eportfolio week 10

Experiment 14 and 15

This week I carry out experiment 14 (Physical Factors: Temperature) and experiment 15 ( Physical Factors: pH of The Extracellular Environment. In experiment 14, the procedures of doing the experiment were as followed. We first scored the underside of all plates into four quadrants with a glassware marker. We labelled each section with the name of the test organism to be inoculated. We included the temperature of incubation (4°C, 20°C 37°C or 60°C) when labelling the cover of each plates. Then, we aseptically inoculated w=each of the plates with E. coli, B. stearothermophilus, P. aeruginosa and S. marcescens by means of a single line of inoculation of each organism in its appropriately labelled section. Then, we appropriately labelled the four Sabouraud broth tubes, including the temperatures of incubation as indicated above. We then gently shook the S. cerevisiae culture to suspend the organisms. We aseptically added one drop of the culture into each of the four tubes of broth media by using a sterile Pasteur pipette. All the plates and the broth cultures were then incubated in an inverted position abd at each of the four experimental temperatures. (4°C, 20°C 37°C or 60°C) for 24 to 48 hours. We then observed all the growth of the culture and classified the organisms as psychrophiles, mesophiles, facultative thermophiles or obligate thermophiles respectively at the next day. This experiment enabled me to determine whether the optimum growth temperature is also the ideal temperature for enzyme-regulated cell activities such as pigment production and carbohydrate fermentation. I also learnt about the diverse growth temperature requirements of bacteria. 

In experiment 15, the procedures of the experiment were as followed. First, I inoculated a series of the appropriately labelled TSB (12 Trypticase soy broth) tubes of media, pH values of 3, 6, 7, and 9 with E. coli by adding 0.1 ml of the saline culture to each.  I repeated the step just now for the inoculation of A. faecalis and S. cerevisiae by using a new sterile pipette each time. Finally, we incubated the A. faecalis and E. coli cultures for 24 to 48 hours at 37°C and the S. cerevisiae cultures for 48 to 72 hours at 25°C. We used the spectrophotometer to determine the absorbance of all cultures and record the readings in the Lab Report.