Normal flora of the skin: There are about 10-10 organisms per squarecentimeter of skin.Organisms may present as:normal or resident flora (stable population) oras transient flora (transit but may multiply for ashort period and are eliminated because ofcompetition from the normal flora).The main resident flora are:Most are located superficially in the stratumcorneum but some are found in the hairfollicles.• S.aureus in specific sites such as the anteriornares and axillae, and hospital personnel.• S.epidermidis, propionibacteria, micrococci
The composition of the normal flora in areas of the body differs because of ecological differences pH, temperature and nutrients (e.g. sebum, fatty acids, urea).The major barriers of the skin: Continuous desquamation of the stratum corneum. Epithelium as mechanical barrier. Lysozyme (in sweat, sebum and tears). Bacteriocins produced by commensals. Bacterial skin infectionsStaphylococcal infections remain localized.1. Boils circumscribed infection of the hair follicle with central suppuration.
2. Carbuncle large abscess, which occur at the back of the neck, especially in diabetic patients.3. Sycosis barbae infection involving the shaving area of the face.Streptococcal infections spread subcutaneously, and lead to the following conditions:1. Cellulitis mostly caused by S.pyogenes and S.aureus may involved. Infection may spread through lymphatic and blood vessels, leading to septicaemia.2. Erysipelas t ype of cellulitis caused by S. pyogenes usually in elderly.Lesions are on the face and limbs; lesion on the face is often butterfly-like with orange-peel
3. Impetigo. seen in young children; vesiclesappear on the skin around the mouth and laterbecome purulent, with honey-like crusts; S.pyogenes and S.aureus are involved.4. Angular cheilitis (angular stomatitis)inflammation of one or both angles of themouth, especially seen in denture-wearingelderly people. Caused by S.aureus and /orCandida infection.5. Necrotizing fasciitis (streptococcal gangrene)rapidly progressing infection involving the skindown to the fascial planes, causing necrosisand tissue loss. The skin initially normal, butthe infection spreads along the fascial planes,destroying the blood supply to the skin. Thenthe skin discolors and becomes necrotic within
Patient toxic and shock and may die within 24hours.Caused by mixed flora including staphylococci,strict anaerobes and Enterobacteriaceae; themajor causative organism is S. pyogenes.Treatment includes excision of skin, antibioticsand supportive therapy.Acne disfiguring facial infection of adolescentscaused by Propionibacterium acnes .Leprosy caused by Mycobacterium leprae ,whichtransmitted by prolonged contact. lives in skinand nerves and cause lepromatous andtuberculoid leprosy.Gram-negative infections caused byPseudomonas and Bacteroids spp. and
Diagnosis of bacterial skin infectionsSpecimens : smears and swabs of pus andexudate from the lesions.Smears stained with Gram-stain.Swabs inoculated in blood agar (aerobically andanaerobically) demonstrate the type ofhaemolysis.Confirmation of isolates by API test.Fungal skin infections mainly caused bydermatophytes ( Microsporum, Epidermophytonand Trichophyton, cause keratinized tissues(hair, nails and skin) infections, and Candidaalbicans .
Viral skin infections1. Human herpesviruses 1 and 2 cause recurrent cold sore and genital lesions; herpetic whitlow.2. Varicella-zoster virus cause chickenpox (primary lesion) and shingles of the skin.3. Papovavirus – warts.4. Coxsackievirus – hand, foot and mouth disease.5. Rubella, chickenpox, measles and glandular
Diagnosis of viral skin infectionsinclude serology or vesicular fluid for electronic microscopy and tissue culture.Wound infectionsa. surgical wound infection b. infection of burns.c. Clostridial wound infections.Surgical wound infectionaccounts for quarter of hospital- acquired infections and frequently results in death.Polymicrobial in nature, and the major pathogens are S. aureus and E. coli, but other coliforms may be involved.If the wound is contaminated, anaerobes, Clostridium spp. and Bacteroids spp. may
Clinical featureswound edges become reddened, with or withoutpus formation; sometimes a wound abscessmay formed unnoticed in the deeper layers anddischarge through the suture line.Spread of infection may occur to adjacenttissues or into blood leading to septicaemia.Breakdown of the wound) – resuture.Pathogenesis and epidemiologyinfection could be endogenous or exogenous(infected person in an adjoining bed, or carrier– member of staff).Reservoir include skin, dust and bed linen.Transmission direct or indirect contact, orairborne.
Factors effecting the incidence of wound infection Overcrowded wards. Presence of foreign bodies and drains. Length of the operation and stay in hospital. Type of wound – clean ( i.e. no incisionthrough R.T, G.I.T, or G.U.T); contaminated(e.g. following surgery in a site with a normalflora); or infected (e.g.drainage of an abscess).Prevention Observation of aseptic and antiseptictechniques during patient preparation andoperation. Implementation of infection control theatreprotocols. Positive-pressure ventilation.
Isolation of patients with discharging wounds(source isolation) and susceptible patients(protective isolation).Infections of burnsburns create moist, and are ideal for bacterialgrowth because the protective skin cover hasbeen lost.Aetiology S. pyogenes, Pseudomonasaeruginosa (has ability for surviving in burnttissue and in burn words) and S. aureus andinfection usually polymicrobial.Pathogenesis and epidemiology if prophylaxis isnot given, bacteria colonize burn wounds within24 hours and cause cellulitis of adjacent tissuesand septicaemia.
Diagnosis of wound infectionsswabs of exudate, tissue or pus are cultured on blood agar, MacConkey s agar, or Robertson s medium.Smears of tissue or exudate are Gram-stained.Clostridial wound infections1. Tetanus, caused by Clostridium tetani,2. Gas gangrene , caused by C. perfringens, C. novyi and C. septicum.Gas gangreneinvolved tissues are black and oedematous with foul-smelling serous exudate and they exhibit sign of crepitus as a result of production of gas by
Disease occur with high mortality rate andexcision or amputation of the affected area orlimb very often required.Treatment Surgical debridement. Antibiotics: penicillin and metronidazole.