Minimum inhibitory concentrations of herbal essential oils and monolaurin for gram-positive and gram-negative bacteria


New, safe antimicrobial agents are needed to prevent and overcome severe bacterial, viral, and fungal infections. Based on our previous experience and that of others, we postulated that herbal essential oils, such as those of origanum, and monolaurin offer such possibilities. We examined in vitro the cidal and/or static effects of oil of origanum, several other essential oils, and monolaurin on Staphylococcus aureus, Bacillus anthracis Sterne, Escherichia coli, Klebsiella pneumoniae, Helicobacter pylori, and Mycobacterium terrae. Origanum proved cidal to all tested organisms with the exception of B. anthracis Sterne in which it was static. Monolaurin was cidal to S. aureus and M. terrae but not to E. coli and K. pneumoniae. Unlike the other two gram-negative organisms, H. pylori were extremely sensitive to monolaurin. Similar to origanum, monolaurin was static to B. anthracis Sterne. Because of their longstanding safety record, origanum and/or monolaurin, alone or combined with antibiotics, might prove useful in the prevention and treatment of severe bacterial infections, especially those that are difficult to treat and/or are antibiotic resistant.


  1. 1.

    U.S. Congress, Office of Technology Assessment: Impacts of antibiotic resistant bacteria, OTA-H-629. U.S. Government Printing Office, Washington DC; 1995

    Google Scholar 

  2. 2.

    Ayliffe GA: The progressive intercontinental spreads of methicillin-resistant Staphylococcus aureus. Clin Infect Dis 24(Suppl 1): S74–S79, 1997

    PubMed  Google Scholar 

  3. 3.

    Cunha BA: Strategies to control antibiotic resistance. Sem Resp Infect 17: 250–258, 2002

    Article  Google Scholar 

  4. 4.

    Edmond MB, Wenzel RP, Pasculle AW: Vancomycin-resistant Staphylococcus aureus: Perspectives on measures needed for control. Ann Intern Med 124: 329–334, 1996

    CAS  PubMed  Google Scholar 

  5. 5.

    Waldvogel WW: New resistance in Staphylococcus aureus. N Eng J Med 340: 556–557, 1999

    Article  CAS  Google Scholar 

  6. 6.

    Burnie J, Matthews R, Jiman-Fatami A, Gottardello P, Hodgetts S, D’arcy S: Analysis of 42 cases of septicemia caused by an epidemic strain of methicillin-resistant Staphylococcus aureus: Evidence of resistance to vancomycin. Clin Infect Dis 31: 684–689, 2000

    Article  CAS  PubMed  Google Scholar 

  7. 7.

    Hiramatsu K, Hanake H, Ino T, Yabuta K, Oguri T, Tenover FC: Methicillin-resistant Staphylococcus aureus clinical strain with reduced vancomycin susceptibility. J Antimicrob Chemother 40: 135–136, 1997

    Article  CAS  PubMed  Google Scholar 

  8. 8.

    Sieradzki K, Roberts RB, Haber SW, Tomasz A: The development of vancomycin resistance in a patient with methicillin-resistant Staphylococcus infection. N Eng J Med 340: 517–523, 1999

    Article  CAS  Google Scholar 

  9. 9.

    Denis O, Nonhoff C, Byl B Knoop C, Bobin-Dubreux S, Struelens MJ: Emergence of vancomycin-intermediate Staphylococcus aureus in a Belgian hospital: Microbiological and clinical features. J Antimicrob Chemother 50: 383–391, 2002

    Article  CAS  PubMed  Google Scholar 

  10. 10.

    Brook I, Elliott TB, Pryor HI, Sautter TE, Gnade BT, Thakar JH, Knudson GB. In vitro resistance of Bacillus anthracis Sterne to doxocycline, macrolides and quinolones. Intern J Antimicrob Agents 18: 559–562, 2001

    Article  CAS  Google Scholar 

  11. 11.

    Brook I, Elliott TB, Harding RA, Bouhaouala SS, Peacock SJ, Ledney GD, Knudson GB: Susceptibility of irradiated mice to Bacillus anthracis Sterne by the intratracheal route of infection. J Med Microbiol 50: 702–711, 2001

    CAS  PubMed  Google Scholar 

  12. 12.

