This document discusses the structures and morphology of bacteria. It describes several key bacterial structures including chromosomes, ribosomes, flagella, pili, plasmids, cell membranes, cell walls, and capsules. It notes the different shapes bacteria can take including coccus, bacillus, coccobacillus, and various helical or curved shapes. The functions of appendages like flagella and pili are explained. Gram positive and Gram negative cell wall structures are compared. Bacteria sizes are typically smaller than eukaryotic cells.

1. 1
2020-2021
Introduction in
Medical microbiology
Lecturer Hussein Ali Kadhum
husseinalikadhum@alkafeel.edu.iq
Stage: 3rd Class- College of Dentistry

2. Bacterial Morphology Arrangement

3. 1- chromosomes: a thread like structure of nucleic acids and protein found in the nucleus of most living
cells, carrying genetic information in the form of genes.
2- pilus ( fimbria) : a series of threads Bacterial colonization involves multiple factors, including
fimbriae or pili, flagella.
3- Ribosomes: a minute particle consisting of RNA and associated proteins, found in large numbers in
the cytoplasm of living cells. They bind messenger RNA and transfer RNA to synthesize polypeptides
and proteins.
4- Flagellum : a slender threadlike structure, especially a microscopic whip like appendage that enables
many protozoa, bacteria, etc., to swim.

4. 5- Plasmid : a genetic structure in a cell that can replicate independently of the chromosomes, typically
a small circular DNA strand in the cytoplasm of a bacterium or protozoan. Plasmids are much used in the
laboratory .manipulation of genes.
6- Cell membrane : the semipermeable membrane surrounding the cytoplasm of a cell.
7- Cell wall : a rigid layer of polysaccharides lying outside the plasma membrane of the cells of plants,
fungi, and bacteria.
8- Capsule or slime layer : is considered a virulence factor because it enhances the ability of bacteria to
cause disease (e.g. prevents phagocytosis). The capsule can protect cells from engulfment by eukaryotic
cells, such as macrophages. ... Capsules also contain water which protects the bacteria against
desiccation.

5. 5
Bacterial Shapes, Arrangements, and Sizes
Variety in shape, size, and arrangement but typically described by one of three basic shapes:
1- coccus - spherical
2- bacillus – rod
3- coccobacillus – very short and plump ( Brucella abortus)
Streptobacilli ( Bacillus subtilus)
diplobacilli
spirillum - helical, comma, twisted rod,
spirochete – spring-like- flexible ( Treponema pallidum)
vibrio – gently curved ( Vibrio cholera)
Spirilla- rigid ( Borrelia species)
Pleomorphic : variable in shape ( Corynebacterium)

6. Shapes of Bacteria

7. Streptococcus sp.

8. Bacterial morphologies (2)

9. Bacterial morphologies (3)

10. Bacterial Cell Structures & Functions
Pili

11. Bacterial Cell Structure
 Appendages ‫الزوائد‬
flagella, pili or fimbriae
 Surface layers ‫السطحية‬ ‫الطبقات‬
capsule, cell wall, cell membrane
 Cytoplasm
nuclear material, ribosome, mesosome, inclusions etc.
 Special structure
endospore

12. Appendages
1. flagella
Some rods and spiral form have this.
a). function: motility
b). origin : cell membrane flagella attach to the cell by hook and basal
body
e.g. E. coli G

13. Flagella
Motility - movement
Swarming occurs with some bacteria
Spread across Petri Dish
Proteus species most evident
Arrangement basis for classification
Monotrichous; 1 flagella
Lophotrichous; tuft at one end
Amphitrichous; both ends
Peritrichous; all around bacteria

15. 2. Fimbriae and Pili
Fimbriae: Shorter than flagella , smaller, hair like appendages
. Only on some gram- bacteria.
a). function: adhere. Not involve in motility. One of the
invasive mechanism on bacteria. Some pathogens cause
diseases due to this (Antigenic characteristic). Prevent
phagocytosis.

16. pili - sex factor. If they make pili, they are + or donors of F
factor.
It is necessary for bacterial conjugation resulting in the transfer
of DNA from one cell to another.
It have been implicated in the ability of bacteria to recognize
specific receptor sites on the host cell membrane.

17. Conjugation in E. coli

18. CELL SURFACE LAYER

19. Capsules can serve numerous functions including
-Virulence factors, protecting bacteria from phagocytosis by immune cells. Pathogens
such as Streptococcus pneumoniae can cause pneumonia if protected by a capsule.
-Permit bacteria to adhere to cell surfaces and structures
-Capsules can be a source of nutrients and energy to microbes. Streptococcus mutans,
which colonizes teeth, ferments the sugar in the capsule and acid byproducts
contribute to tooth decay.
-Prevent cell from drying out .

20. Bacterial cell wall
The cell wall is the outer most component
common to all bacteria some bacteria have
surface feature external to the cell wall, such as
a capsule, flagella and pilli.

21. Functions of the cell wall
- maintains cell shape .
- Acts as a barrier, protects cell contents from external environment .
- maintains cell integrity/osmotic pressure in a hypotonic environment.
- Determines reactivity to Gram stain.
- Attachment site for flagella.
-Contributes to sensitivity to certain antimicrobial agents and the immune system
(antibodies, phagocytes).

22. Gram positive cell walls
Consist of a relatively thick layer of
exposed peptidoglycan (60-90% of the
cell wall) .
Bacteria have something very similar to
a 'roof over their head' called a cell
wall. ... The peptidoglycan layer acts as
the cell wall's backbone, offering
strength to the cell wall. The
peptidoglycan layer is able to allow
sugars, amino acids, and other ions into
the cell as needed.

23. Gram positive cell walls

cells stain purple due to retention of the crystal
violet dye during the gram stain procedure.

Antigens called teichoic acids project out of the
cell wall and aid in typing different gram
positive bacteria. It is a polymer of glycerol or
ribitol joined by phosphate groups , and
cause septic shock.

24. Structure of the Gram-positive Cell Wall

25. EUKARYOTIC
PROKARYOTIC
Most common
Simplest form
Possess membrane
bound structures
and a nucleus
Lack membrane
bound structures
Lack true nucleus
Found in most living
things
Example: bacteria
and cyanobacteria
Prokaryotic vs Eukaryotic

26. Sizes of Cells
• Eukaryotic : are usually larger than
prokaryotic
• Both nutrients and wastes are constantly entering
and exiting cells.
• Vary in size and shape.

27. 27
2020-2021
Thank you