This document discusses the structure and classification of microbes. It begins by defining microorganisms and explaining that they can only be seen under an electron microscope due to their small size. It then outlines the five kingdoms of life - Monera, Protista, Fungi, Plantae, and Animalia. Most of the document focuses on characteristics of the Monera kingdom, which includes bacteria. It describes bacterial cell structures like the cell wall, cytoplasmic membrane, flagella, and endospores. It also discusses different bacterial shapes, arrangements, staining properties and includes examples of some pathogenic bacteria.

1. Structure & Classification of
Microbes
- Khyati Chaudhari

2. MICROORGANISM……?
 Micro means small, very small,
can’t see by naked eyes.
 Which can be seen by using
electron microscope..

3. Classification of Microorganism
 All living organisms are classified into the five kingdoms of life :
1. Monera
2. Protista
3. Fungi
4. Plantae
5. Animalia

4. Kingdom Monera
 Monera is non-nucleated unicellular organisms.
 They are prokaryotes.
 They have a cell wall. They have no membrane-bound organelles
such as mitochondria, Golgi complex.
 They lack a true nucleus. Instead, they have nucleoid, genetic
material without a nuclear membrane.
 Examples include Bacteria, cyanophyceae (Blue-Green algae),
Nitrogen-fixing organisms etc.

5. Kingdom Monera
Some examples include:
 Helicobacter pylori.
 E. coli.
 Hay bacillus.
 Salmonella.
 Staphylococcus aureus.

6. Kingdom Protista
 Protista are simple eukaryotic organisms that are neither animals,
plants nor fungi.
 Protista are unicellular in nature, or they can be found as a colony
of cells.
 Most Protista live in water, damp terrestrial environments, or even
as parasites.
 The term ‘Protista’ is derived from the Greek word “protistos”,
meaning “the very first“.
 The cell of these organisms contain a nucleus which is bound to the
organelles. Some of them even possess structures that aid
locomotion like flagella or cilia.

7. Kingdom Protista
 Examples of protists include algae, amoebas, euglena,
plasmodium, and slime molds.

8. Kingdom Monera

9. Kingdom Fungi
 A fungus is any member of the group of eukaryotic organisms that
includes microorganisms such as yeasts and molds, as well as the
more familiar mushrooms. These organisms are classified as a
kingdom, fungi.
 Fungi are eukaryotic, non-vascular, non-motile and heterotrophic
organisms.
 They may be unicellular or filamentous.
 They reproduce by means of spores.
 Fungi exhibit the phenomenon of alternation of generation.

10. Kingdom Fungi

11. Kingdom Plantae
 Plants: Kingdom Plantae.
 Kingdom Plantae includes all the plants on the earth.
 They include familiar organisms such as trees, herbs, bushes,
grasses, vines, ferns, mosses, and green algae.
 They are multicellular, eukaryotes and consist of a rigid structure
that surrounds the cell membrane called the cell wall.
 Plants also have a green colored pigment called chlorophyll that is
quite important for photosynthesis.

12. Kingdom Plantae

13. Kingdom Animalia
 All animals are members of the Kingdom Animalia, also called
Metazoa.
 This Kingdom does not contain prokaryotes.
 There are over 9 million species of animals found on Earth.
 They range from tiny organisms made up of only a few cells, to the
polar bear and the giant blue whale.
 All of the organisms in this kingdom are multicellular and
heterotrophs - that means they rely on other organisms for food.

14. Kingdom Animalia

15. Classification of Microbes
 Microorganisms are a varied group of several distinct classes of
living beings classified under the Kingdom Protista.
 Based on differences in cellular organization & biochemistry,
Protista has been divided into two groups :
Prokaryotes &
Eukaryotes.

