Antimicrobial Activity of Cilantro on Staphylococcus Epidermis and Escherichia coli
Antimicrobial effects of cilantro against the gram positive bacteria S. epidermis and the gram negative bacteria E. coli were looked at. We predicted that cilantro would act as an antibiotic against S. epidermis but not to E. coli because S. epidermis does not contain an outer membrane whereas E coli. does. We predicted that the semi-permeable outer membrane of E. coli would protect the bacteria from any antimicrobial properties of cilantro. A drop of cilantro juice and water in varying concentrations (1:10, 1:20, 1:40, 1:80) was added to a nutrient agar plate inoculated with S. epidermis and a nutrient agar plate inoculated with E. coli. The plates were incubated for 48 hours and then observed for a zone of clearing where the cilantro juice drop was placed. Cilantro was found to not display antimicrobial activity against either bacterium in the experiment in any of the different dilutions. These results could have to do with the possible contamination of cilantro or the specific bacteria we chose to target. Additional studies of cilantro should be conducted on different types of bacteria in order to gain a better understanding of how the herb works as an antimicrobial.
Herbs and spices have been used for many years for their health benefits and antimicrobial properties (Lai & Roy, 2004). Cilantro, an herb found in many ethnic food dishes, has been shown to have an antibacterial effect on Salmonella choleraesuis due to the compound dodecanal found in the leaves. Dodecanal was found to be twice as potent as the antibiotic gentamicin that is commonly prescribed for Salmonella infections (Kubo, Fujita, Kubo, Nihei, & Ogura, 2004). The antimicrobial properties of cilantro have also been demonstrated against the bacteria’s Staphylococcus aureus, Bacillus cereus, Escherichia coli (Marsh & Arriola, 2009). We decided to conduct our own experiment to see if cilantro had any antimicrobial effect on the bacteria’s Staphylococcus epidermis and Escherichia coli. Experiments about the antimicrobial properties of herbs are interesting because their results can affect the way people choose to eat. For example, if a certain herb is found to delay food spoilage then perhaps people will choose to include it more often in their cuisines. Or, if a study finds that an herb has an antibacterial effect on an organism commonly found on produce, perhaps a fruit and vegetable wash could be produced that contains the herb in order to help prevent infection. We chose both a gram positive bacterium (S. epidermis) and a gram negative bacterium (E. coli) to see if a bacterial outer membrane would inhibit any antibacterial effect of cilantro. Gram negative bacteria have an outer membrane and gram positive bacteria do not (Tortura, Funke, & Case, 2010). We predicted that cilantro would have an antimicrobial effect on S. epidermis but not on E. coli. We inoculated two nutrient agar plates, covering each with one of the bacteria’s, and divided each plate into quarters. We then placed one drop of cilantro juice mixed with water in each of the four sections in different concentrations. This allowed us to see if a minimum concentration of cilantro was needed to produce an antimicrobial effect. We then incubated the plates at 37 degrees Celsius to allow the bacteria to grow and evaluated the plates after 48 hours. We expected to see a clearing of bacteria in at least one of the quadrants of the plate containing S. epidermis and did not expect to see any clearing of bacteria on the E. coli plate. Methods
1. Label one nutrient agar plate S. epidermis and one nutrient agar plate E. coli and divide each plate into quarters. Label each quarter with the different dilutions : 1:10, 1:20, 1:40, and 1:80. 2. Inoculate and label one water blank with S. epidermis and one water blank with E. coli. 3. Create a lawn plate of...
References: Kubo, I., Fujita, K., Kubo, A., Nihei, K., Ogura, T. (2004, May). Antibacterial Activity of Coriander Volatile Compounds against Salmonella choleraesuis. Journal of Agricultural and Food Chemistry, 52, (11), pp 3329–3332.
Lai, P K; Roy, J. Current Medicinal Chemistry11. 11 (Jun 2004): 1451-60.
