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Key reactions for the identification of Clostridium septicum are shown in the two quadrant plates shown in the photograph.Included in the upper photograph are reactions for milk (casein) proteolysis (12 o'clock quadrant), glucose fermentation, DNAse hydrolysis, and starch hydrolysis respectively reading clockwise.The media in the quadrant plate shown in the lower photograph include gelatin hydrolysis (2 o'clock quadrant) and fermentation of each of mannitol, lactose, and rhamnose respectively, reading clockwise.Milk (casein) hydrolysis Glucose fermentation Key reactions for the identification in the upper plate include no proteolysis of milk, fermentation of glucose (yellow red color along the inoculation streak), positive DNAse (reddish clearing around the streak) and negative reaction for starch. Key reactions in the lower plate include hydrolysis of gelatin, fermentation of lactose (yellow pigment), and negative reactions for mannitol and rhamnose (no pigment).Most strains of C. perfringens hydrolyze starch and produce proteolysins of milk, the key reactions that distinguish C. septicum (negative). Reactions to the other tests do not distinguish between the two.

The ability to grow in 6.5% NaCl and to produce acid from mannitol was once considered sufficient to identify S. aureus.Although other Staphylococcus species have these characteristics, mannitol salt agar, as shown here, can still be used for epidemiologic studies in suspected cases of S. aureus outbreaks.As shown in the photograph, the presence of colonies indicates the ability to grow on 6.5% NaCl; and, the yellow pigment of the colonies indicates acid production from mannitol.