Universiti Tunku Abdul Rahman (Kampar Campus)

Faculty of Science, Engineering, and Technology

Bachelor of Science (Hons) Biotechnology

Year 2 Semester 1

UESB 2142 Laboratory 2A

(III) Microbiology

Lecturer: Dr. Teh Yok Lan

Student’s Name: Cheah Hong Leong

Student’s ID: 08AIB03788

Group Member: Samuel Tan Sha Loong

Experiment No. 5

Title: Growth Curve

Date: August 17, 2009

Title: Growth Curve

Objectives:

- To obtain the graphs of the microbial growth of different bacteria through optical

density measurement of the media.

- To compare the growth curve of the bacteria.

Results:

Table 1: Optical Density of Inoculated Nutrient Broth with Time of Pseudomonas aeruginosa

Time (minutes) Optical Density, OD600 (A)To, 0 0.013T1, 15 0.015T2, 30 0.017T3, 45 0.020T4, 60 0.022T5, 75 0.026T6, 90 0.031

Table 2: Optical Density of Inoculated Nutrient Broth with Time of Escherichia coli

Time (minutes) Optical Density, OD600 (A)To, 0 0.023T1, 15 0.020T2, 30 0.074T3, 45 0.085T4, 60 0.226T5, 75 0.262T6, 90 0.223

Table 3: Optical Density of Inoculated Nutrient Broth with Time of Staphylococcus aureus

Time (minutes) Optical Density, OD600 (A)To, 0 0.022T1, 15 0.028T2, 30 0.034T3, 45 0.040T4, 60 0.062T5, 75 0.091T6, 90 0.143

Note: Data in Table 1, 2, and 3 were plotted in “Semi-log Graph: Optical Density of

Inoculated Nutrient Broth versus Time” in Attachment.

Calculation of Generation Time:

Pseudomonas aeruginosa, Generation time = 45 minutes

Escherichia coli, Generation time = T0.100 – T0.050

= (45 – 24) minutes

= 21 minutes

Staphylococcus aureus, Generation time = T0.100 – T0.050

= (87 – 48) minutes

= 39 minutes

Discussion:

Based on the semi-log graph and the calculation, the generation time of

Escherichia coli was the shortest (21 minutes), followed by Staphylococcus aureus (39

minutes) and Pseudomonas aeruginosa (45 minutes). With the shortest generation time,

Escherichia coli was expected to have the greatest growth rate under similar condition

among the three microorganisms, for every 21 minutes, the cell numbers of Escherichia

coli doubled.

Theoretically, the photospectrometry measurement assumes that the bacterial cells

were distributed in the nutrient broth evenly; the optical density obtained can be

proportional to the population of the bacteria in broth only when the assumption

occurred.

However, all the three bacteria have the ability to form biofilm on the flask surface,

which can cause errors in the photospectrometry measurement regarding the total cell

mass of the microorganisms in the nutrient broth.

Stirring of the nutrient broth during the incubation was solving the problem, but

during the incubation in the laboratory practical, non simultaneous timing of the students

from different subgroups made the incubation machine had to be turned on and off

repeatedly. That might lead to the uneven distribution of the bacteria in the broth.

Moreover, sometimes the incubation machine was also did not turned on by the students

after placing the flask into it, leaving the broth unstirred for several minutes.

This might be able to explain the unusual results shown by the Escherichia coli in which

the optical density was unexpectedly dropped at time 15 minute and 90 minute.

Conclusion:

The generation time was shortest for Escherichia coli, followed by Staphylococcus

aureus and Pseudomonas aeruginosa.

References:

Cappuccino, J. G. & Sherman, N. (2008). Microbiology. A Laboratory Manual, 8th ed.,

San Francisco, CA: Pearson Benjamin Cummings.

Escherichia coli. (2009, August 30). In Wikipedia, the free encyclopedia. Retrieved

August 31, 2009, from http://en.wikipedia.org/wiki/Escherichia_coli

Madigan, M. T., Martinko, J. M., Dunlap, P. V., & Clark, D. P. (2009). Brock Biology of

Microorganisms, 12th ed., San Francisco, CA: Pearson Benjamin Cummings.

Pseudomonas aeruginosa. (2009, August 28). In Wikipedia, the free encyclopedia.

Retrieved August 31, 2009, from http://en.wikipedia.org/wiki/Pseudomonas_aeruginosa

Staphylococcus aureus. (2009, August 26). In Wikipedia, the free encyclopedia.

Retrieved August 31, 2009, from http://en.wikipedia.org/wiki/Staphylococcus_aureus

Attachment:

Semi-log Graph: Optical Density of Inoculated Nutrient Broth versus Time