Bacterial skin infections
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.
Which bacteria cause skin infection?
The most common bacteria to cause skin infections are:
- Staphylococcus aureus
- Streptococcus pyogenes
- Overgrowth of Corynebacterium spp. (erythrasma, pitted keratolysis and trichomycosis axillaris)
Less commonly, other bacteria may also cause infection with skin signs. These include:
- Neisseria species, cause of gonorrhoea and meningococcal disease
- Erysipelothrix insidiosa, cause of erysipeloid (usually an animal infection)
- Haemophilus species, 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, 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, cause of granuloma inguinale
- Bacillus anthracis, cause of anthrax
- Clostridium perfringens and other species cause gas gangrene
- Treponema species cause syphilis, yaws and pinta
- Bartonella species cause cat scratch fever, bacillary angiomatosis and bartonellosis
- Mycobacterium species cause tuberculosis, leprosy and atypical mycobacterial infections including Buruli ulcer
- Leptospira, cause of leptospirosis, which may cause bleeding into the skin (purpura)
- Nocardia, cause of nocardiosis
- Yersinia pestis, 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.
- Fusibacterium species, Bacillus fusiformis, Treponema vincenti and other bacteria may result in tropical ulcer
- Burkholderia species, cause of melioidosis and glanders, in which abscesses may be associated with systemic symptoms.
- Actinomcyes species, cause of actinomycosis, in which granular bacteriosis occurs i.e. abscesses and sinus tracts draining sulphur-yellow granules.
- Vibrio vulnificus, a cause of septic shock characterised by blood-filled blisters.
- Brucella species, cause of brucellosis, a febrile illness caught from unvaccinated animals or their unpasteurised milk.
- Salmonella species, particularly S typhi (typhoid fever)
- Aeromonas found in water rarely causes 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.
- Ehrlichiosis and anaplasmosis
Other conditions sometimes caused by bacterial infection include:
- Kawasaki disease (mucocutaneous lymph node syndrome)
- Pseudofolliculitis barbae (shaving bumps)
- 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 10 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
- Swab of inflamed site, eg 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), eg 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 meningococcal disease is suspected), immediate treatment with 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 infection is viral in origin.