2. The growth of a population is an increase in
the number of cells
The requirements for microbial growth are
both physical and chemical
3. Temperature
Psychrophiles (cold loving)
Mesophiles (moderate-temperature loving)
Thermophiles (heat-loving)
pH
Most bacteria grow best at pH 6.5 - 7.5
Acidophiles tolerant to acidity
Osmotic pressure
They require water for growth and made up of 80-90%
water
In hypertonic solution,most microbes undergo plasmolysis
In hypotonic solution wrinkle
Halophiles, can tolerate high salt concentrations
4. Carbon
Carbon is the structural back-bone of living matter
Half the dry weight of bacterial cell is carbon
Chemoheterotrophs, use an organic molecule
Autotroph (chemoautotroph or photoautotroph) derive
their carbon from carbon dioxide
Nitrogen
Nitrogen is needed for protein and nucleic acid
synthesis
Nitrogen can be obtained from the decomposition of
proteins or from NH4
+ or NO3
-
A few bacteria are capable of nitrogen (N2) fixation
5. Oxygen
On the basis of oxygen requirements, organisms are
classified as
obligate aerobes
facultative anaerobes
aerotolerant anaerobes
microaerophilic
capnophilic
Aerobes, facultative anaerobes, and aerotolerant
anaerobes must have the enzymes superoxide dismutase
(2O2
- + 2H+ O2 + H2O2) and either catalase (2H2O2
2H2O + O2) or peroxidase (H2O2 + 2H2 2H2O)
Other chemicals required for microbial growth include
sulfur, phosphorus, trace elements, and, for some
organisms, organic growth factors
6. A culture medium is any material prepared for the
growth of bacteria in a laboratory
Microbes that grow and multiply in or on a culture
medium known as a culture
- Agar is a common solidifying agent for a
culture medium
- Broth medium is a liquid medium
- Semisolid medium
7. TYPE PURPOSE
Chemically defined media Growth of chemoautotrophs and
photoautotrophs, and microbiolo-
gical assay
Complex media, made up of
nutrient such as extract from
yeast, meat, or digest of protein
exp: nutrient agar or nutrient broth
Most heterotrophic bacteria and
fungi are routinely grown on
complex media
Reducing media Cultivation of anaerobic bacteria
Contain ingredients, such as
sodium thioglycholate, that
chemically combine with
dissolved oxygen and depleted
the oxygen in the culture medium
8. TYPE PURPOSE
Differential media
McConkey, Urease medium,
Salmonella Shigella Agar (SSA),
BloodAgar Plate (BAP)
Differentiation of colonies of
desired microbes from others
Selective media
Bismuth Sulfite Agar (BSA), Eosin
Methylene Blue (EMB),
Thiosulphate Citrate Bile Salt
Sucrose(TCBS)
Suppression of unwanted
microbes; encouraging
desired microbes
9. Enrichment media
Selenite broth
Alkali PeptonWater (APW)
Similar to selective media but
designed to increase numbers
of desired microbes to
detectable level
Enriched media
BAP, Chocolate Agar Plate (CAP),
Brain Heart Infusion (BHI)
For fastidious bacteria
Transport media
Cary-Blair (V. cholerae)
Amis (Nesseria gonorrhoe)
It was needed if the specimens
was taken from far places
10. Bacterial Division
Bacteria normally reproduce by binary fission, in which a
single cell divides into two identical cells
Fungi reproduce by budding, aerial spore formation, or
fragmentation
Bacterial division occurs according to a logarithmic
progression : 2 cells 4 cells 8 cells etc.
GenerationTime
The time required for a cell to divide or a population to
double is known as the generation time
Most bacteria have generation time 1 – 3 hours; other require
more than 24 hours per generation
Pathogenic Mycobacterium require > 8 weeks
11.
12.
13. During the lag phase, there is little or no change in
the number of cells, but metabolic activity is high
During the log phase (exponential growth phase),
bacteria multiply at the fastest rate possible under
the conditions provided
During the stationary phase, there is equilibrium
between cell division and death
During the death phase, the number of deaths
exceeds the number of new cells formed
14. A standard plate count reflects the number of viable
microbes and assumes that each bacterium grows into a
single colony; plate count are reported as number of
colony forming units (CFU)
In filtration, bacteria are retained on the surface of a
membrane filter and then transferred to a culture
medium to grow and subsequently be counted
The most probable number (MPN) method can be used
for microbes that will grow in a liquid medium; it is
statistically estimation
In a direct microscopic count, the microbes in a
measured volume of a bacterial suspension are counted
with the use of a specially designed slide Petroff-
Hausser cell counter
15. Turbidity
A spectrophotometer is used to determine turbidity
by measuring the amount of light that passes
through a suspension of cells
McFarland standard
Metabolic Activity
Acid production or oxygen consumption
DryWeight
For filamentous organisms such as fungi, measuring
dry weight is a convenient method of growth
measurement
