Microorganisms Found in Skin Microbiome
Introduction
The skin microflora also commonly known as skin microbiota or the skin microbiome refers to microorganisms that live on human skin. The number of microorganisms on human skin tends to be greater than anywhere else in the human body. These microorganisms can be grouped according to their relationship to our bodies. The first group of these microorganisms is the commensal organisms that derive benefits for living on the human body but do not benefit the human body in any way. The second group is the symbionts which consist of microorganisms that not only benefit from the human body but also bring benefits to humans. The third group is the pathogens that consist of microorganisms that benefit from the human body but causes diseases to humans. Most microorganisms tend to reside on the upper parts of the hair follicles and the shallow layers of the stratum corneum. However, some reside in the deeper areas of the hair follicles (Bryd, 2018). This paper will mainly focus on the laboratory methods performed to identify four types of microorganisms found on the skin microbiome which are; staphylococcus epidermidis, staphylococcus aureus, and staphylococcus warneri.
Staphylococcus Epidermidis
Staphylococcus Epidermidis is a microorganism that commonly lives on human skin. It is in most cases non-pathogenic. It is a gram-positive bacterium that is one of the species belonging to the genus staphylococcus. Although S. epidermidis is infrequently pathogenic, people with a compromised immune system and those with implanted plastic devices that might have been contaminated have higher chances of developing infections. Its association with nosocomial infections in relation to indwelling devices leads to the importance of isolation of these bacteria from blood and not because of chance contamination especially when excessive blood cultures are positive (Byrd et al., 2017)
Staphylococcus Aureus
Staphylococcus Aureus is a form of bacteria that is found in human skin and other upper body parts such as in the nose, axillae, and throat. It is a Gram-positive bacterium with a round shape which is a member of the firmicutes. It is mostly positive for catalase and nitrate reduction. Although this microorganism usually acts as a commensal of the human microbiota, it can also turn into an opportunistic pathogen and can make one sick under certain conditions. As a result, the bacteria have been known to cause skin infections such as abscesses, respiratory diseases such as pneumonia and toxic shock syndrome. Researchers have estimated that almost 20% to 30% of all humans are long-term carriers of staphylococcus aureus. However, the rate of colonization among the adult is higher among health workers, dialysis patients and persons with diabetes is higher as compared to the general population (Taylor, 2017)
Staphylococcus Warneri
Staphylococcus Warneri is a part of the genus staphylococcus and it consists of Gram-positive bacteria. Its cells are spherical and they appear in clusters. It is catalase-positive, coagulase-negative, and oxidase-negative. It is also a common commensal organism found in the parts of human skin flora. S. warneri normally does not cause harm to the human body but may cause infections to patients with weak immune systems. The colonies of S. warneri are commonly yellow or beige occasioned with an orange rim. They are about 2 to 4 mm in diameter after being incubated for 48 hours at about 370C (Freckelton, et al., 2017).
Identification of the Microorganisms
Blood Agar with a Novobiocin (NB) Disc
Staphylococci would produce round, raised opaque colonies which are 1 to 2 mm in diameter. The novobiocin disc is used to detect the sensitivity or resistance to the antibiotic novobiocin. The test result on staphylococcus epidermidis would indicate a gamma reaction on blood agar, no pigment, and sensitivity to novobiocin. However, the test results on staphylococcus Warneri show resistance to novobiocin, gamma reaction. The test results on staphylococcus aureus show beta hemolysis, sensitivity to novobiocin, and absence of pigment.
Production of Deoxyribonuclease (DNase) on DNase agar
Here, DNase negative cultures appear cloudy within the growth where the acid caused the DNA in agar to precipitate out of solution. DNase positive cultures would however form a clear zone around growth after adding IN HCL. staphylococcus epidermidis results are negative and those of staphylococcus aureus and staphylococcus Warneri are positive
The staphyloslide Latex Test
The test applies blue latex particles, containing human antibody IgG and covered with human fibrinogen. Microorganisms with clumping factor and/or protein A covered on the surface leads to the joining of the latex particles. staphylococcus epidermidis and staphylococcus Warneri results are negative while those of staphylococcus aureus is positive. Positive results show the cohesion of latex particles while negative results show no clumping of latex particles.
Monnitol Fermentation on Mannitol Salt agar (MSA)
The fermentation of mannitol turns phenol red PH indicator from red to yellow due to the presence of the acid produced. Staphylococcus epidermidis results would show the absence of mannitol fermentation therefore phenol red would retain its color. Staphylococcus Warneri and staphylococcus aureus would show the presence of mannitol fermentation, therefore, the phenol red PH indicator’s color would turn to yellow from red.
The human skin is on the largest human organ which is colonized by a huge number of microorganisms. Most microorganisms cause no harm to their host and some may even be beneficial to the human body while some may cause harm. Various laboratory methods are used to distinguish these microorganisms through the various characteristics observed.
References
Byrd, A. L., Deming, C., Cassidy, S. K., Harrison, O. J., Ng, W. I., Conlan, S., … & NISC Comparative Sequencing Program. (2017). Staphylococcus aureus and Staphylococcus epidermidis strain diversity underlying pediatric atopic dermatitis. Science translational medicine, 9(397).
Byrd, A. L., Belkaid, Y., & Segre, J. A. (2018). The human skin microbiome. Nature Reviews Microbiology, 16(3), 143.
Freckelton, M. L., Nedved, B. T., & Hadfield, M. G. (2017). Induction of invertebrate larval settlement; different bacteria, different mechanisms? Scientific reports, 7, 42557.
Taylor, T. A., & Unakal, C. G. (2017). Staphylococcus aureus