The document provides a comprehensive overview of bacterial structure, highlighting essential components like the cell wall, plasma membrane, and nucleoid, as well as accessory features such as capsules, flagella, and plasmids. It details various characteristics of bacteria, their growth, physiology, metabolism, and the significance of these structures in identification and pathogenicity. Additionally, the document discusses topics like sterilization, disinfection, and genetics related to bacteria.

1. Bacterial Structure

2. Topic
1 Introduction
2 Structure
3 Growth, physiology & metabolism
4 Identification & tests
5 Sterilization & disinfection
6 Genetics
7 Microbiota
8 Pathogenesis
9 Communities
∞ Bacterial species

4. Characteristics
• Bacteria vary in size from 0.2 microns, but usually about 2 micron, it is
visible with the light microscope (resolving power 0.2 microns). “A red
blood cell measure 7 microns in diameter for comparison.” Bacteria
are prokaryote cells i.e. they have no nucleus, no organelles
(endoplasmic reticulum, mitochondria, Golgi apparatus, lysosomes)

5. • Essential components
Cell wall
Cytoplasmic membrane
Ribosome
Nucleoid
• Accessory components (not every bacteria has)
Capsule Biofilm
Flagella Spores
Plasmid Transposons
Pili & fimbria

8. Plasma membrane
• Phospholipids, proteins, Carbs
• No sterols (except mycoplasma)

9. Plasma membrane
• Thin, elastic and semi- permeable cytoplasmic
• Selective Barrier and transport
• Energy generation
• Synthesis of cell wall components
• Excretion of toxins

11. Cytoplasm
• Aqueous environment
• Nucleoid, ribosomes and numerous other protein and nucleotide
• Cytoskeleton
(filamentous protein)
Target for antibiotics

12. Nucleoid
• Double stranded circular supercoiled DNA

13. Ribosomes
• 70S, being composed of a 30S and a 50S
• Different than eukaryotes
Target for antibiotics!!

15. Inclusion bodies
• Granules
• For Storage, e.g. glycogen and starch
• Sites of viral multiplication in a bacterium

16. Cell Wall
• Rigidity and shape
• Osmotic changes tolerance
• Porous
• Consists of Peptidoglycans mainly

17. Peptidoglycan

18. Peptidoglycan
• Destroyed by lysozyme
• Contains D-alanine

20. Cell wall
• Gram positive vs Gram negative

22. Outer membrane of gram -ve
• Contains lipopolysaccharide (LPS)
• Endotoxin
• Heat stable

23. Lipopolysaccharide
Teichoic Acid &
Lipoteichoic Acid

28. Acid fast stain (Ziehl Neelsen stain)

30. • Some bacteria can not be stained because they are intracellular as
Chlamydiae & Rickettsiae.

31. Culturing Bacteria & Streaking Method

32. Capsule
• Consists largely of water with small solid content
• The solid material is a complex polysaccharide

33. Capsule
• Antiphagocytic
• Adherence
• E.g. to teeth (S.mutans)
• Antigenic
• Quellung reaction

34. Free slime / Glycocalyx / Biofilm
• Extracellular polysaccharide coat
• Adherence
• e.g.: heart valves, skin, catheters, surface of the teeth.

35. Flagella
• locomotor appendages
• Flagellin protein

36. Types of Flagellum
• Monotrichous (polar)
• Amphitrichous
• Lophotrichous
• Peritrichous
• Amphilophotrichous

37. Pseudomonas
Salmonella enterica

38. Pilli and Fimbriae
• Some pili (F pili) are called sex pili, they promote passage of large DNA
from one bacterium amounts to another.

39. Plasmid:
• Extra-chromosomal, circular dsDNA
• Replicate independent of bacterial chromosome
• Transmissible or non-transmissible plasmids
• contain genes that confer some properties such as antibiotic
resistance, virulence factors (exotoxin), genes for pili.
• Plasmids are not essential for cellular survival

40. Transposons:
• Pieces of DNA that moves from one site to another either within or
between the DNAs of bacteria, plasmids and bacteriophages
• “Jumping genes”
• Direct vs Replicative

41. Spores (Endospores)
• Dormant cell, Highly resistant structures are formed to adverse
conditions such as shortage or lack of nutrients
• Resistant to
Heat, drying irradiation, cold
Boiling >1 hrs
* Only moist heat (120 C for 20 minutes) will kill them

42. Spores
• Two peptidoglycan layers and outer keratin
• Impermeable of their cortex and outer coat
• Calcium and dipicolinic acid
• Low water content
• Only Gram +ve

43. Spores

45. Quiz
The main component of the capsule
a) Polysaccharides
b) Proteins
c) Water
d) Peptidoglycans

46. Quiz
Correct about endotoxins
a) Heat stable
b) Is found only in the cell wall of gram-positive bacteria
c) Is found only in the capsule of gram-negative bacteria
d) Made of Glycoproteins

47. Quiz
Which of the following bacterial components is essential
a) Cell wall
b) Capsule
c) Biofilm
d) Spores

48. Quiz
Wrong about spores
a) Method of bacterial reproduction
b) Heat resistant
c) Low water content
d) Are non essential

49. Questions?