Microbiology, 2021

856 21 • Skin and Eye Infections
Figure 21.3 The normal microbiota varies on different regions of the skin, especially in dry versus moist areas. The figure shows the major
organisms commonly found in different locations of a healthy individual’s skin and external mucosa. Note that there is significant variation
among individuals. (credit: modification of work by National Human Genome Research Institute)
CHECK YOUR UNDERSTANDING
• What are the four most common bacteria that are part of the normal skin microbiota?
Infections of the Skin
While the microbiota of the skin can play a protective role, it can also cause harm in certain cases. Often, an
opportunistic pathogen residing in the skin microbiota of one individual may be transmitted to another
individual more susceptible to an infection. For example, methicillin-resistant Staphylococcus aureus (MRSA)
can often take up residence in the nares of health care workers and hospital patients; though harmless on
intact, healthy skin, MRSA can cause infections if introduced into other parts of the body, as might occur
during surgery or via a post-surgical incision or wound. This is one reason why clean surgical sites are so
important.
Injury or damage to the skin can allow microbes to enter deeper tissues, where nutrients are more abundant
and the environment is more conducive to bacterial growth. Wound infections are common after a puncture or
laceration that damages the physical barrier of the skin. Microbes may infect structures in the dermis, such as
hair follicles and glands, causing a localized infection, or they may reach the bloodstream, which can lead to a
systemic infection.
In some cases, infectious microbes can cause a variety of rashes or lesions that differ in their physical
1 Belkaid, Y., and J.A. Segre. “Dialogue Between Skin Microbiota and Immunity,” Science 346 (2014) 6212:954–959.
2 Foulongne, Vincent, et al. “Human Skin Microbiota: High Diversity of DNA Viruses Identified on the Human Skin by High
Throughput Sequencing.” PLoS ONE (2012) 7(6): e38499. doi: 10.1371/journal.pone.0038499.
3 Robinson, C.M., and J.K. Pfeiffer. “Viruses and the Microbiota.” Annual Review of Virology (2014) 1:55–59. doi: 10.1146/annurevvirology-031413-085550.
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