Comparison of the methods of viability determination in Escherichia coli cultures treated with ciprofloxacin

Different methods of viability determination in E. coli treated with ciprofloxacin were compared. There was no complete correlation between the results obtained under determination of the specific growth rate, colony forming ability, membrane potential (Д\|/) and in the "live-dead" test. In particular, only 0.04% of cells in the population retain the ability to form colonies after two hours of exposure to 0.3 ug/ml ciprofloxacin, while the proportion of the "live" cells in the test "live/dead" was 83%. Under treatment with 3 Ug/ml ciprofloxacin, ability to form colonies were showed 0.13% of the cells, whereas in the same conditions in the test «live/dead» almost all cells were not stained with propidium iodide. Unlike colony forming and «live/dead» test, in the test with DiBAC4(3) there was a direct correlation between the number of fluorescent (depolarized) cells and concentration of ciprofloxacin: 30% of cells lost membrane potential under treatment with 0.3 ug/ml ciprofloxacin and 70% under exposure to 3 ug/ml of antibiotic. Expression of sulA::lacZ fusion increased 12 times and 3 times by the action of 0.3 ug/ml and 3 ug/ml of cipro-floxacin, respectively. A reverse correlation between the expression of the sulA gene and the number of colony forming units was found.