lab no 8 lab no 8 environmental factors affecting microbial growth
TRANSCRIPT
LAB NO 8LAB NO 8
Environmental Factors Environmental Factors Affecting Microbial Affecting Microbial
growthgrowth
Environmental Factors Affecting Environmental Factors Affecting Microbial growthMicrobial growth
There are many factors in the environment of the microorganism that can dramatically affect the rate and the extent of the microbial growth.
1. Hydrogen Ion Concentration (PH).2. Moisture content.3. Solute Concentration (osmotic
pressure).4. Oxygen.5. Temperature.
11..Moisture contentMoisture content
Humidity is absolutely necessary for metabolic reactions and multiplication of the microorganism.
However, drying does not kill microorganism, but only prevent them from further multiplication.
⁂ generally, endospores and relatively small cells are more resistant to drying than vegetative and large cells.
22 . .Hydrogen Ion Concentration Hydrogen Ion Concentration (pH)(pH)
The enzymes, electron and nutrient The enzymes, electron and nutrient
transport system found in the cell transport system found in the cell
membrane are sensitive to the membrane are sensitive to the
concentration of hydrogen ions (Hconcentration of hydrogen ions (H++).).
The optimum pH for most bacteria is 6.5 - The optimum pH for most bacteria is 6.5 -
7.57.5
Fungi & acidophilic bacteria [Fungi & acidophilic bacteria [e.g; e.g;
Lactobacillus spLactobacillus sp.] can tolerate acidic pH up .] can tolerate acidic pH up
to 4.to 4.
while basophilic bacteria [e.g;while basophilic bacteria [e.g;VibrioVibrio
choleracholera] can grow at pH up to 9.] can grow at pH up to 9.
※ That’s why certain food are not That’s why certain food are not
easily contaminated with bacteria easily contaminated with bacteria
due to their acidity like citrus fruits.due to their acidity like citrus fruits.
3. Solute Concentration 3. Solute Concentration (osmotic pressure)(osmotic pressure)
The conc. of solutes dissolved in the
aqueous environment of the bacterial cell
can influence the passage of water and
nutrient into the cell.
Some microorganism inhibited or killed by
different concentration of solute such as
NaCl or sugars as a result of their effect on
the osmotic pressure of the medium.
Most microorganisms can grow well Most microorganisms can grow well
at isotonic environment. at isotonic environment.
In Hypertonic environment, cells have In Hypertonic environment, cells have
the tendency to lose water to their the tendency to lose water to their
environment, as the conc. outside the environment, as the conc. outside the
cell is greater than inside the cell.cell is greater than inside the cell.
3. Solute Concentration (cont.)3. Solute Concentration (cont.)
Under this condition, most bacteria
can’t reproduce due to dehydration
of the cells leading to concentration
of solute & electrolytes within the
cells which cause toxic effects.
3. Solute Concentration 3. Solute Concentration (cont.)(cont.)
In general microorganisms are In general microorganisms are
classified into two major groups classified into two major groups according to their oxygen according to their oxygen requirement:requirement:
1. Aerobes: • In which oxygen is absolutely
necessary for growth.2. Anaerobes: • They can reproduce in the absence of
oxygen. In fact oxygen inhibit their growth & in most cases kill them.
4.Oxygen 4.Oxygen
55..TemperatureTemperature Microorganisms can be classified Microorganisms can be classified
according to the optimum according to the optimum temperature for growth into:temperature for growth into:
a)a) Psychrophilic Psychrophilic ((cold-loving);cold-loving); Which can grow best at Which can grow best at
temperature between temperature between 0 - 20ºc.0 - 20ºc.b)b) MesophillicMesophillic (middle-loving);(middle-loving); which can grow best at which can grow best at
temperature between temperature between 20 - 40ºc.20 - 40ºc.c)c) ThermophilicThermophilic (heat-loving);(heat-loving); which can grow best at which can grow best at
temperature between temperature between 40 – 80ºc.40 – 80ºc.
