GCMP2022 INTRODUCTION TO BACTERIA

INTRODUCTION TO
BACTERIA

Prepared by;

SITI ZAIRINI AHMAD
TUTOR OF NURSING
ILKKM KUBANG KERIAN

LEARNING OUTCOME

At the end of this learning session, the students will be
able to
1. Describe the classification of bacteria
2. Describe the structure and function of bacterial

cells
3. Explain factors influencing growth and reproduction

of bacteria

CLASSIFICATION OF BACTERIA

• Medically important bacteria can be subdivided into five main groups according to
their cell shape (morphology) and staining reactions.

• The basic shapes of bacteria include cocci, bacilli, and spiral and variable shaped
(pleomorphic) forms. Each of these morphological forms is further subdivided by
their staining reactions, predominantly the Gram and acid-fast stains. Bacteria are
divided primarily into Gram-positive or Gram-negative microorganisms.

• Other characteristics, including the ability to grow in the presence (aerobic) or
absence (anaerobic) of oxygen, spore formation and motility, are used to divide
the groups further. Subdivision of these groups into genera is made on the basis of
various factors, including culture properties (e.g. conditions required for growth
and colonial morphology), antigenic properties and biochemical reactions. The
medically important genera based on this classification are shown in Table 2.2
(Gram-positives) and Table 2.3 (Gram-negatives).

CLASSIFICATION OF BACTERIA

BACTERIA

SHAPE GRAM STAIN

COCCI BACILLI SPIRILLA VIBRIOS SPIROCHATES NEGATIVE POSITIVE



COCCI

• The cocci (kokkos, berry) are oval or spherical
cells

• These may be arranged in;
- Cocus – Single-celled
- Diplococci – Occur in pairs - pneumococci,
meningococci, gonococci
- Tetrads – Group of four cocci - micrococci
- Sarcina – Cube-like shape –
- Streptococci – Chains-like morphology
- Spathylococci – Grape-like cluster

COCCI

• Strongly gram-positive
• Ferments many carbohydrates

with the production of lactic
acid but no gas
• Non-motile
• Non-spore forming

BACILLI

• The bacilli (bacillus, rod) are rod
shaped.

• These bacilli may show either of the
following arrangement

- Coccobacilli: Length of the bacteria is
approximately the same as its width,
e.g., Brucella.

- Streptobacilli: These are arranged in
chains, e.g., Streptobacillus.

BACILLI

• Gram-positive, endospore-forming, motile
rods

• Mostly saprobic
• Aerobic and catalase positive
• Versatile in degrading complex

macromolecules
• Source of antibiotics
• Primary habitat is soil
• 2 species of medical importance are

Bacillus anthracis and Bacillus cereus

SPIRILLA

• Spirilla: They exhibit rigid spiral
forms, e.g., Spirillum.

• Rigid spirally curved elongate
bacteria

• Spirillaceae is a family of bacteria
Spirochaetes

• It has been described as a
member of Nitrosomonadales, in
Betaproteobacteria

SPIRILLA

• Gram-negative bacteria
• Long, helically coiled (spiral shaped) cells
• Chemoheterotrophic
• Lengths between 5 and 250um and

diameter around 0.1 – 0.6um
• Differ from other bacteria – its flagella /

axial filament ae located between the
inner membrane and outer membrane in
periplasmic space

VIBRIOS

• Comma shaped: They exhibit
curved appearance, e.g., Vibrio.

• Gram-negative, highly motile
curved rods, polar flagella

• Oxidase-positive

• Facultative anaerobic
• Tolerant to alkali but not to acid

SPIROCHATES

• Spirochetes (spira, coil;
chaite, hair) are slender,
flexuous spiral forms, e.g.,
Treponema

• Gram-negative

• Motile long helical corkscrew
appearance

SPIROCHATES

• Spirochetes flagella –
endoflagella

• Aerobic & facultative anaerobes
• Reproduce by transverse fission
• Contains one outer sheath of

glycosaminoglycans
• Contain series of cytoplasmic

tubules (body fibrils)

CLASSIFICATION OF BACTERIA

BACTERIA

SHAPE GRAM STAIN

COCCI BACILLI SPIRILLA VIBRIOS SPIROCHATES NEGATIVE POSITIVE

GRAM POSITIVE

• Gram-positive bacteria are
those that are stained dark
blue or violet by Gram
staining due to the high
amount of peptidoglycan in
the cell wall.

GRAM NEGATIVE

• Gram-negative bacteria are
bacteria that do not retain
crystal violet dye in the
Gram staining protocol.











STRUCTURE AND FUNCTION
OF BACTERIAL CELLS

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BASIC CHARACTERISTIC OF
BACTERIA

• Bacterial are unicellular prokaryotic organism.
• Bacterial cell have simpler internal structure.
• It lacks all membrane bound cell organelles such as

mitochondria, lysosome, golgi, endoplasmic reticulum,
chloroplast, peroxisome, glyoxysome, and true vacuole.
• Bacteria also lacks true membrane bound nucleus and
nucleolus. The bacterial nucleus is known as nucleoid.

