Microbiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes bacteria, fungi, protozoa, and some algae. Bacteria were first observed in the 1670s and microbiology has since developed into a field that utilizes biochemistry, genetics, and other disciplines to study microbes. While much is now known, only about 1% of microbes have been studied so far. Microbiology is divided into subdisciplines that examine topics like microbial physiology, genetics, roles in medicine/veterinary science, and more. Bacteria are classified based on traits like their cell structure, metabolism, habitat, and more.

1. Microbiology
in Greek
micro = small
Bio = life
logy = “to study” or “the study of”

2. Definition
 Microbiology is the study of microorganisms,
which are unicellular or cell-cluster microscopic
organisms. This includes eukaryotes (such as fungi
and protests) and prokaryotes (such as bacteria and
viruses, though viruses are not strictly classed as
living organisms).

3. Comparison between Eucaryotic and Procaryotic Cells
Eucaryotic Procaryotic
Nuclear membrane present absent
Membranous structures
other than cell
membranes
Generally present Generally absent except
mesosomes and
photosynthetic
membranes
Microtubules and
centrioles
present absent
Cytoplasmic ribosomes
(density)
80S 70S
Flagella or cilia When present, have a
complex structure similar
to centrioles
Flagella, when present,
have a simple twisted
protein structure; no cilia
Active cutoplasmic
movements
present Absent (not observed)

4.  Today, most of the work in microbiology is done using
methods from biochemistry and genetics. It is also related to
pathology, immunology, and epidemiology as many
microorganisms are pathogens.
 Although much is now known in the field of microbiology,
advances are being made regularly. The most common
estimates suggest that we have studied only about 1% of all of
the microbes in any given environment. Thus, despite the fact
that over three hundred years have passed since the discovery
of microbes, the field of microbiology is clearly in its infancy
relative to other biological disciplines such as zoology, botany
or even entomology.

5. History
 Bacteria were first observed by Anton van Leeuwenhoek in 1676 using a
single-lens microscope of his own design.
 The name "bacterium" was introduced much later, by Ehrenberg in 1828,
derived from the Greek word bactēria meaning "small stick".
 While Antony van Leeuwenhoek is often cited as the first microbiologist,
the first recorded microbiological observation, that of the fruiting bodies
of molds, was made earlier in 1665 by Robert Hooke.
 The field of bacteriology (later a subdiscipline of microbiology) is
generally considered to have been founded by Ferdinand Cohn (1828-
1898), a botanist whose studies on algae and photosynthetic bacteria led
him to describe several bacteria including Bacillus and Beggiatoa.
Ferdinand Cohn was also the first to formulate a scheme for the
taxonomic classification of bacteria.

6. History
 Louis Pasteur (1822-1895) and Robert Koch (1843-1910)
were contemporaries of Cohn’s and are often considered to
be the founders of medical microbiology.
 Pasteur is most famous for his series of experiments
designed to disprove the then widely held theory of
spontaneous generation, thereby solidifying microbiology’s
identity as a biological science.
 Pasteur also designed methods for food preservation
(pasteurization) and vaccines against several diseases such
as anthrax, fowl cholera and rabies.

7. History
 Robert Koch is best known for his contributions to
the germ theory of disease, proving that specific
diseases were caused by specific pathogenic
microorganisms. He developed a series of criteria
that have become known as the Koch’s postulates.
 Koch was one of the first scientists to focus on the
isolation of bacteria in pure culture resulting in his
description of several novel bacteria including
Mycobacterium tuberculosis, the causative agent of
tuberculosis

8. History
 While Louis Pasteur and Robert Koch are often considered the
founders of microbiology, their work did not accurately reflect
the true diversity of the microbial world because of their
exclusive focus on microorganisms having medical relevance.
 It was not until the work of Martinus Beijerinck (1851-1931)
and Sergei Winogradsky (1856-1953), the founders of general
microbiology (an older term encompassing aspects of
microbial physiology, diversity and ecology), that the true
breadth of microbiology was revealed.
 Sergei Winogradsky was the first to develop the concept of
chemolithotrophy and to thereby reveal the essential role played
by microorganisms in geochemical processes. He was
responsible for the first isolation and description of both
nitrifying and nitrogen-fixing bacteria.

