BACTERIAL COUNTS LAB 9 A L NOOR AMEER

BACTERIAL COUNTS LAB. 9 A. L. NOOR AMEER

WHY WE COUNT BACTERIA ? • In order to observe microbial reproduction, it's necessary to determine numbers of microorganisms, there are different methods used to count the bacteria such as: • A- Total count: ( for counting living and non living cells) • 1 - Direct microscopic count : - Breed method - Haemocytometer ( counting chamber). • 2 - Indirect microscopic count: - Optical density (O. D) by spectrophotometer

• B- Viable plate count: ( for counting living cell only) • 1 - Dilution to extinction • 2 - Pour plate method • 3 - Most probable number (MPN) • 4 - Spread plate method • 5 - Membrane filter method

A- TOTAL COUNT • 1 - Breed method: • No. of cells/ 1 ml culture = the average No. of cells in 10 fields x 5000 x 100 x inverse of dilution if used.

• 2 - Haemocytometer ( counting chamber): • No. of cells/ 1 ml= No. of cells in 5 square x 5 x 100 x 103 x inverse of dilution if used. • Or • No. of cells/ 1 ml= No. of cells in 4 square x 4 x 100 x 103 x inverse of dilution if used. •

• B- Viable plate count: • 1 - Dilution to extinction: • Dilution= part (the transfer volume )/ all (the transfer volume + dilute volume)

THE TYPES OF LIQUIDS ARE USED AS DILUENTS • 1 - Saline ( Na Cl = 0. 85 %). • 2 - Sterile distilled water. • 3 - Peptone water (0. 1 %). • 4 - Nutrient broth ( N. b).

• 2 - Pour plate method: • No. of cells/ ml = No. of colonies x dilution factor. • 3 - Spread plate method: • No. of cells/ ml = No. of colonies x dilution factor.