This document discusses the morphology and structure of bacteria. It begins by introducing bacteria and their size. It then classifies bacteria based on their shape, including cocci, bacilli, coccobacilli, vibrio, spirilla, and spirochete. The document describes the arrangement of bacterial cells and different morphologies seen in cocci and bacilli. It provides details on the anatomy of the bacterial cell, including the cell wall, cell membrane, cytoplasm, ribosomes, nucleoid, and cellular appendages like flagella, pili, capsules, and endospores. It discusses the structure and functions of these various bacterial cell components.

1. BACTERIAL MORPHOLOGY

2. Introduction
⚫Bacteria are unicellular free living
organisms without chlorophyll having
both DNA and RNA.
⚫They are prokaryotic organism i.e they
does not have a true nucleus.
⚫Size of bacteria are usually measured in
terms of microns or micrometers.
⚫Bacteria of medical importance generally
measures 0.2 – 1.5 micrometer.
⚫The smallest body that can be resolved
clearly by human eye is 200micron. Hence
to see bacteria , a light microscope must be
used.

3. Classification of bacteria based on
morphology
This classification is based on their shape.
⚫ Cocci : Spherical or near spherical shaped. Eg: streptococcus,
staphylococcus
⚫ Bacilli : relatively straight or rod shaped. Eg : Salmonella
i. Coccobacilli : Bacilli whose length and width are almost
equal. Eg: brucella
ii. Vibrio : curved or comma-shaped bacilli. Eg: Vibrio cholera
iii. Spirilla : rigid spiral or helical shaped. They are non-
flexible.
iv. Spirochete : these are also spiral shaped bacteria but they are
flexible.
v. Mycoplasma : these are cell wall deficient bacteria and hence
do not possess a stable morphology.
vi. Actinomycetes : these bacteria are long and show branching
similar to fungi.

5. Arrangement of bacterial cells
⚫ Bacteria sometimes show characteristic
cellular arrangement or grouping. The type of
cellular arrangement is determined by the
plane through which binary fission takes place
and by the tendency of the daughter cells to
remain attached even after division.

6. Arrangement in cocci
⚫ Diplococci: Cocci may be arranged in pairs
(diplococci) when cocci divide and remain
together. Eg ; pneumococci, gonococci
⚫ ii. Long chains: Long chains ,when cells adhere
after repeated divisions in one plane. Eg:
Streptococcus, Enterococcus, and Lactococcus
⚫ iii. Grape like clusters: Grape like clusters ,when
cocci divide in random planes. Eg : staphylococcus
aureus
⚫ iv. Tetrads: Square groups of four cells (tetrads)
when cocci divide in two planes as in members of
the genus Micrococcus.
⚫ v. Cubical (octads ) packets: Cubical packets of
eight of cells (genus Sarcina) when cocci divide in
three planes.

7. Arrangements in bacilli
⚫Bacilli split only across their short axes,
therefore, the patterns formed by them are
limited.
⚫Some bacilli may be arranged in chains.
⚫Eg: streptobacilli.
⚫Some are arranged at various angles to
each other, resembling the letter V
presenting a cuneiform or Chinese letter
arrangement and is characteristic of
Corynebacterium diphtheriae.

9. Anatomy of Bacterial Cell

10. ⚫The bacterial cell has an outer layer or cell
envelop consisting of two components – a
rigid cell wall and beneath it a cytoplasmic
or plasma membrane.
⚫The cell envelop encloses the protoplasm,
comprising the cytoplasm, ribosomes,
vacuoles, and the nuclear body.
⚫Some bacteria may possess additional
structures such as capsule, fimbriae and
flagella

11. Cell wall
⚫The cell wall accounts for the shape of the
bacteria.
⚫Chemically the cell wall is composed of
peptidoglycan or murein scaffoldings
(formed by N Acetyl glucosamine and N
acetyl muramic acid alternating in chain
crosslinked by peptide chains.)
⚫In general, the walls of the Gram positive
bacteria have simpler chemical nature than
those of Gram negative bacteria.
⚫The bacterial cell wall contains antigens
that are important in virulence and
immunity.