    Choe CH, Bouhaouala SS, Brook I, Elliott TB, Knudson GB: In vitro development of resistance to ofloxacin and doxycycline in Bacillus anthracis Sterne. Antimicrob Agents Chemother 44: 1766, 2000

    Article  CAS  PubMed  Google Scholar 

  13. 13.

    Pile JC, Malone JD, Eitzen EM, Friedlander AM: Anthrax as a potential biological warfare agent. Arch Intern Med 158: 429–434, 1998

    Article  CAS  PubMed  Google Scholar 

  14. 14.

    Horsburgh Jr CR, Felman S, Ridzon R: Practice guidelines for the treatment of tuberculosis. Clin Infect Dis 31: 633–639, 2000

    Article  PubMed  Google Scholar 

  15. 15.

    Remis RS, Jamieson F, Chedore P, Haddad A, Vernich L: Increasing drug resistance of Mycobacterium tuberculosis isolates in Ontario, Canada, 1987–1998. Clin Infect Dis 31: 427–432, 1998

    Article  Google Scholar 

  16. 16.

    Manohar V, Ingram C, Gray J, Talpur N, Echard BW, Bagchi D, Preuss HG: Antifungal activities of origanum oil against Candida albicans. Mol Cell Biochem 228: 111–117, 2001

    Article  CAS  PubMed  Google Scholar 

  17. 17.

    Manohar V, Ingram C, Gray J, Talpur N, Echard BW, Preuss HG: Antibacterial effects of the edible oil of oregano against Staphlococcus aureus. J Am Coll Nutr 20: 66, 2001 (abstract)

    Google Scholar 

  18. 18.

    Griffiths PA, Babb JR, Fraise AP: Mycobacterium terrae: A potential surrogate for Mycobacterium tuberculosis in a standard disinfectant test. J Hosp Infect 38: 183–192, 1998

    Article  CAS  PubMed  Google Scholar 

  19. 19.

    Kim J, Marshall MR, Wei, C-I: Antibacterial activity of some essential oil components against five foodborne pathogens. J Agric Food Chem 43: 2839–2845, 1995

    Article  CAS  Google Scholar 

  20. 20.

    Carson CF, Cookson BD, Farrelly HD, Riley TV: Susceptibility of methicillin resistant Staphylococcus aureus to the essential oil of Melaleuca alternifolia. J Antimicrob Chemother 35: 421–424, 1995

    CAS  PubMed  Google Scholar 

  21. 21.

    Schmidt MA, Sehnert KW, Smith LH: Beyond Antibiotics. 50 (Or So) Ways to Boost Immunity and Avoid Antibiotics, North Atlantic Books, Berkeley, CA, 1994

    Google Scholar 

  22. 22.

    Ismaiel A, Pierson MD: Inhibition of growth and germination of C botulinum 33A, 40B, and 1623E by essential oil of spices. J Food Sci 55: 1676–1680, 1990

    Google Scholar 

  23. 23.

    Mansour M, Bouttefroy AD, Linder M, Milliere JB: Inhibition of Bacillus licheniformis spore growth in milk by nisin, monolaurin and pH combinations. J Appl Microbiol 86: 311–324, 1999

    Article  CAS  PubMed  Google Scholar 

  24. 24.

    Kivanc M, Akgul A, Dogan A: Inhibitory and stimulatory effects of cumin, oregano and their essential oils on growth and acid production of Lactobacillus plantarum and Leuconostoc mesenteroides. Intern J Food Microbiol 13: 81–86, 1991

    Article  CAS  Google Scholar 

  25. 25.

    Hammer KA, Carson CF, Riley TV: Antimicrobial activity of essential oils and other plant extracts. J Appl Microbiol 86: 985–990, 1999

    Article  CAS  PubMed  Google Scholar 

  26. 26.

    Tucker AO, Maciarello MJ: Oregano: Botany, chemistry, and cultivation. In: G. Charalambus (ed). Spices, Herbs, and Edible Fungi, Elsevier Science, St Louis, MO, 1994, pp 439–456

  27. 27.

    Sivropoulus A, Papanikolaou E, Nikolaou C, Kokkini S, Lanaras T, Arsenakis M: Antimicrobial and cytoxic activities of origanum essential oils. J Agric Food Chem 44: 1202–1205, 1996

    Article  Google Scholar 

  28. 28.

