MICROBExpress™ Bacterial mRNA Enrichment Kit The only bacterial mRNA purification kit available. Using a novel strategy in a a rapid, simple procedure, MICROBExpress removes virtually all of the large rRNA from total bacterial RNA samples.Oligo dT Cellulose Poly(A)Purist™ mRNA Purification Kits Isolate mRNA from total RNA. These kits produce mRNA of higher purity with higher yields than other commercially available mRNA isolation kits.