Chapter 1 Morphology and properties of bacteria

Chapter 1 Morphology and properties of bacteria

Belong to the prokaryote kingdom,the absence of a nuclear membrane and mitotic apparatus and the absence of othe

r organelle besides the ribosome.

Belong to the prokaryote kingdom,the absence of a nuclear membrane and mitotic apparatus and the absence of othe

r organelle besides the ribosome.

Section 1 Size and shapes of bacteria

The unit of measurement is micrometer (μm)

Sizes

basic shapes

• Spherical: coccus• Straight rod: bacillus• Curved or spiral: vibrio or spirillum• Uncharacteristic (e.g., filamentous, pleomorphic, et

c.)

Arrangements

• cocci

In one plane: Diplococcus Streptococcus

In two planes: Tetrad

In three planes: Sarcina

In random planes:Staphylococcus

Cell Arrangement

Coccus Division in plane

（ Diplococcl ）

（ Chain ）

Neisseria

StreptococcusDivision in two planes

（ Tetrad ）

Sarcina

Division in three planes

（ Sarcina ）

Staphylococcus（ Clustor ）

Division in Multi- planes

Tetrad

（ 1 ） diplococcus

S. pneumoniae gonococcus

（ 2 ） streptococcus

α-hemolytic streptococcus

（ 3 ） staphylococcus

S. aureus

Arrangements

• Bacilli

Only in one plane

Bacillus

Streptobacillus

Coccobacillus

bacillus dysenteriae (gram staining)

Bacillus tuberculosis(acid fast stain)

Arrangements

• Spiral bacteria

in single cells

Section 2 Structures of Bacterial cells

• BasicCell wallCellular membraneCytoplasmnucleoid• SpecialCapsuleFlagellumPilusSpore

Bacterial structure

Cell wall-Components

Cell wall-Components

• Peptidoglycan Backbone: alternating N-acetylmuramic acid

(NAM) and N-acetylglucosamine (NAG)

A set of identical tetrapeptide side chains

A set of identical pentapeptide cross bridges(G+)

peptidoglycan

N-acetylglucosamineN-acetylmuramic acid

Staphylococcus aureus金黄色葡萄球菌

E.coli大肠杆菌

Lysozyme breaks this bond

pentaglycine bridge

L-alaD-gluL-lysD-alaD-ala

L-alaD-glu

m-DAPD-alaD-alapenicillin

Cell wall-Components

•Teichoic acid: Organisms: G+ bacteria

Types: the wall teichoic acidthe membrane teichoic acid

Function: acts as a specific antigenic determinantRelation to pathogenicity

Wall teichoic acid

(LTA)

Cell wall-Components

• Outer membrane

Organisms: G- bacteria Composition: Lipoprotein Lipid bilayer Lipopolysaccharide (LPS): lipid A core polysaccharide O-polysaccharide

Outer membrane

Functions:

prevents toxic materials from entering

functions as a harmful endotoxin

possesses the property of antigenic specificity

GlN-MurGlN-MurGlN-MurGlN-MurGlN-Mur GlN-Mur GlN-Mur Gln-Mur

GlN-MurGlN-MurGlN-MurGlN-MurGlN-Mur GlN-Mur GlN-Mur Gln-Mur

GRAM POSITIVEGRAM POSITIVE

GRAM NEGATIVEGRAM NEGATIVE

CytoplasmCytoplasm

CytoplasmCytoplasm

GlN-MurGlN-MurGlN-MurGlN-MurGlN-Mur GlN-Mur GlN-Mur Gln-Mur

Lipoteichoic acid Peptidoglycan-teichoic acid

Cytoplasmic membrane

Inner (cytoplasmic) membrane

Outer Membrane

Lipopolysaccharide

GlN-Mur GlN-Mur GlN-Mur GlN-Mur

Porin

Braun lipoprotein

Peri

plas

mic

spa

ce

Properties of the cell walls of Gram-positive and Gram-negative bacteria

Properties Gram-positive Gram-negative

Peptidoglycan Thicker Thinner

Teichoic acid Yes No

LPS (endotoxin) No Yes

Outer membrane No Yes

Results of enzyme digestion Protoplast Spheroplast

Cell wallFunctions• gives the bacterium its shape • Protecting the cell• Constituting major surface

antigens• Permitting the free diffusion of

low-molecular-weight hydrophilic compounds

• Having pathogenic material

Gram-positive

Gram-negative

The mechanism of some antibiotics

and enzymes killing bacteria • penicillin: Binds to transpeptidase and blocks the formation of whole cell wall of Gram-positive bacteria

•Lysozyme: Destroys the peptidoglycan by cleaving the β-1,4 glycosidic bonds between NAM and NAG

G- G+

N-acetylglucosamineN-acetylmuramic acid

Staphylococcus aureusE.coli

Lysozyme breaks this bond

pentaglycine bridge

L-alaD-gluL-lysD-alaD-ala

L-alaD-glu

m-DAPD-alaD-alapenicillin

G+ and G-

• Penicillin and cephalosporin

• Results of enzyme digestion:Protoplast Spheroplast

L forms

• Definition: bacteria that their peptidoglycan is destroyed or lost by various factors but they can survive under highly osmotic environment.

• Types: Protoplasts(G+) and spheroplasts (G-)• Shape: polymorphism • Staining property: gram-negative • Grow environment: high osmotic • Pathogenicity: chronic

A.Colony of normal bacteria B.fried egg colony of L-form bacteriaC.Granular colony of L-form bacteria

D.filamentous colony of L-form bacteria

• L forms are able to grow and divide

• Caused by antibiotic

• Some L forms can revert to the normal form upon removal of the inducing stimulus

producing chronic infections,being resistant to antibiotic treatment.

B.Cell membrane(Cytoplasmic membrane)

• Composition: composed primarily of proteins and lipids.

• It is a thin,elastic cytoplasmic

membrane,which is 5 ～ 10nm thick

• Visible in some ultrathin sections

• Examined with the electron

microscope

Function

active transport

respiratory chain component

biosynthesis

excretion