Marsh, T., Arriola, P. (2009, May). The Science of Salsa: Antimicrobial Properties of Salsa Components to Learn Scientific Methodology. Journal of Microbiology & Biology Education, Vol 10.
Tortura, G., Funke, B., Case, C. (2010). Microbiology An Introduction. San Francisco: Pearson Education, Inc.
The results of our experiment did not support our hypothesis that cilantro would not have an antimicrobial effect against E. coli due to the bacteria having an outer membrane. Although cilantro did not act as an antibiotic against E. coli, it was probably not because the bacteria have an outer membrane. Research shows that cilantro can in fact affect gram negative bacteria such as Salmonella and E. coli that contain outer membranes. The results of our experiment did not support our hypothesis that cilantro would have an antimicrobial effect on S. epidermis. We hypothesized that because S. epidermis cells do not have an outer membrane, cilantro would be able to penetrate and kill the bacteria. We think there are a few possible explanations for why our results do not support our hypothesis. First, the cilantro might have been contaminated with different kinds of bacteria. This contamination could be the result of the cilantro coming into contact with our hands as we placed it into the mixer. Although we washed our hands, hand washing doesn 't eliminate all bacteria. It only reduces the load of bacteria on the hands (Tortura et al., 2010) the contamination could be the result of using an unsterile mixer. Again, although we washed the mixer before use, it was not sterilized which is the only way to completely eliminate all microbes from an object (Tortura et al., 2010). Finally, the cilantro itself or the bag it was carried in could be the source of contamination. Perhaps someone in the room the day the experiments were conducted coughed or sneezed near the cilantro. This too could cause the cilantro to have lots of bacteria on it. The point is that bacteria are everywhere and the bacteria that were on the cilantro could have come from any number of sources or even a combination of them. Even if sterile technique was used and all objects were sterilized, the cilantro itself cannot be sterilized without destroying its possible antimicrobial properties. The cilantro could have been washed but this would not have eliminated all the bacteria; it would have only reduced the bacterial numbers. A second possible explanation for why our results do not support our hypothesis has to do with the bacteria we were targeting. S. epidermis is an extremely hardy bacterium that is able to withstand dry and salty conditions very well. Most bacteria cannot live under these conditions (Tortura et al., 2010). Perhaps if we had chosen to target a more delicate bacterium, cilantro would have shown an antimicrobial effect. Or perhaps cilantro is only able to target a certain bacteria due to the bacteria 's particular characteristics such as enzymes, porins, proteins, etc.
After researching the antimicrobial effects of cilantro, we learned that cilantro affects the bacterial cell membrane of Salmonella (Kubo et al., 2004). This was interesting to us because Salmonella is a gram negative bacterium. We expected cilantro to primarily affect gram positive bacteria because gram positive bacteria do not contain a protective, semi-permeable outer membrane (Tortura et al., 2010). Further studies should be conducted in order to find out exactly how the compound dodecanal is able to disrupt the bacterial cell membrane.
Studies that look at the possible antimicrobial effects of herbs and spices are important because their results can help people avoid foodborne illnesses. For example, because cilantro has been shown to have antimicrobial effects against Salmonella, people can use this knowledge and incorporate it into their own lives. They might choose to include cilantro more often in their food dishes containing chicken or eggs to help reduce the risk of enteritis from a Salmonella infection. Enteritis is a bacterial infection of the intestine that causes inflammation, fever, and sometimes dysentery. Particularly virulent strains of Salmonella can cause internal bleeding that leads to a systemic infection and sometimes death (Tortura et al., 2010). Not only can individuals choose to use herbs and spices in their food in order to help produce an antimicrobial effect, but companies can also choose to manufacture products containing the antimicrobial components of herbs and spices. Continued research of herbs and spices is important so that humans can continue to produce more effective antimicrobial products such as soaps and fruit/vegetable washes. The products and knowledge gained from research on herbs and spices can help humans’ live healthier lives and avoid infection.
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