Biology & Life Sciences Chapter 19 Homework Infections With Other Poxviruses Remain Localized Historically

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CHAPTER

Microbial Diseases of the

Skin and Wounds

Chapter Outline

Structure of the Skin (pp. 552–553)

Microbiome of the Skin (pp. 553–554)

Bacterial Diseases of the Skin and Wounds (pp. 544–568)

Folliculitis

Staphylococcal Scalded Skin Syndrome

Impetigo (Pyoderma) and Erysipelas

Necrotizing Fasciitis

Acne

Viral Diseases of the Skin and Wounds (pp. 569–581)

Diseases of Poxviruses

Herpes Infections

Warts

Mycoses of the Hair, Nails, and Skin (pp. 581–586)

Superficial Mycoses

Parasitic Infestations of the Skin (pp. 586–588)

Leishmaniasis

Scabies

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Chapter Summary

Structure of the Skin (pp. 552–553)

The skin (or cutaneous membrane) is composed of two distinct layers. The deeper dermis is a

tough leathery structure composed of loosely packed cells, protein and muscle fibers, sweat and

sebaceous (oil) glands, blood vessels, nerve endings, and hair follicles. It provides strength and

resiliency. The superficial epidermis, which is continually replaced, is composed of four or five

layers of tightly packed cells. Basal cells continually divide to produce new epidermal cells. The

cells absorb melanin and become filled with a waterproofing protein called keratin as they are

pushed to the surface.

Microbiome of the Skin (pp. 553–554)

The human microbiome, also called the microbiota, is normally harmless residents of the

body. Prominent skin microbiota include small lipophilic yeasts such as Malassezia, which di-

Bacterial Diseases of the Skin and Wounds (pp. 544–568)

Common bacteria infecting the skin are Staphylococcus, Streptococcus, Propionibacterium,

Bartonella, Pseudomonas, and Rickettsia.

Folliculitis

Folliculitis is an infection of a hair follicle that causes the base of the follicle to become red,

swollen, and pus filled. On the skin, this infection is commonly called a pimple, whereas

at the base of an eyelid it is called a sty. A furuncle (boil) results when the infection spreads to

surrounding tissue. When several furuncles join, a carbuncle is formed.

Staphylococcus epidermidis and Staphylococcus aureus are the most common causes

Staphylococcal Scalded Skin Syndrome

In staphylococcal scalded skin syndrome (SSSS), infection with a strain of S. aureus causes

cells of the outer epidermis to separate from one another and from the underlying tissue. Within

Impetigo (Pyoderma) and Erysipelas

Impetigo, also called pyoderma, is a contagious skin disease characterized by the presence

of small, red patches that develop into oozing, pus-filled vesicles. These vesicles break to form a

honey-colored crust attached firmly to the skin. Preschool children, whose immune systems are

Necrotizing Fasciitis

Necrotizing fasciitis, commonly called “flesh-eating bacteria,” is characterized by sunburn-like

rash, intense sensitivity, pain, and swelling at the infection site, followed by bacterial

digestion of the muscle fascia and adipose tissue, which causes the overlying skin to become

distended and discolored. Flulike symptoms, mental confusion, and toxemia develop. Organ

failure and death are common.

Acne

Acne is most commonly caused by propionibacteria, most commonly Propionibacterium acnes,

which are small, Gram-positive rod-shaped diphtheroids normally found on the skin. Excessive

oil production, typically triggered by the hormones of adolescence, stimulates their growth. The

bacteria secrete chemicals that attract leukocytes and trigger inflammation. Acne is thus charac-

terized by the presence of pimples filled with dead bacteria and living leukocytes. When dead

Cat Scratch Disease

Bartonella henselae, a Gram-negative aerobic bacillus, causes cat scratch disease, a

condition characterized by a few days of fever and malaise, accompanied by localized swelling

at the site of infection and in nearby lymph nodes for several months. The bite or scratch of an

Pseudomonas Infection

Damage to the skin, particularly burns, can allow Pseudomonas aeruginosa to establish skin in-

fections. P. aeruginosa is a Gram-negative, aerobic bacillus that is ubiquitous in soil,

decaying organic matter, and many hospital fomites, including sinks, damp sponges, dialysis

machines, respirators, and humidifiers. Harmless to patients with intact skin, it typically gains

Spotted Fever Rickettsiosis

A number of arthropod-borne bacterial infections with rickettsias cause rashes and are called

spotted fever rickettsioses, the most severe of which is Rocky Mountain spotted fever

(RMSF). RMSF is characterized by a spotted rash that can progress to subcutaneous hemor-

Cutaneous Anthrax

Anthrax has three distinct clinical manifestations: gastrointestinal, inhalation, and cutaneous. All

are caused by Bacillus anthracis. Gastrointestinal anthrax is rare in humans. Cutaneous an-

thrax results when the bacterial endospores enter a wound in the skin, producing a solid skin

Chapter 19 Microbial Diseases of the Skin and Wounds

Gas Gangrene

Ischemia develops when blood supply to a tissue is interrupted. The tissue becomes anaerobic

Viral Diseases of the Skin and Wounds (pp. 569–581)

Many viral diseases are systemic in nature and spread by respiratory and oral routes; neverthe-

less, they often manifest signs and symptoms affecting the skin.

