MORPHOLOGY OF BACTERIA

1. ANSAR AHMAD PARAY…

4. Bacterial Cell wall
 Tough and rigid stracture,surrounding bacterium
 10-25 nm thick
 Weighs 20-25% of dry weight of cell.
 Peptido-glycan Polymer (amino acids + sugars)
 Unique to bacteria

5. Continue…
FUNCTIONS:
1. Protection
2. confers rigidity
3. accounts for shape of bacteria
4. takes part in cell division
5. site of action of several antibiotics
6. contains virulence factor

6. Gram positive and gram negative
bacterial cell wall.
characters Gram negative cell wall Gram positive cell wall
Gram reaction pstain red or pink Stains blue or purple
Peptidoglycan layer Thin (single-layered) Thick (multilayered)
Teichoic acids Absent Present in many
Periplasmic space present Absent
Outer membrane Present Absent
Lipopolysaccharide
(LPS) content
High Virtually none
Lipid and lipoprotein
content
High (due to presence of
outer membrane)
Low (acid-fast bacteria
have lipids linked to
peptidoglycan)

7. Continue…Mesosome Mesosome is less
prominent.
Mesosome is more
prominent.
Toxins produced Primarily Endotoxins Primarily Exotoxins
Resistance to physical
disruption
Low High
Susceptibility to
anionic detergents
Low High
Cell wall composition The cell wall is 70-120 Å
(ångström) thick; two
layered. Lipid content is
20-30% (high), Murein
content is 10-20% (low).
The cell wall is 100-120 Å
thick; single layered.
Lipid content of the cell
wall is low , whereas
Murein content is 70-
80% (higher).
Antibiotic Resistance More resistant
to antibiotics.
More susceptible to
antibiotics

8. positive Bacteria

9.  Outer membrane:
 Phospholipid layer ouside to thin peptidoglycan layer
 Protective barrier to cell wall
 Prevents loss of constituents

10. Cytoplasm matrix
 80% Water {20% Salts-Proteins)
 Osmotic Shock important
 DNA is circular, Haploid
 Advantages of 1N DNA over 2N DNA
 More efficient; grows quicker
 Mutations allow adaptation to environment quicker
 Plasmids; extra circular DNA
 Antibiotic Resistance
 No organelles (Mitochondria, Golgi, etc.)

11. CELL MEMBRANE/PLASMA
MEMBRANE
 Fluid mosac model is accepted model to describe its
stracture
 5-10 nm thick
 Essential for survival of bacteria
 Bilayer Phospholipid
 Site for metabolic proceses
 Water can penetrate
 Flexible
 Not strong, ruptures easily
 Osmotic Pressure created by cytoplasm

12. fluid mosaic model of a cell
membrane

13. Nucleoid
 Lack true nucleus
 Genetic material is located in irregularly shaped
region called nucleoid.
 No nuclear membrane or nucleolus
 Also bacteria posses extracellular DNA called plasmids
 DNA divide by binary fossion
 Posses super coiled circular ds DNA of 1mm length.

14. Capsule and slime layer
 Some bacteria posses a layer of viscous material lying
outside the cell wall called glycocalyx.
 When this glycocalyx layer is well organized not easily
washed off it is called Capsule
 When this layer is thin in form of loose material that
can be washed easily it is called slime layer

15. Function/uses
 Contribute to bacterial virulence
 Protects bacteria from phagocytosis
 Prevent cell from drying
 Prevents from action of lysozyme and bacteriophages
 Biofilm formation and adhension
 Source of nutrients
 Capsule as vaccine

17. FLAGELLA
 Flagellum (singular) is hair like helical structure
emerges from cell wall and cell membrane
 It is responsible for motility of the bacteria
 Size: thin 15-20nm in diameter.
 Flagella is not straight but is helical.
 It is composed of flagellin protein (globular
protein) and known as H antigen.
 Flagella has three parts. Basal body, Hook and
filament

18.  Arrangement basis for classification
 Monotrichous; 1 flagella
 Lophotrichous; tuft at one end
 Amphitrichous; both ends
 Peritrichous; all around bacteria

19. Fimbriae or pili:
 Fimbriae and Pili are filamentous structures composed
of protein (Pilin) that extend from the surface of a cell
and can have many functions.
 Fimbriae are found in gram negative as well as gram
positive bacteria but are shorter in length as compared
to pili.
 Pili are longer than fimbriae and there are only a few
per cell.

21. Pili
Characteristics Fimbriae Pili
Definition
Fimbriae are tiny bristle-
like fibers arising from
the surface of bacterial
cells.
Pili are hair like
microfibers that are thick
tubular structure made
up of pilin.
Length Shorter than pili Longer than fimbriae.
Diameter Thin Thicker than fimbriae.
Number
No. of fimbriae are 200-
400 per cell.
No of pili are less 1-10
per cell.
Made up of Fimbrillin protein. Pilin protein.
Found in
Both gram positive and
gram negative bacteria.
Only gram negative
bacteria.

22. Function
Responsible for cell to
surface attachment.
Specialized for
attachment i.e. enable
the cell to adhere the
surfaces of other
bacteria.
Responsible for
bacterial conjugation.
Two basic function of
pili. They are gene
transfer and
attachment.
Motility
Do not function in active
motility.
Type IV pili shows
twitching type of motility.
Receptors No receptors of other.
Serve as receptor for
certain viruses.
Examples
Salmonella typhimurium,
Shigella dysenteriae.
Escherichia coli,
Neisseria gonorrhoeae.

23. Bacterial spores
 These are dormant form of bacteria ,which are thick
walled and highly resistant .
 Spore formation (sporulation) occurs when nutrients,
such as sources of carbon and nitrogen are depleted.
 These are formed in unfavorable environmental
conditions .
 Bacterial spores formed within the parent cell are
called endospores.
 Sporulation (or sporogenesis) refers to process of
formation of spores from vegetative stage.
 Germination is the transformation of dormant spore
into active vegetative cell.

24.  Bacterial spores are highly resistant to
 Heat
 Dehydration
 Radiation and
 Chemicals.
 Examples of Spore forming Bacteria-
 Bacillus spp
 Clostridium spp

25. Structure of spore
 It comprises of several layers.
 From innermost to the outermost the layers are:
Core → Cortex → Coat → Exosporum

26. Thanks…