4-dimethylaminocinnamaldehyde and indole

A number of substituted 4-aminobenzaldehydes were compared with more commonly employed reagents for the detection of indole-producing organisms among the Enterobacteriaceae. Factors such as rate of colour intensity and stability were compared in tests with reference organisms and clinical isolates, and with appropriate concentrations of pure indolic standards. 2-Methoxy 4-dimethylaminobenzaldehyde and 4-N pyrrolidylbenzaldehyde produced immediate and intense red to purple colourations when used in the indole test both in liquid media and on multipoint inoculated plates. Both reagents were considered to be superior to the traditional Ehrlich's reagent and also to 4-dimethylaminocinnamaldehyde which is often used as an alternative.

Topics: Benzaldehydes; Cinnamates; Enterobacteriaceae; Indicators and Reagents; Indoles

Kovacs indole reagent, p-dimethylaminobenzaldehyde, Ehrlich indole reagent and p-dimethylaminocinnamaldehyde were used as spot indole reagents to test 359 strains of gram-negative rods growing on 5% sheep blood agar, Trypticase soy agar (BBL Microbiology Systems), and MacConkey agar. The p-dimethylaminocinnamaldehyde reagent was the most sensitive of those tested and provided results that were easiest to interpret. The p-dimethylaminocinnamaldehyde reagent was able to detect providencia alcalifaciens indole production because of the red-violet color unique to that organism. All reagents tested were accurate in detecting indole produced by members of the Enterobacteriaceae family, with the exception of P. alcalifaciens.

Topics: Bacteriological Techniques; Benzaldehydes; Cinnamates; Enterobacteriaceae; Evaluation Studies as Topic; Indicators and Reagents; Indoles; Providencia