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 ...