The patented Actero™ Elite Listeria Enrichment Media is a selective medium specifically optimized for single-step recovery and enrichment of Listeria spp. from food and environmental samples. Just add deionized water through the one port and gently massage the bag to rehydrate. There are 15 dry media bags per case. Each case comes with two 0.2 micron filters and each filter can be used up to 10 times.