Microbiology is the study of the biology of microscopic organisms - viruses, bacteria, algae, fungi, slime molds, and protozoa. The methods used to study and manipulate these minute and mostly unicellular organisms differ from those used in most other biological investigations

1. Mr. Osman H. Ali
B.Sc. Microbiology, MPH, HDCH
Bacterial Morphology & Anatomy

2. Introduction:
• Several classes of living organisms
• Based on the organization of their cellular structures,
all living cells can be divided into two groups:
eukaryotic and prokaryotic
 Eukaryotic cell types - Animals, plants, fungi,
protozoa, and algae
 Prokaryotic cell types - bacteria & blue green algae

3. Schematic of typical animal (eukaryotic) cell, showing subcellular
components.
Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle
(5) rough ER (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER
(9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome
(13) centrioles

4. Prokaryotic Cells
 Much smaller (microns) and more simple than
eukaryotes
 Prokaryotes are molecules surrounded by a membrane and
cell wall.
 They lack a true nucleus and don’t have membrane bound
organelles like Mitochondria, Golgi complex, etc.
 Large surface-to-volume ratio : nutrients can easily and
rapidly reach any part of the cells interior

5. Size of Bacteria
 Unit of measurement in bacteriology is the
micron / micrometre (µm)
 Bacteria of medical importance 0.2 – 1.5 µm in
diameter 3 – 5 µm in length

6. 1 micrometer (µm) = thousandth part of millimeter
= 10-3 mm
= 10-6 m
1 nanometer (nm) = thousandth part of micrometer
= 10-3 µm
= 10-6 mm
= 10-9 m
1Angstrom unit (A )= tenth part of nanometer
= 10-10 m

7. Shape of Bacteria
 Cocci – spherical/ oval shaped (major groups)
 Bacilli – rod shaped
 Vibrios – comma shaped
 Spirilla – rigid spiral forms
 Spirochetes – flexible spiral forms
 Actinomycetes – branching filamentous bacteria
 Mycoplasmas – lack cell wall

8. Arrangement of bacteria: Cocci
groups of eight - Sarcina
Cocci in cluster - Staphylococci
Coccus groups of four - Tetrad
In pair- Diplococcus
Cocci in chain - Streptococci

9. Arrangement of bacteria: Bacilli

10. Other shapes of bacteria
Vibrio Spirilla
Spirochetes

11. Anatomy of a Bacterial Cell

12. Anatomy of A Bacterial Cell
• Outer layer - two components:
1. Rigid cell wall
2. Cytoplasmic (Cell/ Plasma) membrane –
present beneath cell wall
• Cytoplasm - gel-like substance enclosed within the cell
membrane
contains cytoplasmic inclusions, ribosomes,
mesosomes and nucleoid
• Additional structures - plasmid, slime layer, capsule, flagella,
fimbriae (pili), spores

13. Structure & Function of Cell
Components

14. Cell Wall
 Outermost layer, encloses cytoplasmic membrane
1. Confers shape and rigidity
2. Peptidoglycan is responsible for the rigidity of the
bacterial cell wall and for the determination of cell
shape
3. 10 - 25 nm thick
4. Composed of Mucopeptide (peptidoglycan/ murein):
formed by N-acetyl glucosamine (NAG) & N-acetyl
muramic acid (NAM) alternating in chains, held by
peptide chains.

17.  Cell wall –
5. Can not be seen by direct light microscopy and do not
stain with simple stains.
6. Can be observed by plasmolysis
7. Carries bacterial antigens – important in virulence &
immunity.
8. Chemical nature of the cell wall helps to divide bacteria
into two broad groups – Gram positive & Gram negative
9. Gram +ve bacteria have simpler chemical nature than
Gram –ve bacteria.
10. Several antibiotics may interfere with cell wall synthesis
e.g. Penicillin, Cephalosporins

18. Gram positive cell wall
ram-positive cell
 wall
• The
thick, multilayered peptidoglycan
is composed
sheath outside
of a
of the
cytoplasmic membrane.
Teichoic acids embedded
extend into
in the
the
peptidoglycan, and lipoteichoic
are linked to and
acids
cytoplasmic membrane

19. Gram negative cell wall
• The Gram-negative cell wall is composed of an outer membrane linked
to thin single-layered peptidoglycan by lipoproteins.
•The peptidoglycan is located within the periplasmic space that is created
between the outer and inner membranes.
•The outer membrane includes porins, which allow the passage of small
hydrophilic molecules across the membrane, and lipopolysaccharide
molecules that extend into extracellular space.

20. Cell Wall

21. Property of bacteria Gram Positive Gram Negative
Thickness of wall 20-80 nm 10 nm
Number of layers in wall 1 2
Peptidoglycan content >50% 10-20%
Teichoic acid in wall + -
Lipid & lipoprotein content 0-3% 58%
Protein content 0% 9%
Lipopolysaccharide 0 13%
Sensitive to penicillin Yes Less sensitive
Digested by lysozyme Yes Weakly
Summary of the differences between Gram
positive & Gram negative bacteria

22. Cytoplasmic (Plasma) membrane
 Thin layer 5-10 nm, separates cell wall from cytoplasm
 Acts as a semipermeable membrane: controls the inflow
and outflow of metabolites
 Passage through membrane depends on:
Molecular size
Specific enzymes (permeases)
 Composed of lipoproteins with small amounts of
carbohydrates

