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Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype
Open accessAbstract
Antimicrobial resistance (AMR) is problematic for the management of chronic wound infection, where biofilms confer increased tolerance to treatments. A wealth of research describes the antimicrobial activity of essential oils, but none have been formulated for clinical use. We screened ten commercially available essential oils from the Lamiaceae plant family (thyme, rosemary, basil, oregano, clary sage) for bacteriostatic, bactericidal, and anti-biofilm activity. TD-GCMS was used to identify highly abundant compounds which were mapped to efficacy data. Thyme essential oils were antimicrobial against both Pseudomonas aeruginosa and Staphylococcus aureus and had the most potent anti-biofilm activity. Three compounds were common and highly abundant in these oils: o -cymene, 2-isopropyl-4-methyl-phenol ( o -thymol/carvacrol), and thymol. The most efficacious red and white thyme oils were formulated into Laponite-based hydrogel emulsions capable of inhibiting both P. aeruginosa and S. aureus in static and dynamic biofilm models . Notably, the efficacy of both gels diverged from that predicted by MIC, MBC, and MBIC values, highlighting the limitations of reductionist analyses in predicting real-world antimicrobial performance. Key points: • Thyme oils are the most efficacious of the Lamiaceae plant oils tested • Thymol isomers and o-cymene are abundant in thyme oils, but minor components also play a role in antimicrobial activity • Hydrogel efficacy arises from interactions between formulation and wound microenvironment
Overview
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TL;DR
Ten Lamiaceae essential oils were screened for antimicrobial and anti-biofilm activity, with thyme oils showing the strongest effects. Red and white thyme oils were formulated into Laponite hydrogels that reduced *P. aeruginosa* and *S. aureus* in a dynamic wound biofilm model, but hydrogel efficacy diverged from MIC/MBC/MBIC predictions.
Key findings
- Thyme oils had the lowest MICs and MBCs against both pathogens. Red thyme (B) had *P. aeruginosa* MIC 0.6 mg/mL and MBC 2.2 mg/mL, and *S. aureus* MIC/MBC 0.6/0.6 mg/mL; white thyme (B) had *P. aeruginosa* MIC 18.8 mg/mL and MBC 75 mg/mL, and *S. aureus* MIC/MBC 0.6/1.2 mg/mL. Only red thyme (B) met the antimicrobial criterion against *P. aeruginosa*, while all four thyme oils did so against *S. aureus*.
- Red thyme (A and B) and white thyme (B) had the most potent anti-biofilm activity. Red thyme (B) MBIC was 0.6 mg/mL for both bacteria; white thyme (B) MBIC was 1.2 mg/mL for both. No MBIC was found for basil, clary sage (A), oregano, or rosemary (A and B) against either bacterium.
- TD-GC-MS showed thyme oils contained the thymol isomer 2-isopropyl-4-methylphenol (o-thymol/carvacrol) at 16.4–65.76%; red thyme (B) also contained 29.9% o-cymene, and white thyme (B) contained 65.7% 2-isopropyl-4-methylphenol plus 14.7% thymol. Six oils contained emollients isopropyl myristate and/or isopropyl palmitate, and these typically had higher MICs.
- Laponite gels with red thyme (B) or white thyme (B) at 8×MIC reduced dynamic biofilms: *P. aeruginosa* red thyme gel −2.33 log at 48 h and −2.51 log at 72 h; white thyme gel −2.94 log and −2.40 log. For *S. aureus*, red thyme gel gave −2.36 log and −2.20 log; white thyme gel gave −2.71 log and −2.49 log. White thyme (B) gel was generally more efficacious in zone-of-inhibition assays, contrary to MIC-based prediction.
Methods
- Ten commercially available Lamiaceae essential oils (thyme, rosemary, basil, oregano, clary sage) were screened against *Pseudomonas aeruginosa* ATCC 9027 and *Staphylococcus aureus* NCTC 13616 (EMRSA-15) using MIC, MBC, and MBIC assays.
- Chemical composition was analysed by TD-GC-MS with NIST library matching (≥75% match factor), semi-quantitative comparison, and ChromMine™ clustering to link composition with MIC/MBC data.
- Red thyme (B) and white thyme (B) were formulated into 4.7% (w/v) Laponite hydrogels at MIC to 8×MIC and tested by zone of inhibition against Neosporin, then in a dynamic chronic wound biofilm flow system at 33°C and 0.322 mL/min with total viable count enumeration; statistical analysis used one-way ANOVA with Dunnett’s or Tukey’s post hoc tests.
Limitations
- The paper states that TD-GC-MS identifies individual components but does not account for synergistic or antagonistic interactions, and that reductionist MIC/MBC/MBIC assays poorly predict real-world antimicrobial performance. It also notes that standardising essential oil composition is difficult because of plant parts, extraction methods, and environmental factors, and that broader translation barriers include insufficient human data and safety concerns.
