An in vitro evaluation of the influence of concentration and duration of exposure on the antimicrobial efficacy of sodium hypochlorite on enterococcus faecalis

Abstract EN

Objectives: To evaluate, in vitro, the effectiveness of different concentrations of sodium hypochlorite [NaOCl] (0.5 %, 1.0 %, 2.5% and 5.25% w/v) in the elimination of Enterococcus faecalis E10e.

Methods: E.

faecalis E10e was grown overnight and allowed to grow until the ‘mid-exponential’ phase.

0.2 ml of the inoculum that was then transferred into 9.8 ml of NaOCl solution.

One ml samples were removed and poured in 9 ml of sodium thiosulphate [Na2S2O3] solution (neutralisation) after 30 sec, 1 min, 2 min, 5 min, 10 min and 30 min.

Serial dilution of each neutralised solution was carried out to give a dilution factor of 10-6.

Subsequently, 0.02 ml of each dilution was plated onto an agar plate, and then incubated at 37C in an aerobic incubator for 24 hrs.

The number of viable colonies (Colony Forming Units / ml) was determined for each plate.

Results: The results showed that 5.25 % NaOCl was the most effective irrigant assessed, killing 100% of bacterial cells in 2 min.

However, the time required by 2.5 %, 1.0 % and 0.5% concentrations was 5 min, 10 min and 30 min, respectively.

Conclusion: There was a statistically significant difference between NaOCl concentrations with respect to the mean number of viable counts recovered, with 5.25 % NaOCl being the most effective irrigant assessed.

There was a strong curvilinear relationship between NaOCl concentrations and time taken to attain zero viable counts (100 % killing).

Key words: E.

faecalis, Sodium hypochlorite, Viable colonies.