Chapter 1. intro. microbiology (2)

1.1 Scopes of Microbiology
Definition;-
 Microbiology :- a subject which deals with living
organisms that are individually too small to be seen
with the naked eye
 Medical microbiology:- deals with microorganism
that cause infectious diseases and the body’s defenses
against disease
Wednesday, March 16, 2022 2

Branches of medical microbiology
Bacteriology – which deals with bacteria
Mycology- which deals with fungi
Protozology – which deals with Protozoa
Virology -studies about viruses
Immunology- body’s defenses against disease

History
 Man kind has always been affected by diseases which
were originally believed to be visitations by the Gods
and meant to punish evil doers
 Hippocratus, father of medicine, observed that ill
health resulted due to changes in air, winds, water,
climate, food, nature of soil and habits of people

Fracastorius (1500 G.C.) proposed that the
agents of communicable disease were living germs,
that could be transmitted by direct contact with
humans and animals, and indirectly by objects ;
but no proof because of lacking experimental
evidence

History cont…
• Antony Van Leeuwenhoek(1674):- the first
person who observe microorganisms using
simple microscope with one lens(266X)
• He called them “animalcules” means small
animals
• They where everywhere
– In water
– Soli
– His teeth scraping

 1796:- Jenner creates a vaccine for small pox
 1859:- Pasteur disprove spontaneous generation
of microorganisms
 1865:- Lister introduce antiseptic techniques
 Developed a system of antiseptic surgery
designed to prevent microorganisms from
entering wounds

 1876:- Koch proves that specific organism cause
specific disease
 In 1910, Ehrlich ( father of Chemotherapy) successfully
treated syphilis using Salvarsan (dioxydiaminoarseno benzol
dihydrochloride)

 1929:- Fleming discovered penicillin
 1892:- Ivanovski:- discover viruses
 Advent of electron microscopy in 1934 by Ruska
made morphological examination of viruses
possible.

Spontaneous generation (Theory of Abiogenesis)
 States that living things originated “spontaneously”
from non-living things
 Fleas from putrid matter
 Mice from dirty hay
 Maggots from meat etc.

 Aristotle (384-322 BC): The founder of a theory
spontaneous generation
 He observed spontaneous existence of fishes from
dried ponds, when the pond was filled with rain
 Francesco Redi (1626-1697): He is the scientist who
first tried to set an experiment to disprove
spontaneous generation
 Utilized jars containing meat. Some were covered, some
were not
 Maggots appeared in uncovered jars
 Results not accepted for microscopic organisms

 The controversy on spontaneous generation took
200 years
 In 1859 Louis pasture disproved the theory of
abiogenesis once and for all

1.2 Germ theory of disease
 Is the idea that diseases may be caused by
microscopic organisms
 The most important contribution to medical science
and practice, ever
 Corner stone of:
 Epidemiology
 Development of antimicrobial drugs
 Development of vaccine
 Hygienic practice
 Public health

 Pasture contributed for the development of germ
theory of disease by disproving theory of spontaneous
generation among microorganisms
 Robert Koch, in 1876 established an experimental
procedure to prove the germ theory of disease
 Which states that specific disease is caused by
specific pathogen
 The scientific procedure is known as Koch’s
Postulate

Koch’s Postulate: - proof of germ theory of disease
 A Micro-organism can be accepted as a causative
agent of an infectious disease only if the following
conditions are satisfied:
1. Microorganism must be associated with the lesion
2. Microorganism must be isolated in pure culture
3. Isolated microorganisms must produce disease
when inoculated in to human or animal
4. Microorganisms must be re-isolated from
intentionally infected animal or human

Exceptions to Koch’s postulate
 Many healthy people carry pathogens but do not exhibit
symptoms of the disease
 Some microbes are very difficult or impossible to grow in vitro
(in the laboratory) in artificial media. Eg. Treponema pallidum
 Certain diseases develop only when an opportunistic pathogen
invades imuno-compromised host
Koch also discovered
 Bacillus anthracis
 Mycobacterium tuberculosis
 Vibrio cholera

Eukaryotic and Prokaryotic cells
All living cells can be classified as either Eukaryotic
and Prokaryotic
 Prokaryotic cell
(Pro -means primitive)
( Karyote - means nucleus)
Prokaryotic cells are less complex cells. Which posses
naked (unbound) DNA with out associated basic
proteins, they divide by binary fission are bounded by
a semi rigid cell wall.
The prokaryotic cells include bacteria

 Eukaryotic cells.
(Eu- means true,
(Karyote- means nucleus)
The Eukaryotic cell is more complex, has membrane
bound nucleus, and many organelles
 Eukaryotic cells include protozoa, fungi, algae,
(green, brown and red algae) and plant and animal
cells