- Evident from the text: the dynamic biofilm experiments used N = 2 biological repeats and n = 2 technical repeats; zone-of-inhibition assays used N = 3 and n = 3; only two pathogens and only two thyme oils were formulated; and no cytotoxicity, safety, or in vivo infected-wound testing is reported.
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In the paper
“Where an MBIC was not achieved the biomass reduction ranged between 12.8 and 43.6% S. aureus.”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Antibiofilm activity of the essential oils
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“The most abundant compounds in clary sage (A), oregano, rosemary (A) and white thyme (A) were isopropyl myristate and isopropyl palmitate which are emollients and texture enhancers used in the cosmetic industry.”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > TD-GCMS of the essential oils
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Thyme oils had the lowest MICs and MBCs against both pathogens.”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Inhibitory and bactericidal activity of the essential oils
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“There was no MBIC for basil, clary sage (A), oregano, or rosemary (A and B), for both bacteria.”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Antibiofilm activity of the essential oils
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“basil, clary sage (B), oregano, red thyme (A and B), and white thyme (A and B) were found to be bactericidal against both pathogens (Table 3).”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Inhibitory and bactericidal activity of the essential oils
plainstates a cause- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
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Percentages, sums and reported differences re-computed from the paper’s own numbers.
Each contradiction between two passages listed here was confirmed by an independent check.
Rated major: it would touch a result — a value a result rests on, reported and recomputed p-values on opposite sides of the significance level, two passages that conflict with no sign which is right, or a cited work retracted before this paper was published.
In the paper
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Efficacy of a laponite hydrogel emulsion of thyme oil
“thyme (B) gel produced a zone of inhibition significantly greater (p < 0.05; one way ANOVA with Dunnett’s post hoc) than the Neosporin at 8 × MIC for S. aureus”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Efficacy of a laponite hydrogel emulsion of thyme oil
“| S. aureus | 8×MIC | 15.14* [+/-0.16] | 24.87* [+/-0.39] | 15.19 |”
Rated minor: it would not touch a result — a value no result rests on, a p-value that stays on the same side of the significance level, or a conflict that is clerical, resolved elsewhere in the paper, or outside its own findings.
In the paper
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Discussion
“Only two oils (red thyme B and white thyme B) met the criteria for classification as antimicrobial essential oils, with MICs between 100 and 1000 µg/mL”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Inhibitory and bactericidal activity of the essential oils
“Therefore, only red thyme (A and B), white thyme (A and B) can be considered antimicrobial against S. aureus and only red thyme (B) can be considered antimicrobial against P. aeruginosa.”
Rated minor: it would not touch a result — a value no result rests on, a p-value that stays on the same side of the significance level, or a conflict that is clerical, resolved elsewhere in the paper, or outside its own findings.
In the paper
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Minor components of the essential oils assessed by TD-GCMS
“o-cymene was present in red thyme (A) and white thyme (A).”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Minor components of the essential oils assessed by TD-GCMS
“| o-cymene | | | | | | | 4.4 [+ / − 0.3] | | | 3.2 [+ / − 0.8] |”
Rated minor: it would not touch a result — a value no result rests on, a p-value that stays on the same side of the significance level, or a conflict that is clerical, resolved elsewhere in the paper, or outside its own findings.
In the paper
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Antibiofilm activity of the essential oils
“Where an MBIC was not achieved the biomass reduction ranged between 12.8 and 43.6% S. aureus.”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Antibiofilm activity of the essential oils
“| Rosemary (B) | Salvia rosmarinus | No MBIC | 43.6 | No MBIC | 28.5 |”
Rated minor: it would not touch a result — a value no result rests on, a p-value that stays on the same side of the significance level, or a conflict that is clerical, resolved elsewhere in the paper, or outside its own findings.
In the paper
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Composition related to inhibitory activity
“clusters 2 (thyme oils) and 3 (oregano oil)”
§ Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype > Results > Composition related to inhibitory activity
“Cluster 3 (yellow) represents white thyme oils (A and B).”
