-fast cell wall is difficult to stain with the Gram stain.
• Mycobacterium and Nocardia are best stained with an acid-fast stain and they are acid-fast bacteria.
• Absence of cell wall - Mycoplasma and Ureaplasma
• Absence of cell wall - contain sterols in their cell membranes
• Absence of cell wall - Bacteria can  lose their cell walls and grow as L-forms in media supplemented with serum or sugar to prevent osmotic rupture of the cell membrane.
• Protoplasts are derived from gram-positive bacteria and totally lacking cell walls.
• Protoplasts are unstable and osmotically fragile. It is produced artificially by lysozyme and hypertonic medium.
• Protoplast requires hypertonic conditions for maintenance.
• Spheroplast are derived from gram-negative bacteria.
• Spheroplast are osmotically fragile and is produced by growth with penicillin. Must be maintained in hypertonic medium.
• L- forms are sometimes spontaneously formed in the body of patients treated with penicillin; more stable than protoplasts or Spheroplasts , they can replicate in ordinary media.
• Hypertonic refers to a greater concentration. A hypertonic solution is one with a higher concentration of solutes outside the cell than inside the cell. Hypotonic refers to a lesser concentration. A hypotonic solution has a lower concentration of solutes outside the cell than inside the cell.
• Capsule is usually made of polysaccharide polymers, although they may also be made of polypeptides. It act as virulence factors in helping the pathogen evade phagocytosis.
• Capsule removal is accomplished by boiling a suspension of the microorganism.
• Capsule does not ordinarily stain with use of common laboratory stains, such as Gram or India ink. It appears as a clear area (“halo”-like) between or surrounding the stained organism.
• During identification of certain bacteria by serologic typing, capsules sometimes must be removed to detect the somatic (cell wall) antigens present underneath them.