Dentistry Microbiology - Lecture 2 Spring 2024.pdf

1. Microbiology
Lecture 2
Spring 2024
Dr. Kareem Adel

2. Prokaryotic and Eukaryotic cells
• All living cells can be classified into two groups,
Prokaryotes and Eukaryotes
based on their ultrastructure.

4. Prokaryotes Eukaryotes
Size Typically small. Typically large.
Nucleus No nuclear membrane or nucleoli. True nucleus (nuclear membrane + nucleoli).
Organelles Absent Present, e.g. Golgi, mitochondria & endoplasmic
reticulum.
Cell wall Complex (contain Peptidoglycan
mainly)
Simple, if present (chitin, cellulose,….)
Ribosomes 70 S 80 S
Chromosome Single circular chromosome without
histones
Multiple linear chromosomes
with histones
Cell division &
reproduction
Asexual (Binary fission) Sexual (meiosis) & Asexual (mitosis)
Contain 1. Bacteria (eubacteria)
2. Archaeabacteria
1. Protozoa
2. Fungi
3. Plants
4. Animals

7. Scientific Nomenclature of Organisms
Binomial name (Linnaeus System)
Scientific names are “Italic or Underlined”.
Sometimes, the genus can be abbreviated in writing, but not in
pronunciation; e.g. E. coli
Genus species
CAPITAL SMALL
Staphylococcus aureus
Escherichia coli
Streptococcus mutans
Candida albicans
Homo sapiens

8. 1. Cell wall
2. Structures external to the cell wall
3. Structures internal to the cell wall
BACTERIAL CELL STRUCTURE

9. Bacterial cell wall
• The cell wall is the rigid layer, that lies just outside the plasma
membrane.
• The most important parts of a prokaryotic cell

10. Functions:
- Responsible for the Bacterial shape
-Protection from mechanical stress, osmotic pressure,
and toxic substances
- Contribute to pathogenicity
-Support for flagella.
- Used to differentiate bacteria into:
Gram positive and Gram negative

11. Structure of the bacterial cell wall
•The bacterial cell wall is composed of network of a unique
substance called peptidoglycan
• The backbone of this polymer is the glycan part which is
composed of alternating aminosugars N-acetylglucose
amine (NAG) & N-acetyl muramic acid (NAM), that are
linked together by glycosidic bonds.
• Each layer of the NAG-NAM are cross-linked with
transpeptide bond interlinked with a peptide bridge

14. LPS
Peptidoglycan
Cell membrane
Gram + Gram -

15. Gram positive cell wall
1. Several layers of peptidoglycan
Gram negative cell walls
1. Thin peptidoglycan "more susceptible to mechanical breakage”
2. Outer membrane: Outer layer → Lipopolysaccharide which is Unique
to the Gm -ve outer membrane

17. Difference between Gram + and Gram – cell wall
Gram negative
Gram positive
One-two layer
More than one layer (3-20)
Peptidoglycan
Less rigid
More rigid
Rigidity
Present
Absent
Lipopolysaccharide
Less susceptible
More susceptible
Digested by lysozyme
Less susceptible
More susceptible
Sensitivity to penicillin