1.3 Structure and classification of Bacteria
 Unicellular
 Typical prokaryotic cell
 Contain both DNA and RNA
 Most grow in artificial media
 Replication is by binary fission
 Contain rigid cell wall except mycoplasma

Bacterial structure is considered at three levels
1. Cell envelope:
Capsule, cell wall and cell membrane
2. Cellular element enclosed with in the cell
envelope:
Ribosome, nuclear material, and cytoplasmic
granules
3. Cellular element external to the cell envelope
(appendages) : Flagellum, Pilus
Bacterial cell structure

Bacterial cell

Cell wall
 Protects the delicate cell protoplast from osmotic
lysis
 Provide rigid support for the cells

Types of cell wall
I. Gram positive cell wall of bacteria
 Has two layers Peptidoglycan (PG) cross linked
with teichoic acid)
 The PG layers is much thicker than Gram
negative bacteria and i.e. 15 – 50 nm thick

Gram positive cell wall …Cont’d
Teichoic acid
 These polymers of glycerol phosphate or ribitol
phosphate are located in the outer layer of the PG cell
wall
 Function of Teichoic acid
 Used to bind (keep) Mg+2 concentration in the
cell wall
 Used to activate autolytic enzyme (enzymes which
are secreted by bacteria usually when it dies

II. Gram negative Cell wall of bacteria
 Is some what complex than Gram positive bacterial
cell wall
 Has thin peptidoglycan layer (3 – 8nm)
 Has high lipid content (lipopolysaccharied) in the
outer membrane
 Has periplasmic space

Fig. Gram-Positive (a) and Gram negative (b) cell wall of bacteria
(a) (b)

Capsule
 Capsules are often regarded as portion of the cell
envelope
 Capsular constituents vary among the different
species of prokaryotes
 Many bacteria have slimy layers, consisting of
polysaccharides only; others have proteins within
the polysaccharide capsule

Capsule … Cont’d
 Some of the important characteristics of capsule
include:
 important in adhesion
 Protects from phagocytosis
 The organism in which capsules have been
demonstrated include: Pneumococci, klebsella,
Escerchia coli, hemophilus influenza, etc.

Cytoplasmic membrane (Plasma membrane)
 It is the actual barrier between the interior and
exterior of the bacteria cell
 The cytoplasmic membrane exhibits a well- defined
selective permeability, excretion of enzyme, and
biosynthesis of cell well and other proteins
 The bacterial transport system and the principal
energy system (oxidative phosphophorylation) are
located in the cytoplasmic membrane

Flagellum
 It is the organ of locomotion in bacterial cell and
consists of filament
 Is free on the surface of bacterial cell
 It is composed of protein named as flagellin

Pili (Fimbriae)
 Interchangeable terms used to designate short, hair-
like structures (finer filaments) on the surfaces of
prokaryotic cells
 Are extruding from the cytoplasmic membrane
 Are shorter and stiffer than flagella, and slightly
smaller in diameter
 Like flagella, they are composed of protein called
pilin

Two functional types of pili may occur independently
or together on some cell
I. Common pili
 Help for attachment of bacteria to epithelial cell
II. Sex pili
 Occur less commonly
 Appear to be specifically involved in bacterial
conjugation, i.e transfer of genetic material (DNA) from
one bacterium to another

Bacterial spores
 Under conditions of limited supply of nutrition,
vegetative forms of certain bacteria form highly
resistant and dehydrated forms, which are called
spores
 These spors are capable of survival under adverse
conditions such as heat, drying, freezing, radiation,
and actions of toxic chemicals
 Spores are usually smooth walled and avoid, in some
species it is spherical

1.4 Identification and nomenclature of bacteria
 In binomial system, each organism is given two
names
 The first is the genus or genera (plural) and the
second is the species
 To express genus capitalize the fist letter of the word
and underline or italicize it for example Esherchia. To
express genus and species together, capitalize the
first letter of the genus name (and then underline or
italicize the entire name- for example Eschelchia coli.
The genes can be abbreviated as E.coli

 Most species name tell as some thing about the
organism
 Its appearances
 Its source
 A characteristic property
 Scientists discover, described or was connected with it
 Escherichia coli – name for microbiologist Theodor
Escherichia and its usual habitat, the colon
 Staphylococcus aureus– characteristic way its cells
aggregate to resemble a bunch of grapes (staphyle-
cluster) and its yellow colonies(aureus- golden)

CLASSIFICATION OF BACTERIA
 Bacteria are classified in to categories and the
classification is based on
1. Morphology
2. Staining
3. Motility
4. Nutritional requirement
5. Bio chemical and metabolic activity
6. Pathogenecity

