Hydrolysis of casein is not a common trait and is therefore useful in the differentiation of Serratia marcescens from the 438 strains of Enterobacteriaceae and Pseudomonadaceae families [12]. Serratia marcescens has the reproducible capability to break down casein producing a clearing on milk agar plates. Casein is a protein precipitated from milk that forms the basis of cheese and certain plastics [5]. Serratia marcescens uses extracellular enzymes called proteases to break down the peptide bonds (CO-NH) in casein [4]. Similarly, an extracellular enzyme called gelatinase breaks down gelatin, an incomplete protein that lacks tryptophan. Gelatin hydrolysis transforms the protein to individual amino acids and causes it to liquefy in cold conditions (under 25 °C) when it would otherwise be solid