- Gram Positive Bacteria retain crystal violet stain (Gram Stain) on microscopy
- Thick peptidoglycan cell layer
- Surrounds the inner plasma membrane of Gram Positive Bacteria and retains crystal violet stain
- Contrast with Gram Negative Bacteria
- Relatively thin Peptidoglycan cell layer (does not retain the crystal violet stain)
- Gram Negative Bacteria are also surrrounded by an additional outer membrane
- Thick peptidoglycan cell layer
- Gram Positive Bacteria have two layers to their cell wall or envelope
- Outer Peptidoglycan cell layer
- Composed of repeated Disaccharides with a side chain of 4 Amino Acids
- Adjacent Amino Acid chains cross-link, and stabilize the peptidoglycan layer into a firm wall
- Transpeptidase (Penicillin binding Protein) is present in the inner cell membrane
- Transpeptidase is an enzyme that catalyzes Amino Acid cross-linking in the peptidoglycan layer
- Inhibited by Penicillin
- Composed of repeated Disaccharides with a side chain of 4 Amino Acids
- Inner cytoplasmic cell membrane
- Phospholipid bilayer with embedded Proteins (e.g. teichoic acid)
- Outer Peptidoglycan cell layer
- Gram Positive Cocci
-
Streptococcus (e.g. Streptococcus Pneumoniae)
- Gram+ Cocci arranged in pairs (e.g. Pneumococcus) or chains
- Catalase negative
-
Staphylococcus (e.g. Staphylococcus Aureus)
- Gram+ Cocci arranged in clusters
- Catalase positive
- Catalase converts Hydrogen Peroxide (from Macrophages, PMNs) into water and oxygen
- Catalase positive organisms on a culture plate will bubble when exposed to Hydrogen Peroxide
- Enterococcus (Previously Group D Streptococcus)
- Gram Positive Spore Forming Rods
-
General
- Bacillus and Clostridium species may lie dormant as spores in harsh environments for years
- Bacillus and Clostridium species exert toxicity in humans via exotoxin release
- Bacillus species are aerobic, while Clostridium species are anaerobic
- Bacillus (aerobic)
-
Clostridium (anaerobic)
- Clostridium botulinum (Botulism)
- Clostridium tetani (Tetanus)
- Clostridium perfringens (Gas Gangrene)
- Clostridium sordellii (Clostridial Toxic Shock Syndrome)
- Clostridium difficile
- Recategorized as Clostridioides difficile in 2016
- Gram Positive Non-Spore Forming Rods
- Listeria monocytogenes
- Erysipelothrix rhusiopathiae
- Primarily a Zoonotic Pathogen (e.g. animal handlers)
- Corynebacteria
- Corynebacterium diphtheriae (diptheria)
- Coryneform Bacteria (Diphtheroids)
- Includes multiple genera in addition to Corynebacteria (e.g. Arcanobacterium, Brevibacterium, Microbacterium)
- Corynebacterium jeikeium
- Corynebacterium urealyticum
- Corynebacterium striatum
- Gram Positive Branching Organisms
- Davis (1990) Microbiology, Lippincott, p. 21-50
- Gladwin (2014) Clinical Microbiology, Medmaster, Miami, p. 1 to 8