1. The document discusses methods for isolating and culturing pure strains of microorganisms including the streak plate method and spread plate technique. These allow for discrete colonies of microbes to grow separately. 2. Specific steps are outlined for isolating Streptococcus thermophilus and Lactobacillus delbrueckii starter cultures from cow's milk samples to produce yogurt. Samples are serially diluted and plated on selective agar then analyzed for biochemical characteristics. 3. The yogurt production process is summarized in 9 steps including adjusting milk, pasteurizing, homogenizing, inoculation with starter cultures, fermentation, cooling, flavoring, and packaging. Specific microbes and fermentation lower the pH

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4. • Once purified, the isolated species can then
be cultivated with the knowledge that only
the desired microorganism is being grown.
Cultivation of
desired
microorganism
 A pure culture can be correctly identified
for accurate studying and testing, and
diagnosis in a clinical environment.
Accurate studying
and testing
 Testing/experimenting with a pure culture
ensures that the same results can be achieved
regardless of how many times the test is
repeated.
Surety of
tests/experiments

5. Robert
Koch
a pioneering microbiologist. Koch’s research and methods helped link the causal nature of
microbes to certain diseases, including anthrax.
In 1881, he urged for the sterilization of surgical instruments using heat. He also invented
methods to purify the bacillus from blood samples and grow pure cultures.
Louis
Pasteur
He is best known to the general public for his invention of the technique of
treating milk and wine to stop bacterial contamination, a process now called pasteurization.
Other
scientists
Casimir Davaine demonstrated the direct transmission of the anthrax bacillus between cows.
Agar was discovered around 1658 by Minoyo Tarozaemon in Japan
Agar was first used in microbiology in 1882 by the German microbiologist Walther Hesse

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7. Fermentation of milk by any other
cultures results in a different dairy
product such as butter or cheese.
These two species are lactic acid
producing bacteria (LAB) and are
gram-positive rods and cocci
respectively.
They do not form spores and are
catalase negative, obligatory
fermentative, microaerophilic and
non-motile.
Isolating the specific starter
cultures ‘’L. bulgaricus’’ and ‘’S.
thermophilus’’can be done using
differential and selective growth
agar mediums.
Once the starter cultures have been
isolated they can be added into a
purified milk sample that is void of
antibiotics and contaminants which
would cause the product to be
different than intended
Because of the starter cultures impact on creating specific products, only
fermentation by the two species Streptococcus
thermophilus and Lactobacillus delbrueckii subsp. bulgaricus produce
yogurt.

8. 1.
2.
In this technique, a serially
diluted specimen containing 2 or
more microbes is used which is
spread over the solidified agar
media plates with the help of a
sterile L-shape glass rod.
The principle behind this method
is that when the Media plate is
spun, at some stage, single cells
will be deposited with the bent
glass rod onto the surface of the
Agar media.
Some of the cells present in the
specimen / diluted specimen will
be separated from each other by a
distance sufficient to allow the
colonies that develop to be free
from each other.
1. Spread plate method

9.  The streak plate method is a rapid qualitative
isolation method.
 The techniques commonly used for isolation
of discrete colonies initially require that the
number of organisms in the inoculums be
reduced.
 It is essentially a dilution technique that
involves spreading a loopful of culture over
the surface of an agar plate.

10. Fresh milk sample was obtained. Samples were serial diluted
with 0.85% (wt/vol) sterile saline supplemented with 0.1%
(wt/vol) peptone as nutrients source to maintain viability of the
isolates in the sample.
The dilutions (10-1−10-3) were spread plated on de Man,
Rogosa, and Sharpe agar (MRSA) and were incubated micro
aerobically for 24 h at 37°C.
Isolates were morphologically and biochemically
characterized for selection of potential L. delbrueckii and S.
thermophilus species.
First, general characterization of isolates by catalase, Gram-
staining, endospore and acid-fast staining to match
characteristics of the genus Lactobacillus and of S. thermophilus
was conducted.
Selected isolates were further analyzed for their ability to grow
on MRS broth (MRSB) incubated at selected temperatures (10°C
and 45°C) and also incubated under selected salinity
concentration (2%, 4% and 5%).
The test tubes containing
a plant sample were
incubated at 37°C for
between 24 and 48 h.
Then a portion of the
medium in a test tube
showing apparent bacterial
growth was frozen in liquid
nitrogen after
supplementation with 20%
glycerol.
Each frozen sample was
thawed and diluted with
sterile 0.85% (w/w) NaCl
solution (saline), and 0.1-
mL aliquots were spread on
both MRS (Oxoid) and
M17 agar plates (Oxoid).
The plates were
incubated anaerobically
using the Anaerogen
system (Oxoid) at 37, 45 or
50°C for between 48 and
72 h to obtain both bacteria
colonies.

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14. • Milk composition may be adjusted to achieve the desired fat and solids content.
• Ingredients such as stabilizers are added at this time.1. Adjust Milk Composition & Blend Ingredients
• The milk mixture is pasteurized at 185°F (85°C) for 30 minutes or at 203°F (95°C) for 10 minutes.
2. Pasteurize Milk
• The blend is homogenized (2000 to 2500 psi) to mix all ingredients thoroughly and improve yogurt
consistency.3. Homogenize
• The milk is cooled to 108°F (42°C) to bring the yogurt to the ideal growth temperature for the starter
culture.4. Cool Milk
• The starter cultures are mixed into the cooled milk.
5. Inoculate with Starter Cultures
• The milk is held at 108°F (42°C) until a pH 4.5 is reached.
• This allows the fermentation to progress to form a soft gel and the characteristic flavor of yogurt.6. Hold
• The yogurt is cooled to 7°C to stop the fermentation process.
7. Cool
• Fruit and flavors are added at different steps depending on the type of yogurt.
8. Add Flavors & Fruit
• The yogurt is pumped from the fermentation vat and packaged as desired.
9. Package

15. Yogurt Milk
There is a dramatic decrease
in the number of microbes
that live in the yogurt niche.
There are more number of
microbes in milk..
Yogurt has high acidic level. Milk has low acidic level.
Yogurt is in semi-solid state. Milk is in liquid state.

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METHOD-PRINCIPLE-PURPOSE-PROCEDURE-
RESULTS/#:~:TEXT=STREAK%20PLATE%20TECHNIQUE%20IS%20USED,WELL%2DSPACED%20FROM%20EACH%20OTHER.
2. HTTPS://MICROBENOTES.COM/SPREAD-PLATE-
TECHNIQUE/
3. HTTPS://MICROBENOTES.COM/STREAK-PLATE-
METHOD-PRINCIPLE-METHODS-SIGNIFICANCE-LIMITATIONS/
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HTTPS://ACADEMIC.OUP.COM/FEMSLE/ARTICLE/269/1/160/493589
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HTTPS://WWW.RESEARCHGATE.NET/PUBLICATION/327983047_ISOLATION_OF_STREPTOCOCCUS_THERMOPHILUS_AND_LACTOBACILLUS_DELBRUECKII_AS_STARTE
R_CULTURE_CANDIDATE_ORIGINATED_FROM_INDONESIAN_COWS_MILK
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HTTPS://ACADEMIC.OUP.COM/JN/ARTICLE/129/1/77/4723223
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8460533.HTML
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