Spice Antimicrobial Testing with Smartphone Analysis

ISEF Category: Translational Medical Science

Subcategory: Drug Identification and Testing  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Some spices do more than flavor food. They can slow microbial growth, and you can measure that in a real experiment. Your phone can turn a clear ring on agar into data. That means your kitchen shelf can become a drug-screening lab, in a very small, very safe way.

What Is It?

This project asks a simple question. Which spice extracts stop microbes from growing best? You place small disks soaked with spice extract on agar, which is the gel-like food microbes grow on. If the extract works, you get a zone of inhibition, a clear ring where growth slowed or stopped.

Think of the agar plate like a lawn. The microbes are the grass. An antimicrobial compound acts like a patch of weed killer, but only where it spreads far enough. Bigger clear zones usually mean stronger activity, but you need careful measurement because diffusion, disk size, and extract strength all affect the result.

You can study this without a hospital lab by using BSL-1 surrogates like Bacillus subtilis and Saccharomyces cerevisiae. These are common teaching organisms. They let you compare plant-based extracts in a way that feels like early drug screening, but stays in a beginner-friendly lab zone.

Why This Is a Good Topic

This is a strong science fair topic because you can change one variable at a time, then measure a clear outcome. You can compare spices, extract methods, or solvent types, and each choice gives you real data. The project connects to antimicrobial discovery, food chemistry, and natural-product screening, which makes it easy to explain to judges. You can also learn how to design controls, measure diffusion effects, and analyze results with basic statistics.

Research Questions

• How does the type of spice extract affect the diameter of the zone of inhibition against Bacillus subtilis?
• How does the type of spice extract affect the diameter of the zone of inhibition against Saccharomyces cerevisiae?
• What is the effect of extraction solvent on antimicrobial activity measured by zone size?
• To what extent does grind size of the spice change the measured inhibition zone?
• Which spice extract produces the largest inhibition zone when tested at the same sample amount?
• Does storing the extract before testing change its antimicrobial effect over time?

Basic Materials

• Prepared agar plates for BSL-1 teaching use, purchased from a reputable educational supplier.
• BSL-1 surrogate cultures such as Bacillus subtilis and Saccharomyces cerevisiae.
• Sterile paper disks or blank diffusion disks.
• Grocery-store spices such as cinnamon, clove, oregano, turmeric, garlic powder, and black pepper.
• Distilled water, ethanol, or another school-approved extraction solvent.
• Small digital kitchen scale with 0.1 g accuracy.
• Disposable transfer pipettes or dropper pipettes.
• Sterile forceps or tweezers.
• Ruler or calipers with millimeter markings.
• Smartphone with a camera and consistent manual settings.
• White light box or simple homemade photo box for uniform imaging.
• Gloves, disinfectant, and waste containers approved by your school or local biosafety rules.

Advanced Materials

• Analytical balance.
• Micropipettes with sterile tips.
• Sterile filtration setup for extract clarification.
• Spectrophotometer for culture standardization.
• Incubator with controlled temperature.
• Calipers for direct zone measurement.
• Reference antimicrobial disks for comparison controls.
• HPLC or HPLC-Lite setup for profiling extract composition.
• ImageJ installed on a computer for zone measurement.
• Smartphone stand or fixed imaging rig for repeatable densitometry.

Software & Tools

• ImageJ: Measures zone diameters and pixel intensity from plate images for repeatable analysis.
• Python: Organizes replicate data, calculates summary statistics, and makes plots.
• Google Sheets: Tracks samples, labels plates, and logs measurements in a clean table.
• R: Runs statistical tests and helps compare extracts across groups.
• NIH ImageJ plugin tools: Support thresholding and image calibration for plate analysis.

Experiment Steps

1. Define the exact comparison you will test, such as spice type, solvent type, or extract strength.
2. Choose one microbial surrogate for the first trial, then add the second only if your setup stays consistent.
3. Build a measurement plan that turns each clear zone into a number, using the same image setup every time.
4. Design controls that separate true antimicrobial activity from solvent effects and disk size effects.
5. Decide how you will standardize extract preparation so each sample starts from the same mass and process.
6. Plan your statistics before you collect data, so you know how you will compare replicates and spot outliers.

Common Pitfalls

• Using uneven lighting for plate photos, which changes the apparent zone size from one image to the next.
• Letting extract concentration vary between samples, which makes spice-to-spice comparisons meaningless.
• Comparing zones without a solvent-only control, which can hide the effect of the carrier liquid.
• Measuring cloudy or fuzzy edges the same way as sharp edges, which adds noise to your data.
• Mixing different disk sizes or saturation levels, which changes diffusion and makes the results unfair.

What Makes This Competitive

A stronger project goes beyond a simple yes or no screen. You can compare multiple extraction methods, quantify image-based zone size, and test whether the extract effect changes across two surrogate organisms. Judges notice careful controls, repeated trials, and a clear analysis plan. If you also connect your results to known compound classes in spices, your project starts to look like real screening work.

Project Variations

• Test spice extracts against a single bacterium first, then compare the same extracts against a yeast surrogate to see whether the pattern changes.
• Compare water, ethanol, and oil-based spice extracts to see which solvent pulls out the most active compounds.
• Use smartphone image analysis to compare fresh spice, dried spice, and store-bought preground spice in the same diffusion assay.

Learn More

• PubMed: Search review articles on plant-derived antimicrobials, spice extracts, and disk diffusion methods.
• NIH NCBI Bookshelf: Find background chapters on microbiology, antimicrobial testing, and experimental design.
• USDA FoodData Central: Check spice composition and food chemistry context for the extracts you test.
• University OpenCourseWare from MIT: Search for biology and chemistry labs on diffusion, controls, and data analysis.
• Journal of Antimicrobial Chemotherapy: Search for methods papers and reviews on zone-of-inhibition assays and natural products.