Microbiology of skin infection Flashcards by Gillian Miller

Gram positive in clusters

Staphylococcus sp

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Staph saprophyticus

Coagnulase negative

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Test for staph aureus

Latex agglutination

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Does coagulase plasma clot in the bottom of the tube?

Yes it does (only staph aureus)

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Novobicin resistant

Staph saprophyticus

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Neonatal meningitis

Group B strep

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Throat, skin infections

Group A strep

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Commensals, endocarditis

Strep viridans

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Which staph produces coagulase

Staph aureus

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Some strains produce:
• Enterotoxin – food poisoning
• SSSST – staph. scalded skin syndrome toxin
• PVL – Panton Valentine Leukocidin

Staph aureus

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Toxins produced by staph aureus

Enterotoxin
SSSST
PVL

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causes urinary tract infection in women of child-bearing age

Staph saprophyticus

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May cause infection in association with implanted artificial material, such as artificial joints, artificial heart valves, intravenous catheters (produces “slime” that allows it to stick to prosthetic material)

Staph epidermis

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Beta-haemolytic

Complete haemolysis

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Alpha-haemolytic

Partial haemolysis

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Gamma haemolytic

No haemolysis

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Toxin produced by beta-haemolytic streptococci

Haemolysin

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Throat, severe skin infections

Group A Beta-haemolytic streptococci

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How do you further classify beta-haemolytic streptococci?

Classify by antigenic structure on surface (SEROLOGICAL GROUPING)
e.g.
– Group A (throat, severe skin infections)
– Group B (meningitis in neonates)

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Name 2 alpha haemolytic strep

Strep pneumonia

Strep viridans

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Name a non-haemolytic streptococci and where you would find it

Enterococcus

commensals of bowel
common cause of UTI

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What does sebum (fatty acids) do?

Inhibits bacterial growth

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Competitive bacterial flora of the skin

Staphylococcus erpidermidis
Corynebacterium (“diptheroids”)
Proprionbacterium

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Boils and carbuncles

Staph aureus

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Infected eczema

Staph aureus

Erysipelas

Strep pyogenes (GROUP A STREP)

Necrotising fasciitis

Strep pyogenes (GROUP A STREP)

is a bacterial skin infection involving the upper dermis that characteristically extends into the superficial cutaneous lymphatics. It is a tender, intensely erythematous, indurated plaque with a sharply demarcated border. Its well-defined margin can help differentiate it from other skin infections (eg, cellulitis).

Erysipelas

Diagnosis of skin infection

- Swab of lesion if surface is broken - Pus or tissue if deeper lesion - +/- blood cultures, if appropriate

Green vial

Aerobic culture bottle

Red/pink vial

Anaerobic culture bottle

Yellow vial

Paediatric culture bottle

Antibiotic for strep pyogenes (Group A strep)

Penicillin (will also be treated by flucloxacillin)

Tinea capitis

Scalp

Tinea barbae

Beard

Tinea corporis

Body

Tinea manuum

Hand

Tinea unguium

Nails

Tinea cruris

Groin

Tinea pedis

Foot

How do dermatophytes enter the skin?

Enter abraded or soggy skin

In which layer do hyphae spread?

Spread in stratum corneum

Which type of tissue do dermatophytes infect?

Infects keratinised tissues only (skin,hair,nails) •Increased epidermal turnover causes scaling • Inflammatory response provoked (dermis) • Hair follicles and shafts invaded

Lesion grows outward and heals in centre, giving a “ring” appearance

Dermatophyte

Males or females more commonly affected in dermatophyte infections?

Males

Who are more commonly affected by scalp ringworm?

Children

Foot and groin ringworm mainly affects who?

Men

Anthropophilic fungi

Other infected humans MOST LIKELY

Zoophilic fungi

Animals (cats, dogs, cattle)

Geophilic fungi

Soil (less common in UK)

Dermatophyte infections, sources of infection

Other infected humans (MOST LIKELY) Animals Soil

How is trichophyton rubrum spread?

Human-human transmission

How is trichophyton mentagraphytes spread?

Human-human transmission

How is microsporum canis spread?

Cats, dogs-humans

Dermatophyte infection diagnosis

``` Clinical appearance • Woods light (fluorescence) • Skin scrapings, nail clippings, hair – Send to laboratory in a “Dermapak” for microscopy and culture – N.B. Culture takes 2 weeks + ```

Where should skin scrapings be taken from?

Taken from the edge of the scaly lesion

Treatment for small areas of infected skin, nails

Clotrimazole (canestan) cream or similar Topical nail paint (amorolfine)

Treatment for scalp dermatophyte infections

Terbinafine ORALLY | Itraconazole ORALLY

Diagnosis of candida?

Swab for culture

Where would you get candida infection?

Candida causes infection in skin folds where area is warm and moist “candida intertrigo” Seen under the breasts in females, groin areas, abdominal skin folds etc, nappy area in babies

Treatment for candida?

Clotrimazole cream | Oral fluconazole

What type of skin infection is scabies?

Parasitic

Infection caused by Sarcoptes scabiei

Scabies

Scabies incubation period?

6 weeks

Intensely itchy rash affecting finger webs, wrists, genital area

Scabies

Treatment for scabies

malathion lotion, applied overnight to whole body and washed off next day – benzyl benzoate (avoid in children)

Where would you get scabies?

Finger webs, wrists, genital areas

This parasitic infection burrows in your skin and makes "tracts"

Scabies

Pediculus capitis

Head louse

Pediculus corporis

Body louse

Vagabond's disease

Pediculus corporis (body louse)

Plithirus pubis

Pubic louse

Treatment for lice (pediculosis)

Malathion lotion

Which type of bacteria can survive in the environment because of their cell wall structure?

Gram positive -these may become a source of infection for other patients

WHO NEEDS SINGLE ROOM ISOLATION

Group A strep MRSA Scabies (also need long sleeved gown)