Peptone Yeast Extract Glucose Broth


Peptone Yeast Extract Glucose Broth (PYG) is a complex liquid medium that supports the growth of a wide range of anaerobic bacteria. Anaerobic bacteria are those that do not require oxygen for their metabolism and can grow in environments with low or no oxygen. PYG broth contains the following components:

  • Peptone: A pancreatic digest of casein, which is a protein found in milk. Peptone provides amino acids, peptides, and other nitrogenous compounds that are essential for bacterial growth and protein synthesis.
  • Yeast extract: A soluble extract of yeast cells, which are fungi. Yeast extract provides vitamins, minerals, and other growth factors that enhance the growth and metabolism of anaerobic bacteria.
  • Glucose: A simple sugar that serves as an energy source for anaerobic bacteria. Glucose is fermented by anaerobic bacteria to produce various organic acids and gases, such as lactic acid, acetic acid, carbon dioxide, and hydrogen. The production of these end products can be used to identify different types of anaerobic bacteria based on their fermentation patterns.
  • L-cysteine: An amino acid that acts as a reducing agent in the medium. L-cysteine lowers the oxidation-reduction potential (ORP) of the medium, which creates a low oxygen environment that favors the growth of anaerobic bacteria. L-cysteine also helps to prevent the formation of toxic oxygen radicals that can damage bacterial cells.
  • Hemin: A compound that contains iron and porphyrin, which are components of hemoglobin, the oxygen-carrying protein in red blood cells. Hemin supplies X factor, which is a growth factor required by some anaerobic bacteria, such as Haemophilus and Actinobacillus species. Hemin also stimulates the production of pigments by some anaerobic bacteria, such as Prevotella and Porphyromonas species.
  • Vitamin K: A fat-soluble vitamin that is involved in blood clotting and bone metabolism. Vitamin K supplies K factor, which is another growth factor required by some anaerobic bacteria, such as Bacteroides and Fusobacterium species.
  • Sodium bicarbonate and dipotassium phosphate: Inorganic salts that act as buffers in the medium. Buffers help to maintain the pH of the medium within a narrow range that is optimal for bacterial growth. The pH of PYG broth is adjusted to 7.3 +/- 0.5 at 25°C before sterilization.
  • Sodium, potassium, calcium, and magnesium salts: Inorganic salts that help to maintain the osmotic balance and provide critical ions used in transport and enzyme activities by bacterial cells.

The final composition of PYG broth per liter of distilled water is:

Component Amount
Peptone 10 g
Yeast extract 10 g
Glucose 5 g
L-cysteine hydrochloride 0.5 g
Hemin 5 mg
Vitamin K 1 mg
Sodium bicarbonate 2 g
Dipotassium phosphate 0.4 g
Sodium chloride 5 g
Potassium chloride 2 g
Calcium chloride dihydrate 0.1 g
Magnesium sulfate heptahydrate 0.1 g