Antimicrobial Substances That Inhibit Microbe Growth Biology Essay

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INTRODUCTION: "An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes" ( The resistance of bacteria and fungi to various antimicrobial agents becomes challenging in the treatment of various infections. "It is well established that some plants contain compounds able to inhibit the microbial growth and virus infection" (Cowan 1999, Simoes 2001, Sinico et al. 2005, Souza et al. 2005, Gurib - Fakim 2006, Bakkali et al 2008). Essential oils are natural aromatic compounds found in the seeds, bark, stems, roots, flowers, and other parts of plants. They can be both beautifully and powerfully fragrant. In addition to giving plants their distinctive smells, essential oils provide plants with protection against predators and disease and play a role in plant pollination. 

Thyme oil is an ancient herb used in medicine by the Greeks, the Egyptians and the Romans. It comes from an evergreen perennial shrub that grows up to 45 cm high. It is extracted from fresh tops and leaves of the plant by water or steam distillation. During the Middle Ages thyme was carried into courtrooms to fight off diseases.

Lavender oil is derived from an evergreen woody shrub about 1 meter high, with gray-green narrow linear leaves and the most beautiful purple-blue flowers, perched on a long stem and a few varieties of it grow wild in the Mediterranean region, but the main producer is France. Lavender oil is extracted from the flowering tops by steam distillation. It is often used in toilet water, as an insecticide or in sachets to be placed between linen. It is also used to clean wounds and to treat burns.

Orange Essential Oil is the oil produced from the fruit of the orange tree. Sweet orange essential oil is citrusy and brightly fragrant, lending itself to uplifting the emotions and the mind. Rather than stimulating, the overall effect is calming, and can act as an antidepressant. It is considered warming, cheering, soothing, and may bring balance to the nervous system and emotions. Uses of Orange Oil include calming palpitations, using in a steam inhaler for bronchitis, and has been reported as helpful for the skin if used in the smallest quantities. "It has also been touted as anti-tumoral, anti-inflammatory and as an anti-coagulant that may improve circulation. In Chinese medicine the dried sweet orange peel is used to treat coughs, colds, anorexia and malignant breast sores. Others include anti-inflammatory, antiseptic, bactericidal, carminative, choleretic, digestive, fungicidal, hypotensive, nervous sedative, stomachic, and overall tonic"(

Many companies add essential oils into their soaps, household cleaners, and detergents, claiming they have an added benefit. Certain stores cell these essential oils claiming they will relieve respiratory infections, help heal, and have antiseptic properties. Many essential oil companies sell books describing what essential oils to buy to cure specific ailments. Websites such as,, and offer tremendous amount of information on certain essential oil's ability to help purify and heal. Although these claims state that essential oils are not meant to replace a doctor's advice and are not FDA approved, many people prefer essential oils as a more natural approach other than modern medications.

In this experiment we will prove that thyme, lavender, and orange essential oils are better antimicrobial agents against gram positive cocci, Streptococcus aureus, than common household agents like Mr. Clean and 5% Bleach.

METHODS: Three Mueller-Hinton agar plates were obtained and inoculated with Streptacoccus aureus. Each of the three plates was divided into four sections with a sharpie marker. The first plate consisted of Lavender, Sterile Water, Mr. Clean and Bleach. The second plate was labeled with Orange, Sterile Water, Mr. Clean, and Bleach. The third plate was labeled with Thyme, Sterile Water, Mr. Clean and Bleach. Than tiny white paper discs were saturated with Lavender, Thyme, Orange, Sterile Water, Mr. Clean, and Bleach. An aseptic technique was used to make sure the discs remained sterile. Each saturated disc was placed on its designated section on the agar. The other two plates were done the same way, only the second one had Thyme instead of Lavender and the third one had Orange instead of Lavender. This was done so each essential oil could be compared to the antiseptic Mr. Clean and Bleach. Each plate was incubated at 37 Celsius. After 24-48 hours the agar plates were measured to see the Zones of Inhibition. The experiment was repeated three times for comparison.

RESULTS: Trial 1. Thyme and Lavender oils showed the most promise. Both fought off the bacteria on the agar plates, whereas Orange Essential Oil, Mr. Clean, Bleach and Sterile Water were all at 0 or less than 5 mm of inhibition.

Trial 2. Thyme fought off the bacteria, whereas Orange and Lavender Essential Oils were at 0 mm of inhibition. Mr. Clean, Bleach and Sterile Water were either at 0 mm or less than 5 mm of inhibition.

Trial 3. Thyme and Lavender oils both had a high degree of inhibition. Orange, Mr. Clean, Bleach and Sterile water were at 0mm or less than 5 mm of inhibition.

As shown in the table, the Thyme and Lavender did a great job of fighting off the bacteria. Orange Essential Oil, Mr. Clean, Bleach and Sterile Water did not work well as an antimicrobial agent, nor did it impact the bacteria.

DISCUSSION: The Lavender and Thyme Essential oils worked as an antimicrobial against Streptococcus aureus. The common household agents that claim to be antimicrobial against various types of bacteria did not do well. Mr. Clean, 5% Bleach and Sterile Water did not impact the bacteria greatly. Although there were some zones of inhibition it wasn't as significant as the Thyme and Lavender Essential Oils. The hypothesis was correct to an extent. After doing numerous amount of research, we believed that Orange would work as well as Thyme and Lavender. The experiments proved us wrong. Mr. Clean, 5% Bleach, Sterile Water and Orange Essential oil did not impact the bacteria. In the research, orange is supposed to be used as an anti-inflammatory, antiseptic, bactericidal, carminative, choleretic, digestive, fungicidal, hypotensive, nervous sedative, stomachic, and overall tonic. In this case orange did not do well as an antimicrobial against Streptococcus aureus.

Lavender and Thyme Essential Oils would be great to use with a treatment of strep throat. Some practitioners suggest inhaling fragrances of lavender and thyme essential oils in addition to antibiotics, since they primarily address the comfort of the patient and not the underlying infection ( "Essential oils showed significant antimicrobial activity against gram positive bacteria and dermatophyte fungi" (Detoni, 690).