Temperature (cont.)Temperature (cont.)
The lethal effect of high temperature on The lethal effect of high temperature on
microorganisms can be attributed to:microorganisms can be attributed to:
1.1. Irreversible denaturation of intracellular Irreversible denaturation of intracellular
proteins such as enzymes and other vital proteins such as enzymes and other vital
components of the cell.components of the cell.
2.2. Water loss due to evaporation leads to Water loss due to evaporation leads to
increase concentration of electrolytes increase concentration of electrolytes
within the cell causing toxic effect. within the cell causing toxic effect.
Temperature (cont.)Temperature (cont.)
Generally, bacterial endospores are more
resistant to adverse environmental conditions
such as drying or high temperature due to:
A. Low water content of spores and low metabolic
activities.
B. Low permeability due to thick spores coat.
C. Presence of dipicolinic acid and dicarboxylic acid
in the spore coat which are complex with divalent
ions particularly calcium to give a heat resistant
complex.
Temperature (cont.)Temperature (cont.)
NOTICE: Bacterial endospores are heat and
chemical resistant as they serve a protective function.
However, the spores of yeast and molds are not resistant to environmental conditions as they serve a reproductive function.
DeterminationDetermination ofof ThermalThermal DeathDeath TimeTime
Thermal death time: of a given species defined as the time
required to sterilize (kill) a standardized pure culture of that species at a specified temperature.
Thermal death point: of a given species defined as the
lowest temperature required to sterilize (kill) a standardized pure culture of that species at a specified time.
DeterminationDetermination ofof ThermalThermal DeathDeath TimeTime
Determination of thermal death time is useful in sterilization processes, preparation of heat killed vaccines, canning of food and many other application.
Materials:- Culture of Bacillus subtilis and E. coli. Nutrient agar plate. Thermometer and water bath.
DeterminationDetermination ofof ThermalThermal DeathDeath TimeTime
55 1010
15152020
B B
E E
5 min5 min
10 min10 min
50 50 ºcºc
7070ºcºc
95 95 ºcºc
Invert & incubate for 48 hrsInvert & incubate for 48 hrs
Result
1.E. coli1.E. coli
Temp. time
5min 10min 15min 20min
50℃70℃95℃
2- B. subtilis;2- B. subtilis;
Compare the result of spore forming microorganism against non-spore forming one. give your comment.
MIC: It is the lowest concentration of
the antimicrobial agent that inhibits the growth of the test organism but not necessarily kills it.
MBC(minimum bactericidal conc.)
It is the lowest concentration of the antimicrobial agent that kills thetest organism.
Bactericidal drugs have MBC 2-4 times MIC.
Bacteriostatic drugs have MBC much higher than MIC.
The breakpoint of an antimicrobial agent:
It is the concentration of the drug which can be achieved in the serum with optimal dose.
Susceptible organisms: are those with MICs at/below the
breakpoint.
Resistant organisms: are those with MICs above the
breakpoint.
Material: Culture of staph. aureus Augmentin Saline Melted nutrient agar bottle Sterile peri dish 4 sterile vials 2 sterile pipette 1ml 1 sterile pipette 5 ml
Procedure:
45°c
S
o.2 ml
AB 1 2 3 4
1 ml 1 ml 1 ml 1 ml
1 ml sterile water
4
Incubate the plate Uninverted at 37°c for 24h
3
21
43
2 1
Results:Measure the diameter of each inhibition zone
The diameter of the inhibition zones are directly
proportional to the conc. of the antibiotic.
Zone diameter
Well diameter
Agar Diffusion MethodResults:
AB conc
Log conc
Zone diameter
Well diameter
X X²
100
50
25
12.5
X = X = Zone diameter – Well diameter Zone diameter – Well diameter 22
If Original Antibiotic Conc. = 200 µg/ml
x²x²
Log concLog conc
Anti-log = MICAnti-log = MIC
x
x
x
x
concconc
MICMIC
If use semi-log paper, then No need to calculate Log conc.
x²x²
x
x
x
x
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