A Method for the Reclamation of Agar

Abstract

The possibility that a shortage of agar may occur in the near future has prompted experiments to devise a simple method for the reclamation of used agar media. Methods of reclamation reported by several German bacteriologists during World War I have not proved entirely satisfactory in the Laboratory, Station Hospital, Fort Bragg, North Carolina. It has been found that plain nutrient agar media, which are extensively used, may be easily and satisfactorily reclaimed by employing an alternate freezing and thawing technic. Probably this process is not feasible from a commercial standpoint. However, it has proved successful where one is concerned with relatively small quantities. With simple modifications the procedure can be adapted to the purification of Endo's agar, eosin-methylene-blue agar, or any other dye containing agar media. Although not yet attempted, agar media containing sugar can probably be similarly reclaimed. Blood agar medium may be treated in the same manner as plain nutrient agar. The procedure for reclamation of plain nutrient agar without added dye is here described. Pool the agar medium to be processed and autoclave at 15 lb. pressure for 15 min. Adjust the reaction to pH 7.0. Place the melted agar in an ice cube tray and permit to solidify at room temperature. Make parallel cuts lengthwise and crosswise of the agar mass. Freeze completely in the freezing compartment of an electric refrigerator. Break the frozen mass into conveniently sized pieces, place in a gauze sack and let thaw at room temperature. The water carries with it much of the unused soluble ingredients and impurities leaving partially purified solid agar which is insoluble in cold water. Add sufficient distilled water to double the original volume of medium. Melt thoroughly in a boiling water bath or Arnold steamer and cool of 55°C.