Skin Infections

(1) Fungal infections:

# Tinea infections, including:

1.Tinea pedis (feet) 2.Tinea cruris (groin) 3.Tinea corporis (body) 4. Tinea capitis (head)

# Candidiasis of skin, nail or feet

# Pityriasis versicolor, caused by Malassezia furfur, and characterized by non-itchy hypo-or hyperpigmented macules.

Pityriasis versicolor

(2) Pediculosis pubis, caused by crab lice; and affects the head, body, pubic area.

(3) Scabies, caused by the insect Sarcoptes scabiei, and characterized by:

* Affects finger clefts, forearms and genitalia * Acquired by sexual close contact.

(4) Viral skin infection, caused by herpes virus, enteroviruses, Measles virus, & Rubella virus

(5) Commensal skin bacteria cause acne vulgaris

Acne vulgaris

Tinea infections

Symptoms:

@ Scaly lesions with raised margins. @ Commonly seen during child hood. @ Infect skin, nails and hair. @ Acquired from domestic or farm animals

Aetiology:

@ Caused by three fungal genera: * Trichophyton, * Microsporum * Epidermophyton

Trichophyton EpidermophytonMicrosporum

Features of tinea infections:

@ Tinea pedis (feet): Infects interdigital spaces and causes itching, and blisters. * It is caused by Trichophyton rubrum and Trichophyton interdigitale

@ Tinea cruris (groin): Causes genitourinary infection.

@ Tinea corporis (body): Known as 'ringworm’. * It infects the arms, trunk and legs. * It caused by Trichophyton rubrum

@ Tinea capitis: Infects scalp and hair. Causes scaling of scalp, dandruff, broken hair

Tinea pedis Tinea capitis

Lab. Diagnosis of tinea infections:

@ Presence of scales is diagnostic. Wood’s ultraviolet lamp shows Microsporum (only) as green illumination.

@ Specimens collected are: Skin scales, nail clippings, and hair. Skin scales are obtained from edge of the lesion. Swabs are unsuitable.

@ Microscopy: Using potassium hydroxide.

@ Culture: Selective Sabouraud agar containing cycloheximide. Incubation at room temp. up to 3 weeks.

Acquired from animal (cats, dogs, rodents, cattle)

Microsporum canis

Acquired from soil

Microsporum gypseum

Acquired from school mates and colleagues

Trichophyton rubrum

Epidermophyton floccosum

Sources of Tinea infections

Infections of Wounds, Abscesses, Burns

Possible Pathogens:

# Pseudomonas aeruginosa, Proteus, E. coli, Bacteroides, Klebsiella, Pasteurella.

# Staph. aureus, Strep. pyogenes, Enterococci, Ana. streptococci, Cl. tetani, Mycobacteria, Cl. perfringens, Actinomycetes

# Mycetoma, Histoplasma, Blastomyces, Candida albicans, Cryptococcus neoformans.

C. albicans

Association with Pyogenic Infections:

@ S. aureus causes abscesses & skin infection

@ P. aeruginosa is associated with burns and hospital cross infections.

@ E. coli, Proteus, Pseudomonas, & Bacteroides are isolated from abdominal abscesses.

@ Cl. perfringens causes deep wounds infections and gas gangrene.

@ Cl. tetani causes umbilical neonatal infection.

@ Myco. tuberculosis causes cold abscesses.

TB cold abscess

Lab. Diagnosis of of Wounds,Abscesses, and Burns infections

Collection and Transport:

@ Collect pus. If pus is absent, use a swab and transport in Amies transport medium.

@ If mycetoma is suspected, collect from sinus

@ If tuberculosis is suspected, aspirate pus.

Macroscopy:

@ Report pus colour: red, brown, grey, yellow@ Examine granules: colour, shape, size, and consistency.

Colour of pus

Microscopy

@ Examine Gram smear for: Staphylococci, streptococci, enterococci, Proteus, E. coli, Pseudomonas, Bacteroides, Cl. perfringens.

@ Examine for ZN stain for acid fast bacilli.

@ Examine KOH smear for:

# Budding (Candida and Cryptococcus)

# Branching (Nocardia)

# Mycetoma granules (black, red, yellow, etc)

# Actinomyces yellow granules.

Mycetoma

Culture:

@ Inoculate blood agar and Mc Conkey agar plates and incubate aerobically overnight.

@ Inoculate a neomycin plate & another blood agar plate and incubate anaerobically for 48 hr

@ Inoculate a cooked meat medium and incubate up to 72 hours.

@ Decontaminate TB specimens by adding 4% sodium hydroxide for 10 min., and inoculate an LJ slope and incubate for 8 weeks

@ For fungi, inoculate a Sabouraud agar

Examination of Cultures

@ LJ slope: M. TB with raised, dry, creamy colonies.

@ Blood, neomycin, Mac Conkey agar: Look for colonies of aerobic and anaerobic bacteria

@ Cooked meat medium, Look for: # Turbidity, reddening of meat, and gas bubbles (Cl. Perfringens) # Decomposition and blackening of the meat (Bacteroides)

@ Subculture the cooked meat medium if the anaerobic plates were sterile.