The study of living organisms
Cell the basic functioning Unit of all living things
There are 2 Types of Cells
The study of living organisms
THE UNIVERSAL PRINCIPLE OF LIFE
All cellular life has the following characteristics in common.
The following criteria are the MINIMAL REQUIREMENTS of life
•All cells have a CELL MEMBRANE
•All cellular life CONTAINS DNA as its genetic material.
•All cells contain several varieties of RNA molecules and PROTEINS.
•All cells are composed of the same BASIC CHEMICALS:
carbohydrates, proteins, nucleic acids, minerals, fats and vitamins
•All cells REGULATE the flow of nutrients and wastes
•All cells REPRODUCE and are the result of reproduction
•All cells require a SUPPLY OF ENERGY
Microbiology is the study of living organisms of microscopic size
include bacteria, fungi, algae protozoa and viruses
it is concerned with their form, structure, reproduction, physiology,
metabolism and classification.
It also includes the study of their effects
on human beings
and on other animals and plants
their ability to make physical and chemical
changes in our environment
Major Field Of Microbiology
Medical Microbiology Causative agents of Disease,
diagnostic Procedures for
identification of causative agents,
Aquatic Microbiology Water Purification, Microbiology
examination, biological degradation
Food Microbiology Contamination & spoilage of Food,
preservative & preparation of food,
food born diseases and their
ANCIENT MICROBIOLOGICAL HISTORY
Ancient man recognized many of the factors involved in disease.
Early civilizations on Crete, India, Pakistan and Scotland
invented toilets and sewers; lavatories, dating around 2800 BC
The first cities to use water pipes (of clay) were in the Indus Valley of
Pakistan around 2700 BC. Metal water pipes were used in Egypt (2450 BC)
and the palace of Knossos on Crete around 2000 BC had clay pipes.
Most ancient peoples recognized that some diseases were communicable
and isolated individuals thought to carry "infections
Sadly, we know that this knowledge did not help most of our ancestors and
that the human life span was, until the last 200 years, more often than not
cut short due to infectious disease.
Even today approximately 15,000,000 CHILDREN DIE PER YEAR,
mainly from infectious diseases that are preventable with basic
sanitation, immunization and simple medical treatments. One might
honestly question just how far we have come in our treatment of disease.
An excellent synopsis of the history of Microbiology
ANCIENT MICROBIOLOGICAL HISTORY
The first person to report seeing microbes under the microscope
was an Englishman, Robert Hooke.
he saw the cellular structure of plants around 1665.
He also saw fungi which he drew.
However, because his lens were of poor quality
he was apparently unable to "see" bacteria.
Anton van Leeuwenhoek was a man born before
his time. Although not the FIRST TO DISCOVER THE
MICROSCOPE or to use magnifying lens, he was the
first to see and describe bacteria.
Group of Micro-organism
The major groups are as follows.
are relatively simple organisms the most primitive types and unicellular.
All Algae cells contain chlorophyll and are capable of photosynthesis.
Algae are found most commonly in aquatic environments or in deep soil.
are very small non-cellular parasites or pathogens of plant animals
and bacteria. Virus can be cultivated only in living cells
Unicellular and consist of nucleated mass of cytoplasm, parasites but
the known protozoa are few that cause disease in human beings and
Lower plants devoid of chlorophyll they are usually multi-cellular but
are not differentiated into roots stems and leaves
Bacterial World History
In the 1800s people (mainly the poor) began to use hospitals.
Hospitals also became centers of physician
In 1841 (30 years before the GERM THEORY of disease
was established) young doctor IGNAZ SEMMELWEIS
was hired to run a maternity ward in a Vienna hospital. He
reasoned that there was an
that caused deaths and that one could transfer it.
Acting on this assumption, Semmelweis instituted sanitary
measures which included having the doctors wash their
hands in disinfectant and change from lab coats dripping
with pus and blood from the autopsy room to clean lab
coats before examining patients or assisting in a birth.
The greatest biologist of the nineteenth
century was Louis Pasteur (1822 1895).