16. Cont.…
 Bacteria & blue-green algae are prokaryotes & while fungi, slime
molds & protozoa are eukaryotes.

17. Character Prokaryotes Eukaryotes
Nucleus
Nuclear membrane Absent Present
Nucleolus Absent Present
Chromosome Circular (1) Linear (>1)
Cytoplasm
Mitochondria Absent Present
Lysosomes Absent Present
Golgi apparatus Absent Present
Endoplasmic reticulum Absent Present
Chemical composition
Sterols Absent Present
Muramic acid Present Absent
 Some differences between prokaryotes & eukaryotes

18. Prokaryotic cell

20. Size of bacteria
 The unit of measurement used in bacteriology is the micron
(micrometer, µm).
 The limit of resolution with the unaided eye is about 200 microns.
 Bacteria, being much smaller, can be visualized only under
magnification.
 Bacteria of medical importance generally measure 0.2-1.5 µm in
diameter & about 3-3 µm in length.

21.  Morphology is a branch of biology that deals with the form of living
organisms & with relationships between their structures. Particular
form, shape or structure.
Morphological types of bacteria

22. Morphological types of bacteria
 Bacteria are classified
according to their shape.
1. Cocci
– from kokkos meaning
berry. They are spherical or oval
cells.

23. Morphological types of bacteria
2. Bacilli
-From baculus meaning rod.
-They are rod shaped cells.

24. Morphological types of bacteria
3. Vibrio
- They are comma-shaped
curve rods & derive their name
from their characteristic vibratory
motility.

25. Morphological types of bacteria
4. Spirilla
- They are rigid spiral forms.

26. Morphological types of bacteria
5. Spirochetes
- word came from speira
means coil & chaite means hair.
-they are flexuous spiral
forms.

27. Morphological types of bacteria
6. Actinomycetes
- This word came from Actis
means ray & Mykes means
fungus.
- They are branching
filamentous bacteria, so called
because of their resemblance to
the radiating rays of the sun,
when seen in tissue lesions.

28. Morphological types of bacteria
7. Mycoplasma
- are bacteria that do not have a
cell wall & hence do not possesses a
fixed shape. They occur as round or
oval bodies & as interlacing
filaments.
- Mycoplasma are bacteria that
have no cell wall and therefore have
no definite shape.

29. Arrangement of cocci
 Bacteria sometimes show characteristics cellular arrangement or
grouping .
 Thus, cocci may be arranged in pairs, chains, group of four, group
of eight, or grape like clusters.

30. Arrangement of cocci
In pair- d=Diplococci In chain- Streptococci

31. Arrangement of cocci
Group of 4- Tetrads Group of 8- Sarcina

32. Arrangement of cocci
 In grape like clusters-
staphylococci

33. Arrangement of bacteria
 Some bacilli are arranged at
angles to each other,
presenting a Chinese latter
pattern. They called corny
bacterium.

34. Bacterial cell structure & functions

36. Cell wall
 It is outer covering of most cells that protects the bacterial cell and
gives it shape.
 Bacterial cell walls are made of peptidoglycan (polysaccharides +n
protein) AKA murein.
 Mycoplasma are bacteria that have no cell wall and therefore have
no definite shape.
 The rigid structure of peptidoglycan gives the bacterial cell shape,
surrounds the plasma membrane and provides prokaryotes with
protection from the environment.

37. Cell wall
 Going further out, the bacterial world divides into two major
classes: Gram-positive and Gram-negative .
 Amount and location of peptidoglycan in the cell wall determines
whether a bacterium is G+ve or G-ve.

38. Gram-positive
 G+ve bacteria have a simpler chemical nature.
 G+ve bacteria possess thick cell wall containing many layers of
peptidoglycan and teichoic acids.
 In G+ ve cells, peptidoglycan is the outermost structure and makes
up as much as 90% of the thick compact cell wall.
 The cell wall caries bacterial antigens that are important in their
ability to cause disease & protect against disease.

