Download to grow. - Med4just

5345
Yazan Al-mansour
Microbial growth
Hani Masaadeh
Second
1
1-11-2015
0
Our lecture today is about controlling the growth of
microorganisms
The objective of this lecture:
several factors that affect the growth of a microorganism
(Temperature, moisture, ph..)
To control the growth of microorganisms, we have In vivo
and in vitro
In vivo: when we apply antibiotics.
In vitro: when we use chemical and physical methods to control
the microorganism.
The types of microorganisms: we classified microorganisms
according to the 1-Tempreture
2-condition, which is called the optimal condition of some
microorganisms (psychrophilic, mesophilic, thermophilic,
halophilic, haloduric, alkaliphilic, acidophilic, and piezophilic).
The importance of using “asptic techniques” in microbiology
laboratory and hospitals is to avoid the contamination.
Draw a bacterial growth curve and label its four phases.
Differentiate between sterilization, disinfection, and
sanitization.
Sterilization: is a term referring to any process which kills
all types of microorganisms. We also call it “Bactericidal”
which describes the chemical agent which kills the
microorganism.
Disinfection: antimicrobial agents that are applied to nonliving objects to destroy microorganisms (reduce the number of
microorganisms). We also call it “Bacteriostatic” which
describes the chemical agent which inhibits growth of
microorganisms.
Sanitization: reduction of the microbial population to a safe
level as determined by the public health standards.
1
The processes of pasteurization and lyophilization:
Pasteurization: sterilization of milk, occurs at temperature 6 to3
centigrade for 30 mins.
Lyophilization: when we make the bacterial growth from liquid
or broth phase to powder phase, so we can keep it up to 5 years.
This is for the purpose of (research papers, demonstration for
students).
Several physical methods used to inhibit the growth of
microorganisms (heating).
Differentiate between bactericidal and bacteriostatic
agents.
Bactericidal: kills all the forms of microorganism.
Bacteriostatic: inhibits the growth or the multiplication of
microorganisms.
-The microbial growth: is the increase in the number of cells,
not cell size.
By binary fission (the duplication of bacterial cells as 1 cell
becomes 2 and these 2 become 4 and so on).
- We have some types of slow microorganisms such as
mycobacterium tuberculosis, which means that the
multiplication will take a long time (18-24h). Not as the common
microorganism E.coli, salmonella which takes (15mins) to grow.
- At some locations, we need to increase the growth of
microorganisms, such as in the microbiology lab. In other
locations we need to inhibit or kill the microorganism, such as
in hospitals or operation rooms to get a sterile area.
- Colonies ( ‫) مستعمرات جرثومية‬: groups of cells large enough to
be seen without a microscope. Each colony contains more than
one million bacterial cell, or a population of billions of cells.
- The colonies are different from one microorganism to another.
We can differentiate between them by the differential and
selective media.
2
Now we have factors which are important for microbial growth.
- Temperature: (mesophiles, thermophiles, secrophiles..) the
classification here is according to the optimal temperature for
one type of microorganism.
- Moisture: if we want to prepare a media for moisture, it is done
by sterile distilled water.
- Osmotic pressure
- PH (acidic, alkaline, neutral)
- Barometric pressure
- Gases (oxygen aerobic and nonaerobic bacteria)
- Radiation: plays a high role in sterilization.
- Chemicals
-Presence of neighboring microbes.
The requirements for microbial growth can be divided into two
main categories: physical and chemical.
- Physical requirements include temperature, pH and Osmotic
pressure.
- Chemical requirements include sources of carbon, nitrogen
and sulfur.
Now let's talk about it in details..
Physical requirements:
A) Temperature
- The minimum growth temperature is the lowest temperature
at which the species will grow.
- The optimum growth temperature is the temperature at
which the species grows best.
-The maximum growth temperature is the highest temperature
at which Growth is possible.
The bacteria can grow at maximum and minimum
temperature, but the multiplication of the bacteria won’t be very
3
fast. For example, “E.coli” prefers the temperature of a human
body which is around 36-37 and it’s the optimum temperature of
it.
In the previous figure you can see the type of bacteria which
grows at different temperatures ..
- Psychrophiles: refers to cold conditions (-10 _ 20).
- Thermophiles: refers to Nonpathogenic bacteria, because it
needs higher temperature than the body temperature (40 _70).
- Mesophiles: refers to pathogenic bacteria which grows best in
moderate temperature, neither too hot or too cold, like the
body’s temperature (10 _50) .
B) PH.
- most bacteria prefers neutral pH, between 6.5 and 7.5
- Acidophiles grow in acidic conditions: One microorganism
which is highly pathogenic and grows in acidic conditions is
called Microbacterium tuberculosis or any acid fast bacteria.
Molds and yeasts grow over a greater range of pH than
bacteria, but the optimum pH is between 5 and 6 (acidic
4
environments).
- Alkalinity also inhibits microbial growth but is rarely used to
preserve foods. Example for alkaline: bacterium Vibrio-cholerea
(pH 8.8).
c) Osmotic pressure
- Microorganisms obtain almost all of their nutrients in solution
from the surrounding water (humid environment).
- They require water for growth and 80 to 90% of them is water.
