Morphologically bacteria can resemble: Cocci (Singular: coccus) Bacilli (rods) (Singular: rod, bacillus) Vibrios (Singular: vibrio) Spirilla (Singular: spirillum) Spirochaetes (Singular: spirochaete) Morphology of Bacteria These are round or oval bacteria measuring about 0.5–1.0 um in diameter. When multiplying, cocci may form pairs, chains, or irregular groups: cocci in pairs are called diplococci, e.g. meningococci and gonococci. cocci in chains are called streptococci, e.g. Streptococcus pyogenes. cocci in irregular groups are called staphylococci, e.g. Staphylococcus aureus. Gram reaction: Staphylococci and streptococci are Gram-positive, whereas diplococci can be Gram-positive or Gram negative. When multiplying, bacterial rods do not usually remain attached to one another, but separate. Occasionally, however, they may: form chains, e.g. Streptobacillus species. form branching chains, e.g. lactobacilli. mass together, e.g. Mycobacterium leprae. remain attached at various angles resembling Chinese letters, e.g. Corynebacterium diphtheriae. The rods of the genera Bacillus and Clostridium are able to form resistant spores when conditions for vegetative growth are unfavorable. Many rods are motile having a single flagellum, or several flagella, at one or both ends or surrounding the entire organism. Gram reaction: Many rods are Gram-negative such as the large group of enterobacteria. Gram-positive rods include Clostridium species, Corynebacterium species, Bacillus anthracis, and Listeria monocytogenes. Note: Some coccobacilli, such as Yersinia species, show bipolar staining when stained with methylene blue or Giemsa. These are small slightly curved rods measuring 3–4 um in length by 0.5 um in width. Most vibrios are motile with a single flagellum at one end. They show rapid darting motility, e.g. Vibrio cholerae. Gram reaction: Vibrios are Gram-negative. These are small, regularly coiled, rigid organisms measuring about 3–4 um in length. Each coil measures about 1 um. Spirilla are motile with groups of flagella at both ends. An example of a spirillum is Spirillum minus. Gram reaction: Spirilla are Gram negative.

1. Sengamala Thayaar Educational Trust Women’s College
(Affiliated to Bharathidasan University)
(Accredited with ‘A’ Grade {3.45/4.00} By NAAC)
(An ISO 9001: 2015 Certified Institution)
Sundarakkottai, Mannargudi-614 016.
Thiruvarur (Dt.), Tamil Nadu, India.
MICROBIOLOGY
Mrs. T. TAMILVANI
ASSISTANT PROFESSOR
PG & RESEARCH DEPARTMENT OF MICROBIOLOGY

2. MORPHOLOGY OF BACTERIA
CONTENTS
➢ INTRODUCTION
➢ SIZE OF BACTERIA
➢ SHAPE OF BACTERIA
➢ ARRANGEMENTS OF BACTERIAL CELLS
➢ STRUCTURE OF BACTERIAL CELL

3. INTRODUCTION
Bacteria is unicellular, prokaryotic, free-living microscopic
microorganisms capable of performing all the essential
functions of life.
They possess both deoxyribonucleic acid (DNA) and
Ribonucleic acid (RNA).
They occur in water, soil, air, food, and all natural
environment (Omnipresent).
They can survive extremes of temperature, pH, oxygen, and
atmospheric pressure.

4. SIZE OF BACTERIA
• Bacteria are very small microorganisms which are
visible under the microscope.
• They are having the size range in microns.
• Bacteria are stained by staining reagents
and then visualized under high power of
magnification (1000X) of compound microscope.
• An electron microscope is used for clear
visualization of internal structure of bacteria.

5. SHAPE OF BACTERIA
• On the basis of shape bacteria are classified as
1. Cocci
2. Bacilli
3. Vibrios
4. Spirilla
5. Spirochetes
6. Actinomycetes
7. Mycoplasma

6. 1. Cocci
• Cocci are small, spherical or oval cells. In greek ‘Kokkos’ means
berry. Eg: micrococcus
2. Bacilli
• They are rod shaped cells. Eg: Bacillus anthracis.
• It is derived from greek word “ Bacillus” meaningstick.
• In some of the bacilli the length of cell may be equal to width.
Such bacillary forms are known as coccobacilli. Eg: Bracella.

7. 3. Vibrios
They are comma shapedcurved rods.Eg:Vibrio comma.
4. Spirilla
• They are longer rigid rods with several curves or coils.
• They have a helical shape and rigid body.
• Eg: Spirillum ruprem.

8. • 5. Spirochetes
They are slender and flexuous spiral forms.
6. Actinomycetes
The characteristic shape is due to the presence of rigid cell wall. Eg:
Streptomyces.
They are branching filamentous bacteria.
Eg: Streptomyces species.

9. • 7. Mycoplasma
• They are cell wall deficient bacteria and hence do not possess
stable morphology. They occur as round or oval bodies with
interlacing filaments.

