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Alexander Ogston was a surgeon and bacteriologist most famous for his discovery of Staphylococcus aureus in the year 1880. With a great admiration for Joseph Lister and his value of antisepsis, Ogston rejected the belief that the formation of pus was a natural part of the healing process. Since post-operative patients of Lister did not show any signs of inflammation in their wounds, Ogston sought out to find the reason. After successfully isolating S. aureus from pus, he would go on to publish his clinical observations and laboratory studies describing diseases caused by it and its role in the formation of suppuration (Orenstein, n.d.).
Some physical characteristics of the bacteria Staphylococcus aureus can be determined from its name. Staphylococcus is derived from the Greek root staphyle, which translates to a bunch of grapes (Golden Staph, 2015). This refers to the arrangement of the bacteria when looking at them through a microscope after a gram staining process. Gram staining also reveals that the bacteria are Gram-positive, meaning it has a thick peptidoglycan layer. They are facultative anaerobes that have evolved to thrive in harsh environments such as human skin, which is dry and salty.
At some point in everyone’s life, these bacteria can be found in their nostrils. Roughly one out of three healthy adults are considered long term carriers of S. aureus (one year or more) and about 60% will be colonized at some time during a given year (Taylor, 2019). Once inside the nose, the bacteria can spread to other parts of the body.
S. aureus can colonize nearly any part of the body given its opportunistic nature. The bacteria will exploit of broken skin or other entry points to cause disease in other areas. Infections have been known to cause systematic complications. Once it can grow inside a wound, S. aureus will spread through the bloodstream forming abscesses in the heart, the bones, the brain, or other tissues.
In a vast majority of cases, S. aureus is a harmless bacterium found in our microbial flora. However, after a successful invasion through a cut, a person can experience an infection that ranges from mild to severe. Some cases have even documented death as a result of infection from this bacterium. Minor skin infections include pimples, impetigo, boils, cellulitis, folliculitis, carbuncles, scalded skin syndrome, and abscesses. Abscesses are generally caused by infections of the skin and form as a result of your body’s inflammatory response to defend itself. They are filled with pus, bacteria, and other debris (Rayner & Munckhof, 2015). Treatment typically involves drainage of the infected site and the use of antibiotics. Life-threatening diseases include: pneumonia- infection of one or both lungs; meningitis- infection of the membranes lining the brain; osteomyelitis – infection of the bone and bone marrow; endocarditis – infection of the heart valves; toxic shock syndrome, bacteremia, and sepsis. Sepsis is also a result of your body’s response to an infection. In the fight against invading pathogens, your body will naturally release chemicals. If your body’s response is out of balance when this happens, sepsis will result. The imbalance will bring about changes that are harmful to the organ systems.
Treating S. aureus infections can be problematic in some cases because many strains have developed a resistance to commonly used antibacterial medications. This type of bacteria is known as Methicillin-resistant Staphylococcus aureus (MRSA). According to the CDC, around two in every 100 people carry MRSA. Even though so many people carry MRSA bacteria in their nostrils, most will not develop serious MRSA infections (MRSA, n.d.) Methicillin-susceptible Staphylococcus aureus (MSSA) is a strain of staphylococcus that responds well to the medicines used to treat them because they are not resistant to certain antibiotics.
Staph infections are a concern for the medical community because it is especially dangerous for those who are immunocompromised, which is common for patients staying in a hospital setting. Some states, such as California, require by law that patients get tested for MRSA once admitted to the hospital for surgery and are considered susceptible for such an infection (MRSA Testing, n.d.). Some hospitals also screen patients for MRSA upon discharge from the hospital to make sure they do not take a MRSA strain home with them. Employees are tested periodically, as they are most likely to be carriers of the bacteria. This is important as it will help to prevent the spread of the bacteria.
The mannitol salt agar (MSA) test required the following materials: one Mannitol salt agar plate, a permanent marker/wax pencil, two sterile cotton swabs, and a parafilm. Using a permanent marker or wax pencil, the MSA plate was divided into two sections. One half was labeled ear while the other half was labeled nose to indicate the environments we swabbed. One sterile cotton swab was carefully removed from its wrapping, so it would not come into contact with any other object. It was then used to swab the mucous membranes inside the nostrils. The cotton swab was then rubbed over the surface of the agar plate labeled nose. Those same steps were repeated, only this time the ear was swabbed and placed over the section labeled ear. Used swabs were discarded in the waste bin and lids for the agar plates are secured on with the use of parafilm. The agar plate was placed in a 37 degrees Celsius room for 48 hours. The following lab day, the plates were examined for color and quality of growth.