39. Gram-negative
 G-ve bacteria have relatively thin cell wall consisting of few layers
of peptidoglycan surrounded by a second lipid membrane
containing lipopolysaccharides and lipoproteins
 The LPS present on the cell walls of G-ve bacteria account for their
endotoxic activity & O antigen specificity.
 Peptidoglycan makes up only 5 – 20% of the cell wall and is not
outermost layer, but lies between the plasma membrane and an
outer membrane.
 The endotoxins are responsible for inducing fever, tissue necrosis
&death.

40. Gram-negative
 The outermost layer of the G-ve bacterial cell wall is called the
outer membrane.
 It is similar to the plasma membrane, but is less permeable .
 It contains various proteins called outer membrane proteins
(OMP).

41. Cell wall characteristics Gram-positive Gram-negative
Thickness Thicker Thinner
Variety of amino acids Few Several
Aromatic & Sulphur
containing amino acids
Absent Present
Lipids Absent or scanty Present
Teichoic acid present Absent

42. Cell wall
 Antibiotics such as penicillin inhibit the formation of peptidoglycan
cross-links in the bacterial cell wall.
 The enzyme lysozyme, found in human tears, also digests the cell
wall of bacteria and is the body's main defense against eye
infections.

43. Cytoplasmic membrane
 The cytoplasmic membrane or plasma membrane is a thin layer
lining the inner surface of the cell wall.
 Which separating it from the cytoplasm.
 It works as semipermeable membrane by regulating the flow of
substances in and out of the cell.
 It consists of both lipids and proteins.
 It protects the cell from its surroundings.

45. Periplasmic space
 Gram-nagative bacteria :
-space between the cytoplasmic membrane and the cell wall and
space found between cell wall and the outer membrane.
 Gram-positive bacteria :
-space between the cytoplasmic membrane and the cell wall.
 The periplasm is filled with water and proteins.

46. Periplasmic cell
 However periplasm contains proteins and other molecules distinct
from those in the cytoplasm because the membrane prevents the
free exchange between these two compartments.
 Periplasmic proteins have various functions in cellular processes
including: transport, degradation and motility.
 Periplasm controls molecular traffic entering and leaving the cell.

47. Cytoplasm
 Cytoplasm is portion of the cell that lies within the plasma
membrane.
 substances within the plasma membrane, excluding the genetic
material.
 It is gel-like matrix composed of mostly water(4/5 th ), enzymes,
nutrients, wastes, and gases.
 It contains cell structures - ribosomes, chromosome and plasmids ,
as well as the components necessary for bacterial metabolism.
 It carries out very important functions for the cell - growth,
metabolism, and replication .

48. Constituents of cytoplasm are…
 Proteins including enzymes
 Vitamins
 Ions
 Nucleic acids and their precursors
 Amino acids and their precursors
 Sugars, carbohydrates and their derivatives
 Fatty acids and their derivatives

49. Ribosomes- protein synthesis machinery
 It consists of RNA and protein.
 Smaller than the ribosomes in eukaryotic cells-but have a similar
function.
 They are centers of protein synthesis.

50. Mesosomes
 Mesosomes are seen as
vesicular folds within the
plasma membrane, protruding
into the cytoplasm.
 They are more prominent in
Gram-positive bacteria.
 They are the principal sites of
the respiratory enzymes in
bacteria & are like the
mitochondria of eukaryotes in
function.

51. Mesosomes
 Mesosomes also coordinate nuclear & cytoplasmic division during
binary fission due to their position near the nuclear body.

52. Intracytoplasmic inclusions
 Inclusion bodies: Bacteria can have within their cytoplasm a variety
of small bodies collectively referred to as inclusion bodies.
 Some are called granules and other are called vesicles.
 Inclusions are considered to be nonliving components of the cell
that do not possess metabolic activity and are not bounded by
membranes.
 The most common inclusions are volutin, glycogen, lipid droplets,
droplets, crystals and pigments.