Diseases of Poxviruses

Poxviruses cause smallpox, the first human disease to be eradicated globally in nature.

They also cause three diseases of animals: orf (sheep and goat pox), cowpox, and monkeypox,

which rarely affect humans. Cowpox was used for the eradication of smallpox. All poxviruses

produce lesions that progress through a series of stages: from flat macules to raised papules to

fluid-filled vesicles to pus-filled pustules (also known as pox or pocks). The pustules dry to

Herpes Infections

Human herpesvirus 1 (HHV-1) and 2 (HHV-2) cause the painful, itchy skin lesions of herpes on

lips (commonly called fever blisters or cold sores) or genitalia (genital herpes), and may be ac-

Warts

Warts (papillomas) are generally benign growths of the epithelium of the skin or mucous

membranes. Warts in specific locations are known by specific names: fingers and toes, seed

Chickenpox and Shingles

Chickenpox (clinically called varicella) is highly infectious. About two to three weeks after in-

fection with the virus, patients, typically children, develop a fever and characteristic itchy rash

which begins as macules which progress to papules and then to fluid-filled vesicles.

In about 15–20% of individuals who have had chickenpox, stress, aging, or immune suppression

Rubella

Rubella (also called German measles and three-day measles) is a generally harmless disease in

children, causing only slightly swollen lymph nodes and a mild rash that lasts about three days.

Infections of pregnant women, however, result in a range of birth defects, including cardiac ab-

normalities, deafness, blindness, mental retardation, microcephaly, and growth retardation.

Measles (Rubeola)

Measles, also known as rubeola or red measles, is the most contagious and one of the more se-

rious of the childhood viral diseases. Measles begins with fever, sore throat, headache, dry

cough, and conjunctivitis followed 2 days later by Koplik’s spots on the mucous membranes of

Chapter 19 Microbial Diseases of the Skin and Wounds

the mouth. These fade within 1–2 days and are followed by red, raised (maculopapular) lesions.

Rare complications include pneumonia, encephalitis, deafness, blindness and the extremely seri-

Other Viral Rashes

Erythema infectiosum (also called fifth disease) is a respiratory disease caused by an ssDNA

virus called B19 virus in the genus Erythrovirus, family Parvoviridae. It causes a mild red rash

that begins on the cheeks and spreads to the arms, thighs, buttocks, and trunk. Treatment in-

Mycoses of the Hair, Nails, and Skin (pp. 581–586)

Mycoses are fungal diseases, and are classified according to the location within the body. The

fungi that cause mycoses are mainly opportunistic. Physicians classify mycoses as superficial

Superficial Mycoses

Superficial mycoses, which are the most common fungal infections, are confined to the hair,

nails, and outer layers of the skin, all of which are composed of dead cells filled with keratin. In-

fection is spread by direct contact.

Pityriasis versicolor is also called versicolor and is caused by a basidiomycete called Malas-

sezia furfur. In pityriasis, fungal interference with melanin production causes hypo– or hyper-

pigmented patches of skin. The fungus feeds on skin oil. Superficial fungi produce keratinase,

Cutaneous Mycoses

Dermatophytoses are cutaneous infections caused by dermatophytes, fungi that feed on

keratin and colonize dead layers of skin, nails, and hair. Colonization stimulates cell-mediated

immune responses that damage deeper tissues. Common dermatophytoses (formerly called

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Wound Mycoses

Some fungi grow on deeper tissues in the body and eventually grow up into the epidermis

to produce lesions on the skin’s surface. Microscopic examination of tissue samples is

diagnostic for these infections.

Four species of ascomycete fungi cause chromoblastomycosis, which initially manifests as

small, itchy but painless, scaly lesions on the skin but progresses to large, wartlike lesions that

grow to extensive tumors, causing inflammation and abscesses. Treatment is difficult and is

most successful in early infections. It involves removal of infected and surrounding tissue and

oral antifungal agents such as thiabendazole and 5-fluorocytosine.

Parasitic Infestations of the Skin (pp. 586–588)

Some parasitic protozoa and arthropods infect the skin and cause diseases.

Leishmaniasis

Leishmaniasis is a zoonosis—a disease of animals transmitted to humans. Leishmania is an in-

tracellular parasitic flagellated protozoan, transmitted to humans by sand flies, and causes this

disease of the skin and oral mucous membrane in humans. Upon infection it becomes an intra-

cellular parasite of macrophages. It causes any of three forms of leishmaniasis: cutaneous

Scabies

The mite Sarcoptes scabiei causes scabies, a disease characterized by intensely itchy lesions, by

burrowing into human skin and triggering inflammation and type IV hypersensitivity. The mite