The mannitol salt agar plate contains the sugar mannitol, sodium chloride, and the pH indicator phenol red. Phenol red turns yellow below a pH of 6.8, red at a pH between 7.4 and 8.4, and pink at a pH of 8.4 and above. Mannitol provides the substrate for fermentation and makes the medium differential. Sodium chloride makes the medium selective because its concentration is high enough to kill most bacteria. Staphylococci thrive on MSA because the environment is similar to that of the human skin, a place S. aureus adapted to survive. Phenol red serves as an indicator that will change color in the presence of fermentation with an acid end-product. While most staphylococci are able to grow on MSA, not all are able to ferment mannitol. The MSA plate will remain unchanged in those cases. S. aureus is capable of fermenting mannitol, so we can expect the pH on the medium to decrease, resulting in a yellow color change (Vital Source, n.d.).
I tested positive for S. aureus colonization in my ears indicated by a yellow color change on the MSA plate. I tested negative for S. aureus in my nose indicated by the lack of color change on the MSA plate. Since the color did not change, it is safe to say there were no bacteria present capable of fermenting the mannitol resulting in an acid end-product. The likely bacteria were Staphylococcus epidermis, since they thrived on the MSA plate but were unable to ferment the mannitol the way S. aureus can.
Nose and Ear Swab for S. aureus
My individual results were comparable to the overall class results. I am part of the majority of class that is colonized by S. aureus in some way. I was also part of the majority that tested negative in the nostrils and positive in the ears. The class results were significantly higher than then overall population. As previously stated, roughly one out of three healthy adults are considered carriers of S. aureus (30%). Our class results showed that 75% of the tested students were carriers. I have acne on my right cheek that could be a symptom of the S. aureus infection in my ears. I sleep on my right side which is how the bacteria may transfer from my ear to my pillow to my face causing skin break outs. One common method of transmission is through direct contact with objects that are contaminated by the bacteria, so this could be a reasonable explanation for my acne. S. aureus is also transmitted through air droplets that remain suspended in the air when an infected person releases them from their body via coughing or sneezing.
Applying an antibacterial cream such as Neosporin to the nostrils and using soaps containing an antibacterial agent such as hexachlorophene to wash the skin reduces the colonization of Staphylococcus aureus. Prolonged use can even completely eradicate the colonies making a carrier free from the bacteria. Because S. aureus is mostly transmitted by the hands, handwashing and regular use of hand sanitizers is recommended to scale down the number of bacteria spread in this manner.
Different types of antibiotics used to treat S. aureus infections include β-lactam antibiotics such as Ceftaroline, vancomycin, linezolid, daptomycin, and tigecycline. Lucloxacillin and dicloxacillin are commonly prescribed for serious MSSA infections.
Cephalosporins, clindamycin, lincomycin and erythromycin are given to those suffering from less serious MSSA infections such as skin and soft tissue infections. Severe MRSA infections should be treated with vancomycin or teicoplanin since that bacteria is resistant to most other antibiotics.
- Department of Health & Human Services. (2015, February 28). Staphylococcus aureus – golden staph. Retrieved from https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/staphylococcus-aureus-golden-staph
- MRSA Testing. (n.d.). Retrieved from https://www.ucsfhealth.org/education/mrsa_testing/
- MRSA | CDC. (n.d.). Retrieved from https://www.cdc.gov/mrsa/index.html
- Orenstein, A. (n.d.). The Discovery and Naming of Staphylococcus aureus. Retrieved from http://www.antimicrobe.org/h04c.files/history/S-aureus.pdf
- Pearson. (2013, November 18). Staphylococcus aureus bacteria turns immune system against itself. Retrieved from https://www.uchicagomedicine.org/forefront/news/2013/november/staphylococcus-aureus-bacteria-turns-immune-system-against-itself
- Rayner, C., & Munckhof, W. J. (2005, December). Antibiotics currently used in the treatment of infections caused by Staphylococcus aureus. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/16271060
- Sepsis. (2018, November 16). Retrieved from https://www.mayoclinic.org/diseases-conditions/sepsis/symptoms-causes/syc-20351214
- Skin Abscess (Boil). (n.d.). Retrieved from https://www.mercy.com/health-care-services/primary-care-family-medicine/conditions/skin-abscess
- Staphylococcus aureus Infections – Infections. (n.d.). Retrieved from https://www.merckmanuals.com/home/infections/bacterial-infections-gram-positive-bacteria/staphylococcus-aureus-infections
- Taylor, T. A. (2019, March 27). Staphylococcus Aureus. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK441868/
- VitalSource Bookshelf Online. (n.d.). Retrieved from https://bookshelf.vitalsource.com/#/books/9781617312502/cfi/271!/4/[email protected]:0.00
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