Types of Skin and Wound Infections and Microbes
Superficial skin infections
Superficial infections occur primarily in the outer layers of the skin but may extend deeper into the underlying (subcutaneous) layer.
Examples of bacteria that can cause skin infections include:
- Bacteria that are often normally found on the skin (normal flora), such as species of Staphylococcus (staph) and Streptococcus (strep), are common causes.
- Antibiotic-resistant bacteria, such as MRSA (Methicillin-resistant Staphylococcus aureus)
- Vibrio or Aeromonas species, often found in brackish water
- Pseudomonas aeruginosa is associated with hot tubs.
- Bacteroides and Clostridium species may cause deeper wound infections.
- Tularemia—this infection is caused by Francisella tularensis bacteria. They primarily infect rabbits and rodents, but humans can get infections through tick or deer fly bites or contact with infected animals that can result in skin ulcers.
- Anthrax—this is an infection caused by the bacteria Bacillus anthracis. It can infect the skin as well as the respiratory or digestive tracts. The bacteria live in the soil and primarily infect animals, such as cattle, deer, sheep and goats. Humans can be infected by handling the animals or their hair, hide, or meat. Natural cases of human anthrax infection are rare in the U.S.
Typical bacterial skin infections include:
- Infected hair follicles (folliculitis)
- Boils (furuncles)
- Collection of boils involving several hair follicles and deeper layers of tissue (carbuncles)
- Impetigo—skin lesions and blisters (vesicles)
- Pressure sores (bed sores) and ulcers—these may be found in people who are immobilized or bedridden for long periods of time
- Cellulitis—an infection often involving the subcutaneous and connective tissue of skin, causing redness, heat, and swelling
- Necrotizing fasciitis—a serious but uncommon infection that can spread rapidly and destroy skin, fat, muscle tissue and fascia, the layer of tissue covering muscle groups. This type of infection often involves Group A streptococci, which are sometimes referred to as "flesh-eating bacteria."
Examples of common fungal skin infections include:
- Athlete's foot
- Yeast infections cause by Candida species may occur in the mouth (thrush) or on other moist areas of the skin.
Read the article on Fungal Infections to learn more.
Examples of viruses that cause skin infections include:
- Human papilloma virus (HPV) can cause common and plantar warts.
- Herpes simplex virus types 1 & 2 (HSV-1, HSV-2) are responsible for a skin infection known as herpetic whitlow.
Examples of wound infections
- Bites—wound infections due to bites tend to reflect the microbes present in the saliva and mouth of the human or animal that created the bite wound. Human bites may become infected with a variety of bacteria that are part of the normal oral flora. The majority of animal bites are from dogs and cats, and the most common bacteria is Pasteurella multocida.
- Trauma—trauma can be the result of any physical force, causing various wounds susceptible to infection, ranging from superficial scrapes to deep, penetrating wounds. Wounds that are initially contaminated, such as with the dirt or other material, have a higher risk of becoming infected. It is not uncommon for deep and contaminated wounds to have more than one type of bacteria causing the infection.
A deep puncture wound could allow bacteria such as Clostridium tetani (the cause of tetanus) to grow. Because most people in the U.S. are immunized against tetanus, this is very rare. Vaccination must be updated for tetanus every 10 years. Booster shots are often given in the emergency room, where people receive treatment for deep or puncture wounds.
Other types (species) of Clostridium bacteria, such as Clostridium perfringes, can cause serious wound and surgical infections, such as gas gangrene.
- Surgery—surgical sites are most commonly infected with the person's normal skin and/or digestive tract flora, the same microbes seen with superficial infections. They may also become infected by exposure to microbes in the hospital environment. Hospital-acquired bacteria often have an increased resistance to antibiotics, such as MRSA.
- Burns—burns can range from mild to severe, affecting different layers of the skin. First-degree burns involve the epidermis. Second-degree burns penetrate to the dermis. Third-degree burns penetrate through all of the layers of the skin and frequently damage the tissues below it. With increasing tissue damage, risk of infection increases.
Burn wounds are initially sterile but because of the dead tissue at their center – the eschar (scab) – and the loss of the skin's protection, bacteria normally found on the outer layer of skin will begin to grow within the wound. The affected person is at an increased risk for infection and more serious complications. Initial infections tend to be bacterial. Fungal infections due to Candida, Aspergillus, Fusarium, and other species may arise later since they are resistant to antibiotics. Viral infections, such as those caused by the herpes simplex virus, may also occur.