Bacterial Activity Lab Report

ASSAYING PLANT SUBSTANCES FOR ANTIBACTERIAL ACTIVITY

PURPOSE

To test plant extracts to see if they possess antibacterial activity.

PROCEDURE

First create a list of plant extracts being tested and choose 2 extracts per group. The plants being tested are Oregano, Tea tree, Eucalyptus and Colloidal Silver.
Obtain two nutrient agar plates and using a permanent marker draw four quadrants on the bottom of each agar plate. Using a sterile pipet transfer 250 ml of E. coli broth to the middle of each petri dish and evenly spread bacterial culture around the agar plate. Cover and allow the culture to soak into agar for at east 15 minutes. Using sterile forceps, carefully place one filter disk from designated sample into the middle of each
As a group, we chose oregano and colloidal silver as our samples. In our agar plate #1, the zone of inhibition for oregano and colloidal silver measured at 7mm. For agar plate #2, the zone of inhibition for oregano measured at 7mm, and for colloidal silver at 6.75mm. We were not the only group who used oregano as a sample, their results measured at 7.5mm. The results for the groups that tested tea tree for antibacterial activity, varied greatly. For one group, tea tree’s zone of inhibition measured at 9mm and for another group it measured at 12mm. Eucalyptus was measured by only one group and the z.o.i measurement for eucalyptus was 9.75mm. The negative control (H₂O) and positive control (Ampicillin) were tested by all groups. For water the z.o.i. measured at 6.5mm, 7mm, and 7mm. Ampicillin’s z.o.i. measured at 11.5mm, 11.25mm and 9.5mm. Figure 2 and table 1 depicts our results as a class. The results show that tea tree and eucalyptus have about the same antibacterial activity as the positive control (ampicillin) used in this experiment. Oregano and colloidal silver’s zone of inhibition were closer to h2O, which concludes that at the amount used for both there is no antibacterial
Also, not all z.o.i. were a perfect circle, some were oddly shaped which meant you had to use you best judgement on where to start your measurements. This may have led to some inconstancies of results. In future experiments when measurements are involved, the use of the same instrument could minimize errors. When comparing the results of tea tree and eucalyptus to that of ampicillin, it is clear that they both have antibacterial properties similar to ampicillin. Changing the antibiotic or positive control and retesting both tea tree and eucalyptus would be one way to demonstrate their effectiveness. Oregano has been used for medicinal purposes, in this experiment it failed to prove that it has antibacterial properties. I wonder if at a higher concentration or using a different bacterial culture would change the results of oregano. This experiment called for the use of 37ºC dry heat incubator with an incubation time of 24-48 hours. E.coli grows any where from 10ºC - 45ºC so changing the temperature to a slightly higher temperature could've caused the samples to activate antibacterial properties otherwise not activated by a lower temp. Also, the amount of incubation could be lengthen to see if that changes the