8 soil is teaming with a microbes An experiment was conducte

8. soil is teaming with a microbes. An experiment was conducted to see the population of gram negative bacteria to gram positive bacteria in a moist vs dry soil. A serial dilution was performed and plated on a (nutrient agar) general purpose and eosin methylene blue (selective/differential) media. After 48 hour incubation, the results were read. The results are given in table 2. Table 2: The microbial growth from moist and dry soil samples grown on a nutrient agar and eosin methylene blue agar. Dry soil Moist Soil EMB (CFU) EMB Plate D NA (CFU) (CFU) (CFU) TN TC INTC \"TNTC TNTC TN TC TNTC TNTC 145 TNTC o (OS) What is the original concentration (CFUlg for the moist soil on NA medium? Q8) What is the original concentration (CFU/g) for the moist soil on EMB medium? What is the original concentration (CFU/g) for the dry soil on NA medium? 10-5

Solution

Ans. Eosin and methylene blue inhibits growth of gram-positive bacterial but allows growth of gram-negative bacteria. So, it’s a selective media.

So, the number of colonies on EMB agar consists of gram-negative bacteria only.

Nutrient agar is a general-purpose media. It supports the growth of both gram-positive as well as gram-negative bacteria.   

8A. 10^-5 dilution, EMB agar, 57 colonies in moist soil, and

10^-5 dilution, EMB agar, 95 colonies in dry soil, and

8B. For moist soil- number of cells in 1.0 mL or 1.0 g original culture

            (No. of gram-negative + gram positive bacteria) = CFU count of NA agar, moist soil

= 1.5 x 10⁹ cells

            (No. of gram-negative bacteria) = CFU count of EMB agar, moist soil

= 5.7 x 10⁶ cells

            No. of gram-positive bacteria = CFU count of NA agar - CFU count of EMB agar

                                                            = (1.5 x 10⁹ cells) – (5.7 x 10⁶ cells)

                                                            = 1.49 x 10⁹ cells                    

G(+ve) : G (-ve) = (1.49 x 10⁹ cells) / (5.7 x 10⁶ cells) = 262 : 1

8C. For Dry soil- number of cells in 1.0 mL or 1.0 g original culture

            (No. of gram-negative + gram positive bacteria) = CFU count of NA agar, moist soil

= 1.45 x 10⁸ cells

            (No. of gram-negative bacteria) = CFU count of EMB agar, moist soil

= 9.5 x 10⁶ cells

            No. of gram-positive bacteria = CFU count of NA agar - CFU count of EMB agar

                                                            = (1.45 x 10⁸ cells) – (9.5 x 10⁶ cells)

                                                            = 1.36 x 10⁸ cells                    

G(+ve) : G (-ve) = (1.36 x 10⁸ cells) / (9.5 x 10⁶ cells) = 143 : 1

Ans. 8D. The moist soil supports larger number of microbes because CFU count on NA plate from moist soil (1.5 x 10⁹ cells) is greater than that of dry soil (1.45 x 10⁸ cells).