Introduction to the Spice Lab Research Project (10 points)
Investigating the antibiotic properties of spices
Learning Goals: Your lab group will work collaboratively as scientists to design and perform
experiments to quantitatively assess the ability of different spices to inhibit the growth of
bacteria. You will contribute to the composition of a scientific paper which will describe the
rationale and background needed to understand your research question, summarize the results
of your experiment, and describe their implications.
Assignment: Write two research questions and complete all associated reading
questions.
Objectives:
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To utilize the principles of the scientific method include hypothesis and prediction
formation, experimental design, data collection, and interpretation of results.
To practice writing a scientific paper.
To apply statistical analysis to real-world data and practice graphical representation of
data.
Overview:
Humans have been discovering and using the medicinal properties of plants for millennia. Many
of our over-the-counter and prescription medications contain chemicals initially found and
derived from plants. For example, salicylic acid, the active ingredient in aspirin, was originally
derived from willow bark and quinine, a compound used to protect against malaria, is extracted
from the cinchona tree. A whopping 40% of modern prescription medicines come from plant
extracts or compounds discovered in plants!
The antimicrobial properties of plant spices are a particularly active area of research. Plants
produce spices as a defense response to nearly continuous attack from animals like mammals,
birds, and insects as well as microorganisms like bacteria and fungi. The chemicals that give
spices their distinctive flavors are used by plants to deter herbivores or to inhibit the cell
growth/division of fungi and bacteria.
Many scientific studies have analyzed the antimicrobial abilities of a diverse array of plant
spices. Different spices are reported to vary in their antibiotic strength with some showing no
antimicrobial properties. Further, there are conflicting reports in the literature about the efficacy
of certain spices in deterring the growth of different bacterial species, the concentration of
spices required to inhibit bacterial growth, and whether a blend of several spices shows
advantages over a single spice used in isolation.
Spices extracts could provide a readily accessible, low-cost treatment for certain infections,
particularly in developing countries in which access to healthcare may be limited or cost
prohibitive. However, a first step to implementing these treatments is the definitive identification
of which spices are effective against each bacterial strain, how concentrated extracts should be,
and under which circumstances the treatments are most effective.
Over the course of the semester, your group will apply the scientific method to investigate the
antibiotic capabilities of spices.
Introduction to Experimental Design:
As we discussed in lecture, the scientific
method is a logical process used to
investigate the world. You will begin with
observations made by reading a paper
from the scientific literature and then use
your background knowledge to form
questions, hypotheses, predictions,
design an experiment, and analyze your
results. Your group will include all
members of your lab table.
Examining the antibiotic properties of
spices:
We can assess the antibiotic abilities of
spices by creating spice extracts and
analyzing their ability to inhibit bacterial
growth. To make a spice extract, you
simply grind a small amount of spice in
isopropyl alcohol, releasing the spice
chemicals into the alcohol. We can assess
the effects of the extract on bacterial
growth by soaking a piece of filter paper in the extract and applying the paper to a petri dish
coated with bacteria. As the bacteria grow, you can measure the area around the filter paper
that remains free of bacteria. This region without bacteria is call the “zone of inhibition.” If the
spice has antimicrobial properties, you will observe the zone with bigger zones indicating
stronger antimicrobial action.
Filter paper
“lawn” of bacteria
Zone of inhibi on
(no bacterial growth)
Smaller zone of inhibi on
= less effec ve an bio c
No zone of inhibi on
= no an bio c proper es
For your experiment, you will be plating out bacteria and examining the ability of spice extracts
to inhibit their growth. Develop at least two research questions based on the information in this
handout and your assigned reading. Examine the supply list below while forming your questions
as it contains all the materials that are available to you. If there is a spice or other plan
component you’d like to test, please feel free to bring it to lab for the experimental design day!
Materials Provided:
Isopropyl alcohol
Mortar and pestle
Distilled water
Sterile filter paper
Forceps
Balance
Rulers
Nutrient agar plates (up to 4 per group)
Culture of E. coli cells
Culture of B. cereus
Plating beads
Spices: garlic, onion, oregano, chili powder, black pepper, cinnamon (or bring your own)
Parafilm
37oC incubator
Write your two research questions below (please specify the bacteria and spices of interest in
your questions):
1.
2.
Questions about Arora and Kaur, 1999:
Being able to read and understand most scientific articles requires practice. Since you’ll need to
find and read scientific papers for your research project, this assignment is meant to introduce
you to a research article related to your research project and help you understand both the
content and guide you through the process of how to read the scientific literature.
Read Arora and Kaur, 1999 (posted in Carmen) while following along with the question prompts
below. The questions are arranged by each section of the article. Reading this article should be
helpful in designing your own research questions!
Abstract
The abstract of scientific articles contains a brief summary of all the key sections in the paper,
including the major findings of the study.
1. After reading this abstract, what was the question the authors were asking? (You’ll notice that
there are no question marks, but you can infer the scientific question the authors were trying to
answer.)
2. Describe in one sentence (in your own words) the major conclusion from this study.
Introduction
This section illustrates some key points of a good introduction. The authors begin with a broad
review of previous research related to their topic and gradually focus and information more
directly related to their research question. The authors also provide justification for why their
research question is interesting and important.
3. Describe in one sentence (in your own words) the justification the authors provide for why
their research question is interesting and important.
Materials and Methods
This section should provide a detailed account of the procedures. The detail of the methods
should be sufficient that another scientist could repeat the test without any additional guidance.
Understanding exactly how research is conducted is essential for interpreting results.
4. In each description of their experiments, Arora and Kaur mention that they repeated their
tests 3 times. Why did they replicate their experiments? Provide at least two reasons for
replication.
Results
5. In your own words, briefly describe what Figure 1 shows. (Hint: the axes and legend tell you
everything you need to know!)
Discussion
In the discussion, authors compare the results from their studies with other studies to illustrate
why their experiments were important and of interest to the scientific community. They also
provide interpretation and context for their findings.
6. The authors mention that garlic extracts had significant inhibitory action in gram negative
bacteria. Research gram negative bacteria and describe why treatments for gram negative
bacterial infections are a particularly important modern human health issue. Use a reliable
source (peer-reviewed or from a governmental agency like the Centers for Disease Control aka
CDC) and provide the citation for your source beneath your answer. As always, answer in your
own words.
Please submit your completed answers to the “Spice Lab Reading
Assignment” assignment in Carmen.