CHAPTER 13
BACTERIAL INFECTION OF THE SKIN
iΧΫ΄υΗj
1. Primary pyodermas
2. Secondary bacterial infections
3. Cutaneous involvement in systemic bacterial infections (exclusive of venereal diseases and mycobacterium infections)
A. Impetigoi^αo]j - group A streptococci and Staphylococcus aureus
1. Impetigo contagiosai`υ«^αo]j - primarily due to group A streptococci
2. Impetigo bullosai αv«^αo]j- primarily due to Staph. aureus of phage group II
B. FolliculitisiΡXEΡοj
1. Superficial
a. Follicular impetigo (Bockhart's impetigo)iΡο«^αo]E{bNng^αo]j -usually due to Staph. aureus but in conditions of lowered host resistance (corticosteroid and antibiotic therapy, etc.) may be due to a variety of opportunistic organisms (gram-negative coliform bacilli, particularly). The lesions consist of small globular pustules, each located about a hair.
b. Pseudomas aeruginosa - associated with water exposure
2. Deep
a. Sycosis barbaeiqν«Ραj(usually Staph. aureus)
b. Pyoderma faciale (usually Staph. aureus)
c. Folliculitis decalvansiΓ―«Ροj -rare condition, producing a scarring type of alopecia of the scalp, attributed to chronic infection with Staph. aureus, but this etiologic role is not clearly established
C. Furuncles and CarbunclesiΉΒ^αj(Staph. aureus)
D. Paronychiaiάsj-usually of bacterial origin due to Staph. aureus or group A streptococci; rarely, a chronic form of the disease is due to Pseudomonas aeruginosa
E. Ecthymai^αj - group A streptococci initially may also be due to Pseudomonas
F. ErysipelasiOΕj- group A streptococci
G. CellulitisiIβ|Dj -group A streptococci, Staph. aureus, and, less commonly, a variety of other organisms, especially in compromised hosts
H. LymphangitisipΗj- usually group A streptococci, but occasionally Staph. aureus and other organisms
I. ErythrasmaigFAαj -Corynebacterium minutissimum
A-1 Impetigo contagiosai`υ«^αo]^ΖΡΠj
Definition
Impetigo is a primary, initially vesicular, later crusted superficial infection of the skin. It is commonly due to group A streptococci. Staph. aureus is the etiology of bullous impetigo.
Epidermiology and bacteriology
Impetigo is a highly communicable infection predominantly of preschool-age children. Its peak seasonal incidence is in the later summer and early fall.
Pathogenesis and pathology
Group A streptococci appear on normal skin of children about 10 days prior to the development of impetigo and they are not recovered from the nose and throat of the same patients until 14-20 days after skin acquisition of the organism.
Cutaneous lesions
Streptococcal impetigo begins as transient, thin-roofed, small vesicles, sometimes with a small inflammatory halo. Pustulation rapidly occurs. Vesicles and pustules easily rupture. The purulent discharge subsequently dries, forming a thick, soft, golden-yellow "stuck-on" crust the hallmark of impetigo.
A-2 Bullous impetigoi αv«^αo]j
Three types of skin lesions can be produced by phage group II staphylococci: (1) bullous impetigo, (2) exfoliative disease (staphylococcal scalded-skin syndrome), (3) nonstreptococcal scarlatiniform eruption. All three represent varying cutaneous responses to an extracellular exfoliative toxin ("exfoliatin") produced by these staphylococci.
B-1 Superficial Follicular impetigoi\έ«Ρο«^αo]j
Superficial folliculitisi\έ«Ροj
It is a form of impetigo in which a small dome-shaped pustule occurs at the opening of a hair follicle, often on the scalps of children.
B-2 Deep Follicular impetigoi[έ«Ρο«^αo]j
This is a deep folliculitis with perifollicular inflammation occurring in the bearded areas of the face. If uncared for, the lesions become deeper seated and chronic. Local treatment with warm saline compresses and local antibiotics (mupirocin or bacitracin) is sufficient to control the infection. More extensive cases require systemic antibiotic therapy.
C. Furuncles and CarbunclesiΉΒ^αj
Definition
A furuncle, or boil, is a deep-seated inflammatory nodule that develops about a hair follicle, usually from a preceding, more superficial folliculitis. A carbuncle is a more extensive, deeper, infiltrated lesion that develops when suppuration occurs in thick inelastic skin.
E. Ecthymai^αj
Definition
This disease is very similar to the superficial vesiculopurulent pyoderma, impetigo. It begins in the same fashion, but the process extends more deeply, penetrating through the epidermis to produce a shallow ulcer. Group A streptococci often initiate the disease or complicate preexisting superficial ulcers.
Clinical manifestations
The lesions tend to occur most commonly on the lower extremities of children or neglected elderly patients following minor trauma such as insect bites or excoriations.
F. ErysipelasiOΕj
A characteristic type of superficial cellulitis of the skin with marked lymphatic ? vessel involvement due to group A (or very uncommonly group C or G) streptococci. Group B streptococci may cause erysipelas in the newborn. Rarely, a similar clinical picture may be produced by infection with Staph. aureus.
G. Acute Cellulitisi}«Iβ|Dj
Definition
This is an acute, spreading inflammation of the skin involving particularly the deeper subcutaneous tissues. Group A streptococci and Staph. aureus are by far the most common etiologic agents, but occasionally other bacteria are implicated (e.g., group B streptococci in the new born; rarely pneumococci; in patients with underlying diabetes mellitus or an immunosuppressive illness, a variety of atypical organisms such as gram-negative bacilli and even cryptococci can be the etiology as a result of injury or blood-borne dissemination).
Clinical manifestations
History: Usually there is a history of an antecedent lesion (stasis ulcer, puncture wound), followed within a day or two by local erythema and tenderness. Systemic symptoms (malaise, fever, and chills) may then develop rapidly. Erythema at the site of infection rapidly intensifies and spreads. Local pain is often marked.
Cutaneous lesions: The involved area may be extensive with a markedly red, hot, infiltrated edematous appearance. The borders of the lesion are not elevated or sharply defined. Tender regional lymphadenopathy is common, often with lymphangitis extending proximally. Superficial vesicles may form and rupture. Local abscesses may develop with necrosis of overlying skin.
H. Acute Lymphangitisi}«pΗj
Definition
Acute lymphangitis is an inflammatory process involving the subcutaneous lymphatic channels. It is due most often to group A streptococci but occasionally may be caused by Staph. aureus; rarely, soft tissue infections with other organisms, such as Pasteurella multocida, may be associated with acute lymphangitis.
Clinical manifestations
History: The portal of entry is commonly a wound on an extremity, an infected blister, or a paronychia.
I. ErythrasmaigFAαj
Definition
Erythrasma is a common superficial bacterial infection of the skin characterized by well-defined but irregular reddish brown patches, occurring in the intertriginous areas, or by fissuring and maceration in the toe clefts.
Cutaneous Lesions
The lesions are reddish-brown, rather superficial, finely scaly and finely wrinkled, and slowly spreading macular patches. Axillary and genitocrural areas are the principal sites of infection.