Gram Positive vs Gram Negative Bacteria

What are the subdivisions of gram positive anaerobes?

Cocci - Fingoldia, Peptococcus, Anaerococcus. Bacilli - Proprionibacterium, Clostridium, Actinomyces, Lactobacillus.

What are the subdivisions of gram-negative aerobes?

Cocci - Neisseria. Bacilli - Enterobacteriae.

What are the types of staphylococci and how do they arrange themselves?

Staphs clump together in clusters if they produce coagulase, but don't clump if they don't. Coagulase-negative Staphs. Coagulase-positive Staphs.

What are the types of streptococci and how do they arrange themselves?

Streps arrange themselves in chains. Alpha-haemolytic Streps. Beta-haemolytic Streps (group A, group B, group C/F/G). Non-haemolytic Streps (group D).

Describe the process of gram-staining

Fix bacteria - usually using Bunsen burner - onto a slide. Application of crystal violet (purple dye). This diffuses into cell wall. Application of iodine (mordant). Tis fixes crystal violet in the cell wall. Alcohol wash (acetone) which decolourises by washing away crystal violet, cell membranes and gram-negative organisms but has no effect on gram-positives. Under a microscope at this point will only see gram positives and blank areas. Application of safarin/neutral red (counterstain).

What are the structural differences between gram positive and gram negative bacteria?

Gram Positive = Thick layer of peptidoglycan (multi-layered). Amino acids cross-link peptidoglycan strands. Stabilised by teichoic acid and lipoteichoic acid. High murein content in cell wall. Lower lipid content. Gram Negative = Thinner layer of peptidoglycan (single layer). Amino acids cross-link peptidoglycan strands. Stabilised by teichoic acid and lipoteichoic acid. Impermeable Low murein content in cell wall. Higher lipid content. Outer membrane also present which contains phospholipid bilayer, lipopolysaccharide and transmembrane proteins.

What are the 2 key genera of gram-negative bacteria?

Gram-negative anaerobes. Gram-negative aerobes.

Structure of bacterial cytoplasmic membranes

Phospholipid bilayer and transmembrane proteins. Same in gram positive and gram negative bacteria.

What is the function of bacterial cell walls?

Primary function of cell walls is to provide rigidity and shape. Protects the cell membrane from osmotic, chemical and mechanical pressure. Facilitates movement of gases, water and molecules into/out of the cell. Contains antigens which help evade the immune system.

Function of bacterial cytoplasmic membranes

Passive diffusion of gases. Movement of water/ions. Facilitated diffusion of molecules. Active transport of molecules.

What is the need for gram-staining?

Allows differentiation between gram positive and gram negative organisms based on colour. Allows description of the morphology of bacteria (bacilli appear as rods, cocci appear as spheres).

What are the subdivisions of gram positive aerobes?

Cocci - Staphylococci, Streptococci. Bacilli - Nocardia, Bacillus, Listeria, Corynebacteria, Gardnerella.

Which type of bacteria are more susceptible to antibiotics?

Gram positive bacteria are more susceptible to antibiotics, whereas gram negative bacteria are more resistant.

Why do gram positive and gram negative bacteria gram stain differently and what colours do they stain?

Gram positive bacteria have lots of peptidoglycan in their cell wall which allows them to retain crystal violet dye, so they stain purple-blue. Gram negative bacteria have less peptidoglycan in their cell wall so cannot retain crystal violet dye, so they stain red-pink.

What are the 2 key genera of gram positive bacteria?

Gram-positive anaerobes. Gram positive aerobes.