9. Microbiology
The field of microbiology can be generally divided into several
subdisciplines:
 Microbial physiology: The study of how the microbial cell
functions biochemically. Includes the study of microbial
growth, microbial metabolism and microbial cell structure.
 Microbial genetics: The study of how genes are organised and
regulated in microbes in relation to their cellular functions.
Closely related to the field of molecular biology.
 Medical microbiology: The study of the role of microbes in
human illness. Includes the study of microbial pathogenesis and
epidemiology and is related to the study of disease pathology
and immunology.

10. Types of microbiology
 Veterinary microbiology: The study of the role in
microbes in veterinary medicine.
 Environmental microbiology: The study of the
function and diversity of microbes in their natural
environments. Includes the study of microbial
ecology, microbially-mediated nutrient cycling,
geomicrobiology, microbial diversity and
bioremediation. Characterisation of key bacterial
habitats such as the rhizosphere and phyllosphere.

11. Types of microbiology
 Evolutionary microbiology: The study of the evolution
of microbes. Includes the study of bacterial systematics
and taxonomy.
 Industrial microbiology: The exploitation of microbes
for use in industrial processes. Examples include
industrial fermentation and wastewater treatment. Closely
linked to the biotechnology industry. This field also
includes brewing, an important application of
microbiology.
 Aeromicrobiology: The study of Airborne
Microorganisms.
 Food Microbiology: The study of Microorganisms
causing Food Spoilage.

12. Benefits of microbiology
 While microbes are often viewed negatively due to
their association with many human illnesses, microbes
are also responsible for many beneficial processes
such as industrial fermentation (e.g. the production of
alcohol and dairy products), antibiotic production and
as vehicles for cloning in higher organisms such as
plants.
 Scientists have also exploited their knowledge of
microbes to produce biotechnologically important
enzymes such as Taq polymerase, reported genes for
use in other genetic systems and novel molecular
biology techniques such as the yeast two-hybrid
system.

13. Bacteria
 Microorganism – any organism too small to be viewed by the
unaided eye, as bacteria, protozoa, and some fungi and algae
 Bacterium/Bacteria - microorganisms made up of a single cell that
has no distinct nucleus. Bacteria reproduce by fission or by forming
spores.
 One of the three domains of life (the others being Eukarya and
ARCHAEA), also called Eubacteria.
 They are unicellular prokaryotic microorganisms which generally
possess rigid cell walls, multiply by cell division, and exhibit three
principal forms: round or coccal, rod like or bacillary, and spiral or
spirochetal.

14. Morphology of the bacteria
General Concepts
 Gross Morphology
 Bacteria have characteristic shapes (cocci, rods, spirals, etc.)
and often occur in characteristic aggregates (pairs, chains,
tetrads, clusters, etc.). These traits are usually typical for a
genus and are diagnostically useful.
 Cell Structure
 Prokaryotes have a nucleoid (nuclear body) rather than an
enveloped nucleus and lack membrane-bound cytoplasmic
organelles. The plasma membrane in prokaryotes performs
many of the functions carried out by membranous organelles
in eukaryotes. Multiplication is by binary fission.

16. Chromosome
 Is not surrounded by nuclear membrane
 does not have a definitive shape
 usually consists of single, circular DNA molecule and
serves as the control centre of the bacterial cell,
containing the genomic information needed for
producing several thousand enzymes and proteins
 a typical bacterial chromosome contains approximately
10,000 genes

17. Cytoplasm
 Semiliquid, surrounds the chromosome, is
contained within the plasma membrane
 consists of water, enzymes, oxygen (in some
cases), waste products, essential nutrients,
proteins, carbohydrates, and lipids - a complex
mixture of all the materials required by cell for its
metabolic functions

18. Surface Structures
 Flagella: The flagella of motile bacteria differ in structure from
eukaryotic flagella. A basal body anchored in the plasma membrane
and cell wall gives rise to a cylindrical protein filament. The
flagellum moves by whirling about its long axis. The number and
arrangement of flagella on the cell are diagnostically useful.
 Pili (Fimbriae): Pili are slender, hairlike, proteinaceous appendages
on the surface of many (particularly Gram-negative) bacteria. They
are important in adhesion to host surfaces.
 Capsules: Some bacteria form a thick outer capsule of high-
molecular-weight, viscous polysaccharide gel; others have more
amorphous slime layers. Capsules confer resistance to phagocytosis.

