Microbiology Strx and Fnxn Flashcards
What is a microbe?
Bacteria (prokaryote)
Protozoa (eukaryote)
Fungi (eukaryote)
Viruses (neither prokaryotic nor eukaryotic)
Prokaryote
Bacterial Strx
Bacterial Strx ctd.
Rods
Aka “bacillus”
Two bacilli together – Diplobacilli
Chains of bacilli are called streptobacilli
Other arrangements are called “palisades”
Side by side/ “X” “V” or “Y” figures
Cocci
Spirochete: Flexible undulating corkscrew
Spirillum: RIGID corkscrew shape
Bacterial Strx properties
Inner workings
Flagella and pili (fimbriae)
Capsule
Cytoplasmic membrane
Cell envelope
Gram positive
Gram negative
The Gram stain
Mesosome
Plasmid DNA
PK locomotion
Flagella & pilli
Whatever is external on bacteria is HIGHLY ANTIGENIC
Flagella -some have >1.
Used by bacteria for locomotion.
Composed of flagellin.
Different arrangements of flagella:
Monotrichous (Vibrio cholerae)
Lophotrichous (Bartonella bacilliformis)
Amphitrichous (Spirillum serpens)
Peritrichous (Escherichia coli)
Recognition of flagella helps determine which antimicrobial to use
The Flagellar Motor
Made of the protein flagellin and consists of a filament and basal region. The basal region has a hook and a basal body which has a rod and rings. Gram positive organisms have 2 rings, one in the cell wall and one in the cell membrane. Gram negative organisms have 4 rings, 2 in the cell wall and 2 in the cell membrane.
Pili (Fimbriae)
The Capsule
Some have these. Those that can…
A slimy outer coating not found in all bacteria.
Usually a complex of high molecular weight polysaccharides.
A.k.a. Slime or glycocalyx (generally more loosely associated – adherence properties).
Special Note: BIOFILMS.
Can be antiphagocytic - resistant to macrophage cells that would try to engulf it.
Cytoplasmic membrane
Peptidogycan
Gram Positive and Gram Negative Bacterial Cell Envelopes
The Gram Stain
The gram stain procedure was originally developed by the Danish physician Hans Christian Gram (no kidding) to differentiate pneumococci (Streptococcus pneumoniae) from Klebsiella pneumoniae.
The difference between gram-positive and gram-negative bacteria is in the permeability of the cell wall to “purple colored iodine-dye complexes” when treated with the decolorizing solvent.
Gram-positive bacteria retain purple iodine-dye complexes after the treatment with the decolorizing agent, gram-negative bacteria do not retain complexes when decolorized. Safranin is used after decolorization treatment to “counterstain” gram-negatives.
Gram Stain Process
Works due to diff in peptidoglycan in bacterial cell walls
Bacteria are heat fixed to a slide.
Crystal violet is added – all cells stain blue.
Iodine fixes the stain into the bacterial cell.
Alcohol decolorizes gram negative bacteria. Gram positives remain blue/purple.
Safranin (counterstain) stains the gram negative bacteria a pink color.
Gram Positives
Found only in the gram + cell wall are:
- Teichoic acids / Teichuronic acids*
- Lipoteichoic acid (LTA)*
- Polysaccharides*
Teichoic Acid.
A water soluble polymer of ribitol or glycerol residues joined by phosphodiester linkages.
Teichuronic Acid.
Similar to teichoic acid, but made in phosphate-limiting conditions.
Lipoteichoic Acid (LTA).
Lipid attached to Teichoic Acid – Adhesin!
Polysaccharides.
Most likely composites of sugars released from teichoic and teichuronic acid.
Gram Negatives
Found only in the gram negative cell wall are:
Lipoproteins
Periplasmic space
Outer membrane
Lipopolysaccharide
Periplasmic space
A gel-like matrix between the cytoplasmic membrane and the outer membrane
Contains enzymes for nutrient breakdown and substrate binding proteins, including penicillin binding proteins.
Lipoprotein
Cross-links outer membrane to peptidoglycan
In the periplasmic space
Outer Membrane
A phospholipid bilayer containing lipopolysaccharides (later) Contains porins (non-specific pore proteins), anchor proteins and transport proteins. Protects the cell from hydrolytic enzymes.
Lipopolysaccharide (LPS)
Made of Lipid A (a complex lipid) covalently attached to a polysaccharide with core and terminal repeat units.
LPS (Lipid A) = endotoxin. It is extremely toxic to animals.
The lipid portion of LPS is attached to the outer membrane by hydrophobic bonds.
The polysaccharide chain of repeating units is called the O-antigen, is exposed to the outside of the cell, and is antigenic.
The Mycoplasma (and Ureaplasma)
The smallest free-living organisms.
NO CELL WALL!
That means no peptidoglycan.
Bacterial stains don’t work well.
The only barrier is the cytoplasmic membrane.
Membranes contain sterols – required for growth (not synthesized by the bacterium).
Many mycoplasmal pathogens exhibit filamentous or flask-shaped appearances and display prominent and specialized polar tip organelles that mediate attachment to host target cells.