Structure Outside BASIC CHARACTERISTIC OF
• Capsule
• Flagella BACTERIA
• Pili
• Sheath Structure Inside
• Prostheca • Cell wall
• Stalks • Cytoplasmic membrane
• Nucleoid
• Mesosome
• Ribosome
• Cytoplasm
• Spore



CAPSULE

• Capsule is 0.2µm thick viscus layer outer layer to the cell
wall.

• Capsule is 98% water and 2% polysaccharide or
glycoprotein/ polypeptide or both.

• There are two types of capsule.
- Macro-capsule: thickness of 0.2µm or more, visible
under light microscope
- Microcapsule: thickness less than 0.2µm, visible under
Electron microscope

CAPSULE

• Capsule is very delicate structure. It can be removed
by vigorous washing. Capsule is most important
virulence factor of bacteria.

• Function:
- It helps in attachments as well as it
prevent the cell from desiccation and
drying.
- Capsule resist phagocytosis by WBCs



FLAGELLA

• It is 15-20 nm hair like helical structure emerges from cell
wall.

• Flagella is not straight but is helical. It is composed of
flagellin protein (globular protein) and known as H
antigen.

• Flagella has three parts. Basal body, Hook and filament
• Function:

- It helps motility of the bacteria



PILI / PILUS / FIMBRIAE

• Pili are hollow filamentous and non-helical structure.
• They are numerous and shorter than flagella
• Pili is the characteristic feature of gram –ve bacteria.
• Pili is composed of pilin protein.
• Bacteria containing pili: Shigella, Proteus, Neisseria

gonorrhoae, E. coli

PILI / PILUS / FIMBRIAE

• Function:
- Attachment: pili helps the bacteria to attach the host cell
surface. Most of the human pathogens of respiratory tract,
urinary tract are attached with the help of pili.
- Pili (fimbrae) possess antigenic property
- Specialized function: some pili are modified for specialized
function. Eg. Sex pilus (F-pili) help in transfer of DNA from
donor to recipient cell during conjugation.
- F-pili also act as receptor for bacteriophage.



SHEATH

• Some bacteria forming chain or trichome are enclosed by a
hollow tube like structure known as Sheath.

• Aquatic bacteria mostly form sheath
• Some sheathed bacteria are; Sphaerotilus, leptothrix,

clonothrix etc
• Function:

- Mechanical support
- Sometime sheath is impregnated with ferric or manganese

hydroxide which provide strength to sheath.



PROSTHECAE

• Prosthecae are semi-rigid extension of cell wall and
cell membrane

• One bacteria may contains one or many prosthecae.
• Some prosthecae develop bud at the tip and hence

helps in reproduction.
• Some prosthecate bacteria are: Caulibacter, Stella,

Prosthecobacter, Hyphomicrobium

PROSTHECAE

• Function:
- Prosthecae increase surface area for nutrition
absorption. It is usually formed in bacteria living
in very dilute environment where concentration
of nutrition is low.
- Helps in adhesion
- Asexual reproduction by budding



STALK

• It is non-living ribbon like tubular structure.
• It is formed by excretory product of bacteria.
• Some stalked bacteria are: Gallionella, Planctomyces
• Function:

- Helps in attachment to solid surface.



CELL WALL

• It is an important structure of a bacteria.
• It give shape to the organism.
• On the basis of cell wall composition, bacteria are

classified into two major group ie. Gram Positive and
gram negative.

CELL WALL

Peptidoglycan:
• It consists of glycan backbone formed by repeated

unit of NAG (n-acetyl Glucosamine) and NAM (N-
acetyl muramic acid) and the glycan backbone is cross
linked by peptide bond.
• Peptidoglycan layer is present in cell wall of both gram
positive as well as gram negative bacteria. However,
gram positive have thick layer of peptidoglycan.

CELL WALL

Teichoic acid:
• Teichoic acid is water soluble polymer of glycerol

or ribitol phosphate present in gram positive
bacteria.
• It constitutes about 50% of dry weight of cell wall.
• It is the major surface antigen of gram positive
bacteria

CELL WALL

Outer membrane
• It is an additional layer present in gram negative

bacteria.
• It is composed of lipid bilayer, protein and lipo-

polysaccharide (LPS)

CELL WALL

LPS
• LPS is composed of lipid-A and polysaccharide.
• Lipid-A: it is phosphorylated glucosamine

disaccharide. It is antigenic
• Polysaccharide: it consists of core-polysaccharide

and O-polysaccharide.



CELL MEMBRANE

• Cell membrane is the inner layer that lies inside the
cell wall and encloses the cytoplasm.

• It is also known as cytoplasmic membrane or plasma
membrane.

• It is about 80nm thick.

CELL MEMBRANE

• Cell membrane of bacteria is composed of
phospholipid and proteins.

• Function:
- It is selectively permeable as it allows to pass
selective substances such as sugar, aminoacids
across it.