Antimicrobial efficacy of chlorine agents against selected oral pathogens

Abstract

Objectives: Method-dependent comparison of antimicrobial agents' efficacy against oral pathogens.

Materials and methods: Several sodium hypochlorite solutions (NaOCl)-Perisolv^®, Carisolv^® and Dakin's solution-were equated with chlorhexidine (CHX) and hydrogen peroxide (H₂O₂) against ten oral micro-organisms related to caries and periodontitis using different minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) techniques. Agents were adjusted to the final 70 mmol/L concentration of active chlorine molecule.

Results: Apart from H₂O₂ and the amino acids of Perisolv^®, all the agents revealed an antimicrobial effect. Agar diffusion test ranked CHX (p < 0.05) as the most effective against all ten specimens, followed by the NaOCl of Perisolv^® and Dakin's solution. Correspondingly, in broth microdilution on agar, CHX was the most effective in eradicating micro-organisms at 0.03 mmol/L compared with 2.2 mmol/L of Dakin's solution. In contrast, the bactericidal concentration of Dakin's solution was the most effective at 0.2 mmol/L, (p < 0.001), followed by Perisolv^® (2.14 mmol/L), CHX (2.38 mmol/L) and Carisolv^® (3.33 mmol/L) after 5 and 10 min in broth dilution test. In live/dead analysis, 60-min exposure to a 2-fold concentration of agents resulted in two-log Aggregatibacter actinomycetemcomitans inhibition by CHX (35 mmol/L) whilst Streptococcus mutans was more susceptible, in 0.8 and 8.8 mmol/L, after 10 min to CHX and Dakin's respectively.

Conclusion: Replacement of CHX with tested hypochlorite agents showed evident potential and promoted rapid antimicrobial effect.

Clinical relevance: Effective antimicrobial agents are crucial in controlling pathogen-induced oral infections increasing clinical possibilities to combat oral biofilms. Additionally, CHX substitution with hypochlorite agents could eliminate CHX's adverse effects.

Keywords: Chlorhexidine; Chlorine compounds; Dakin’s; Dental caries; Oral disease; Periodontitis.

Fig. 1

Study design and methods flow chart

Fig. 2

Volume (μL, MV, SD) of 70 mmol agents needed to eradicate five bacterial strains in each group of bacteria (caries and periodontal)

Fig. 3

Broth microdilution on agar plates in duplicate. Growth inhibition of Streptococcus mutans IB (top two rows) and Streptococcus mutans OMZ65 (bottom two rows) on Mitis Salivarius Bacitracin agar by test agents at different concentrations from the left: Plate A: 70, 35, 17.5, 8.8, 4.4, 2.2 mmol L^-1; Plate B: 1.1, 0.5, 0.3, 0.14, 0.07, 0.03 mmol L^-1. Drops without colonies (or empty agar surface) equal the MBC value, indicating that the test solution has reduced ≥ 99% of the bacteria. Positive and negative controls worked as expected, not shown

Fig. 4

Standard curve of S. mutans and A. actinomycetemcomitans by Syto 9, live/dead (green 490; red 650nm; blue nonlinear fit curve)

Fig. 5

Time-kill curves for all the tested irrigants and one bacterium from each group; AA (periodontal) SM-IB (cariogenic). Twelve 2-fold dilutions are plotted, and the antimicrobial was added at start timepoint and monitored up to 1 h