Patent ID: 7645594

Claim:
A method of preparing an assay sample for detecting bacteria by a flow cytometer, comprising: providing a diluent comprising a cationic surfactant, a buffer for maintaining a pH of 2.0-4.5 and an effective amount of a substance capable of reducing nitrite ions and a staining solution comprising a polymethine dye for staining bacteria; mixing a urine sample with the diluent; and preparing the assay sample by mixing the mixture of the urine sample and the diluent with the staining solution; wherein the polymethine dye is at least one selected from the following group consisting of: wherein R 1 is a hydrogen atom or a C 1-3 alkyl group; R 2 — and R 3 are a hydrogen atom, a C 1-3 alkyl group or a C 1-3 alkoxy group; R 4 is a hydrogen atom, an acyl group or a C 1-3 alkyl group; R 5 is a hydrogen atom or a C 1-3 alkyl group which may be substituted; Z is a sulfur atom, an oxygen atom or a carbon atom substituted with a C 1-3 alkyl group; n is 1 or 2; X is an anion; and (11) a compound represented by the following general formula: wherein R 6 is a hydrogen atom or a C 1-18 alkyl group; R 7 and R 8 are a hydrogen atom, a C 1-3 alkyl group or a C 1-3 alkoxy group; R 9 is a hydrogen atom, an acyl group or a C 1-18 alkyl group; Z is sulfur, oxygen or a carbon atom having a C 1-3 alkyl group; n is 0, 1 or 2; X − is an anion; and wherein the cationic surfactant is a quaternary ammonium salt represented by the following formula: wherein R 10 is a C 6-18 alkyl group or a benzyl group; R 11 , R 12 and R 13 , the same or different, are a C 1-3 alkyl group or a benzyl group; Y − is a halogen ion.