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Infectious Disease Online

Cutaneous Infections and Infestations:

Bacterial, Rickettsial and Chlamydial Infections

Dr Sampurna Roy MD                       




Bacteria form part of the normal resident flora of the skin.

In certain conditions these are of pathogenic importance.

Visit: Cutaneous Infections and Infestations

Superficial pyogenic infection (pyodermas): These are usually caused by staphylococcus aureus and strains of Streptococcus. These are usually characterized by a dense acute inflammatory infiltrate. Hair follicles may also be infected causing folliculitis.

Staphylococcal Infection


Staphylococcal scalded skin syndrome

Toxic Shock Syndrome

Streptococcal Infection


Cornybacterial Infections:

Biopsy may appear normal.

The lesion is usually limited to the stratum corneum.


Erythrasma: Locatd in skin folds.

This is an example of "invisible dermatosis".

Caused by diptheroid bacilli, Cornybacterium minutissimum. Special stain : Small coccobacilli are demonstrated by Gram , PAS and methenamine silver preparations.

Pitted keratolysis : Often located on the plantar  surface of the feet. Pits appear as multiple crateriform defect in the stratum corneum.

Filamentous and coccoid organisms are demonstrated by Gram and methenamine silver stain.


Chlamydial Infection 


Lymphogranuloma Venereum



Deep pyogenic Infection (Cellulitis): Cellulitis is a diffuse inflammation of the connective tissue of the skin and deeper soft tissue.

Erysipelas: Form of cellulitis. Subepidermal edema with formation of vesiculobullous lesion. There may be a dense diffuse neutrophilic infiltrate and in some cases vascular and lymphatic dilatation.

Necrotizing fasciitis: (Flesh eating bacteria).

Rare form of cellulitis, usually located on the leg.It progresses to necrosis of skin and underlying tissues and may spread into the underlying muscle. Histologicallly there is necrosis of the epidermis, dermis and upper subcutis. There is septic vasculitis with inflammation of the vessel wall. Thrombi may be present in the lumen.

Clostridial myonecrosis (Gas gangrene)

Blastomycosis-like pyoderma



Rickettsial Infection:

Usually produces acute febrile illness together with headache and myalgia.

Histologically, there is lymphocytic vasculitis and areas of coagulative necrosis of the epidermis and dermis.

Rocky Mountain Spotted Fever

Epidemic Typhus

Scrub Typhus







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