Imbalance of skin microorganisms and the associated dangers

This informal CPD article ‘Imbalance of skin microorganisms and the associated dangers’ was provided by The Edge Medical Writing, an organisation who offers high quality medical writing support, tailored to meet the needs of medical education, product development, and the dissemination of medical information.

The skin provides an excellent ecological habitat for various microorganisms. Indeed, the aggregate of microorganisms on the surface and in the deep layers of the skin, in the saliva and oral mucosa, in the conjunctiva, and in the gastrointestinal tracts are called normal flora or human microbiota. This article will focus only on the microbiota or normal flora on the skin surface.

A diverse microbial flora is associated with the skin and mucous membranes of every human being from shortly after birth until death. The human body, which contains 10¹³ cells, routinely harbors 10¹⁴ bacteria.¹ The normal microbial flora is relatively stable, with specific genera populating various body regions during particular periods in an individual's life. Although, as healthcare providers, we are aware that these harmless microorganisms on the skin become pathogenic when they change their habitat and can cause a series of emerging and re-emerging diseases.

Skin microorganisms or skin microbiota

Skin, the largest organ in the body, also called the integument, is a good microenvironment. The skin regions have been compared to the geographic areas of Earth: the cool woods of the scalp, the tundra of the forearm, and the tropical rainforest of the armpit. There are three essential regions on the skin:¹

• Axilla, perineum, and toe webs.
• Hand, face, and trunk.
• Upper arms and legs. 

Skin sites of the partial occlusion (axilla, perineum, and toe webs) harbor more microorganisms than less occluded areas (legs, arms, and trunk). These differences may relate to increased amounts of moisture, higher body temperature, and higher concentrations of skin surface lipids. In addition, as the microenvironment, the skin has three sites with fluid and oil composition differences.¹ As a result, these sites have different microorganisms inhabiting them.

• Dry body sites (forearm, hands, legs, and feet). The microbes found in these sites are Staphylococcus epidermidis and Staphylococcus hominis.
• Moist body sites (elbow creases beneath the breast, in-between toes, and groins). The microbes found in these sites are members of Corynebacterium.
• Sebaceous or oily sites (head, neck, and trunk). These sites harbor Demodex folliculorum, Demodex brevis and Malassezie spp.

Fungi are also found all over the body sites.

How do these microorganisms attach to the skin?

Microorganisms on the skin surface face the mechanical stress of being removed by fluid flow, discarding, or epithelial turnover. Due to this unfavorable condition, they express a series of molecules to establish themselves attached to the epithelial surface, such as febrile projections and surface-anchored proteins that bind to human matrix proteins.² Others may produce multi-layered collections called biofilms with a sticky extracellular matrix providing additional protection from removal. This does not imply that the skin should be abraded during laboratory tests.

If the skin is cut open, any microorganisms, depending on the site abraded, will enter the susceptible opening and cause infections ranging from abscess to purulent discharges, UTI, and others.³ Collection of skin samples should be done with swabs dampened in normal saline. The wet swab will be rubbed gently on the site of the skin to be checked, and the skin is immediately carried out.

Do these skin microorganisms have beneficial effects?

It is evident that not all microorganisms are harmful; some are innocuous and have beneficial effects. Richard Gallo says that microbes on our skin have co-evolved with our body to help protect it and maintain health.

An experiment conducted by Richard Gallo and his team has found that two commensal species of Staphylococcus bacteria, S. epidermidis and S. hominis, secrete natural antibiotic molecules that can disrupt the cell membranes of other bacteria, like the disease-causing S. aureus that frequently colonizes the skin of individuals with atopic dermatitis.⁴ Gallo is a distinguished professor and the founding chairman of the Department of Dermatology at the University of California, San Diego, United States.

Studies by Lindsay Kalan, a microbiologist at the University of Wisconsin, Madison, United States, show that bacteria on our healthy skin prevent pathogens from invading and occupying the skin.⁴ These skin commensal bacteria achieve this by using nutrients on our skin for other invaders to utilize and by producing bioactive metabolites that participate in host-microbiome balance or crosstalk. Most of these metabolites are made from the outcome of their utilization of substances or nutrients on the different skin sites. Most of these metabolites are bactericidal, while most are bacteriostatic, then rendering the skin protected.

Supporting research has demonstrated that skin microbes regulate our innate immune response. For instance, Gallo and his team showed that S.epidermidis produces a molecule that prevents inflammatory cytokine release from skin cells.⁴ The skin flora can help promote wound healing and reduce inflammation by this mechanism. This bacterium can also assist in protecting against skin cancer.

Certain strains of S. epidermidis produce a molecule that can inhibit melanoma and other cancer cells.⁴ As a health care provider, you have a role in ensuring your patients are well enlightened that they should take good care of their skin, not to reduce or proliferate the number of their normal flora.

Imbalance of the skin microorganisms and disease

As the properly functioning skin microbiome supports the immune system, destabilizing its equilibrium may contribute to several skin disorders. Alteration of the proportions of organisms in the skin microorganisms, which internal and external stressors can cause, defines dysbiosis, or the imbalance of skin microorganisms. This dysbiosis can result in the following skin disorders:⁴

• Acne is a skin condition that occurs when lipids and dead skin cells clog hair follicles. It is associated with a skin microbiome unbalanced with lipophilic commensal bacteria like Cutibacterium acnes.
• Atopic dermatitis is a chronic inflammatory skin disease with a strong genetic component involving a disruption of the skin barrier and immune system, resulting in increased susceptibility to infections and allergens.
• Seborrheic dermatitis and dandruff.
• Rosacea.

Beware of substances and chemicals that can cause dysbiosis of skin flora

Patients, you are advised to know that age, sex, perspiration rate, physiological differences in the skin environment, hormonal production rate, skin surface PH, and food are essential factors in the imbalance of skin microorganisms.⁴ In addition, healthcare providers must know that exposure to antibiotic medications and radiation appears to have repercussions for skin microorganisms. Doctors, during your prognosis, call your attention to the fact that a choice of an antibiotic, when abused, can erode some class of skin microorganisms, thereby rendering the skin vulnerable to the diseases mentioned above and others.⁴

Finally, many questions are asked if using alcohol-based sanitizers and medicated soaps in bathing can reduce the number of skin microorganisms. Kalan says it is unlikely they affect one's skin microorganisms very much. Though the skin microorganisms are stable over time, it is advisable to be safe by reducing the use of these chemicals.

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References

 1. Davis CP. Normal Flora. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 6.

2. Otto M. Physical stress and bacterial colonization. FEMS Microbiol Rev. 2014 Nov;38(6):1250-70. doi: 10.1111/1574-6976.12088. Epub 2014 Sep 29. PMID: 25212723; PMCID: PMC4227950.

3. Lee TY, Wang CW, Chen TW, Liao GS, Fan HL, Chan DC. Refractory urinary tract infection complicated rectus sheath abscess: A case report. Urol Case Rep. 2017 Nov 22;16:81-82. doi: 10.1016/j.eucr.2017.11.011. PMID: 29204359; PMCID: PMC5709308.

4. Bates M. The Role of the Skin Microbiome in Health and Disease. IEEE PULSE. Published online Sept. 9, 2022. https://www.embs.org/pulse/articles/the-role-of-the-skin-microbiome-in-health-and-disease/. Accessed June 8, 2023.