SERIAL DILUTION AND QUADRANT STREAKING

Serial Dilution

a common microbiological technique used to estimate the concentration of microorganisms in a sample.

Serial Dilution

In water testing, this helps determine the bacterial load in a given water source by reducing the concentration of microorganisms to a countable level.

Serial Dilution

is used to reduce bacterial concentration for easier counting. 

Serial Dilution

Performed in a series of steps, usually in factors of 10 (logarithmic dilutions).

30-300 CFU

What is the CFU range for an accurate plate count?

• Sterile test tubes 

• Sterile distilled water 

• Pipettes & tips 

• Sterile petri dishes 

• Prepared EMB & NA plates 

• Sterile spreader 

• Incubator (37°C, 24-48 hrs)

• Manual autoclave and alcohol lamp

What are the materials and equipment needed for serial dilution?

Buffered peptone water

a diluent and pre-enrichment broth used in microbiology, particularly for food safety testing. It helps recover injured microorganisms, like Salmonella, from various food sources and other materials.

• Statistical significance 

• Too Few To Count (TFTC)

If there are fewer than 30 colonies, the count may be unreliable due to statistical variations.

• Counting ease

• Too Numerous To Count (TNTC)

If there are more than 300 colonies, it becomes difficult to distinguish and count individual colonies, leading to potential error.

Streak Plate Method

If you want to study a specific bacteria, you need to get a pure culture of that bacteria first and this is the best method to isolate a pure colony. 

Robert Heinrich Hermann Koch 

One of the Founder of Bacteriology and Nobel Prize 1905 in Physiology or Medicine

Robert Heinrich Hermann Koch 

Discovered specific causative agents of anthrax disease cycle (1876), tuberculosis (1882) and cholera (1883) and gave experimental support for the concept of infectious disease 

Robert Heinrich Hermann Koch 

Pioneered the use of agar as a base for culture media 

Robert Heinrich Hermann Koch 

Developed the pour plate method and streak plate method

Pure Culture

contains only one type of microorganism, all cells are genetically identical and are derived from a single cell or organism.

Streak Plate Method

A laboratory technique used to isolate and purify microorganisms from a mixed culture or sample.

Quadrant Streaking

one of the most common and easiest methods used to obtain isolated pure colonies, leading to discrete colony growth.

Quadrant Streaking

Spreading a small amount of the sample across the surface of agar plates in a specific pattern 

Quadrant Streaking

Allows individual cells to be deposited on the agar surface and grow into distinct COLONIES

Use only a tiny amount of inoculum. Get only one colony. If it's too tiny, get 1-3 colonies as long as discrete colonies. 

What makes a streak plate method successful?

It will kill the bacteria

What happens if the loop is too hot?

the numbers will not decrease and it is not enough for individual colonies to form.

What would a streak plate look like if you had not sterilized the loop between streaking into new areas of the plate?

Streak plate is used to isolate and purify a particular bacteria species from a mixture of bacteria while spread plating is used to enumerate and quantify bacteria in a sample. 

When would you use spread plating instead of streak plating?