General properties of bacteria week 3 Flashcards
Complete the attached table.
Define the following cell shapes/arrangements
diplococci
tetracoccyus
sarcina
streptococci
staphylococcus
neisseriae
coccus=round
sarcina: cocci in packets of 8, 16, 32 cells
streptococci: cocci in chains
staphylococci: cocci in grape like ireggularly shaped clusters
neisseriae: coffee bean shaped
bacillus
coccobacilli
palisades
vibrios
spirilla
spirochetes
bacillus: rod shaped
coccobacilli: have features of cocci and rods
palisades arrangement: rods lying next to one another (see PP)
vibrios: curved rods
spirilla: loose spirals
spirochetes: tight spirals
What surface layers may be found outside of the the cell wall of some bacteria?
capsules or slime
Describe the properties of bacterial capsules and slime.
Where in the cell are they synthesized?
What effect does removal of the capsule or slime have on a bacteria?
How do capsules and slime function as virulence factors?
How is the capsular antigen of S. Pneumoniae used?
A. Surface layers: Capsules or Slime outside the cell wall
- Viscous gel, high molecular weight polysaccharides in some; loose, amorphous slime layer in others
- Synthesized on the plasma membrane, secreted through the cell wall
- Not essential for viability - remove physically or by mutation without killing
- Aids in adherence to tissues (heart valves, artificial devices, catheters); virulence factor
- Resists phagocytosis: virulence factor
- Capsular antigen of S. pneumoniae used in:
- vaccines
- differentiating one type from another, with specific antibodies in outbreaks
What is a cell wall? What bacteria have cell walls?
What are the functions of cell walls?
T or F: Bacterial cell walls are not antigenic.
Cell Wall: Thick and continuous barrier around all bacteria, except Mycoplasma
- Protects cell membrane from physical (such as bile salts) and osmotic damage
- Maintains shape
a. Spheres (cocci)
b. Rods (bacilli)
c. Spirals (spirochetes) - Forms a septum that separates daughter cells in cell division
- Interacts with host defense-is antigenic
5. Used in serological identification
6. Enzymes to make wall are targets for antibiotics
Explain the cell wall components of gram-positive bacteria.
What is autolysin?
Gram positive cell wall
a. Lipoteichoic acids (LTA): all gram (+) bacteria
- Polymers of ribitol or glycerol
linked to lipid and linked to peptidoglycan
- Negative charge sequesters cations (Ca2+, Mg2+, etc). have antimicrobial peptides that attack cell wall bc negatively charged
- Antigenic determinant, specific to each species
b. Peptidoglycan (murein, mucopeptide) - Backbone of β1,4-N-acetylmuramyl-N-acetylglucosamine (glycan)
- Autolysin cleaves peptidoglycan to allow new cell wall components in.
What is transpeptidation? Explain the details of this process.
-Tetrapeptides are cross-linked by transpeptidation: originally a pentapeptide;
L-lys in one peptide is linked via a polyglycine peptide to the subterminal D-ala on the next, releasing the terminal D-ala.
Tetrapeptides are bound to peptidoglycan structure.
Explain how penicillin, cephalosporin, and lysozyme work.
Where is lysozyme found naturally?
-Penicillin binds to the transpeptidase (a “penicillin binding protein”) because penicillin has the shape of the D-ala.
- Kills cell only if the cell is actively making cell wall
- Autolysin continues to open the cell wall
- Penicillin blocks insertion of new peptidoglycan
- Cell wall weakens and cell explodes.
No effect on cells that are not growing.
-Cephalosporins also block cell wall synthesis
Lysozyme cleaves the glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine
Kills bacteria
- Common enzyme in human tissues and secretions
- Natural antibacterial defense
Explain the difference in the peptidoglycan layer btwn gram positive and gram negative bacteria.
What is DAP (diaminopimelic acid)? Where is it found? In what bacteria? (gram neg, pos, both?)
Peptidoglycan layer in gram positive bacteria is much thicker than in gram negative. 25-30 layers in gram positive vs 3-5 in gram negative.
In the peptidoglycan of many gram (-) and some gram (+) bacteria, DAP (diaminopimelic acid, precursor of lys) replaces L-Lys.
State the layers of the cell wall/envelope of gram negative bacteria.
Explain what is contained in each layer and their functions.
Explain how one of the components of gram negative cell walls can induce fever.
Gram negative cell “envelope” (wall) is 2 lipid bilayers with a thin peptidoglycan monolayer between.
a. In the peptidoglycan of many gram (-) and some gram (+) bacteria, DAP (diaminopimelic acid, precursor of lys) replaces L-Lys
b. Outer lipid bilayer of gram negative envelope
- barrier, excludes hydrophilic compounds, some antibiotics
- lipoproteins covalently linked to the peptidoglycan
- outer membrane proteins
-
porins are the most abundant;
- Some are channels for small hydrophilic molecules
- Others mediate specific uptake of metabolites and iron
-
porins are the most abundant;
- endotoxin: lipopolysaccharide (LPS) is in the bacterial outer cell membrane
LPS–> macrophage–> IL-1–> hypothalamus fever, endotoxic shock.
