[Study on tetrazolium salt colorimetric assay for growth and survival of bacteria]

To establish a tetrazolium salt(MTT) colorimetric assay for bacteria growth and survival, living or boiling killed bacteria S. aureus and E. coli were incubated with MTT in microdilution plate for 36-37 degrees C at different time. DMSO was added as formazan dissolvent and the mixtures were measured for optical density(A) or absorbence at 510 nm wave length. Living bacteria were incubated with different amount of MTT for different time. The formazan were dissolved with different amount of DMSO and the A value were measured at different wave length. The results showed that yellow MTT could be reduced into blue formazan by living bacteria S. aureus and E. coli and the A value was directly proportional to concentration of the bacteria. A values of bacteria decreased with increasing of boiling time. To some extents, absorbence of living bacteria was direct proportion to MTT concentration and incubation time in the range of 0-2 hours. DMSO was good dissolvent for bacteria formazan and the highest absorbence could be reached in wave length range of 510-530 nm. It was suggested that MTT colorimetric assay could be used for measurement of bacteria growth and survival, and its optimal parameters were as follows: MTT concentration is 0.3 mg/ml. MTT incubation time was 2 hours. DMSO amount as dissoventis was 2-fold volume of bacteria suspension. Measurement wave length was 510-530 nm.