Bacterial skin infections

Introduction

Some bacteria live on normal skin and cause no harm, such as some Staphylococcus species, Corynebacterium spp., Brevibacterium spp and Acinetobacter. Propionibacteria live in the hair follicles of adult skin and contribute to acne. See DermNet's page on the microorganisms found on the skin.

Some bacteria invade normal skin, broken skin from eczema/dermatitis or wounds (causing wound infection). Bacteria, like viruses, may also sometimes result in exanthems (rashes).

Which bacteria cause skin infection? 

Staphylococcus aureus

• Folliculitis
• Furunculosis (boils) and abscesses
• Impetigo (school sores) and ecthyma
• Methicillin (meticillin) resistant Staph. aureus
• Staphylococcal scalded skin syndrome
• Toxic shock syndrome
• Tropical pyomyositis
• Botryomycosis (pyoderma vegetans)

Streptococcus pyogenes

• Cellulitis
• Erysipelas
• Impetigo
• Necrotising fasciitis
• Infectious gangrene
• Scarlet fever
• Rheumatic fever, erythema marginatum

Corynebacterium species 

• Erythrasma
• Pitted keratolysis
• Trichomycosis axillaris

Less common bacteria may also cause infection with skin signs. These include:

• Neisseria species, the cause of gonorrhoea and meningococcal disease
• Erysipelothrix insidiosa, the cause of erysipeloid (usually an animal infection)
• Haemophilus species, the cause of chancroid and cellulitis in young children
• Helicobacter pylori, a stomach infection, which may be associated with some cases of chronic urticaria and rosacea
• Klebsiella rhinoscleromatis, the cause of rhinoscleroma
• Mycoplasma pneumoniae, a cause of pneumonia, causes non-specific erythema, bullous eruptions, urticarial rashes, erythema multiforme, mucositis and rarely, SJS/TEN
• Pseudomonas aeruginosa causes wound infections, athlete's foot, gram-negative folliculitis, chronic paronychia (green nail syndrome), spa pool folliculitis and ecthyma gangrenosum
• Calymmatobacterium granulomatis, the cause of granuloma inguinale
• Bacillus anthracis, the cause of anthrax
• Clostridium perfringens and other species cause gas gangrene
• Listeria monocytogenes rarely causes cutaneous listeriosis.
• Treponema species cause syphilis, yaws and pinta
• Bartonella species cause cat scratch fever, bacillary angiomatosis, Carrion disease, and bartonellosis
• Mycobacterium species cause tuberculosis, leprosy and atypical mycobacterial infections including Buruli ulcer
• Leptospira, the cause of leptospirosis, which may cause bleeding into the skin (purpura)
• Nocardia, the cause of nocardiosis
• Yersinia pestis, the cause of bubonic plague, which causes swollen lymph glands and pustules, ulcers and scabs on the skin
• Serratia marcescens, a facultative anaerobic gram-negative bacillus that may rarely cause skin infections such as cellulitis, abscesses and ulcers; usually in patients with immunodeficiency.
• Fusobacterium species, Bacillus fusiformis, Treponema vincenti and other bacteria may result in tropical ulcer
• Burkholderia species, the cause of melioidosis and glanders, in which abscesses may be associated with systemic symptoms.
• Actinomyces species, the cause of actinomycosis, in which granular bacteriosis occurs, with abscesses and sinus tracts draining sulphur-yellow granules.
• Vibrio vulnificus, a cause of septic shock characterised by blood-filled blisters.
• Brucella species, the cause of brucellosis, a febrile illness caught from unvaccinated animals or their unpasteurised milk.
• Salmonella species, particularly S. typhi (typhoid fever)
• Aeromonas species, found in water, rarely cause skin and soft tissue infections

Tick-borne bacterial infections include:

• Lyme disease, due to Borrelia burgdorferi
• Relapsing fever, due to Babesia microti
• Tularaemia, due to Francisella tularensis
• Rickettsial diseases (some of these also transmitted by body louse, fleas, mosquitoes and mites).
• Ehrlichiosis and anaplasmosis.

Other conditions sometimes caused by or associated with bacterial infection include:

• Kawasaki disease (mucocutaneous lymph node syndrome)
• Pseudofolliculitis barbae (shaving bumps)
• Sarcoidosis
• Scalp folliculitis
• Osler nodes and Janeway lesions (bacterial endocarditis)
• Vaginitis and bacterial vaginosis.

Which tests should be done?

Laboratory tests for bacterial infections may include:

• Full blood count: bacterial infection often raises the white cell count with increased neutrophils
• C-reactive protein (CRP): elevated > 50 in serious bacterial infections
• Procalcitonin: blood test marker for generalised sepsis due to bacterial infection
• Serology: tests ten days apart to determine immune response to a particular organism
• Polymerase chain reaction (PCR) and ELISA tests for specific organisms
• Blood culture: if high fever > 38C
• A swab of the inflamed site, such as throat, skin lesions for culture.

How are bacterial infections treated?

Minor bacterial infections may resolve without treatment. However, persistent and serious bacterial infections are treated with antibiotics. These are available for localised topical use (creams, gels, solutions), such as antibiotics for acne, or as systemic treatment as tablets, capsules and intramuscular or intravenous injections.

It is best to take samples to test which organism is responsible for an infection before commencing antibiotics. If the infection is serious (eg, if meningococcal disease is suspected), immediate treatment with a broad-spectrum antibiotic may commence. Once the specific organism causing infection has been determined, the antibiotic may be changed to a narrow-spectrum antibiotic directed against this organism.

Antibiotics have important individual risks and societal impact and should not be prescribed or taken if they are not required or if they are unlikely to be of benefit, for example, if the infection is viral in origin. Adverse reactions include cutaneous effects.