Trial of a rapid measurement method by absorption photometer for the determination of the number of bacteria in the air

Abstract

A quick method to measure the number and the concentration of airborne bacteria was examined by combining bacteria staining with a crystal violet solution and absorptiometry. The suspension of the bacteria isolated from the environment was adjusted to 3.0 × 10(8) colony forming units (CFU) / ml in E. coli equivalent, and a 10-fold dilution series was created. After centrifugation of each bacterial suspension, the supernatant was removed and the bacteria were stained by adding a crystal violet solution. The sample was centrifuged again, and the supernatant was collected and named the unabsorbed sample. The residual bacteria were washed two times, and ethanol was added to the stained cells. The recovered solution collected by centrifugation of the cells was named the recovered sample.The chemicals in the samples were examined by high performance liquid chromatography, but no peak could be observed without the staining material. Absorption spectrophotometry showed that the determination limit of bacteria in the unabsorbed samples was 3.0 × 10(7) CFU / ml in E. coli equivalent and that in the recovered samples was 3.0 × 10(8) CFU / ml, indicating that the unabsorbed sample had a lower determination limit.