25. Cytoplasm
 Colloidal system of variety of organic & inorganic
solutes in viscous watery solution
 Contains:
ribosomes,
mesosomes,
inclusions
vacuoles
Cytoplasm

26. Cytoplasmic Components
 Ribosomes Protein synthesis
70 S
Mesosomes –
1. Multilaminated structures formed as invaginations
of plasma membrane
2. Principal sites of respiratory enzymes
3. Coordinate nuclear & cytoplasmic division during binary fission
4. More prominent in Gram +ve bacteria
Intracytoplasmic inclusions
Reserve of energy & phosphate for cell metabolism
e.g. Metachromatic granules in diphtheria bacilli

27. Nucleus
 No nucleolus
 No nuclear membrane
 Oval or elongated bodies generally 1 per cell
 Genome –
 single, circular double stranded DNA.
 Haploid
 Divides by binary fission
Nucleus

28. Additional Organelles
1. Plasmid:
 Extranuclear genetic elements consisting of DNA
 Transmitted to daughter cells during binary fission
 May be transferred from one bacterium to another
 Not essential for life of the cell
 Confer certain properties e.g. drug resistance, toxicity

29. Additional Organelles
2. Capsule & Slime layer:
 Viscous layer secreted around the cell
wall.
 Polysaccharide / polypeptide in
nature
a) Capsule – sharply defined structure,
antigenic in nature
• Protects bacteria from lytic enzymes
• Inhibits phagocytosis
• Stained by negative staining using
India Ink
• Can be demonstrated by Quellung
reaction (capsule swelling reaction)
b) Slime layer – loose undemarcated
secretion

30. Capsular material:
Antigenic in nature
can be demonstrated by serological methods
Repeated subcultures in vitro lead to loss of capsule and also of
virulence.

31. Additional Organelles
3. Flagella –
 Long (3 to 12 µm), filamentous surface appendages
 Organs of locomotion present in motile bacteria
 Chemically, composed of proteins called flagellins
 The number and distribution of flagella on the bacterial
surface are characteristic for a given species - hence are
useful in identifying and classifying bacteria
 Flagella may serve as antigenic determinants (e.g. the H
antigens of Gram-negative enteric bacteria)
 Presence shown by motility e.g. hanging drop
preparation

32.  Each flagellum consists of 3 parts
1. Filament
2. Hook
3. Basal body

33. Types of flagellar arrangement
Polar/ Monotrichous – single
flagellum at one pole
Lophotrichous – tuft of flagella at one
pole
Amphitrichous – flagella at both
poles
Peritrichous – flagella all over
Amphilophotrichous – tuft of flagella at
both ends

35. Additional Organelles
4. Fimbriae/ Pili –
 Thin, hairlike appendages on the surface of many Gram
negative bacteria
 10-20µ long, acts as organs of adhesion (attachment) -
allowing bacteria to colonize environmental surfaces or
cells and resist flushing
 Made up of proteins called pilins.
 Pili can be of two types –
 Common pili - short & abundant
 Sex pili - small number (one to six), very long pili,
helps in conjugation (process of transfer of DNA)

37. Additional Organelles
5. Spores :
 Highly resistant resting stages formed during
adverse environment (depletion of nutrients)
 Formed inside the parent cell, hence called
Endospores
 Very resistant to heat, radiation and drying and can
remain
dormant for hundreds of years.

38. The cycle of spore formation and germination
At the beginning of spore formation, a septum forms, separating
the nascent spore from the rest of the cell and all of the genetic
material of the cell is copied into the newly-forming cell. The
spore contents are dehydrated and the protective outer coatings
are laid down. Once the spore is matured it is released from the
cell. On germination, the spore contents rehydrate and a new
bacterium emerges and multiplies.

39. Shape & position of bacterial spore
Oval central
Spherical central
Oval sub terminal
Oval sub terminal
Oval terminal
Spherical terminal
Free spore
Non bulging
Bulging

40. Pleomorphism & Involution forms
 Pleomorphism : great variation in shape & size of
individual cells
e.g. Proteus species
 Involution forms :
swollen & aberrant forms in ageing cultures, especially in the
presence of high salt concentration
e.g. plague bacillus
 Cause – defective cell wall synthesis
Involution forms can also be developed due to activity of
autolytic enzymes

41. Differences between prokaryotic & eukaryotic cells
Character Prokaryotes Eukaryotes
Nucleus Nuclear
membrane
Absent Present
Nucleolus Absent Present
Chromosome One circular One or more paired
and linear
Cell division Binary fission Mitosis
Cytoplasmic
membrane
Structure and
Composition
fluid phospholipid
bilayer, lacks sterols
fluid phospholipid
bilayer containing
sterols
Function Incapable of
endocytosis
(phagocytosis and
pinocytosis) and
exocytosis
Capable of
endocytosis and
exocytosis

42. Differences between prokaryotic & eukaryotic cells
Character Prokaryotes Eukaryotes
Cytoplasm Mitochondria Absent Present
Lysosomes Absent Present
Golgi
apparatus
Absent Present
Endoplasmic
reticulum
Absent Present
Vacuoles Absent Present
Ribosomes 70 S 80 S

43. Differences between prokaryotic & eukaryotic
cells
Character Prokaryotes Eukaryotes
Cell Wall Present Animals & Protozoans
– Absent
Plants, Fungi & Algae -
Present
Composition Peptidoglycan –
complex
carbohydrate
Cellulose or chitin
Locomotor
organelles
Flagella Flagella/ Cilia

44. Thank You !
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