Can common acne medications stop the bacteria that cause breakouts? Propionibacterium acnes (P. acnes) lives on skin and feeds on oil from pores. When it multiplies too fast, it triggers inflammation. You spread P. acnes bacteria across three agar plates. On each plate, you place a filter paper disk soaked in one of three medications: Tetracycline, Clindamycin, or Benzoyl peroxide. Each medication is mixed at the same concentration (5mg in 10ml water). After four days, you measure the inhibition zone (the bacteria-free ring around each disk). All three medications create a clear zone. Tetracycline produces the largest at 48mm. Clindamycin follows at 44mm. Benzoyl peroxide shows the smallest zone at 27mm.