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NCBI Bookshelf. Baron S, editor. Medical Microbiology. Skin diseases can be caused by viruses, bacteria, fungi, or parasites. Herpes simplex is the most common viral skin disease. Of the dermatophytic fungi, Trichophyton rubrum is the most prevalent cause of skin and nail infections. Primary Infections : Primary skin infections have a characteristic clinical picture and disease course, are caused by a single pathogen, and usually affect normal skin. Impetigo, folliculitis, and boils are common types. These organisms usually enter through a break in the skin such as an insect bite.
Many systemic infections involve skin symptoms caused either by the pathogen or by toxins; examples are measles, varicella, gonococcemia, and staphylococcal scalded skin syndrome. Dermatophytic fungi have a strong affinity for keratin and therefore invade keratinized tissue of the nails, hair, and skin. Secondary Infections : Secondary infections occur in skin that is already diseased. Because of the underlying disease, the clinical picture and course of these infections vary. Intertrigo and toe web infection are examples. Most skin infections cause erythema, edema, and other s of inflammation.
Focal accumulations of pus furuncles or fluid vesicles, bullae may form. Alternatively, lesions may be scaling with no obvious inflammation. Nail infections cause discoloration of the nail and thickening of the nail plate. Ultraviolet light Wood's lamp is helpful in diagnosing erythrasma and some toe web and fungal infections. Microscopic examination of a KOH preparation of skin scales, nail scrapings, or loose hair is useful for fungal infections.
For viral infections, stained smears of vesicle fluid are examined under the microscope for typical cytopathology. Cleansing and degerming I need a Springfield deep in my ass skin with a soap or detergent containing an antimicrobial agent may be useful.
Drying agents, such as aluminum chloride, and keratinolytic agents, such as topical salicylate, are also helpful. Topical antimicrobial agents can be used for some infections, but systemic therapy may be necessary for patients with extensive disease. Skin diseases are caused by viruses, rickettsiae, bacteria, fungi, and parasites. This chapter focuses on the common bacterial diseases of skin. Viral infections are also described, but of the cutaneous fungal diseases, only nail infections are included. The other fungal diseases are described in the Mycology section. Skin infections may be either primary or secondary Fig.
Primary infections have characteristic morphologies and courses, are initiated by single organisms, and usually occur in normal skin. They are most frequently caused by Staphylococcus aureusStreptococcus pyogenesand coryneform bacteria. Impetigo, folliculitis, boils, and erythrasma are common examples. Systemic infections may also have skin manifestations. Secondary infections originate in diseased skin as a superimposed condition. Intertrigo and toe web infections are examples of secondary infections. Clinical manifestations vary from disease to disease. Most skin diseases involve erythema, edema, and other s of inflammation.
Focal accumulations of pus furuncles or fluid vesicles and bullae may form, but lesions may also be scaling without obvious inflammation. Specimens are collected with a blade or by swabbing the involved areas of the skin. When pustules or vesicles are present, the roof or crust is removed with a sterile surgical blade. The pus or exudate is spread as thinly as possible on a clear glass slide for Gram staining. For actinomycetes, pus is collected from closed lesions by aspirations with a sterile needle and syringe. Material is collected from draining sinuses by holding a sterile test tube at the edge of the lesion and allowing the pus and granules to run into the tube.
Granules are aggregates of inflammatory cells, debris, proteinaceous material and delicate branching filaments. Pus and other exudates are examined microscopically for the presence of granules. Vesicles are cleaned with 70 percent alcohol followed by sterile saline. Viruses are obtained by unroofing a vesicle with a needle or a scalpel blade. The fluid is collected with a swab or with a tuberculin syringe with a to gauge needle. The fluid obtained from fresh vesicles may contain enough viruses for culture.
Direct smears are prepared by scraping cells from the base of the lesions.
The cells are smeared on a slide, fixed, and stained with Giemsa or Wright stain or with specific antibodies conjugated to fluorescein or peroxidase. Cutaneous samples are obtained by scraping skin scales or infected nails into a sterile Petri dish or a clean envelope. For suppurative lesions of deep skin and subcutaneous tissues, aspiration with a sterile needle and syringe is recommended.
Direct mounts are made by mixing a small portion of the sample in two or three drops of physiologic saline or KOH on a microscopic slide. A glass coverslip is placed over the preparation before microscopic examination. Most pathogenic skin bacteria grow on artificial media, and selection of the medium is important. For general use, blood agar plates preferably 5 percent defibrinated sheep blood are recommended. In many situations, a selective medium combined with a general-purpose medium is recommended.
For example, Staphylococcus aureus may overgrow Streptococcus pyogenes in blood agar medium when both organisms are present. Cultures for meningococci, gonocci, and brucellae must be incubated in a CO 2 atmosphere. If tuberculosis or fungal infection is suspected, specimens are collected on appropriate media and incubated aerobically.
Viruses are cultured on tissue cultures selected for the virus that may be contained in the specimen. The classification of bacterial skin infections pyodermas is an attempt to integrate various clinical entities in an organized manner. An arbitrary but useful classification for primary and secondary bacterial infections is presented in Table The list is not complete and includes only the more common skin diseases. Three forms of impetigo are recognized on the basis of clinical, bacteriologic, and histologic findings.
The lesions have a thick, adherent, recurrent, dirty yellow crust with an erythematous margin. This form of impetigo is the most common skin infection in children. Impetigo in infants is highly contagious and requires prompt treatment.
The lesions in bullous staphylococcal impetigo, which are always caused by S aureusare superficial, thin-walled, and bullous. When a lesion ruptures, a thin, transparent, varnish-like crust appears which can be distinguished from the stuck-on crust of common impetigo. This distinctive appearance of bullous impetigo from the local action of the epidermolytic toxin exfoliation.
The lesions most often are found in groups in a single reglon. Ecthyma is a deeper form of impetigo. Lesions usually occur on the legs and other areas of the body that are generally covered, and they often occur as a complication of debility and infestation. The ulcers have a punched-out appearance when the crust or purulent materials are removed.
The lesions heal slowly and leave scars. Streptococcus pyogenes is the most common agent of cellulitis, a diffuse inflammation of loose connective tissue, particularly subcutaneous tissue. The pathogen generally invades through a breach in the skin surface, and infection is fostered by the presence of tissue edema.
Cellulitis may arise in normal skin. However, the lesion of cellulitis is erythematous, edematous, brawny, and tender, with borders that are poorly defined.I need a Springfield deep in my ass
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