Fluorometric quantitation of broth-cultured mycoplasmas by using alkaline ethidium bromide

Rapid fluorometric quantification of bacterial cells using Redsafe nucleic acid stain

BACKGROUND AND OBJECTIVES

Numerous procedures in biology and medicine require the counting of cells. Direct enumeration of Colony Forming Units (CFUs) is time-consuming and dreary accurate cell counting on plates with high numbers of CFUs is error prone. In this study we report a new indirect cell counting method that was developed based on the use of Redsafe fluorometric assay. The usefulness of Redsafe, a nucleic acid stain, in liquid medium is based on the binding of the fluorescent dye to DNA.

MATERIALS AND METHODS

Redsafe fluorometric assay was evaluated in comparison with MTT colorimetric assay as a colourimetric assay for enumeration of bacterial cells.

RESULTS

Obtained results showed that fluorometric assay threshold for LB grown E. coli is 6×10(4) CFU/ml. Redsafe fluorescent assay can be used as a rapid and inexpensive method for bacterial enumeration and quantification with increased sensitivity.

CONCLUSION

The sensitivity of the Redsafe fluorometric assay for detection and enumeration of bacterial cells was 2-log-unit more than that was observed for the MTT assay.

Abortive base-excision repair of radiation-induced clustered DNA lesions in Escherichia coli

It has been postulated that ionizing radiation produces a unique form of cellular DNA damage called "clustered damages" or "multiply damaged sites". Here, we show that clustered DNA damages are indeed formed in Escherichia coli by ionizing radiation and are converted to lethal double-strand breaks during attempted base-excision repair. In wild-type cells possessing the oxidative DNA glycosylases that cleave DNA at repairable single damages, double-strand breaks are formed at radiation-induced clusters during postirradiation incubation and also in a dose-dependent fashion. E. coli mutants lacking these enzymes do not form double-strand breaks postirradiation and are substantially more radioresistant than wild-type cells. Furthermore, overproduction of one of the oxidative DNA glycosylases in mutant cells confers a radiosensitive phenotype and an increase in the number of double-strand breaks. Thus, the effect of the oxidative DNA glycosylases in potentiating DNA damage must be considered when estimating radiation risk.