All living organisms require nutrients --the various chemical compounds that
organisms used in order to sustain life.
Nutrients also serve as the sources of
carbon, oxygen, hydrogen, nitrogen,
phosphorus and sulfur (as well as other;
sodium, potassium, chlorine, magnesium,
calcium, trace elements such as iron,
iodine and zinc.)
About two dozen of the
approximately 92 naturally occurring
elements are essential to life.
Cells consist of anywhere between
70% and 95% water.
All living organisms require water to
carry out their normal metabolic
processes, and most of them will die
in the environments containing too
protozoan cysts can survive
completely in the drying
process called dessication.
microorganism has an
optimal, a minimum, and a
temperature at which
the organisms grows best
A temperature BELOW on which
organism ceases to grow.
ABOVE, temperatures which an
Microorganisms that grows best at
They can be found in hot springs,
compost pits and silage as well as in
and near hydrothermal vents at the
bottom of the ocean.
Organisms that favor the
temperatures above 100 degrees
Celsius are referred to as
hyperthermophiles (or extreme
Example: pylorobus fumarii– has
found living at around 113 degrees
Microbes that grows best at
This group includes most of the
species that grow on plants and
animals and in warm soil and
Most pathogens and members of the
indigenous microflora are mesophilic.
Prefer cold temperatures. They thrive
in cold ocean water. At high
altitudes, algae (often pink) can be
seen living on snow.
growth temperature of one
group of psychropiles ( called
psychrotrophs ) is at
The term pH refers to the
hydrogen ion concentration of
the solution and thus the acidity
or alkalinity of a solution.
Most organisms prefer a neutral
growth medium (pH 7.0 – 7.4)
Acidophilic microbes or the
acidophiles such as those that can
live in the stomach and pickled foods
prefer a pH of 2-5.
Fungi prefer acidic environments
pefer an alkaline
environment pH greater than
8.5. examples of these are
can be found living inside the
Osmotic pressure is the pressure
that is exerted on a cell membrane
by solutions both inside and outside
When cells are suspended in a
solution, the ideal situation is that
the pressure inside the cell is equal
to the pressure of the solution
outside the cell.
Substances dissolved in liquids are
When the concentration of solute in
the environment outside of a cell is
greater that the concentration of
solutes inside the cell, the solution in
which the cell is suspended is said to
OSMOSIS is also defined as the
movement of a solvent through a
permeable membrane, from a
solution having a higher
concentration of solute..
If the cell is a human cell, such as
red blood cell, the loss of the water
causes the cell to shrink. This
shrinkage is called CRENATION.
IF THE CELL IS A BACTERIAL
CELL, having a rigid cell wall,
the cell does not shrink. Instead,
the cell membrane and
cytoplasm shrink away from the
cell wall. This condition is known
WHEN THE CONCENTRATION of
the solutes outside the cell is
less than the concentration of
the solutes inside the cell, the
solution in which the cell is
suspended is said to be
CELLS swell up, and sometimes
burst, when place into hypotonic
If the cell burst, the bursting is
called hemolysis. If a bacterial cell is
placed in a hypotonic solution, the
cell may not burst. But the fluid
pressure within the cell increases
This increased pressure in the cells
having rigid cell walls such as plant
cells and bacteria.
If the pressure becomes so great
that the cell ruptures, the escape of
cytoplasm from the cell is referred to
WHEN THE CONCENTRATION OF
solutes outside a cell equals the
concentration of solutes inside the
cell, the solution is said to be
THOSE microbes that prefer salty
environments, such as concentrated
salt water found in great salt lake
and salt evaporation ponds, are
ORGANISMS that do not prefer to
live in a salty environments but
capable of surviving there are called
MOST bacteria are not affected
by minor changes in barometric
pressure. Some thrive at normal
atmospheric pressure, about
14.7 pounds per square inch or
known as piezophiles,
thrive deep in the oceans and
in oil wells, where the
atmospheric pressure is very
Microorganisms vary with respect to
the type of the gaseous atmosphere
that they require.
For example; some microbes (obligate
aerobes) prefer the same atmosphere
that humans do.
20-21% oxygen and 78-79% nitrogen
with all other atmospheric gases
combined representing less than 1%.
Obligate anaerobes are killed by
the presence of oxygen.
To grow a particular
microorganism in the laboratory,
it is necessary, to provide the
atmosphere that it requires.
Example; to obtain the
maximum growth in the
laboratory, capnophiles require
increased concentrations of
carbon dioxide. Usually from
5%-10% Carbon dioxide.
