3 - Bacterial cell shape / gram-stain

What is used for bacterial identification?

Light microscopy

What to look for? in bacterial identification.

Size / shape / motility via flagella / spores / capsule / cell arrangement

What are the different types of cell arrangement? (4)

isolated cells / pairs of cells / chains / clumps

What bacteria is an example for ‘chains’ cell arrangement?

Streptococcus spp

What bacteria is an example for ‘pairs of rods’ cell arrangement?

Escherichia coli

What bacteria is an example for ‘cluster/clumps’ cell arrangement?

Staphylococcus spp

What are all types of stains?

Gram stain / flagella stain / capsule stain / spore stain

What do gram stains do?

Differentiate cell wall structure

Gram stain history

1884 by Christian Gram

Colour for Gram +ve?

Purple

Colour for Gram -ve?

Pink

Architecture of Gram -ve cell surfaces?

Diderm

Architecture of Gram +ve cell surfaces?

Monoderm

Gram stain process/ method:

1. Heat fix

2. Crystal violet

3. Fixed with Gram’s iodine

4. Decolourise with ethanol / acetone

5. Counterstain

What gives cell SHAPE of a bacteria?

Rigid structures

Biological functions of peptidoglycan:

rigid structure of wall gives cell shape / protect from osmotic lysis / withstand high internal osmotic pressure.

Which gram wall can withstand high internal pressure?

Gram +ve

Which gram wall can withstand lower internal pressure?

Gram -ve

What internal osmotic pressure can Gram +ve handle?

High internal pressure

What internal osmotic pressure can Gram -ve handle?

Lower internal pressure

What is retained if you boiled cells in strong detergent?

Largely intact peptidoglycan bag

How can u extract peptidoglycan from cells?

Boiling cells in strong detergent.

What are some weaknesses of peptidoglycan?

Lysozyme / antibiotics / bacteriophage lysins

Give an example of a bacteria that lacks peptidoglycan.

Mycoplasma genitalium / mycoplasma gallisepticum

What gives cells pleiomorphic structure?

Lack of peptidoglycan / no rigid cell walls

What is pleiomorphic?

Variable (cell) shape

What effects do antibiotics have on bacteria without peptidoglycan?

insensitive to antibiotics that target peptidoglycan

Location and function of sterols?

in cell membrane / for stability

What is needed for stability for cells without peptidoglycan?

Sterols

What is the basic structural feature of peptidoglycan?

Alternating amino sugars, form a glycan chain / covalently linked to peptide chains.

What are the amino sugars that form the glycan chain in peptidoglycan.

NAG / NAM

What does NAG stand for?

N-acetyl glucosamine

What does NAM stand for?

N-acetyl muramic acid

What does the inter-peptide chain do? (in peptidoglycan)

form a strong highly cross-linked structure

Is Gram +ve, homogenous or heterogeneous?

Homogeneous

Is Gram -ve, homogenous or heterogeneous?

Heterogeneous

What is the structure of Gram +ve bacteria?

Homogeneous / single thicker layer

What is the structure of Gram -ve bacteria?

Heterogeneous / multiple layers

What does the cell wall of Gram +ve bacteria consist of? (2 main molecules)

Peptidoglycan / teichoic acid (TA)

What are the different TA’s in Gram +ve bacteria?

Wall teichoic acid & Lipoteichoic acid / WTA & LTA

What is teichoic acid /TA ?

Polymer of glycerol 3C or ribitol 5C phosphate

Where is WTA found?

Covalently bonded to NAM in peptidoglycan

What does WTA stand for?

Wall teichoic acid

Where is LTA found?

embedded in membrane via a lipid component.

What does LTA stand for?

Lipoteichoic acid

What is in the outer membrane of the cell walls of Gram -ve bacteria?

Lipopolysaccharide (LPS) / proteins (porins) / lipids

What is on both sides of the PG layer in Gram -ve bacteria?

Periplasmic space

Where is the periplasmic space located?

Both sides of the PG layer of Gram -ve cell walls

What are the different types of shapes in bacteria?

Spiral / spirochetes / square & flat / star / absolutely huge

Structure of spiral shape bacteria

Rigid helix

Structure of spirochetes shape bacteria

Flexible / helical / v.long

Structure of star shape bacteria?

Flat / 6 pronged star shaped

Where is spirillum spp. found in?

water cooling tower / stagnant waters