14. Gram positive bacteria cell wall
⚫ It is about 80nm thick.
⚫ It is composed mostly of peptidoglycan ( 60-
90% of the cell wall is peptidoglycan) and are
responsible for retaining the crystal violet
during gram staining.
⚫ In addition, gram positive bacteria contain
theichoic acid (which consist primarily of an
alcohol and phosphate ). Thecoic acid acts as a
surface antigen, it binds with magnesium ion
and protect bacteria from thermal injuries.
⚫ Some bacterias like the Mycobacterium have
large amount of lipid in their cell wall and
hence they exhibit acid fast staining due to the
presence of mycolic acid.

16. Gram negative bacteria cell wall
⚫ Cell wall of gram negative bacteria is a complex structure.
⚫ Peptidoglycan layer in cell wall of gram negative bacteria is
only single-unit thick i.e it contribute only 5-10% of cell wall.
⚫ The outer portion of cell wall consist of an outer membrane
which is attached to the peptidoglycan layer by lipoproteins.
⚫ Outer membrane
⚫ The outer membrane is a bilayered structure. The inner layer is
formed by phospholipid while the outer layer is formed by
Lipopolysaccharide (LPS).
⚫ The outer membrane provides resistance to the bacterial cell
from various chemical including antibiotics, dyes, disinfectants
and lysosymes.
⚫ The outer membrane has unique proteins called porins which
permit passage of molecules into periplasm. ( Periplasm is a gel
like fluid between the outermembrane and plasma membrane.

17. Lipopolysaccharide (LPS)
⚫it is a complex molecule that contains lipid
and carbohydrate and consist of 3
components.
1. Lipid A : it is present in the top layer of
outer membrane. It acts as an endotoxin
and is responsible for the endotoxic
activities like fever, tissue necrosis etc
2. Core polysaccharide : these are sugars and
their role is to provide stability.
3. Polysaccharide O : is a sugar molecule
extending outwards from the core
polysaccharide. It is also called as O
Antigen. It is useful for distinguishing
species of gram negative bacteria.

19. Functions of cell wall
1. Provide shape to bacteria.
2. Prevent bacterial cell from bursting.
3. Role in division of bacteria
4. Resistance to harmful effects of
environment

20. Cytoplasmic (Plasma) Membrane
⚫ It is a semipermeable membrane which lies beneath the cell wall.
⚫ Chemically it is composed of phospholipids and proteins (integral
proteins and peripheral proteins).
⚫ Lipid molecules are arranged in a double layer with their
hydrophilic polar regions externally aligned and in contact with a
layer of protein at each surface.
⚫ Functions of Cytoplasmic Membrane
i. Semipermeable membrane—controlling the inflow and outflow
of metabolites to and from the protoplasm i.e transport of
nutrients into celland elimination of waste material.
ii. Housing enzymes involved in outer membrane synthesis, cell
wall synthesis, and manufacturing of extracellular structures.
iii. Housing many sensory and chemotaxis proteins that monitor
chemical and physical changes in the environment.
iv. Generation of chemical energy (i.e, ATP).
v. It helps in DNA replication.

22. Cytoplasm
⚫ Bacterial cytoplasm is a viscous watery
solution containing organic and inorganic
solutes like ribosomes, vacuoles, inclusion
bodies etc.
⚫ They lack mitochondria and endoplasmic
reticulum.

23. Ribosomes
⚫ These are the centre of protein synthesis.
⚫ They are composed of ribosomal RNA and ribosomal protein.
⚫ They are 10-20 nm size, with a sedimentation constant of 70 S
(S for Svedberg units).
⚫ Each 70 S unit consists of a 30 Sand a 50 S subunits.
Intracytoplasmic inclusions
⚫ These are source of stored energy.
⚫ These are usually seen in bacteria growing in conditions of
nutritional deficiencies and disappear when deficit nutrients
are supplied.
⚫ These inclusions may contain polysaccharides, lipids, sulphur
granules, volutin granules ( phosphate granules seen in
diphtheria bacilli.)

