Figure 1. Study design. The described procedure was adopted for 32 bacterial filters from each of the following manufactures: Portex LTD (Hythe, Kent, England), B. Braun (Melsungen, Germany), and Corning Costar (Cambridge, MA). At the indicated times, filtrates were subjected to microbial cultures as indicated in methods. SDM - normal saline, dexamethasone, and morphine hydrochloride; BDM bupivacaine, dexamethasone, and morphine hydrochloride; SM - Streptococcus milleri I at a final titer of 1.5 x 105bacteria/ml.