Introduction and Brief about Bacteriology, Bacterial Structure, Difference Between Gram Positive and Gram Negative Bacteria, Flagellar structure, Cell wall Structure,

1. Bacteriology – 1
ZAG
Bacterial Structure, Gram positive and gram negative

2. Discovery of Bacteria
 Dutch Scientist “Antonie Leeuwenhoek” was the first
to report microbes in 1673, such as Bacteria and
protozoa.
 Robert Koch formulated “Germ theory of disease”.
He isolated typical rod shaped bacteria with squarish
ends from the blood of sheep that had died of
anthrax.
 Then he discovered bacteria that caused
tuberculosis and cholera.

3. Structure of bacteria; Size
 Bacteria range in size from 0.1 to 600 micro meter.
 The smallest (Mycoplasma) are about 100 to 200 nm
while the largest (E.coli), bacillus shaped, has an
average size of 1.1 to 1.5 wide by 2.0 to 6.0 micro
meter long.
 Some spirochetes ocassionally reach 500 micro
meter in length while staphylococci and streptococci
are 0.75 to 1.25 micro meter in diameter.

4. Structure of bacteria; Shape
 Bacteria are classified into these categories;
 Cocci : Spherical or oval shaped
 Staphylococcus, streptococcus, Diplococcus pneumoniae
 Bacilli : Rod Shaped
 Escherichia coli, Bacillus subtilis, Pseudomonas
 Spiral : Spirally coiled
 Spirochete
 Comma
 Vibrio Cholera

5. Bacterial Cell Wall Structure
 Cell Wall
 Cell wall is only absent in Mycoplasma.
 On the basis of Cell wall structural composition, bacteria
can be divided into two groups;
 Gram positive
 Gram negative

6. Characteristics Gram Positive Gram Negative
Chemical Make up Peptidoglycan (50% of dry
weight in some bacterial cell)
Techoic acid
Lipotechoic acid
Lipids (1-4%)
Peptidoglycan (10% of dry weight)
Lipoproteins
Lipopolysaccharides
Lipids (11-12%)
Thickness 20-80 nm 8-11 nm
Outer membrane No Yes
Periplasmic space Present in some Present in all
Permeability More permeable Less permeable
Stain Retention Retain the crystal violet stain
during gram staining
Retain safranin stain during gram
staining
Appearance under
microscope
Appear in purple color under the
microscope by staining
Give red to pink colour under the
microscope by staining
Basal Body of flagellum Two rings Four rings
Pilli No pilli Pilli are present
Examples Lactobacillus, Actinomyces,
Bacillus, Clostridium,
Corynebacterium,
Staphylococci, and
Streptococci
Acetobacter, Chlamydia, Borrelia,
Bortadella, Burkholderia,
Enterobacter, Escherichia,
Helicobacter, Klebsiella and
Neisseria

7. Flagella
 Extremely thin, hair like appendages, originate from basal body, made of
flagellin.
 On the basis of presence and number of flagella bacteria are classified as;
 Atrichous : Bacteria are without flagella
 Monotrichous : When single polar flagellum is present
 E.g. Vibrio cholrae
 Lophotrichous : If Tuft of flagella is present only at one pole of bacteria.
 E.g. Spirillum
 Amphitrichous : if tuft of flagella are present on each pole
 E.g. Alkaligens faecalis
 Peritrichous : Flagella sorrounds the whole cell
 E.g. Salmonella Typhi , Escherichia coli
 Cocci very rarely have flagella

8. Parts of Flagella
Each flagellum consists of three distinct parts- Filament, Hook and
Basal Body.
 The filament lies external to the cell.
 Hook is embedded in the cell envelope.
 Basal Body is attached to the cytoplasmic membrane by ring-like structures.

9. Slime / Capsule
 Many bacterial cells secrete some extracellular material in the
form of a capsule or a slime layer.
 A Slime layer is loosely associated with the bacterium and
can be easily washed off.
 whereas a Capsule is attached tightly to the bacterium and
has definite boundaries.
 Capsules are usually polymers of simple sugars
(polysaccharides), although the capsule of Bacillus
anthracis is made of polyglutamic acid.
 Examples of Capsulated bacteria are;
 E.coli
 Streptococcus pneumonae
 Bacillus anthrasis

10. Cysts
 Cysts are dormant, thick walled, desiccation
resistant forms.
 Develop during differentiation of vegetative cells
which can germinate under suitable conditions.
 They are not heat resistant.

11. Plasmids
 Many bacteria contain plasmid in addition to
chromosome.
 They are circular double stranded DNA molecules.
 Self replicating and are not essential for bacterial growth
and metabolism.
 They often contain drug resistant, heavy metals, disease,
and insect resistant genes on them
 Used as vectors.

12. Spores
 They are metabolically dormant bodies and are produced
at later stages of cell growth.
 Spores are resistant to adverse physical environmental
conditions such as light, high temperature, desiccation,
Ph and chemical agents.
 These are either internal (endospores) or external
(exospores).
 Under favourable conditions they germinate and form
vegetative cells.