Technologists and technicians who
work in clinical microbiology
laboratories must be able to isolate
microorganisms from clinical
specimen, so that they can gather
information that will enable
identification of any pathogens that
TODAY’S laboratories still use many
of the same basic tools that were
used in the past.
For example the use compound light
microscope, petri dishes solid culture
media, tubes containing liquid
culture media, bunsen burner, and
With respect to humans, the
term growth refers to an
increase in size;
for example; going from a tiny
new born to a large adult.
Although bacteria do increase in size,
before cell division, bacterial growth
refers to an increase in the number of
organisms rather than increase in their
Bacteria multiply by binary fission. The
time it takes a particular bacterial
species to undergo binary fission is
called organism generation time.
each bacteria cell
reaches its optimum size, it
divides by binary fission, into
two daughter cell.
The media that are used in the
microbiology laboratories to
culture bacteria are referred to
as ARTIFICIAL MEDIA OR
they do not occur naturally;
rather than they are prepared in
One way to classify media on
whether the exact contents of the
media are known.
A CHEMICALLY DEFINED MEDIUM is
one which all ingredients are known.
A COMPLEX MEDIUM is one which all
ingredients are not known.
Culture media can also be
categorized as liquid or solid. Liquid
media also known as broth are
contained in tube and are thus often
referred to as tubed media.
Solid media are prepared by adding
agar to liquid media and pouring the
media into tubes or petri dishes
where the media solidifies.
An enriched medium is a broth
or solid medium containing a
rich supply of special nutrients
that promotes the growth of
fastidious organisms. Blood agar
and chocolate agar are examples
of enriched media.
It is used to discourage the
growth of certain organisms
without inhibiting growth of the
organism being sought.
one to readily
differentiate among the
various types of organisms
that are growing on the
In clinical microbiology
laboratories, culture media are
routinely inoculated with clinical
specimens(i.e specimens that
have been collected from
patience suspected with
ASEPTIC technique is practiced to
prevent microbiology professionals
from becoming infected and also
prevent contamination of their work
environment and of clinical
specimens, cultures, and subcultures
AFTER media are inoculated,
they must be incubated that
contains the appropriate
atmosphere and moisture level
and is set to maintain the
The three types of incubators
used in microbiology incubators
are CO2 incubators, non- CO2
incubators and anaerobic
STERILIZATION– involves the
destruction or elimination of all
microbes, including cells, spores,
DISINFECTION– involve the
elimination of most of all
PASTEURIZATION– it’s a method
of disinfecting liquids.
DISINFECTANTS--- are chemicals
used to disinfect inanimate objects
such as bedside equipments and
operating rooms. Disinfectants do
not kill spores.
ANTISEPTICS--- are solutions used
to disinfect skin and other living
SANITATION– Is the reduction of
microbial populations to levels
considered safe by public health
standards, such as those applied
-----Disinfectant or antiseptic that kill
**agents having the suffix ―cidal‖ kill
organisms, whereas agents having
the suffix ―static‖ merely inhibit their
growth and reproduction
--- is a drug or chemical that inhibits
reproduction of microorganisms, but
does not necessarily kill them.
A BACTERIOSTATIC AGENT is one
that specifically inhibits the
metabolism and reproduction of
THE methods used to destroy or
inhibit microbial life are either
physical or chemical, and
sometimes both types are used.
Commonly used in hospitals,
clinics and laboratories to
destroy or control pathogens
include heat, the combination of
heat and pressure, dessication,
radiation, sonic disruption, and
HEAT--- is the most common type of
sterilization for inanimate objects
able to withstand high temperature.
COLD--- refrigeration cannot be
relied upon to kill microorganisms; it
merely slows down their metabolism
and their rate of growth.
RADIATION– pertains to the use of
rays in order to inhibit the growth of
ULTRASONIC WAVES– are used
frequently as a means of cleaning
FILTRATION—used to filter or
separate cells, larger viruses,
bacteria and certain
microorganisms from the liquid
or gases on which they are
refers to the use of chemical
agents to inhibit the growth
of pathogens either
temporarily or permanently..
Various factors affect the efficiency
or effectiveness of a disinfectant.
1. Prior cleaning of the object or
surface to be disinfected.
2. The organic load that is present on
the materials being treated.
3. The concentration of the
4. The bioburden
Some disinfectants (e.g, surface
active soaps and detergents,
alcohols, phenolic compounds)
target and destroy cell membranes.
Others (e.g, halogens, hydrogen
peroxide, salts of heavy metals,
formaldehyde, ethylene oxide)
destroy enzymes and structural
also attack cell walls
or nucleic acids.
*antimicrobial chemical agents
that can safely be applied to
skin are called antiseptics.