Colony Count

Second test conducted on well diffusion positive extracts, colony count shows the extent of bacterial growth and checks whether extract is bacteriostatic.

 

Steps:

For the test, bacteria culture was added to either tannic acid or tea extract and LB broth. For control, saline is used instead. 5 replicates were performed, and the tubes were incubated overnight at 30°C with shaking. The absorbance of each tube was determined using a UV-vis spectrophotometer set at 600 nm. The test and control were serial diluted according to the absorbance. This was done by transferring 0.1 ml of the test or control to 0.9 ml of saline. For two of the dilutions, 0.1 ml of the test or control was plated on Luria-Bertani agar plates. This was repeated for all tubes, and the plates were incubated overnight. The number of colonies on each plate was recorded the next day.