His work had both practical use and
profound theoretical significance.
“On the practical side, what discovery in
the history of mankind is more important
than the germ theory of disease?”
The size, shape and arrangement of bacteria,
and other microbes, is the result of their
genes and thus is a defining characteristic called
The most common bacterial shapes are
RODS, COCCI, and SPIRAL.
However, within each of these groups
are hundreds of unique variations
External from cell wall are capsules, Flagella, and Pili
and external to cytoplasmic membrane is the cell wall
They are essential structure for viability
They are composed of unique components found nowhere else
It is rigid structure that gives shape to the cells
They provide for immunological distinction among the strain of
the Gram-positive Bacteria the cell wall is thick
(15-80 nanometers), consisting of several layers of
In the Gram-negative Bacteria the cell wall is
relatively thin (10 nanometers) and is composed of
a single layer of peptidoglycan surrounded by a
membranous structure called the outer membrane.
The outer membrane of Gram-negative bacteria
invariably contains a unique component, lipo-
polysaccharide (LPS) which is toxic to animals.
Bacterial cell wall structure Gram-negative Bacterial Membrane Structure
Gram-negative Cell Membrane
•Gram-negative bacteria are
surrounded by two
•The outer membrane functions
as an efficient permeability
lipopolysaccharides (LPS) and
Gram-positive Bacterial Membrane Structure
•The lipid bilayer cell
membrane of most of the
Gram-positive bacteria is
covered by a porous
Gram Staining method
The basic differences in surface structures of
Gram-positive and Gram-negative
bacteria explain the results of Gram staining
In a rich culture medium bacteria, grown under
aerobic conditions, achieve a final concentration of
2-5 x 109 cells per ml in about 12-18 hours.
In the case of bacteria the timeline could, in theory,
start with a single cell and end 24 hours later
(assuming no death) with a bacterial-mass near the
weight of the earth.
Another way to look at this is that a single
bacterium can produce, in about 12 hours, ~5
billion offspring in two milliliters of medium;
something it has taken the human 3.5 billion years
An organism that is able to live and grow in the presence of atmospheric
oxygen is termed as aerobe.
An organism that is able to live and grow in the absence of atmospheric
oxygen is termed as anaerobe.
Some bacteria, such as M. tuberculosis, require oxygen because their
ATP-generating system is dependent on oxygen as the hydrogen acceptor.
Other bacteria, such as E.coli, utilize oxygen to generate energy by
respiration if it is present, but they can use the fermentation pathway to
synthesize ATP in the absence of sufficient oxygen.
They vary in their response to oxygen exposure; some can survive but
are not able to grow, whereas others are killed rapidly.
The body surfaces support the growth of a variety of
bacteria and fungi, which collectively are called
The NORMAL FLORA.
The normal flora comprises a PERMANENT population of organisms.
The normal flora extensively populates many areas of the body.
The members of normal flora play a role both in the maintenance of health
and in the causation of disease in a significant ways.
Although these organisms are nonpathogenic in their usual anatomic
location. They can be pathogenic in other parts of the body.
They may serve a nutritional function. The intestinal bacteria produce several
vitamin B.and vitamin K. poorly nourished people who were treated with
oral antibiotics can suffer vitamin deficiencies as a result of the reduction
in the normal flora. However since germ-free animal are well nourished,
the normal flora is not essential for proper nutrition.
If a microorganism is capable of causing disease its called
“PATHOGEN” and this phenomenon is called “PATHOGENESIS”.
VIRULENCE: is a quantitative measure of pathogenicity and is measured
by the number of organisms required to cause disease.
LD 50: Lethal Dose is the no. of organisms needed to kill half of the hosts.
ID 50: Infectious Dose (50%) is the no. of organisms needed to cause
infection in half of the patient.
Pathogens cause disease by two major mechanisms,
Toxin Production and
TOXINS are divided into EXOTOXIN & ENDOTOXIN.
