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. 2020 Jan 18;25(2):400.
doi: 10.3390/molecules25020400.

Biodegradability of Dental Care Antimicrobial Agents Chlorhexidine and Octenidine by Ligninolytic Fungi

Lucie Linhartová  1   2 , Klára Michalíková  1   2 , Kamila Šrédlová  1   2 , Tomáš Cajthaml  1   2
Affiliations

Biodegradability of Dental Care Antimicrobial Agents Chlorhexidine and Octenidine by Ligninolytic Fungi

Lucie Linhartová et al. Molecules. .

Abstract

Chlorhexidine (CHX) and octenidine (OCT), antimicrobial compounds used in oral care products (toothpastes and mouthwashes), were recently revealed to interfere with human sex hormone receptor pathways. Experiments employing model organisms-white-rot fungi Irpex lacteus and Pleurotus ostreatus-were carried out in order to investigate the biodegradability of these endocrine-disrupting compounds and the capability of the fungi and their extracellular enzyme apparatuses to biodegrade CHX and OCT. Up to 70% ± 6% of CHX was eliminated in comparison with a heat-killed control after 21 days of in vivo incubation. An additional in vitro experiment confirmed manganese-dependent peroxidase and laccase are partially responsible for the removal of CHX. Up to 48% ± 7% of OCT was removed in the same in vivo experiment, but the strong sorption of OCT on fungal biomass prevented a clear evaluation of the involvement of the fungi or extracellular enzymes. On the other hand, metabolites indicating the enzymatic transformation of both CHX and OCT were detected and their chemical structures were proposed by means of liquid chromatography-mass spectrometry. Complete biodegradation by the ligninolytic fungi was not achieved for any of the studied analytes, which emphasizes their recalcitrant character with low possibility to be removed from the environment.

Keywords: chlorhexidine; dental hygiene; laccase; ligninolytic fungi; manganese-dependent peroxidase; octenidine; personal care products; quaternary ammonium compounds; recalcitrant pollutant.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Residual concentration of (a) chlorhexidine (CHX) and (b) octenidine (OCT) after the 21-day in vivo degradation by I. lacteus and P. ostreatus related to the respective heat-killed controls (HKCs). The red (CHX) and blue (OCT) line graphs show extraction recovery during the experiment expressed as the HKC and abiotic control (AC) ratio. Error bars represent standard deviation (n = 3). The asterisk marks a significant difference between the individual harvesting day and the control group—0 d (post hoc Dunnett’s Test).
Figure 1
Figure 1
Residual concentration of (a) chlorhexidine (CHX) and (b) octenidine (OCT) after the 21-day in vivo degradation by I. lacteus and P. ostreatus related to the respective heat-killed controls (HKCs). The red (CHX) and blue (OCT) line graphs show extraction recovery during the experiment expressed as the HKC and abiotic control (AC) ratio. Error bars represent standard deviation (n = 3). The asterisk marks a significant difference between the individual harvesting day and the control group—0 d (post hoc Dunnett’s Test).
Figure 2
Figure 2
In vitro degradation of chlorhexidine (CHX) in concentrated extracellular liquids of I. lacteus (manganese-dependent peroxidase, MnP) and P. ostreatus (laccase, Lac). Initial concentration of CHX was 5 µg/mL in both experiments. The red line graphs show the recovery of CHX extraction during the experiment expressed as the heat-killed control (HKC) and abiotic control (AC) ratio. Error bars represent standard deviation (n = 3). The asterisk marks a significant difference between the individual harvesting day and the control group—0 d (post-hoc Dunnett’s Test).
Figure 3
Figure 3
In vitro degradation of octenidine (OCT) in concentrated extracellular liquids of I. lacteus (manganese-dependent peroxidase, MnP) and P. ostreatus (laccase, Lac). Initial concentration of OCT was 5 µg/mL in both experiments. The blue line graphs show the recovery of OCT extraction during the experiment expressed as the heat-killed control (HKC) and abiotic control (AC) ratio. Error bars represent standard deviation (n = 3). The asterisk marks a significant difference between the individual harvesting day and the control group—0 d (post-hoc Dunnett’s Test).
Figure 4
Figure 4
LC-UV plots of degradation samples acquired during in vitro chlorhexidine (CHX) degradation in the concentrated extracellular liquid of I. lacteus supplemented with Mn2+ and H2O2. The UV absorption spectra of specific peaks are given in the insets.
Figure 5
Figure 5
LC-UV plots of degradation samples acquired during in vitro octenidine (OCT) degradation in the concentrated extracellular liquid of I. lacteus supplemented with Mn2+ and H2O2. The UV absorption spectra of specific peaks are given in the insets.
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