Culture media containing glycerol that are ph and color stable when heat

Abstract

A heat stable culture medium is prepared by substituting glycerol for carbohydrate components such as dextrose that are prone to Maillard reactions. A preferred medium contains pancreatic digest of casein, soytone, soluble starch, a phosphate buffer system, a salt, a pH indicator, and glycerol as a primary carbon source. The culture medium is pH and color stable when exposed to steam sterilization, including post-manufacture steam sterilization when used as the medium of a self-contained biological indicator. A self-contained sterility indicator device contains a flexible cylindrical tube having an opening at one end. The tube contains a submicron screen as a gas transmissive, bacteria impermeable window, an adsorbent wick bearing at one end viable microorganisms, and a frangible glass ampule containing the culture medium. The end of the wick containing microorganisms is located away from the ampule and adjacent the screen. A cap that seals the tube opening has an open position, and a closed position that seals the window and prevents media evaporation. During sterilization, the microorganisms adjacent the screen are exposed directly to sterilant. After sterilization, the cap is moved to the closed position, and the ampule is broken by applying pressure to sides of the flexible tube to release the culture medium. The medium is adsorbed by the wick and transported to the end containing microorganisms. After incubation, the device is examined to determine from the color of the indicator whether or not microorganism growth has occurred.