as the resorufin beta d glucuronic acid itself fig1 table 1 as described above indicators based on the glucuronic acid ester can be produced at lower costs making present applications less expensive and even enabling new applications that were too costly to be implemented with the glucuronic acid based indicators in the present invention the beta d glucuronic acid based indicator is produced in situ from the ester of the beta d glucuronic acid compound the hydrolysis of the ester can be achieved by the activity of a c1 4 esterase hydroxyl ions or other factors known to hydrolyze such ester compounds these factors can be inherent in the sample matrix or can be added to the sample matrix depending on the type of the assay and sample matrix the hydrolysis conditions have to be selected so that they do not interfere with the assay as a whole in preferred embodiments the method is used with matrices that already exhibit an ester hydrolysing activity itself e g as in an enrichment broth for e coli in further embodiments the ester hydrolyzing activity is conferred to the matrix in an extra step e g by addition of a c1 4 esterase depending on the application indicator moieties for the beta d glucuronic acid ester based indicators can be chosen from the following list resorufin 7 hydroxycoumarin 7 hydroxy 4 methylcoumarin 7 hydroxy coumarin 3 carboxylic acid 7 methoxycoumarin 7 hydroxy 3 acetylcoumarin 7 hydroxy 4 trifluoromethylcoumarin 7 hydroxycoumarin 4 acetic acid 7 hydroxy 3 ethoxycarbonylcoumarin 6 chloro 7 hydroxy 4 methylcoumarin 3 cyano 7 hydroxycoumarin 3 chloro 7 hydroxy 4 methylcoumarin alizarin fluorescein fluorescein beta d glucuronide 6 chloro 2 5 chloro 2 hydroxyphenyl 4 1h quinazolinone elf u00ae 97 phenolphthalein phenolsulfonphthalein.