Skin and wound infection

1. Lecture №
Skin and wound
infection

2. Normal flora of the skin:
There are about 10-10 organisms per square
centimeter of skin.
Organisms may present as:
normal or resident flora (stable population) or
as transient flora (transit but may multiply for a
short period and are eliminated because of
competition from the normal flora).
The main resident flora are:
Most are located superficially in the stratum
corneum but some are found in the hair
follicles.
• S.aureus in specific sites such as the anterior
nares and axillae, and hospital personnel.
• S.epidermidis, propionibacteria, micrococci

3. 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 infections
Staphylococcal infections remain localized.
1. Boils circumscribed infection of the hair
follicle with central suppuration.

4. 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

5. 3. Impetigo. seen in young children; vesicles
appear on the skin around the mouth and later
become purulent, with honey-like crusts; S.
pyogenes and S.aureus are involved.
4. Angular cheilitis (angular stomatitis)
inflammation of one or both angles of the
mouth, especially seen in denture-wearing
elderly people. Caused by S.aureus and /or
Candida infection.
5. Necrotizing fasciitis (streptococcal gangrene)
rapidly progressing infection involving the skin
down to the fascial planes, causing necrosis
and tissue loss. The skin initially normal, but
the infection spreads along the fascial planes,
destroying the blood supply to the skin. Then
the skin discolors and becomes necrotic within

6. Patient toxic and shock and may die within 24
hours.
Caused by mixed flora including staphylococci,
strict anaerobes and Enterobacteriaceae; the
major causative organism is S. pyogenes.
Treatment includes excision of skin, antibiotics
and supportive therapy.
Acne disfiguring facial infection of adolescents
caused by Propionibacterium acnes .
Leprosy caused by Mycobacterium leprae ,which
transmitted by prolonged contact. lives in skin
and nerves and cause lepromatous and
tuberculoid leprosy.
Gram-negative infections caused by
Pseudomonas and Bacteroids spp. and

7. Diagnosis of bacterial skin infections
Specimens : smears and swabs of pus and
exudate from the lesions.
Smears stained with Gram-stain.
Swabs inoculated in blood agar (aerobically and
anaerobically) demonstrate the type of
haemolysis.
Confirmation of isolates by API test.
Fungal skin infections mainly caused by
dermatophytes ( Microsporum, Epidermophyton
and Trichophyton, cause keratinized tissues
(hair, nails and skin) infections, and Candida
albicans .

8. Viral skin infections
1. 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

9. Diagnosis of viral skin infections
include serology or vesicular fluid for
electronic microscopy and tissue culture.
Wound infections
a. surgical wound infection b. infection of burns.
c. Clostridial wound infections.
Surgical wound infection
accounts 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

10. Clinical features
wound edges become reddened, with or without
pus formation; sometimes a wound abscess
may formed unnoticed in the deeper layers and
discharge through the suture line.
Spread of infection may occur to adjacent
tissues or into blood leading to septicaemia.
Breakdown of the wound) – resuture.
Pathogenesis and epidemiology
infection 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, or
airborne.

11. 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 incision
through R.T, G.I.T, or G.U.T); contaminated
(e.g. following surgery in a site with a normal
flora); or infected (e.g.drainage of an abscess).
Prevention
Observation of aseptic and antiseptic
techniques during patient preparation and
operation.
Implementation of infection control theatre
protocols.
Positive-pressure ventilation.

12. Isolation of patients with discharging wounds
(source isolation) and susceptible patients
(protective isolation).
Infections of burns
burns create moist, and are ideal for bacterial
growth because the protective skin cover has
been lost.
Aetiology S. pyogenes, Pseudomonas
aeruginosa (has ability for surviving in burnt
tissue and in burn words) and S. aureus and
infection usually polymicrobial.
Pathogenesis and epidemiology if prophylaxis is
not given, bacteria colonize burn wounds within
24 hours and cause cellulitis of adjacent tissues
and septicaemia.

13. Diagnosis of wound infections
swabs 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 infections
1. Tetanus, caused by Clostridium tetani,
2. Gas gangrene , caused by C. perfringens, C.
novyi and C. septicum.
Gas gangrene
involved tissues are black and oedematous with
foul-smelling serous exudate and they exhibit
sign of crepitus as a result of production of
gas by

14. Disease occur with high mortality rate and
excision or amputation of the affected area or
limb very often required.
Treatment
Surgical debridement.
Antibiotics: penicillin and metronidazole.

15. THE END