53. Intracytoplasmic inclusions
 Volutin granules need special staining techniques such as Albert’s
or Ponder’s stain to demonstrate the granules more clearly.
 Volutin granules are characteristically present in corynebacterium
diphtheria & are believed to store energy for cell metabolism.
 Polysaccharides granules & lipid granules are storage product.
 Vacuoles are fluid containing cavities separated from the cytoplasm
by a membrane.
 Their function & significance are uncertain.

54. Nucleus
 Bacterial nuclei may be seen
by electron microscopy.
 They appear as oval or
elongated bodies, generally
one per cell.
 The bacterial chromosome is
haploid & replicates by simple
binary fission instead of
mitosis as in other cells.

55. Nucleus
 Bacteria may possess extra-nuclear genetic elements consisting of DNA, called
plasmids, which carry genetic information.
 They can be transmitted to daughter cells during binary fission & also transferred
from one bacterium to another, either through conjugation or by bacteriophages.
 They confer properties such as toxigenicity & drug resistance on the cell.

56. Slime layer & capsule
 Many bacteria secrete a sticky material around the cell surface.
 When this is organized into a sharply defined structure, as in
streptococcus pneumonia, it is known as the capsule.
 Capsules may be polysaccharide or polypeptide.
 Large capsules may be readily demonstrated by negative staining
with India ink, when they are seen as clear halos around organism,
against a black background.

57. Slime layer & capsule
 Capsules protect bacteria from lytic enzymes found in nature & also
contribute to the virulence of pathogenic bacteria by inhibiting
phagocytosis.

58. Flagella
 Made up of protein subunits called flagellin.
 Each flagellum is attached to cell membrane with the help of
proteins other than flagellin.
 Flagella are the organ of the locomotion.
 The basal region has a hook like structure and a complex basal
body. The basal body consists of a central rod or shaft surrounded
by a set of rings.

59. Flagellar Arrangement
 Bacterial species differ in the number and arrangement of flagella
on their surface.
 Bacteria may have one, a few, or many flagella in different positions
on the cell.

60. Flagellar Arrangement
 Atrichous – no flagella
 Monotrichous - single flagellum
 Amphitrichous a flagellum at each end
 Lophotrichous - clusters of flagella at the poles of the cell
 Peritrichous - flagella distributed over the entire surface of the cell.

62. Fimbriae
 Hollow, hair like structures made of protein is called fimbrie or pili.
 They are shorter & thinner than flagella (about 0.5 µm long & less
than 10 nm thick) & project from the cell surface as straight
filaments.
 They arise from the cell membrane.

63. Fimbriae
 Fimbriae can be seen only under the electron microscope.
 They function as organs of attachment, helping the cell adhere
firmly to particles of various kinds.

64. Spores
 Some bacteria, particularly
members of the genera
Bacillus & Clostridium have
the ability to from highly
resistant resting stages called
spores.

65. Spores
 Sporulation (formation of spores) helps bacterial survival for long
periods under unfavorable conditions.
 Each bacterium forms one spore, which on germination forms a
method of reproduction.
 As bacterial spores are formed inside the parent cell, they are called
endospores.

66. Spore
 The fully developed spore has
at its core the nuclear body,
surrounded by the spore wall.
 Outside this spore cortex,
which is enclosed by multi
layered tough spore coat.
 Some spore have an
additional outer covering
called exosporium, which may
have distinctive ridges &
grooves.
 E.g. B. anthracis.

67. Shape & position

68. Resistance
 They are extremely resistant to drying & relatively resistant to
chemicals & heat.
 Though some spores may resist boiling for prolonged periods,
spores of all medically important species are destroyed by
autoclaving at 120 °C for 15 minutes.
 Methods of sterilization & disinfection should ensure that spores
are destroyed in addition to vegetative cells.
 Spores germinate in optimal conditions.

69. Resistance
 The spore wall is shed & the germ cell appears by rupturing the
spore coat & elongates to form the vegetative bacterium.

70. Pleomorphism
 Pleomorphism is the ability of some microorganisms to alter their
morphology( shape & size), biological functions or reproductive
modes in response to environmental conditions.