In negative tests, there is rarely any growth. Properties (Serratia marcescens) Capsule: Negative (-ve) Catalase: Positive (+ve) Citrate: Positive (+ve) Flagella: Positive (+ve) Gas: Variable: Gelatin Hydrolysis: Positive (+ve) Gram Staining: Negative (-ve) H2S: Negative (-ve) Indole: Negative (-ve) Motility: Positive (+ve) MR (Methyl Red) Negative (-ve) Nitrate Reduction: Positive (+ve) OF. If the test was followed as described above, the culture will have changed to blue in the presence of alkali/bases (indicating a positive test). (Tasha Sturm, Cabrillo College, Aptos, CA)įigure 5: Close-up view of Serratia marcescens growing on Casein Media showing casein hydrolysis indicated by a zone of clearing around the growing colony. Retrieve the incubated culture from the incubator. (Tasha Sturm, Cabrillo College, Aptos, CA)įigure 4: Close-up view of Serratia marcescens growing on Casein Media showing casein hydrolysis indicated by a zone of clearing around the growing colony. (Tasha Sturm, Cabrillo College, Aptos, CA)įigure 3: Close-up view of Pseudomonas aeruginosa growing on Casein Media showing casein hydrolysis indicated by a zone of clearing around the growing colony. (Tasha Sturm, Cabrillo College, Aptos, CA)įigure 2: Casein Plates/Milk Agar inoculated Casein Plates/Milk Agar inoculated with (A) Pseudomonas aeruginosa, where casein hydrolysis is indicated by a zone of clearing around the growing colony (green color masking clearing in agar is the diffusable bacterial pigment pyocyanin) (B) Serratia marcescens, where casein hydrolysis is indicated by a zone of clearing around the growing colony (red pigment of bacterium is due to prodigiosin production) (C) Escherichia coli, no casein hydrolysis. Bacterial pigments can be seen distinctly on this agar. When digested by exoenzymes, the white agar turns clear and colorless. Casein is responsible for the white color of milk. The optimal TCA concentration used for 1. Gelatin concentrations below 1.6 gave reactions that were slower and difficult to interpret. ![]() Soluble peptides can then be absorbed by the cell. Using Bacillus subtilis and Serratia marcescens as our initial gelatinase positive test organisms we found a gelatin concentration of 1.6 to be the most effective. This medium is used to detect the production of proteases/caseases that digest casein to soluble peptides. Download the PowerPoint PowerPoint Contentsįigure 1: Uninoculated Casein Plates/Milk Agar contains skim milk (lactose and casein), peptone, and agar.
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