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Citations
Cites
Vaou, N., Stavropoulou, E., Voidarou, C., Tsigalou, C., & Bezirtzoglou, E. (2021) · Microorganisms · doi:10.3390/microorganisms9102041 · Cited by 993
Antibacterial Activity of Terpenes and Terpenoids Present in Essential Oils
Guimarães, A. C., Meireles, L. M., Lemos, M. F., Guimarães, M. C. C., Endringer, D. C., Fronza, M., & Scherer, R. (2019) · Molecules · doi:10.3390/molecules24132471 · Cited by 821
Antimicrobial susceptibility testing in biofilm-growing bacteria
Macia, M. D., Rojo-Molinero, E., & Oliver, A. (2014) · Clinical Microbiology and Infection · doi:10.1111/1469-0691.12651 · Cited by 537
Guest, J. F., Fuller, G. W., & Vowden, P. (2020) · BMJ Open · doi:10.1136/bmjopen-2020-045253 · Cited by 536
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Essential Oils: Chemistry and Pharmacological Activities
de Sousa, D. P., Damasceno, R. O. S., Amorati, R., Elshabrawy, H. A., de Castro, R. D., Bezerra, D. P., Nunes, V. R. V., Gomes, R. C., & Lima, T. C. (2023) · Biomolecules · doi:10.3390/biom13071144 · Cited by 459
Biofilms and Wounds: An Overview of the Evidence
Percival, S. L., McCarty, S. M., & Lipsky, B. (2015) · Advances in Wound Care · doi:10.1089/wound.2014.0557 · Cited by 423
Vaou, N., Stavropoulou, E., Voidarou, C. (., Tsakris, Z., Rozos, G., Tsigalou, C., & Bezirtzoglou, E. (2022) · Antibiotics · doi:10.3390/antibiotics11081014 · Cited by 406
Antimicrobial Activity of Basil, Oregano, and Thyme Essential Oils
Sakkas, H., & Papadopoulou, C. (2017) · Journal of Microbiology and Biotechnology · doi:10.4014/jmb.1608.08024 · Cited by 358
Abourehab, M. A. S., Rajendran, R. R., Singh, A., Pramanik, S., Shrivastav, P., Ansari, M. J., Manne, R., Amaral, L. S., & Deepak, A. (2022) · International Journal of Molecular Sciences · doi:10.3390/ijms23169035 · Cited by 317
Research works printed but not linked: 1
- Cooper R, Gray D (2012) Is manuka honey a credible alterative to silver in wound care? Wounds UK 8(4):54–64
Cited by
Friska, V., Yunus, M., & Razoki, R. (2026) · Journal of Pharmaceutical And Sciences · doi:10.36490/journal-jps.com.v9i2.1618
Zych, S., Adaszyńska-Skwirzyńska, M., Dzięcioł, M., Konieczka, P., Kozłowski, K., Witkowska, D., & Szewczuk, M. A. (2026) · International Journal of Molecular Sciences · doi:10.3390/ijms272210124
Metadata
- Authors
- Aftab, N., Varghese, P., Khalid, A., Umar, A. K., Wallis, C. J., Bates, M., & Hooper, S. E.
- Affiliations
- Cardiff Metropolitan University (GB)
- Corresponding author
- Hooper, Sarah E.
- Venue
- Applied Microbiology and Biotechnology
- Published
- 2025-12-01
- Volume
- 109
- Issue
- 1
- Pages
- 253-253
- ISSN
- 0175-7598 (ISSN-L)
- 1432-0614
- PMC
- PMC12672839
- OpenAlex
- W4416888196
- Semantic Scholar
- c155561032a9808d18053c22a439636266b1a744
- Cited by
- 2
- References
- 74
- Citations by year
- 2026: 2
- FWCI
- 0.69
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- cc-by
- creativecommons.org/licenses/by/4.0 (tdm)
- creativecommons.org/licenses/by/4.0 (vor, 1 d)
- Locations
- Applied Microbiology and Biotechnology (publishedVersion, cc-by)
- PubMed (publishedVersion)
- PubMed Central (publishedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Funders
- Microbiology Society
- Applied Microbiology International
- Cardiff Met Research & Innovation
- Topics
- Life Sciences › Agricultural and Biological Sciences › Food Science › Essential Oils and Antimicrobial Activity
- Life Sciences › Immunology and Microbiology › Applied Microbiology and Biotechnology › Antimicrobial agents and applications
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Bacterial biofilms and quorum sensing
- Keywords
- essential oils, thyme essential oil, Lamiaceae, antimicrobial activity, antibiofilm activity, chronic wound infection, Pseudomonas aeruginosa, Staphylococcus aureus, thymol, o-cymene, carvacrol, topical gel formulation, antimicrobial resistance, biofilm tolerance
- MeSH terms
- Cymenes, Anti-Infective Agents, Anti-Bacterial Agents, Gels, Microbial Sensitivity Tests, Oils, Volatile, Plant Oils, Pseudomonas aeruginosa, Staphylococcus aureus, Thymol, Biofilms, Lamiaceae, Thymus Plant
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- CoChat. (2026). Citation check: Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype. https://app.cochat.ai/papers/10.1007/s00253-025-13650-8
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- Aftab, N., Varghese, P., Khalid, A., Umar, A. K., Wallis, C. J., Bates, M., & Hooper, S. E. (2025). Linking chemical-composition to antimicrobial efficacy: development of an essential oil-based topical gel prototype. Applied Microbiology and Biotechnology. https://doi.org/10.1007/s00253-025-13650-8
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