10. ARRANGEMENT OF BACTERIAL CELLS
•Cocci appears as several characteristics arrangement or grouping.
1.Diplococci : They split in one plane and remains in
pair. Eg: diplococcus pneumoniae.
2.Streptococci :These cells divide in one planes and
remain attached , to form chains. Eg: streptococcus
lactis.
3.Tetracocci :They divide in two planes and live in groups
of four. Eg: Gaffyka tetragena.
4.Staphylococci : Cocci cells divide in three planes in
an irregular pattern. These cells produce bunches of
cocci as in grapes. Eg: staphylococcus aureus,
staphylococcus albus.
5.Sarcinae
• Sarcinae cells divide in three planes in a regular pattern.
• These cells produces a cuboidal arrangement of group of a eight cells.
• Eg: Micrococcus tetragena.

11. Bacterial Structures
• Flagella
• Pili
• Capsule
• Plasma Membrane
• Cytoplasm
• Cell Wall
• Ribosomes
• mesosomes
• Inclusions
• Spores

12. Flagella
• Flagella are long, slender, thin hair-like cytoplasmic
appendages, which are responsible for the motility of
bacteria.
• These are the organs of locomotion.
• They are 0.01 to 0.02 µm in diameter, 3 to 20 µm in length.
• Flagella are made up of a protein- flagellin.
• The flagellum has three basic parts ,
1. Filament
2. Hook
3. Basal body

13. • Filament is the thin, cylindrical, long
outermost region with a
• constant diameter.
• The filament is attached to a slightly wider
hook.
• The basal body is composed of a small
central rod inserted into a series of rings.
• Gram negative bacteria contain four rings as
L-ring, P-ring, S- ring, M-ring whereas gram
positive bacteria have only S and M rings in
basal body.

14. Types of flagella
• Flagella may be seen on bacterial body in following manner.
1. Monotrichous: These bacteria have single polar flagellum. Eg:
vibrio cholera
2. Lophotrichous: These bacteria have two or more flagella only
at one end of the cell. Eg: pseudomonas fluorescence.
3. Amphitrichous: These bacteria have single polar flagella or
tuft of flagella at both poles. Eg :Aquaspirillum serpens.
4. Peritrichous: Several flagella present all over the surface of
bacteria. Eg: Escherichia coli, Salmonella typhi.

15. CELL WALL
• Cell wall is rigid structure which gives definite shape to cell,
situated between the capsule and cytoplasmic membrane.
• It is about 10 – 20 nm in thickness and constitutes 20-30 % of
• dry weight of cell.
• The cell wall cannot be seen by direct light microscopy and does
not stain easily by different staining reagents.
• The cell wall of bacteria contains diaminopimelic acid (DAP),
muramic acid and teichoic acid. These substances are joined
together to give rise to a complex polymeric structure known as
peptidoglycan or murein or mucopeptide.
• Peptidoglycan is the major constituent of the cell wall of gram
positive bacteria (50 to 90 %) where as in gram negative bacterial
cell wall its presence is only 5 -10 %.

16. A comparison of cell walls of gram positive and gram negative bacteria

17. Gram stain
• Gram stain divides the bacteria into Gram positive & Gram negative.
• The basic procedure :
i. Take a heat fixed bacterial smear.
ii. Flood the smear with CRYSTALVIOLET or Methyl violet for 1 minute,
then wash with water. [PRIMARY STAIN]
iii. Flood the smear with IODINE for 1 minute, then wash with water.
iv. Flood the smear with ETHANOL-ACETONE, quickly, then wash
with water. [DECOLOR]
iii. Flood the smear with SAFRANIN for 1 minute, then wash with water.
[COUNTERSTAIN]
vi. Blot the smear, air dry and observe.

18. Crystalviolet
Gram's iodine
Decolorise with
acetone
Counterstain with
e.g. methyl red
Gram-positives
appear purple
Gram-negatives
appear pink
The Gram Stain

19. Gram-positive rods
Gram-negative rods
Gram-positive cocci
Gram-negative cocci
Gram-positiveCocci
• Staphylococci
• Staphylococcus aureus
• Staph. Epidermidis
• Gram-Negative Cocci
• Neisseria gonorrhoea
• Neisseria meningitides
• Enteric Bacteria
– E. coli
– Salmonella
– Shigella
– Yersinia
– Pseudomonas
– Proteus
– Vibrio cholerae
– Klebsiella
pneumoniae
Gram-Negative Bacilli

20. Classification: Dichotomous Key
Simple Stain
Cocci
Gram Stain
Gram
negative cocci
Gram
positive
cocci
Mannitol Salt
yellow pink
Staphylococcus
aureus
Staphylococcus
epidermis
Bacilli
Gram Stain
Gram
negative
bacilli
Gram positive bacilli
No
color
change
Salmonella
pullorum
Pink
colonies
E. coli
Enterobacter
aerogenes
Dr.T.V.RaoMD
Acid Fast stain
MacConkey’s
Acid Fast
Mycobacterium
tuberculosis
Not
acid
fast
Endospore stain
Forms
endospores
Bacillus subtilus
smegmatis
Since we will be
working with a
limited number
of bacterial
species and
identification
techniques, we
will be using a
limited
dichotemous key
in lab.
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