24. Mesosomes
⚫ Mesosomes are invaginations of the plasma
membrane in the shape of vesicles, tubules, or
lamellae.
⚫ They are generally more prominent in gram-
positive bacteria.
⚫ There are 2 types of mesosomes:- lateral and septal
Function
⚫ They have respiratory enzymes and are believed to
be involved in bacterial respiration ( analogous too
mitochondria of eukaryotes)
⚫ They (septal mesosomes) may be involved in cell
wall formation during cell division.
⚫ They also probably play a role in chromosome
replication and distribution to daughter cells.

25. Nucleoid
⚫ Bacteria lacks true nucleus, but the genetic
material is located in an irregular shaped
region called nucleoide.
⚫ They does not possess a nuclear membrane
(separating them from the cytoplasm)or
nucleolus.
⚫ The genetic material of a bacterial cell is
contained in a single, long molecule of
double-stranded deoxyribonucleic acid
(DNA) which can be extracted in the form
of a closed circular thread. It measures
about 1mm.
⚫ The bacterial chromosome is haploid and
replicates by simple fission instead of by
mitosis as in higher cells

26. Plasmid
⚫ These are extranuclear genetic elements
in the cytoplasm and it consists of DNA.
⚫ Also called as episomes.
⚫ Plasmids are not essential for host growth
and reproduction, but may confer on it
certain properties such as drug resistance,
resistance to toxic metal ,ability to
degrade complex organic molecules etc
which may constitute a survival
advantage.
⚫ These are transmitted from one bacteria
to another by conjugation (sexual
reproduction) or binary fission.

27. Cellular Appendages

28. Capsule and slime layer
⚫ Some bacteria possesses a layer of amorphous viscous
material lying outside cell wall called glycocalyx.
⚫ When it is well organised and not easily washed off, it
is called capsule. Eg: streptococcus pneumonia
⚫ If it is diffuse, unorganised and easily washed off it is
referred as a slime layer as in Leuconostoc.
⚫ Capsules too thin to be seen under the light
microscope are called microcapsules. Eg :Neisseria
meningitidis
⚫ Some bacteria may have both a capsule and a slime
layer (for example, Streptococcus salivarius).
⚫ Capsules and slime layers usually are composed of
polysaccharide (for example pneumococcus) or of
polypeptide in some bacteria (for example, Bacillus
anthracis and Yersinia pestis).

29. Capsule and slime layer
Functions of Capsule
i. Virulence factor: Capsules often act as a
virulence factor by protecting the bacterium
from ingestion by phagocytosis, and
noncapsulate mutant of these bacteria are
nonvirulent. Repeated subcultures in vitro
lead to the loss of capsule and also of
virulence.
ii. Protection of the cell: In protecting the
cell from attack by various kinds of
antibacterial agents, e.g. bacteriophages,
colicines, complement, lysozyme and other
lytic enzymes.
iii. Can act as a source of nutrients and
energy. Eg : Streptococcus mutans, which
colonizes teeth, ferments the sugar in the
capsule and so formed acid by-products
contribute to the tooth decay.
iv. Identification and typing of bacteria:
Capsular antigen is specific for bacteria and
can be used for identification and typing of
bacteria.

30. Flagella
⚫ These are cytoplasmic Appendages protruding through cell wall. They are the
organ of locomotion.
⚫ It has three parts :
i. Filament: The filament is the longest and most obvious portion which
extends from the cell surface to the tip. It is a hollow cylinder made of
single protein called flagellin.
ii. Hook: The hook is a short, curved segment which links the filament to
its basal body.
iii. Basal body: The basal body is embedded in the cytoplasmic
membrane.
In the gram-negative bacteria, the basal body has four rings connected to
a central rod (L, P, S and M). The outer L and P rings associated with the
lipopolysaccharide and peptidoglycan layers respectively. S ring is
located just above the cytoplasmic membrane and the inner M ring
contacts the cytoplasmic membrane.
Gram-positive bacteria have only two basal body rings, an inner ring
connected to the cytoplasmic membrane and an outer one probably
attached to peptidoglycan.

