Chapter 1: Bacterial Taxonomy Flashcards
How to do a Gram stain
(1) Pour on a crystal violet stain (a blue dye) and wait 60 seconds
(2) Wash off with water and flood with iodine solution. Wait 60 seconds
(3) Wash off with water and then “decolorize” with 95% EtOH
(4) Finally, counter-stain with safranin (red dye) wait 30 seconds and wash off with water
Blue Gram stain =
Gram-positive
Red Gram stain =
Gram-negative
Gram - positive cell walls
Very thick, extensive cross-linking of the amino acid side chain
Outer cell wall composed of the complex cross-linked peptidoglycan (teichoic acid), polysaccharides, and other proteins
Inner surface of the cell wall touches the cytoplasmic membrane that span the lipid bilayer
Bacterial cytoplasmic membrane has no cholesterol or other sterols
Teichoic acid- antigenic determinant, it is important for serologic identification of many gram-positive species
Gram - negative cell walls
Cell wall is very thin with a fairly simple cross-linking pattern 3 layers (does not include the periplasmic space btwn inner membrane and pep) (1)Cytoplasmic membrane surrounded by peptidoglycan layer - Contains phospholipid bilayer with embedded proteins (2)Peptidoglycan layer: extremely thin- No teichoic acid, Small helical lipoprotein called murein lipoprotein (Originates from peptidoglycan layer and extends outward to bind to third outer membrane) (3) Outer cell membrane - 2 layers of phopholipid and hydrophobic tails in the center, Outermost portion contains lipopolysaccharide (LPS) , Embedded are porin proteins: allow passage of nutrients (Unique to gram-negative)
Periplasmic space: filled with gel that contains proteins and enzymes
Peptidoglycan
Cell wall composed of repeating disaccharides with 4 amino acids in a side chain extending from each disaccharide
Amino-acid chains of the peptidoglycan covalently bind to other amino acids from neighboring chains (Results in a stable cross-linked structure)
What catalyzes the formation of linkage in peptidogylcan?
Transpeptidase: catalyzes the formation of linkage - Located in inner cytoplasmic membrane, Antibiotic penicillin binds to and inhibits enzyme, Enzyme is thus called penicillin binding protein
LPS
Composed of 3 covalently linked components
O-specific chain or O-antigen
Core polysaccharide (water soluble)
Lipid A
O-specific chain or O-antigen
Outer carbohydrate chains of 1-50 oligosaccharide units that extend into the surrounding media
Differ between organisms
Antigenic determinants
TIP: O for Outer
Lipid A
Interior to the core polysaccharide
A disaccharide, multiple fatty acids reaching into the membrane
Known as the gram-negative ENDOTOXIN
- When bacterial cells are lysed by immune system, fragments of membrane containing lipid A are released –>Cause fever, diarrhea, possibly fatal endotoxic shock
Gram negative or gram positive? Has a low lipid content in cell wall, no endotoxin, periplasmic space, or porin channel?
Gram-positive
What are the four major shapes of bacteria?
(1) Cocci- spherical
(2) Bacilli- Rods. Short bacilli are called coccobacilli
(3) Spiral Forms: Comma-shaped, S-shaped, spiral-shaped
(4) Pleomorphic Lacking a distinct shape (like jello)
What are the 7 types of gram-positive bacteria/
3 Cocci, 4 are rod-shaped (bacilli)
- Streptococcus, Enterococcus (form strips of cocci)
- Staphylococcus (form clusters of cocci)
Spore producing bacterium
- Bacillus
- Clostridium
DO NOT produce spores
- Corynebacterium
- Listeria
What are the only groups of cocci and spiral-shaped Gram-negative bacteria?
Only two groups of cocci (diplo)
- Neisseria and maraxella
1 group of spiral-shaped
- Spirochetes
- Treponema pallidum —>syphilis
Rest are rods or pleomorphic
What bacteria has no cell wall, has a simple cell membrane and cant be either gram positive or negative?
mycoplasma