20. Cytoplasmic Structures
 Plasma Membrane: The bacterial plasma membrane is composed
primarily of protein and phospholipid (about 3:1). It performs many
functions, including transport, biosynthesis, and energy transduction.
 Organelles: The bacterial cytoplasm is densely packed with 70S
ribosomes. Other granules represent metabolic reserves (e.g., poly-b-
hydroxybutyrate, polysaccharide, polymetaphosphate, and
metachromatic granules).
 Endospores: Bacillus and Clostridium species can produce
endospores: heat-resistant, dehydrated resting cells that are formed
intracellularly and contain a genome and all essential metabolic
machinery. The endospore is encased in a complex protective spore
coat.

21. Important Chemical Components of Surface Structures
 Cell Wall Peptidoglycans: Both Gram-positive and Gram-negative
bacteria possess cell wall peptidoglycans, which confer the characteristic
cell shape and provide the cell with mechanical protection. Peptidoglycans
are unique to prokaryotic organisms and consist of a glycan backbone of
muramic acid and glucosamine (both N-acetylated), and peptide chains
highly cross-linked with bridges in Gram-positive bacteria (e.g.,
Staphylococcus aureus) or partially cross-linked in Gram-negative bacteria
(e.g., ). The cross-linking transpeptidase enzymes are some of the targets
for b-lactam antibiotics.
 Teichoic Acids: Teichoic acids are polyol phosphate polymers bearing a
strong negative charge. They are covalently linked to the peptidoglycan in
some Gram-positive bacteria. They are strongly antigenic, but are
generally absent in Gram-negative bacteria.

22. Important Chemical Components of Surface
Structures
 Lipoteichoic Acids: Lipoteichoic acids as membrane teichoic acids are
polymers of amphiphitic glycophosphates with the lipophilic glycolipid and
anchored in the cytoplasmic membrane. They are antigenic, cytotoxic and
adhesins (e.g., Streptococcus pyogenes).
 Lipopolysaccharides: One of the major components of the outer membrane
of Gram-negative bacteria is lipopolysaccharide (endotoxin), a complex
molecule consisting of a lipid A anchor, a polysaccharide core, and chains
of carbohydrates. Sugars in the polysaccharide chains confer serologic
specificity.
 Wall-Less Forms: Two groups of bacteria devoid of cell wall
peptidoglycans are the Mycoplasma species, which possess a surface
membrane structure, and the L-forms that arise from either Gram-positive or
Gram-negative bacterial cells that have lost their ability to produce the
peptidoglycan structures.

26. Rickettsias and Chlamydias
 Are coccoid, rod-shaped, or pleomorphic (irregular) GR-negative bacteria with
a bacterial-type cell wall; unlike viruses, they contain both DNA and RNA.
 Most known forms are obligate intracellular parasites.
 Rickettsias: because they appear to have leaky cell membranes, most rickettsias
must live inside another cell to retain all the neccesary cellular substances.
They are usually transmitted by arthropod vectors (carriers): lice, fleas, ticks -
by their bites or waste products (exception - Coxiella burnetti, that cause of Q
fever - airborne or foodborne).
 Chlamydias: are probably the most primitive of all bacteria because they lack
the enzymes required to perform many essential metabolic activities,
particularly production of ATP. They are obligate intracellular parasites that are
transferred by direct contact between hosts, not by arthropods.

27. Mycoplasmas
 are the smallest of the cellular microbes.
 Because they lack cell walls, they assume many
shapes, from coccoid to filamentous.
 Sometimes they are confused with the L-forms of
bacteria.
 Because they have no cell wall, they are resistant
to treatment with penicillin and other antibiotics
that work by inhibiting cell wall synthesis

28. Classification of the bacteria

29. Purposes
 What do we learn from our classification?
 How useful is it?
 Is there a preferred classification of organisms
from which we can learn more than we can from
alternative classifications?