Morphology: - Bacteria vary widely in size, ranging
from 0.2 µm to 10µm long
There are three basic shapes
1. Spherical or coccoid/cocci- (singular –coccus)
2. Rods or bacilli (singular - bacillus)
3. Spirals (Singular - Spirillum)

A B C
Fig . Different bacterial morphologies A. Cocci, B. Bacilli, C. Spiral shape

 The cells of cocci may be found in various
arrangements depending on the species and the way
they divide
e.g – Micrococcus:-Cocci occurring single
- Diplococci- Pairs of cocci
- Strepto cocci – Cocci in chain
- Staphylococci- Cocci in cluster

 Bacilli (rods) may be short or long, thick or thin,
pointed or with blunt ends
- Some rods resemble cocci and are often called
coccobacilli because they are very short small
bacilli
- Some bacilli stack up next to each other eg.
Diphteroids
- Some are coma shaped e.g. V.cholara

 Spiralls usually occur singly
-The different species of spirilla varies in size,
length, rigidity, number and amplitude of their
coils

Fig. different bacterial arrangements

1.5 Bacterial growth and genetics
 For optimal growth and multiplication, bacteria
requires nutrients, such as water, energy, carbon,
nitrogen and some inorganic salts
 Bacteria also require various environmental factors
for growth in optimum concentration. These include
Oxygen/Carbon dioxide, pH, temperature
 All bacteria need some form of the element Carbon,
H, O2, S, P, and N for growth
 Special elements such as K, Ca, Fe, Mn, Mg, Co, Cu,
Zn are needed by certain bacteria

1. Nutrient requirement
 Depending on their nutritional requirement bacteria can be
classified
 Autotrophs: - are free-living, non-pathogenic bacteria,
most of which can use carbon dioxide as their carbon
source.
 The energy needed for their metabolism can be obtained
from
(a) Sunlight-photoautotrophs and
(b) inorganic compounds by oxidation-chemoautotrophs
 Heterotrophs are generally parasitic bacteria which require
more complex organic compounds than carbon dioxide
as their source of carbon and energy, e.g. sugar

2. Temperature requirement
 Most pathogenic bacteria grow best at an optimum
temperature of 370C
 Based on temperature requirement, microorganisms
can be broadly classified into
 Psycrophilic- are those bacteria, which grow in the
range of -5 to 200C
 These bacteria include those which cause spoilages
of food at refrigeration temperature (2-8oc)

 Mesophilic- are those bacteria, which grow at 20-
450C and show optimum growth at 37oC
 all medically important bacteria (pathogenic
bacteria) belong to this group
 Thermophilic – are those organisms which prefer
high temperature (50-800C)
 May cause spoilage of under processed canned
food

3. Oxygen requirement
The need of oxygen for particular bacterium reflects its
mechanism to meet the requirement of energy
On the basis of this requirement, bacteria have been
divided in to:
 Obligate Anaerobes-these grow only in the
environment devoid of oxygen
 e.g. clostridium
 Facultative anaerobes- these can grow under both
aerobic and anaerobic conditions, e.g.
enterobacteriaceae

 Obligate aerobes- these cannot grow unless oxygen
is present in the medium, e.g. pseudomonas
 Microaerophilic- these organisms lower
concentration of oxygen than are present in the
air(10%) e.g. campylobacter
 Carboxyphilic – live and grow best in atmosphere
which contain increased amount of co2 (5-10%).e.g
Neisseria meningitidis, Neisseria gonorrheae

 Aerotolerant anaerobes – These bacteria oxidize
nutrient substrates without using elemental
oxygen Unlike obligate anaerobes, they can
tolerate the presence of oxygen

4. pH requirement
Most pathogenic bacteria require a pH of 7.2-7.6 for their
optimal growth. Based on pH requirement bacteria can be
classified as
 Neutrophilic:- bacteria grow best at neutral pH (pH=7)
 Most pathogenic micro-organism best grow at neutral
pH (pH=7)
 Acidophilic
 Bacterial grow best at acidic pH (pH<7)
 E.g. Lactobacilli
 Alkalophilic
 Bacterial grow best at Alkaline pH (pH>7)
 E.g. Vibrio cholerae grow at a pH of 8.6

Bacterial growth
 Bacteria divide by binary fission
 When a bacterial cell reaches a certain size, it divides to form
two daughter cells
 Nuclear division precedes cell division
 The Lag Phase; short duration in which bacteria adapt
themselves to new environment
 Exponential phase, log or logarithmic; the population can
double with fast growing bacteria
 Stationary Phase; the number of new cells produced
balances the number of cells that die resulting in a steady
state
 The death/decline phase; number of bacteria dying is much
more than those dividing and hence there is gradual decline
in the total number of organism

Bacterial growth curve

Chapter 1. intro. microbiology (2)

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