Antibacterial and Antibiofilm Effects of Different Samples of Five Commercially Available Essential Oils

Abstract

Essential oils (EOs) have gained economic importance due to their biological activities, and increasing amounts are demanded everywhere. However, substantial differences between the same essential oil samples from different suppliers are reported-concerning their chemical composition and bioactivities-due to numerous companies involved in EOs production and the continuous development of online sales. The present study investigates the antibacterial and antibiofilm activities of two to four samples of five commercially available essential oils (Oregano, Eucalyptus, Rosemary, Clove, and Peppermint oils) produced by autochthonous companies. The manufacturers provided all EOs' chemical compositions determined through GC-MS. The EOs' bioactivities were investigated in vitro against Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The antibacterial and antibiofilm effects (ABE% and, respectively, ABfE%) were evaluated spectrophotometrically at 562 and 570 nm using microplate cultivation techniques. The essential oils' calculated parameters were compared with those of three standard broad-spectrum antibiotics: Amoxicillin/Clavulanic acid, Gentamycin, and Streptomycin. The results showed that at the first dilution (D1 = 25 mg/mL), all EOs exhibited antibacterial and antibiofilm activity against all Gram-positive and Gram-negative bacteria tested, and MIC value > 25 mg/mL. Generally, both effects progressively decreased from D1 to D3. Only EOs with a considerable content of highly active metabolites revealed insignificant differences. E. coli showed the lowest susceptibility to all commercially available essential oils-15 EO samples had undetected antibacterial and antibiofilm effects at D2 and D3. Peppermint and Clove oils recorded the most significant differences regarding chemical composition and antibacterial/antibiofilm activities. All registered differences could be due to different places for harvesting the raw plant material, various technological processes through which these essential oils were obtained, the preservation conditions, and complex interactions between constituents.

Keywords: Clove oil; Eucalyptus oil; Oregano oil; Peppermint oil; Rosemary oil; antibacterial activity; antibiofilm effect; bioactive constituents; principal component analysis.

Figure 1

PCA-Biplot displays the correlations between bioactive constituents and antibacterial and antibiofilm effects on Gram-positive and Gram-negative bacteria in each EEO and REO sample. EEOs 1–2—Eucalyptus essential oils from two different manufacturers; REOs 1–2—Rosemary essential oils from two different manufacturers; S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy.

Figure 2

PCA-Biplot displays the correlations between bioactive constituents’ content and antibacterial and antibiofilm effects on Gram-positive and Gram-negative bacteria in each CEO sample. CEOs 1–3—Clove essential oils from three different manufacturers; S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy.

Figure 3

PCA-Biplot displaying the correlations between bioactive constituents’ content and antibacterial and antibiofilm effects on Gram-positive and Gram-negative bacteria in each PEO sample; PEO1–4—Peppermint essential oil from four different manufacturers; S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy.

Figure 4

(A) PCA-Biplot displays the antibacterial and antibiofilm efficacy of essential oils and antibacterial drugs against Gram-positive and Gram-negative bacteria. (B) AHC-Dendrogram. C1–C5 —clusters: C1 (PEO1, PEO2), C2 (PEO3, PEO4), C3 (CEO1, OEO1, OEO3), C4 (CEO2, CEO3), C5 (REO1, REO2, EEO1, EEO2). GEN—Gentamicin; STR—Streptomycin; AMC—Amoxicillin-Clavulanic acid; OEOs 1–2—Oregano essential oils from two different manufacturers; EEOs 1–2—Eucalyptus essential oils from two different manufacturers; REOs 1–2—Rosemary essential oils from two different manufacturers; CEOs 1–3—Clove essential oils from three different manufacturers; PEOs 1–4—Peppermint essential oils from four different manufacturers; S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy.

Figure 5

(A) Chemical composition of OEO samples provided by the manufacturers, compared to ISO 13171:2016 standard. (B) Bioactive constituents and antibacterial and antibiofilm effects of OEOs. The correlation between chemical constituents and antibacterial and antibiofilm activities of Oregano oil samples. S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy, ISO St.Min./Max.—the constituents’ content limits from ISO 13171:2016 standard.

Figure 6

(A,B) Chemical composition of EEOs and REOs samples provided by the manufacturers, compared to Ph. Eur. 10 limits (Min/Max). (C,D) Bioactive constituents and antibacterial and antibiofilm effects of EEOs (C) and REOs (D).

Figure 7

(A,B) Chemical composition of EO samples provided by the manufacturers, compared to Ph. Eur. 10 limits (Min/Max). (A) Clove oils (CEO1, CEO2, and CEO3); (B) Peppermint oils (PEO1, PEO2, PEO3, and PEO4); Ph. Eur.Min./Max.—the bioactive compounds content limits according to Ph. Eur. 10. (C,D) The correlation between chemical constituents and antibacterial and antibiofilm activities of Clove oil (C) and Peppermint oil (D) samples. S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy.

Figure 7

(A,B) Chemical composition of EO samples provided by the manufacturers, compared to Ph. Eur. 10 limits (Min/Max). (A) Clove oils (CEO1, CEO2, and CEO3); (B) Peppermint oils (PEO1, PEO2, PEO3, and PEO4); Ph. Eur.Min./Max.—the bioactive compounds content limits according to Ph. Eur. 10. (C,D) The correlation between chemical constituents and antibacterial and antibiofilm activities of Clove oil (C) and Peppermint oil (D) samples. S.a.—S. aureus, E.c.—E. coli, P.a.—P. aeruginosa, ABE—Antibacterial efficacy, ABfE—Antibiofilm efficacy.