Assessment of the antimicrobial effects of sodium hypochlorite on Enterococcus faecalis by D 2 O-labeled single-cell Raman micro-spectroscopy.

Objectives: To systematically evaluate the feasibility of D ₂ O-labeled single-cell Raman micro-spectroscopy in drug resistance research and test the susceptibility of Enterococcus faecalis ( E. faecalis )to sodium hypochlorite.
Methods: 1) The growth of E. faecalis in different doses of D ₂ O and the regularity of D ₂ O intake were evaluated through absorbance measurement and D ₂ O-labeled single-cell Raman micro-spectroscopy to examine the universality of D ₂ O-labeled single-cell Raman micro-spectroscopy in bacterial resistance research. 2) Broth dilution method and absorbance measurement were performed to determine the minimum inhibitory concentration (MIC) of NaClO against E. faecalis and the MIC based on metabolic activity (MIC-MA) in vitro via D ₂ O-labeled single-cell raman micro-spectroscopy.
Results: 1) The growth of E. faecalis was not significantly inhibited by ≤40% D ₂ O in the medium. E. faecalis could actively metabolize D ₂ O and exhibit a C-D ratio in specific areas of Raman micro-spectroscopy results. The C-D ratio of E. faecalis at the stationary phase was positively correlated with D ₂ O concentration. 2) The MIC and MIC-MA of NaClO against E. faecalis were 0.45 and 0.9 g·L ^-1 , respectively. The concentration of MIC-MA was twice that of MIC.
Conclusions: D ₂ O-labeled single-cell Raman micro-spectroscopy is important in screening antimicrobial agents and evaluating the efficacy of antimicrobial agents. It is suitable for evaluating the effect of drugs on bacterial metabolic activities. NaClO showed an effective antimicrobial activity against E. faecalis . E. faecalis ceased propagation yet remained highly metabolically active when it was exposed to NaClO at the MIC level. The metabolic activity of most cells was inhibited only when they were exposed to NaClO at the MIC-MA level.