Rapid Method for Simultaneous Detection of the Arginine Dihydrolase System and Amino Acid Decarboxylases in Microorganisms

A specific procedure has been developed for the detection of the first two enzymes involved in the arginine dihydrolase system and the detection of the decarboxylases of arginine, glutamic acid, histidine, lysine, ornithine, phenylalanine, tryptophan, and tyrosine. A loopful of growth of each organism from dihydrolase-decarboxylase induction agar medium (or broth) was washed and incubated separately with 0.2-ml samples of three test media supplemented with different amino acids. Each spent test medium was dansylated, and the dansyl derivatives were separated by two-dimensional thin-layer chromatography on polyamide sheets. The end products (citrulline, ornithine, gamma-amino-n-butyric acid, and amines) produced during incubation were estimated by comparing the fluorescent intensities of end products from the spent test media and of the corresponding parent amino acids from test medium controls after thin-layer chromatography. The method is reproducible, requiring incubation of an organism in three test media for 1 h for simultaneous detection of the first two enzymes involved in the arginine dihydrolase system and of eight amino acid decarboxylases. This method has been successfully applied to gram-positive and gram-negative microorganisms and also to Mycoplasmatales. It could simplify and improve the accuracy of the corresponding biochemical tests performed in clinical laboratories for the identification and differentiation of microorganisms, and it may prove particularly useful for the differentiation of species of Pseudomonas and Mycoplasma.