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INTRODUCTION TO CHAPTER

Within hours after birth, the skin's surface becomes a host for a vast assortment of microorganisms.1 Species of staphylococcus, corynebacterium, Propionibacterium acnes, and a multitude of other bacteria, yeast, and fungi begin to colonize the skin, each organism with a predilection for specific body sites.2 The skin's microbiome changes over time modified by environmental exposures and hormonal shifts. A growing volume of studies highlight the essential function of the skin's microorganisms in protecting us from pathogens and regulating the immune system.3 A pathogenic shift in the skin flora, or dysbiosis, has been described in acne, atopic dermatitis, and chronic wounds, but is likely to contribute to many other disease processes.2

The host immune system is an essential factor in influencing the microbiome, but the interactions are complex and differ by disease process. For example, individuals with atopic dermatitis tend to have decreased microbiome diversity with a lower prevalence of bacterial species that are anti-inflammatory.4 In contrast, diabetic ulcers that are deeper or chronic demonstrate more microbial diversity than those that are more shallow or present for a shorter duration.5 Ongoing research in this field will help to highlight the interface between the human microbiome and disease pathogenesis. In most cases, our microbiome is protective, serving as an important component of the skin's barrier function. Disruption of this barrier caused by mechanical trauma or intrinsic cutaneous disease alters the skin's biodiversity and inflammatory pathways allowing for skin infections to propagate.2

Most bacterial skin infections are caused by coagulase positive Staphylococcus aureus or group A beta hemolytic streptococci. These common skin infections previously resulted in serious illness and death until the 1950s when penicillin became widely available. By the early 1960s scattered cases of methicillin-resistant staphylococcus (MRSA) were already emerging. From the late 1960s to the mid-1990s, MRSA infections became a major problem especially in large urban hospitals. In the past decade, improved infection control measures have decreased hospital acquired MRSA infections, but community acquired cases have continued to increase.

Syphilis has been called "the great masquerader" and "the great imitator" based on the many varied presentations of the cutaneous and systemic findings. Patients with secondary syphilis usually present with rashes that mimic common papulosquamous skin diseases but can manifest skin findings that mimic almost any cutaneous disorder.

IMPETIGO

Introduction

Key points for impetigo

  • Staphylococcus aureus is the most common cause, but group A beta hemolytic streptococci including the nephritogenic strains may also cause impetigo.

  • ✓ Impetigo presents with a red macule or papule that quickly becomes a vesicle which ruptures resulting in erosions with honey-colored crusts.

  • ✓ Removal of the crusts and topical antibiotics are sufficient therapies for most patients.

Impetigo is a common, highly contagious, and superficial skin infection. Nonbullous impetigo accounts ...

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