32. Arrangement of flagella
The number and location of flagella are
distinctive for each genus. There are four types
of flagella arrangement:
• Monotrichous —Single polar flagellum (e.g.
Cholera vibrio).
• Amphitrichous—Single flagellum at both ends
(e.g. Alcaligenes faecalis).
• Lophotrichous—Tuft of flagella at one or both
ends (e.g. spirilla).
• Peritrichous—Flagella surrounding the cell
(e.g. Typhoid bacilli).

33. Fimbria or Pili
⚫ These are hair like appendages projecting
from cell surface.
⚫ They are made of proteins called pilin.
⚫ They are generally seen in gram negative
bacteria.
⚫ They are antigenic.
⚫ They are not involved in motility and
hence can be seen in both motile and
non- motile bacteria.
⚫ Fimbria are organ of adhesion. This
enhances virulence of bacteria.

35. Types:
1. Common: They function as organs of adhesions
that allow attachment of a bacterial cell to other
cells or surfaces.
Based on morphology, adhesive property and
antigenic nature they are of 6 types.
1. Sex pili : These are longer and fewer in number
than other fimbriae. They are found on ‘male’
bacteria and help in the attachment of those cells
to ‘female’ bacteria, forming hollow conjugation
tubes through which, it is assumed, genetic
material is transferred from the donor to the
recipient cell.
2. Col 1 : These are associated with colicin factor 1.

36. Types of common pili
Type I Thick, haemagglutination positive, mannose sensitive
Type II Thick, haemagglutination positive, mannose sensitive
Type III Thin, haemagglutination positive, mannose resistant
Type IV Thinner, haemagglutination positive
Type V Monopolar fimbriae seen in pseudomonas
Type VI Fimbriae are very long and seen in klebsiella.

37. BACTERIAL SPORES
⚫ Spores are highly resistant resting (or dormat) stage of
the bacteria formed in unfavorable environmemal
conditions as a result of depletion of exogenous
nutrients.
⚫ Bacterial spores formed within the parent cell, are
called endospores and the remaining part of the
bacteria is called the sporangium.
⚫ Structure: Bacterial spore comprises of several layers.
From innermost towards the outermost, the layers are:
core- inner membrane - spore coat- exosporium
⚫ The core is the inner most part containing the DNA
material and is walled off from the cortex by an inner
membrane and 1he germ cell wall.
⚫ Cortex and the coat layers lies external to the core,
and are separated from each other by an outer
membrane.
⚫ The outermost layer is called as the exosporium.
⚫ Example of spore forming bacteria are bacillus and
clostridium.

39. Sporulation
It refers tonthe process of formation of spore from vegetative
stage of bacteria. It is not a method of reproduction because the
bacteria do not divide during sporulation.
Sporulation commences when growth of bacteria ceases due to
lack of nutrients.
1. The bacterial DNA replicates and divides into two DNA
molecules.
2. A transverse septum grows across the cell from the cell
membrane forming forespore and sporangium.
3. The forespore is subsequently completely encircled by
dividing septum as a dou ble layered membrane.The inner
layer becomes the inner membrane. Between the two layers
is laid spore cortex and outer layer is transformed into spore
coat which consists of several layers
4. In some species from outer layer also develops exosporium
which bears ridges and folds
5. Maturation of spore occurs and it acquires properties of heat
resistance and refractility.
6. Finally lytic enzymes destroys the sporangium releasing the
spore.

41. Germination
⚫ It is the process of conversion of a spore into
vegetative cell under suitable condition.
⚫ It occurs in 3 stages:
a. Activation : This process requires agents like
heat, low pH etc which damage the coat of
spore and help in germination.
b. Initiation : Once activated, the spore loses its
refractility and swells up if the conditions are
favourable.
c. Outgrowth : The spore wall is shed and the
germ cell appears by rupturing the remaining
spore coat.The germ cell elongates to form
the vegetative bacterium.

42. Thank you