Essential Oils from Ugandan Aromatic Medicinal Plants: Chemical Composition and Growth Inhibitory Effects on Oral Pathogens

Abstract

The study assessed the growth inhibitory effects of essential oils extracted from ten Ugandan medicinal plants (Bidens pilosa, Helichrysum odoratissimum, Vernonia amygdalina, Hoslundia opposita, Ocimum gratissimum, Cymbopogon citratus, Cymbopogon nardus, Teclea nobilis, Zanthoxylum chalybeum, and Lantana trifolia) used traditionally in the management of oral diseases against oral pathogens. Chemical compositions of the oils were explored by GC-MS. Inhibitory effects of the oils were assessed on periodontopathic Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans and cariogenic Streptococcus mutans and Lactobacillus acidophilus using broth dilution methods at concentrations of 1%, 0.1%, and 0.01%. The most sensitive organism was A. actinomycetemcomitans. Its growth was markedly inhibited by six of the oils at all the concentrations tested. Essential oil from C. nardus exhibited the highest activity with complete growth inhibition of A. actinomycetemcomitans and P. gingivalis at all the three concentrations tested, the major constituents in the oil being mainly oxygenated sesquiterpenes. Most of the oils exhibited limited effects on L. acidophilus. We conclude that essential oils from the studied plants show marked growth inhibitory effects on periodontopathic A. actinomycetemcomitans and P. gingivalis, moderate effects on cariogenic S. mutans, and the least effect on L. acidophilus. The present study constitutes a basis for further investigations and development of certain oils into alternative antiplaque agents.

Figure 1

Inhibitory effects of plant essential oils on bacterial growth determined by colony forming units (CFU) assay. The individual bars show the number of surviving bacteria expressed as a percentage of control (n = 4, error bar = S.E.M). Differences in CFU in the control plate and CFU in each tested concentration of the oil or chlorhexidine (in the original dataset) statistically analyzed using independent Student's t-test: ^∗ p < 0.05 to 0.0001, ^∗∗ p < 0.0001 compared with the control. The plant essential oil in-test concentration is in percentage of final assay volume. (a) Gram-negative bacteria: A. actinomycetemcomitans, P. gingivalis. (b) Gram-positive bacteria: S. mutans, L. acidophilus,and B. megaterium. Positive control: CHX = chlorhexidine. Plant species names: B.pi = Bidens pilosa; H.od = Helichrysum odoratissimum; V.am = Vernonia amygdalina; H.op = Hoslundia opposita; O.gr = Ocimum gratissimum; C.ci = Cymbopogon citratus; C.na = Cymbopogon nardus; T.no = Teclea nobilis Delile; Z.ch = Zanthoxylum chalybeum; L.tr = Lantana trifolia. Plant family names: (A) = Asteraceae; (L) = Lamiaceae; (P) = Poaceae; (R) = Rutaceae; (V) = Verbenaceae.