This lab introduces students to experimental design in an inquiry lab exercise that investigates the gut microbiome, basic microbiology techniques, and the broader topic of bacteriology. Fruit flies are used as a model system to study the impact that foods, food additives, and/or antibiotics have on the gut microbiome. One of the major bacteria in the guts of fruit flies is Lactobacillus, which is easy to grow in the lab. This exercise is done in three consecutive lab sessions. During Lab 1, students prepare a standard nutritive medium that has been mixed with a substance of their choice, add the fruit flies to the medium, and practice serial dilution with a simulation. During Lab 2, students plate mashed fruit flies on MRS medium to look at the change in Lactobacillus levels. During Lab 3, students count and determine the change in the number of Lactobacillus in their tested substance, Gram stain selected colonies, and discuss their results as a class. SALG surveys indicated a significant gain in their understanding of the microbiology concepts introduced in this lab.