See attached for LPS structure
lipid A is the most toxic component of the LPS molecule, required for insertion in the outer leaflet. Can change the number of FA on lipid A to make it less antigenic
Core: 2-keto-3-deoxyoctonic acid (KDO) and heptose sugars
O antigens: long polysaccharide chains (25-40) linked to the LPS core, are important for classification of Salmonella sp. Can modulate O antigen
c. Periplasmic space: between inner and outer membranes, contains:
- hydrolytic enzymes (nucleases, alkaline phosphatase)
- binding proteins for sugars, amino acids, and ions
- β-lactamase (enzyme that destroys penicillin)
d. Inner membrane is the plasma membrane
Explain how a gram stain is performed.
1) Fixation: Start with heat-fixed bacterial smear
2) Apply primary stain : Flood slide with crystal violet stain. (pos charged, binds to peptidoglycan within cell walls)
3) Apply mordant : Flood the slide with iodine.
(This is to fix the crystal violet so that it wont leave cells easily. Iodine is neg charged, forms complex with crystal violet)
4) Apply decolorizer : Flood slide with acetone or
alcohol. (Do not leave the decolorizer on too long or it may remove stain from the Gram-positive cells as well)
- Both (+) and (-) organisms take up crystal violet and iodine
- Complex is trapped inside (+) cell by 95% alcohol dehydration, due to reduced porosity of the thick cell wall: Gram (+) = violet
- Not trapped by thin peptidoglycan of gram (-) cell, alcohol extracts the complex.
5) Apply secondary stain (counterstain) : Flood slide with safranin.
6) Visualize : Gently blot the slide dry. It is now ready to
be viewed under oil immersion (1000x TM) with a bright-field compound microscope.
Explain the acid stain procedure.
What bacterium require acid stain? Why?
Expain the relationship btwn these kinds of bacteria and WBCs.
Acid-fast stain: Mycobacterium walls contain large amounts of waxes
- -Impervious to many harsh chemicals including acids.
- -WBC’s can’t kill them.
- -Cost to bacterium: grows slowly.
Mycobacterium are technically gram positive bacteria but do not stain well with gram stain due to mycolic acid: waxy lipid in cell wall (see PP).
Acid stain procedure:
- Carbolfuschin stain dyes all bacteria red
- Acid alcohol is applied for decolorizer (removed carbolfuschin from non-acid staining/acid-fast negative bacteria)
- Brilliant green or methylene blue is applied to color acid fast negative cells green or blue, respectively
State the structure and functions of the plasma membrane of bacteria.
Plasma membrane (limiting membrane around cell cytoplasm)
- Lipid bilayer, like a eukaryotic membrane
- Plasma membrane functions
- a. Osmotic barrier
- b. Active transport
- c. Respiratory chain components: like mitochondria
- Energy-tranducing systems, ATPase of proton pump-H+
- d. Biosynthesis of phospholipids, peptidoglycan, LPS, capsular polysaccharides
- e. Excretion of hydrolytic enzymes
What are flagella? What are their functions?
How do bacterial flagella work?
What are H-antigens?
Surface Appendages
-
Flagella move bacterium toward attractants, away from repellents (chemotaxis). Flagella functions: motility and adhesion. Note they are similar to cilia in humans but are very different structurally.
a. thrust for propulsion/swimming: rotation of the basal body of the propeller-like flagellum. Derives energy from proton gradient across the membrane
b. flagella can be sheared off and will regenerate
c. motility property used to classify bacteria
d. flagellar (H) antigens are species-specific. Used to identify and classify species (Salmonella)
What are pili? What are the two types and how do they differ?
What are their functions?
What role do they play in the ability to fight off bacteria by the immune system?
Pili are thin, hair-like appendages
a. Common pili (type I vs type IV)
- Protein at the tip of the pilus adheres to unique epithelial surface sugar: important role in colonization; virulence factor.
- Changeable - outflanks the immune system (gonococci)
- escape from phagocytosis
b. Sex pili: cell to cell adhesion for conjugation (DNA transfer)
Type I pilli:
- widely expressed in bacteria
- 7-8 nm in diameter
- several hundreds
- heteropolymeric mannose binding fibers
Type IV pilli:
- in gram pos and neg bacteria
- involved in adhesion and twitching motility
- 6-7 nm
- pimarily polar
- PilA is main filament protein (see PP-min 45 of lecture)
