Cold atmospheric plasma offers significant potential as a nonthermal decontamination tool for food and medical applications. We present results of a dielectric barrier discharge (DBD) plasma induced in a gas confined by a polymer package. The resultant discharge and contained afterglow are found to have a strong antimicrobial effect. Index Terms— Atmospheric-pressure plasmas, glow discharges, nonthermal plasma, plasma diagnostics. D IELECTRIC barrier discharge (DBD) plasma is generally induced within small gaps of the millimeter range in inert gases (He, Ar). The present work develops a DBD setup that can achieve microbial reductions in sealed packages of much larger gap sizes. Fig. 1(top) is a photograph of cherry tomatoes being treated with helium gas plasma, generated inside a 3.5 L sealed commercial polypropylene package. The discharge is confined to the diameter of the electrodes. The image was taken using an Olympus E620 single lens reflex camera with 40-mm lens at 200 ISO. The image was integrated over 30 s duration to effectively capture the discharge. The strong antibacterial effects of the plasma setup are clear from the scanning electron micrographs in Fig. 1(bottom). The cell surface of Listeria spp are dramatically altered leading to Manuscript received November 6, 2013; revised March 9, 2014; accepted April 28, 2014.