30. Principles
 Morphology
 staining
 motility
 growth
 atmospheric requirements
 nutritional requirements
 biochemical and metabolic activities
 pathogenicity
 amino acid sequencing
 genetic composition

31. Principles
 Gram stain (cell wall structure)
 Mole percent G+C in the genome
 Growth temperature
 Ability to form heat stable spores
 Electron acceptors for respiration (if any)
 Photosynthetic ability
 Motility
 Cell shape
 Ability to use various carbon and nitrogen sources
 Special nutritional requirements (e.g., vitamins)

32. Classification of the bacteria
Bacteria can be classified:
 by their response to OXYGEN: aerobic, anaerobic, or facultatively
anaerobic;
 by the mode by which they obtain their ENERGY: chemotrophy
(via chemical reaction) or phototrophy (via light reaction); for
chemotrophs by their source of chemical energy: chemolithotrophy
(from inorganic compounds) or chemoorganotrophy (from organic
compounds);
 by their source for CARBON; NITROGEN, etc.: heterotrophy (from
organic sources) or autotrophy (from carbon dioxide).
 They can also be classified by whether or not they stain (based on
the structure of their CELL WALLS) with crystal violet dye: gram-
negative or gram-positive.

33. History
 Aristotle: plants, animals, microorganisms (appearance
and behaviour)
 Carolus Linnaeus (18th century): binominal system - each
organism is given two names (e.g. Homo sapiens). First
name is the genus, and second is the specific epithet. The
first and second names together are referred to as the
species.
 Whittaker: five kingdoms - Animalia, Plantae, Fungi,
Protista (algae and protozoa), Procaryotae or Monera
(cyanobacteria and bacteria). Each kingdoms consist of
divisions or phyla which, in turn, are divided into classes,
orders, families, genera, species

34. Bergey’s Manual of determinative
bacteriology
Kingdom
Phylum
Class
Order
Family
Genus
Species

35. Kingdom and Phylum
Five kingdoms:
 Animalia (for animals)
 Plantae (for plants)
 Fungi (for fungi)
 Protista (for algae and protozoa)
 Procaryotae:
Phylum I - Photobacteria (cyanobacteria)
Phylum II - Scotobacteria (bacteria)

36. Kingdom – Procaryotae
Phylum – II Scotobacteria
Class – 1 Bacteria
Order – 14 group Gr (+) cocci
Family – Micrococcaceae
Genus – Staphylococcus
Species – Staphylococcus aureus

37. Bacteria
group family genus species
1-4 Non pathogenic for
human
5 Spirochetes Spirochaetaceae Treponema
Borrelia
Leptospira
Treponema pallidum
Borrelia recurrentis
Leptospira interrogans
6 Spiral and
curved bacteria
Spirillaceae Spirillum Spirillum minor
7 Gr(-) aerobic
bacillus and cocci
5 family, more
important
Pseudomonadaceae
Pseudomonas Pseudomonas
aeroginosa
8 Gr(-) facultative
anaerobic bacillus
Enterobacteriaceae
Vibrionaceae
12 genus:
Salmonella,
Shigella,
Klebsiella,
Proteus,
Yersinia
Vibrio
Salmonella typhi …
9 Gr(-)anaerobic
bacteria
Bacteroidaceae

38. 10 Gr(-) cocci and
coccobacilli
Neisseriaceae 4 Neisseria N. gonorrhoeae
N. meningitidis
11 Gr(-) anaerobic
cocci
Veillonellaceae 3 Veillonella
12 Gr(-)hemolitotroph
13 Metanobacteria
14 Gr(+) cocci Micrococcaceae
Streptococcaceae
Peptococcaceae
Staphylococcus
Streptococcus
Peptococcus
S. aureus
S. pneumoniae
15 Spore forming
bacilli
Bacillaceae Bacillus
Clostridium
B. antracis
C. tetani
C. botulinum
16 Gr(+) bacilli Lactobacillaceae Lactobacilli
Listeria
17 Actinomycetes Corynobacteriaceae
Actinomyceae
Mycobacteriaceae
Corynobacterium
Actinomyces
Mycobacterium
C. diphteriae
A. israilii
M. tuberculosis
M. leprae
18 Ricketsiales
Chlamydiales
3 Ricketsiaceae
Chlamydiaceae
Ricketsia
Chlamydia
R.provacheka
C. trachomatis
19 Mycoplasmes Mycoplasmaceae
Achleplasmataceae
Mycoplasma