- Extreme or obligate halophiles are organisms that have
adapted so well to high salt concentrations that they need it for
their growth (in the Dead Sea).
- Facultative halophiles do not require high salt concentrations
but are able to grow at salt concentrations of 2 to 15%.
- Most microorganisms must be grown in a medium that is
nearly all water.
Chemical Requirements for the bacterial growth: When we see
the composition of the media, we will find some of those that are
present.
 Carbon  Nitrogen  Sulfur  Phosphorus  Potassium,
magnesium and calcium  Oxygen
- Oxygen a very important factor because some bacteria can
only grow in the presence of oxygen (Aerobic) and some can
only grow in the absence of oxygen (Anaerobic) and others can
grow in both.
5
Grows in the
presence of
O2, notice
bacteria
grows just on
the surface
Grows in
presence or
absence of O2
“ like E.coli “
Grows in the
absence of O2
“clostridium
perfringens “
Grows better
in the absence
of O2, but
Resists the
presence of O2
Anaerobic but
can Grow in
the presence
of a small
amount of O2
Chemical Requirements: Organic growth factors.
 Essential organic compounds that an organism can’t
synthesize must be obtained from the environment.
 Vitamins, amino acids, purines and pyrimidines
 Most bacteria can synthesize all of their own vitamins and are
not dependent on outside sources.
Culture Media: is a liquid or a gel designed to support the
growth of microorganisms.
There are different types of media for growing different types of
cells.
6
-About agar, on a semi solid media there is an agar but a little
amount of it.
- On a liquid media, there is no agar at all.
Give nutrients
Give nutrients
inhibit the grow of bacteria
give solidification for media
for humidity
fbffffrfvvfffff
fffffff vvvvvv
-E.coli needs carbohydrates to grow, such as glucose and lactose,
carbohydrates give e.coli pigmentation (color).nj
On lactose fermenter, gives a red or a pink colony.
On glucose fermenter, gives a colorless colony.
7
Anaerobic Culture Methods )‫(طرق زراعة البكتيريا الالهوائيه‬
-Because anaerobic bacteria might be killed due to the exposure to
oxygen, a special media called the reducing media must be used.
- Reducing media
Contains chemicals (sodium thioglycolate) that combine O2 and
deplete the oxygen in the culture medium. (The oxygen found on
the surface of thioglycolate media. liquid media) ‫(بتمنع وصول‬
.)‫االكسجين للبكتيريا‬
-Special anaerobic jars are used to grow anaerobes on Petri plates
to observe individual colonies. The mechanism is that the Culture
plates are placed in the jar, and oxygen is removed by the addition
of a packet of chemicals which react with oxygen to form water.
”jars” .‫زجاجه خاصة عشان تنمو البكتيريا الالهوائيه فيها‬
-Use of transparent anaerobic champers, equipped with air locks
and filled with inert gases.
Capnophiles Require High CO2:
Microbes that grow better at high CO2 concentrations are called
capnophiles (capno: smoke (CO2), philes: loving). Examples:
(Nesseria Meningitides, Nesseria gonorrhea)
CO2 culture methods:
a) Candle jar, Cultures are placed in a sealed jar containing a
lighted candle, which consumes O2 and produces CO2. What
happened here is as following; There is a candle with flame, so
when the jar was closed the flamed candle consumed O2 and
produced CO2, so with the presence of CO2 and Solid media (Petri
plate), after 24 hours we will have Capnophiles bacteria present on
the bottom of the jar, we can also use liquid Media as in tubes.
) ‫(أالحتراق يولد ثاني أكسيد الكربون‬
8
b) CO2-packet The packet consists of a bag containing a Petri
plate and CO2 generator.
) ‫(مضخة خاصه لثاني أكسيد الكربون‬
9
media types : We have different types of media used in the growth
of microorganisms:
1-selective 2- Differential 3-Enrichment
Selective Media, Selective and differential media are used to
detect the presence of specific microorganisms associated with
disease or poor sanitation.
- Selective media are designed to suppress the growth of
unwanted microbes and encourage growth of the desired
microbes. (Just one type of microorganism will be suppressed in
this media).
) ‫(بتحط مواد بتمنع نمو أي بكتيريا غير الي بدها ياها‬
Example: bismuth sulfite agar is used to isolate the typhoid
bacterium (Salmonella typhi) from feces.
Example: Sabourraud’s dextrose agar (pH 5.6), is used to isolate
fungi that outgrows most bacteria at this pH.
Differential Media, in this media we use an indicator to
differentiate between the pigmentation of two microorganisms.
- Make it easy to distinguish colonies of the desired organism
from other colonies growing on the same plate. Example,
10
MacConkey agar: is a culture medium designed to selectively
grow Gram-negative bacteria and differentiate them by lactose
fermentation.
*MacConkey agar color:
-The lactose fermenter bacteria give: pink colonies (e.coli).
-Non-lactose fermenter bacteria give: colorless colonies
(Salmonella).
at the end , forgive me for any mistake . .
“We cannot direct the wind but we can adjust the sails.”
this is a new beginning for us in second exams
we can do it . . .
Edited by: Salam Mustafa
11