Abstract
Enterococci are able to survive endodontic procedures and contribute to the failure of endodontic therapy. Thus, it is essential to identify novel ways of eradicating them from infected root canals. One such approach may be the use of antimicrobials such as plant essential oils. Enterococcal strains were isolated from endodontically treated teeth by standard microbiological methods. Susceptibility to antibiotics was evaluated by the disc-diffusion method. The minimal inhibitory concentration (MIC) of geranium essential oil was investigated by microdilution in 96-well microplates in Mueller Hinton Broth II. Biofilm eradication concentrations were checked in dentin tests. Geranium essential oil inhibited enterococcal strains at concentrations ranging from 1.8–4.5 mg/mL. No correlation was shown between resistance to antibiotics and the MICs of the test antimicrobials. The MICs of the test oil were lower than those found to show cytotoxic effects on the HMEC-1 cell line. Geranium essential oil eradicated enterococcal biofilm at concentrations of 150 mg/mL. Geranium essential oil inhibits the growth of endodontic enterococcal species at lower concentrations than those required to reach IC50 against the HMEC-1 cell line, and is effective against bacteria protected in biofilm at higher concentrations. In addition, bacteria do not develop resistance to essential oils. Hence, geranium essential oil represents a possible alternative to other antimicrobials during endodontic procedures.
Highlights
Enterococcal strains are frequently found in the human digestive and genitourinary tracts
The results of the present study show that test oil had Minimal Inhibitory Concentration (MIC) values ranging from 1.8–4.5 mg/mL when used against clinical strains of E. faecalis isolated from root canals
Our recent results confirmed that geranium essential oil is effective against enterococci at concentrations lower than those at which toxicity to human HMEC-1 cells had formerly been observed. These results show that geranium oil may be safer towards HMEC-1 cells than the other previously tested oils [15] and may be an alternative antimicrobial to use in endodontic procedures
Summary
Enterococcal strains are frequently found in the human digestive and genitourinary tracts. Rao et al recommended the use of essential oils as additives to antibacterial agents against oral pathogens, and to food products and mouthwashes for preventing and treating dental caries. They investigated the activity of essential oils against some oral microorganisms such as Streptococcus mutans, Streptococcus salivarius, Streptococcus mitis, Lactobacillus fermentum, Streptococcus anginosus, Streptococcus mutans, Streptococcus gordonii, Lactobacillus acidophilus and Staphylococcus aureus obtaining good results [7]. The cutaneous application of this oil may suppress the inflammatory symptoms related to neutrophil accumulation and edema [9] and it has been shown to have a synergistic effect against Staphylococcus aureus when combined with norfloxacin [10] To continue this line of investigation, we decided to determine whether Enterococcus spp. isolated from endodontic infections may be inhibited by geranium essential oil. The aims of the study were to evaluate the susceptibility to geranium essential oil of enterococcal strains in: (a) planktonic state and (b) grown on dentin
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