Morphology and Anatomy
Of Bacteria
Lec. 3
M.Sc. Shahalaa Ali
MAIN TOPICS
 At the end of the Lecture , the students will be able to
understand:
1- Classification of bacteria depending on their morphology and
Gram staining property.
2- Anatomy of Bacterial Cell.
3- Various Bacterial cell appendages and their functions.
Classification of bacteria depending on their morphology and
Gram staining property.
 Most clinically relevant bacterial species range in size from 0.25 to 1 um in
width and to 3 um in length ,
 Thus requiring microscopy for visualization.
 Just as bacterial species and genera vary in their metabolic processes ,
their cells also vary in size , morphology and cell – to –cell arrangements
and chemical composition and structure of the cell wall.
 Bacterial cell wall differences provide the basis for the Gram stain , a
fundamental staining technique used in bacterial identification schemes.
 This staining procedure separates almost all medically relevant bacteria
into two general types:
1- gram –positive bacteria ( deep blue or purple)
2- gram – negative bacteria ( pink to red )
Shape of Bacteria
.Cocci – arranged in group (clusters ) , pair or chains .
.Bacilli – arranged in chain , pair , and some bacilli are curved ,
comma shaped , or cuneiform shaped .
Anatomy of Bacteria cell
 Structure of Bacterial Cell
A- Cell Envelope
1- Cell Wall
2- Cell membrane ( plasma membrane , Cytoplasmic membrane )
B- Cytoplasm
1- Nucleoid
2- Ribosomes
3- Granules / Inclusion bodies
4- Mesosomes
5- Spores
6- Plasmids
C- Appendages
1- Pilli
2- Flagella
3- Capsule
Cell Wall
 Is a tough & rigid structure surrounding the bacterium like a shell .
 Weighs about 20-25 % of the dry weight of the cell .
 Functions :
 Accounts for shape of cell.
 Provides protection to the cell against osmotic damage .
 Confers rigidity upon bacteria .
 Takes part in cell division .
 Possesses target site for antibiotics , lysozymes and bacteriophages
 Carries bacterial antigens that are important in virulence and
immunity .
S . No. Character 1 Thickness 2 Periplasmic space 3 Lipids 4 Teichoic acid 5 Peptidoglycan Gram Positive Thicker Absent Absent or small Present 16-80nm Gram Negative
Thinner
Present
Present
Absent
2nm
Gram Positive Cell Wall
 Peptidoglycan : thicker (16-80nm) than gram negative bacteria
(2nm).
 Teichoic acid :
1- Contains in a significant amount which is absent in gram negative .
2- Constitute major surface Ags .
3- Two types (wall teichoic acid and lipoteichoic acid ) .
Gram Negative Cell Wall
 Gram negative cell wall components
-Lipoprotein layer
-Outer membrane
complex structure with following
-LPS (Lipopolysaccharide) :
1- constitutes endotoxin of GNB
2- Determine major surface Ag
3- Toxicity (pyrogenicity , lethal effect , tissue necrosis )
-Periplasmic space
-Peptidoglycan
. Lipoprotein Layer:
- Connects the peptidoglycan to outer membrane
- . Outer membrane :
- Contains certain proteins called as OMP (outer membrane protein) .
- Target sites for phages , antibiotics and bacteriocins .
- .Lipopolysaccharides ( LPS ) :
- Consist of lipid A attached to a polysaccharide.
-Constitutes the endotoxin of GNB .
- . Periplasmic space :
- Space between inner and outer membrane.
- Contains various binding proteins for specific substrates.
Peptidoglycan :
Rigid part of cell wall peptidoglycan mucopeptide( murein)
composed of N-acetyl muramic acid and N-acetyl glucosaminde
alternating in chains ,cross linked by peptide subunits.
Bacterial with Defective Cell Wall
 Synthesis of cell wall interfered or inhibited by many factors :
_ Antibiotics
_ Bacteriophage
_ Lysozyme
Cell membrane : Cytoplasmic Membrane
. Is 5-10nm thick elastic semipermeable layer lies beneath for
separating it from cell cytoplasm .
. Acts as an osmotic barrier .
. Acts as a semipermeable membrane controlling the inflow and
outflow of metabolites to and from the protoplasm .
. Contains enzymes necessary for cell wall synthesis (cytochrome
oxidase , enzymes of tricarboxylic acid ) .
Cytoplasm
 Is a colloidal system containing variety of organic and inorganic
solutes in a viscous watery solution .
 Lacks:
1- Mitochondria
2- Endoplasmic reticulum
 Contains:
1- 70% water of bacterial mass.
2- Ribosomes .
3- Mesosomes
4- Vacuoles.
5- Inclusions
Ribosomes
 Centre for protein synthesis.
 Are composed of
1- Ribosomal RNA (rRNA)
2-Ribosomal proteins.
Intracytoplasmic inclusions
1- Source of stored energy
2- Are grow under conditions of nutritional deficiency and disappear
when deficient nutrients are supplied .
3- Volutin or metachromatic granules are +nt in C. dipyheria.
Nucleoid
 Bacteria don’t have true nucleus and there is no
nuclear membrane or nucleolus.
 Nucleiod is present irregularly shaped region
containing DNA.
 Bacterial DNA is haploid replicates by
simple binary fission and maintains bacterial genetic
characteristics.
 Some bacteria may possess extra- nuclear genetic
material in the cytoplasm consisting of DNA named as
Plasmids or episomes .
Capsule and Slime layer
 Is amorphous viscid bacterial secretion of bacteria
surrounds outer layer
 when diffuses into surrounding medium and remains as a loose
under marcated secretion as “Slime layer” when it is
organized into a defined structure known as “Capsule”
.
 FUNCTIONS:
1- Antiphagocytic in nature.
2- Antigenic.
3- Virulence.
Flagella :
 Cytoplasmic appendages protruding through cell wall.
 Composed of a protein (flagellin) (5-20um in length and 0.01-
0.02um in diameter) .
 Organ of locomotion.
 All motile bacteria contains either one or more flagella .
Part and composition :
. Three parts:
1- Flament
2- Hook
3- Basal body
Arrangements / types
1 –Monotrichous.
2- Amphitrichous.
3- Lophotrichous.
4- Peritrichous.
Fimbriae
Hair like appendage projecting from cell surface
-Also called as “Pili”
.
-Composed of protein called pilin.
-Unrelated to motility.
- Functions: 1-Adhesion .2- Transfer of genetic material.
Endospores
 Are highly resistant resting stage formed in unfavorate
environmental conditions .
- Depletion of nutrients.
- .Sporulation is not a method of reproduction as bacteria
is not divide during sporulation .
- .each vegetative cells one spore one
vegetative bacterium.
Morphology of Spore
1- Core
2- Forespore
3- Spore membrane
4- Spore cortex
5- Spore coat
6- Exosporium