The document provides an overview of bacterial cell structures and morphology, emphasizing their unicellular and prokaryotic nature, as well as the characteristics of their cell walls and appendages. It details bacterial shapes, sizes, and arrangements, alongside a description of components like flagella and pili, highlighting their roles in motility and adherence. Additionally, it covers special structures such as endospores, focusing on their resilience and relevance in medicine.

1. MICROOBIOLOGY
Dr.S.Sundaresan
Tagore Medical College and Hospital

2. Bacterial Cell Structures &
Morphology

3. Bacteria are:
 Unicellular, prokaryotes
 Have both DNA and RNA
 Divide by Binary fission
 No mitochondria
 Rigid cell wall containing
peptidoglycan

4. Size matters
Animal cell
1 micron
10 microns
Bacterial cells

5. Bacterial Morphology and Structure

6. Bacterial Morphology
Morphology = shape (shape, size and
arrangement)
Size
 0.20 to 2.0 um in diameter
 2 to 8 um in length.
Shape
 spherical (coccus)
 rod (bacillus)
 spiral
 Pleomorphic (variable shapes)
Arrangement: can be:
Single, double . Chains, in groups or irregular

7. Common Shapes & Arrangement

8. Bacterial Morphology Arrangement
1. Bacilli
a.Streptobacilli
b. Bacilli
2. Cocci
a. Cocci
b. Diplococci
c. Streptococci
d. Staphylococci
e. Sarcina ( 3D )
f. Gaffkya( 2D )

9. Bacterial Cell Structure
 Surface layers - capsule, cell wall, cell
membrane
 Cytoplasm - nuclear material, ribosome,
mesosome, inclusions etc.
 Appendages - flagella, pili or fimbriae
 Special structure - Spore

10. Bacterial cells

11. Bacterial Cell Structure

12. General structure: mucopolysaccharide i.e.
peptidoglycan. It is made by N-acetylglucosamine
and N-acetylmuramic acid. The entire cell wall
structure is cross linked by covalent bonds.
It provides the rigidity necessary to maintain the
integrity of the cell.
* N-acetylmuramic acid is unique to prokaryotic cell.
2. Bacterial Cell Wall

13. (a). Gram positive bacterial cell wall
Thick peptidoglycan layer
pentaglycin cross linkage.
All have lipoteichoic acid.

14. (b) Gram -negative
 Thin peptidoglycan
 Tetrapeptide cross linkage
 A second membrane structure: protein and
lipopolysaccharide
 Toxicity : endotoxin on lipid A of lipopolysaccharide.
glucosamine- glucosamine-long
 polysaccharide- repeated sequences of a few .

15. Cell walls of bacteria(1)

16. Cell Membrane Function:
a. control permeability
b. transport e’s and protons for cellular metabolism
c. contain enzymes to synthesis and transport
cell wall substance and for metabolism
d. secret hydrolytic enzymes
e. regulate cell division.

17. III. Cytoplasm
80% water, nucleic acids, proteins, carbohydrates, lipid
and inorganic ions etc.
1. Bacterial chromosomes
a single large circular double stranded DNA no histone
proteins. The only proteins associated with the
bacterial chromosomes are the ones for DNA
replication, transcription etc.
2. Ribosome
protein synthesis

18. The bacterial chromosome and
supercoiling

19. 3. Mesosomes
A large invaginations of the plasma membrane,
irregular in shape.
a. increase in membrane surface, which may be
useful as a site for enzyme activity in respiration
and transport.
b. may participate in cell replication by serving as a
place of attachment for the bacterial chromosome.

20. 4. Inclusions
Not separate by a membrane but distinct.
Granules of various kinds:
* glycogen,
*polyhydroxybutyric acid droplets (PHB)
i.e. fat droplets
* inorganic metaphosphate (metachromatic granules) - in
general, starvation of cell for almost any nutrients
leads to the formation of this to serve as an
intracellular phosphate reservoir.

21. II. CELL SURFACE LAYER
1. Capsule or slime layer
Many bacteria are able to secrete material
that adheres to the bacterial cell but is
actually external to the cell.
It consists of polypeptide and
polysaccharide on bacilli. Most of them
have only polysaccharide. It is a protective
layer that resists host phagocytosis.
Medically important.

22. 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 which consists of set(s) of rings and rods
Gram - : 2 sets of ring and rods, L, P, S, M rings and
rods
e.g. E. coli
Gram + : S, M rings and rods
e.g. B. megaterium

23. Organ of bacterial locomotion

24. Structure of the flagellum

25. Flagella movement(1)

26. Flagella movement(2)

27. Flagella movement(3)

28. b).Origin (continued)
– The structure of the bacterial flagella allows it to spin
like a propeller and thereby propel the bacterial cell;
clockwise or counter clockwise ( Eucaryotic , wave
like motion.
– Bacterial flagella provides the bacterium with
mechanism for swimming toward or away from
chemical stimuli, a behavior is knows as
CHEMOTAXIX, chemosenors in the cell envelope
can detect certain chemicals and signal the flagella to
respond.

29. c). position
monotrichous
lophotrichous
peritrichous
d). structure
protein in nature: subunit flagellin

30. Flagellae

31. Flagellae

32. 2. Pili or Fimbriae
Shorter than flagella and straighter , smaller.
Only on some gram- bacteria.
a). function: adhere. One of the invasive
mechanism on bacteria. Some pathogens
cause diseases due to this. If mutant
(fimbriae) not virulent. Prevent
phagocytosis.

33. Important bacterial cell components
3: Pili (Fimbrae)
 Found on Gram negative
bacteria, shorter and finer than
flagella
 Two classes:
 ordinary pili ‘colonisation
antigens’. Protein,
attachment to host cells.
Can be involved in host
cell invasion e.g. Neisseria
meningitidis
 sex pili, role in conjugation
(transfer of plasmid DNA)

34. 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. In addition, number of
bacteria virus infect only those bacteria have F
pilus.

35. b). Origin: Cell membrane
c). Position: common pili , numerous over the cell,
usually called fimbriae sex pile, 1-4/cell
d). Structure: composed of proteins which can be
dissociated into smaller unit
Pilin . It belongs to a class of protein Lectin which
bond to cell surface polysaccharide.

36. IV. Special Structure
* Endospores
Spore former: sporobactobacilli and sporosarcinae - no
medical importance. bacillus and clostridium have
medical importance.
* Position: median, sub-terminal and terminal have
small water, high calcium content and dipicolinic acid
(calcium dipicolinate)
extremely resistant to heat, UV, chemicals etc. may be
due to many S containing A.A for disulfide groups.

37. Gram positive, bacillus,
anaerobic, spores
Clostridium spp

38. • After the active growth period approaching
the stationary growth phase, a structure
called forespore develops within the cells.
• It consists of coat, cortex and nuclear
structure.
The process of endospore
formation

39. Vegetative/spore-containing
cells(1)

40. Vegetative/spore-containing
cells(2)