EXOTOXINS are polypeptides released by the cell, whereas
ENDOTOXINS are lipopolysachrides, which form an integral part of the
Invasive bacteria grow to large number locally and cause symptoms in
that area by producing a variety of enzymes that damage adjacent host
Infection is a morbid state caused by the multiplication of the pathogenic
micro-organisms within the body.
TYPES OF INFECTIONS
There are two types of infections, Acute and Chronic.
Onset Rapid Slow
Severity Greater Slower
Duration Short Prolonged
Sites of Infection
Upper Respiratory Tract Reproductive System
Dental Skin & Soft Tissues
Urinary Tract Gastrointestinal Tract
A typical acute infectious disease has 4 stages;
The INCUBATION PERIOD which is time between
the acquisition of the organism (or toxin) and the
beginning of symptoms (this time varies from hours
to days to weeks depending on the organism)
The PRODROME PERIOD during which nonspecific
symptoms such as fever, malaise, and loss of
The SPECIFIC ILLNESS PERIOD during which the
overt characteristic signs, symptoms of the disease
The RECOVERY PERIOD during which the illness
abates and the patient returns to the healthy state.
Typical Stages of An Infectious Disease
Signs of infection in the body
When pathogens overcome the natural defence of the body, the
body responds by sending out certain signals, which indicate that
an infection is present in the body.
These signals are known as the SIGNS and SYMPTOMS of disease.
A SYMPTOM is subjective, a feeling experienced & reported by
A SIGN is objective i.e. it can be observed and measured by the
Sign of infection may local (occurring in the immediate vicinity of
the infection), or systemic (affecting the entire body).
Six typical signs of infection are as follows:
LOCAL SIGNS (Inflammatory responses to infection)
Host defence are composed of two complementary,
frequently interacting systems:
protect against microorganisms in general.
Specific natural & acquired immunity:
protect against a particular microorganism.
Medicines (antibiotics) are the specific defences against
a particular microorganism.
Infections contracted during a HOSPITAL STAY
involving an organism that is a "hospital strain"
of the infectious agent.
These infections are usually picked up from the personnel
transporting the infectious agent from one patient to
another from instruments, often inserted into sensitive
parts of the body (e.g. catheters, needles, proctoscopes
etc.), on the equipment (e.g. bed pans, beds, sheets,
dishes, flowers etc.)
Nosocomial bacteria are often very resistant to antibiotics
having been exposed to a variety of antibiotics while in
the hospital. It is estimated that 2 to 10% of US-hospital
patients ACQUIRE A NOSOCOMIAL INFECTION during
These are individuals whose general condition of health
renders them MORE SUSCEPTIBLE to infectious agent and
infectious agent gaining a foothold in their bodies.
•People who have suffered serious trauma and
injury by accident or intention (an operation).
•Those undergoing treatment with
immunosuppressive drugs or anticancer drugs.
•Those suffering extreme stress (e.g. students
before difficult exams).
•Those suffering or recovering from a serious
•Those suffering from diabetes.
•Those who have recently experienced childbirth.
Refers to the fact that a particular disease is
NORMALLY FOUND IN A PARTICULAR AREA
a relatively SUDDEN INCREASE in the number of cases of a
particular disease in a PARTICULAR PLACE OR AREA
An epidemic that encompasses the ENTIRE WORLD. AIDS is a
pandemic; the flu is often pandemic. In the past pandemics were
rare, but through the combination of world wide rapid travel and
the burgeoning human population (~6 billion), pandemics are
likely to be increasingly in our future.
the study of the origin, cause and spread of disease
MODE OF TRANSMISSION =
This refers to how the disease is spread between
hosts. Obviously in combating any infectious disease
it is crucial to know how it is spread, but this also
applies to hereditary diseases.
These are humans or other animals in
which the infectious agent is growing
and reproducing with little or no visible
harm to the current host
MORTALITY AND MORBIDITY:
Morbidity refers to the number of people who catch a
disease, whereas mortality refers to the number of people
who die from a disease. This data is usually presented in
terms of numbers per 100,000. For example, chickenpox
has a high morbidity, but a very low mortality. Conversely
AIDS has a low morbidity, but a high mortality.