A Laboratory Activity Demonstrating the Antibacterial Effects of Extracts from Two Plant Species, Moringa oleifera and Allium sativum (Garlic) †

Images of laboratory procedures. (A) Materials needed for the activity; (B) Moringa seed with hull removed; (C) Mortar and pestle grinding of moringa seed; (D) Ground moringa seed slurry being poured into a 15-mL centrifuge tube; (E) Slurry supernatant sterilized through a membrane filter (0.2–0.45 μm); (F) Sterile disks soaked in sterile extracts; (G) Plating extract-soaked disks onto inoculated plates; (H) Disk placement on plates of either E. coli (left) or B. cereus (right); (I) Zones of inhibition apparent on plates following 24-hour incubation (37°C).

Measuring zones of inhibition after 24-hour incubation. Inhibition of bacterial growth was evaluated by measuring the diameter (mm) of each zone of inhibition. Comparisons of individual antibacterial agents can be made between the gram-negative E. coli (A) and the gram-positive B. cereus (B). Disks clockwise from top left: P, penicillin; T, tetracycline; G, garlic; M, moringa.

Average improvement of student performance on the pre- and post-lab activity quiz. Significant gains in student understanding were evident for questions 3, 4, and 5. The questions presented to the students are given in Table 1 and in Appendices 1 and 2 . Data were compiled from the responses of 29 students. Statistical differences were determined by converting the pre- and post-lab quiz scores to percentages, which were then normalized for the statistical analysis. In this form, the chi-squared test could be applied using the CHITEST function of Excel. The resulting p value calculated for these 29 sets of pre- and post-lab scores was 4 × 10−38 (<0.05).

Student evaluation of the laboratory activity. The survey results showed that almost 90% of the students strongly agreed or agreed that they enjoyed the activity (question 1), the instructions were easy to follow (question 2), and they were interested in the results (question 3). Nearly 94% of the students strongly agreed or agreed that the techniques were relevant and useful (question 4). Perhaps most importantly, about 85% of the students agreed (nearly one-half strongly agreeing) that the exercise highlights the value of medicinal plants as potential producers of antibacterial agents (question 5), which was identified as a specific goal of the activity (Objective 6). The questions as presented to the students are given in Appendix 5 .