glycocalyxcell wall

plasma membrane

Cytoplasmicor cell membrane

Cell cytoplasm

fimbriae

pili

LABCONCEPT 5.1

Prokaryotic Cell

Features not present on all cells

2 types of Bacterial Cell Walls LABFACT 5.1

glycocalyx

(1) Gram-positive cell wall (2) Gram-negative cell wall

Gram-positive bacteria Gram-negative bacteria

glycocalyx

What is peptidoglycan ?

Sugarbackbone

Tetrapeptide(amino acid)crossbridge

Connecting chainof amino acids

Figure 3.13 Possible structure of peptidoglycan.

peptidoglycan

Gram-positive bacteria

Gram-negative bacteria

LABFACT 5.1

Peptidoglycan layer

(cell wall)

Gram-positive bacterial cell wall

Cytoplasmic

membrane

Teichoic acid

Lipoteichoic acid

Integral

protein

Cell wall = thick layer of peptidoglycanCell wall contains unique polyalcohols called teichoic acids

Appear purplefollowing Gram

staining procedure

LABFACT 5.1

Integral

proteins

Outer

membrane

of cell wall

Peptidoglycan

layer of cell wall

Cytoplasmic

membrane

Lipopolysaccharide

(LPS) layer, containing

lipid A

Porin

Porin

(sectioned)

Periplasmic space

Phospholipid layers

Cell wall = a thin layer of peptidoglycan + Outer membrane or OM

OM is a phospholipid bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)

OM is protective - may impede the treatment of disease

Lipid A portion of LPS can cause fever, vasodilation, inflammation, shock, and blood clotting

Gram-Negative Bacterial Cell Walls

Appear pinkfollowing Gram

staining procedure

LABFACT 5.1

Gram-Positive vs Gram-Negative Bacterial Cell Walls

Gram-Positive Gram-Negative

Peptidoglycan PRS – THICK PRS – THIN

Outer Membrane PRS

Periplasmic Space PRS - ONE PRS - TWO

LPS (lipopolysaccharide)

ABS PRS

Porin ABS PRS

Techoic Acid PRS ABS

PRS = PRESENTABS= ABSENT

LABFACT 5.1

Gram-positive bacteria

Gram-negative bacteria

How to perform Gram Staining Reaction ?

purple

pink

LABFACT 5.2

Thick peptidoglycan in cell wall

Thin peptidoglycanin cell wall

Thick peptidoglycan prevents decolorization

Mechanism behind Gram Staining Reaction LABFACT 5.3

Gram Staining Method

Crystal Violet

Primary Stain Step

Gram positive cell wall

Gram negative cell wall

LABFACT 5.3

Gram Staining Method

Gram’s Iodine

Mordant Step

Gram Staining Method

Alcohol

Decolorizing Step

25 sec

Gram Staining Method

Safranin

Counter Stain Step

Gram Staining

Simple/Differential Stain ?

Peptidoglycan layer

(cell wall)

Gram-positive cell wall

Cytoplasmic

membrane

Teichoic acid

Lipoteichoic acid

Integral

proteinSome gram positive bacteria have up to 60% mycolic acid (waxy lipids) which helps cells survive desiccation – called Acid Fast bacteria

Acid Fast bacteria cell wall

mycolic acid

Acid Fast Bacterial Cell Wall LABFACT 6.1

LABCONCEPT 6.1

Some Gram positive bacteria cannot be stained by Gram staining procedure

They have a waxy lipid called mycolic acid in their cell wall (60 %)

which prevents water-soluble stains from penetrating the cell wall

mycolic acid

Acid Fast bacteria cell wall

LABFACT 6.1

LABCONCEPT 6.1Acid Fast Bacterial Cell Wall

Acid-Fast Staining Method

HEAT

Carbolfuchsin

Primary Stain StepZiehl-Neelsen Method

How to perform Acid-Fast Staining Method ?

Mechanism behind Acid-Fast Staining Method

LABCONCEPT 6.2

Acid-Fast Staining Method

Acid Alcohol

Acid-Fast

Non Acid-Fast

Decolorizing Step

Acid Fast Staining Method

Methylene Blue

Counter Stain Step

prs in Cytoplasm of some Bacteria

• Unique structures produced by some bacteria

• Those which make endospores also make endotoxins

• E.g. bacteria causing anthrax, tetanus, gangrene

• Defensive strategy against unfavorable conditions

• Vegetative cells transform into endospores when multiple nutrients are limited

• Resistant to extreme conditions such as heat, radiation, chemicals

EndosporesLABFACT 7.1

LABCONCEPT 7.1

In canning industry heat is used to kill microorganisms inside cans – but endospore

containing bacteria can survive heat

Why are endospore making bacteria dangerous ?

Vegetative Bacterial Cell Endospore Free spore

Environmental Challenges

Heat

Chemical

Starvation

Spore germinates

LABFACT 7.2

Vegetative Bacterial Cell Endospore Free spore

Spore germinates

1 1

1 1Bacteria Bacteria

Spores are not part of bacterial reproductive cycle

Endospore

bacterial reproduction is 1 bacteria = 2 bacteria

Spores are metabolically inactive with tough special cell walls

Location of endospores unique for different

spore-forming bacteria

LABFACT 7.3

Schaeffer-Fulton Staining Method for Endospores

HEAT

Malachite Green

Primary Stain Step

Vegetative Bacterial Cell

Endospore containingLABFACT 7.4

Schaeffer Fulton Staining Method for Endospores

Water

Decolorizing Step

NO HEAT

X

Vegetative Bacterial Cell

Endospore containing

Schaeffer Fulton Staining Method for Endospores

Safranin

Vegetative Bacterial Cell

Endospore containing

Vegetative Bacterial Cell

Endospore containingCounter Stain Step

Crystal Violet Staining LABFACT 7.5

External Structures of Bacterial Cells

• Glycocalyces

• Structure - Gelatinous, sticky substance surrounding the outside of the cell. Composed of polysaccharides or polypeptides, or both

• Function 1) avoid dessication

2) adhesion,

3) protect from host defense

glycocalyx cell wall

cell membranecell membranebacteria

LABCONCEPT 8.1

A Type of Glycocalyces

(1) Capsule

• Firmly attached to cell surface

• Prevent bacteria from being recognized

by host – avoid phagocytosis by immune

cells

Capsule enhances the

ability of bacteria to

cause disease

LABFACT 8.1

Figure 14.8 Relative virulence of some microbial pathogens.

Virulence

Degree of

pathogenicity – not

about severity of

the disease it

causes

But how easily it

causes disease

LABCONCEPT 8.2

Capsule enhances the ability

of bacteria to cause disease –

makes them more virulent

LABCONCEPT 8.3

Observe Capsule stained slide