    Siddiqui YM, Ettayebi M, Haddad A, Al-Ahdal MN: Effect of essential oils on enveloped viruses: Antiviral activity of oregano and clove oils on Herpes simplex virus type 1 and Newcastle disease virus. Medi Sci Res 24: 185–186, 1996

    CAS  Google Scholar 

  29. 29.

    Enig MG: Lauric oils as antimicrobial agents: Theory of effect, scientific rationale, and dietary application as adjunct nutritional support for HIV-infected individuals. In: R.R.Watson (ed). Nutrients and Foods in AI12/3/04 CRC Press, Boca Raton, FL, 1998, pp 81–97

    Google Scholar 

  30. 30.

    Kabara JJ: Lipids as host-resistance factors of human milk. Nutr Rev 38: 65–73, 1980

    CAS  PubMed  Google Scholar 

  31. 31.

    Kabara JJ, Vrable R: Antimicrobial lipids: Natural and synthetic acids and monoglycerides. Lipids 12: 753–759, 1977

    CAS  PubMed  Google Scholar 

  32. 32.

    Conley AJ, Kabara JJ: Antimicrobial action of esters of polyhydric alcohols. Antimicrob Agents Chemother 4: 501–506, 1973

    CAS  PubMed  Google Scholar 

  33. 33.

    Schlievert PM, Deringer JR, Kim MH, Projan SJ, Novick RP: Effect of glycerol monolaurate on bacterial growth and toxin production. Antimicrob Agents Chemother 36: 626–631, 1992

    CAS  PubMed  Google Scholar 

  34. 34.

    Projan SJ, Brown-Skrobot S, Schlievert PM: Glycerol monolaurate inhibits the production of B-lactamase, toxic shock syndrome toxin-1, and other staphylococcal exoproteins by interfering with signal transduction. J Bacteriol 176: 4204–4209, 1994

    CAS  PubMed  Google Scholar 

  35. 35.

    Ruzin A, Novick RP: glycerol monolaurate as inhibitors of signal transduction in Staphylococcus aureus. J Bacteriol 182: 2668–2671, 2000

    Article  CAS  PubMed  Google Scholar 

  36. 36.

    Ruzin A, Novick RP: Glycerol monolaurate inhibits induction of vancomycin resistance in Enterococcus faecalis. J Bacteriol ([0-9]+): 182–185, 1998

    CAS  PubMed  Google Scholar 

  37. 37.

    Bergsson G, Arnfinnsson J, Karlsson SM, Steingrimsson O, Thormar H: In vitro inactivation of Chlamydia trachomatis by fatty acids and monoglycerides. Antimicrob Agents Chemother 42: 2290–2294, 1998

    CAS  PubMed  Google Scholar 

  38. 38.

    Thormar H, Isaacs CE, Brown HR, Barshatzky MR, Pessolano T: Inactivation of enveloped viruses and killing of cells by fatty acids and monoglycerides. Antimicrob Agents Chemother 31: 27–31, 1987

    CAS  PubMed  Google Scholar 

  39. 39.

    Isaacs CE, Kashyap S, Heird WC, Thormar H: Anitiviral and antibacterial lipids in human milk and infant formula feed. Arch Dis Childhood 65: 272–273, 1991

    Google Scholar 

  40. 40.

    Isaacs CE, Thormar H: The role of milk-derived antimicrobial lipids as antiviral and antibacterial agents. Adv Exper Med Biol ([0-9]+): 159–165, 1991

    CAS  Google Scholar 

  41. 41.

    Petschow BW, Batema RP, Ford LL: Susceptibility of Helicobacter pylori to bactericidal properties of medium-chain monoglycerides and free fatty acids. Antimicrob Agents Chemother 40: 302–306, 1996

    CAS  PubMed  Google Scholar 

  42. 42.

    CDC: Helicobacter pylori and peptic ulcer disease. (entered May 12, 2003)

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Correspondence to Harry G. Preuss.

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Preuss, H.G., Echard, B., Enig, M. et al. Minimum inhibitory concentrations of herbal essential oils and monolaurin for gram-positive and gram-negative bacteria. Mol Cell Biochem 272, 29–34 (2005).

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  • oregano oil
  • monolaurin
  • antibacterial effect
  • essential oils