Common bacterial and fungal infections of the foot.

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No matter how clean your feet are, they are constantly in contact with microorganisms that can potentially cause an infection. The most common culprits are fungi and bacteria.

In most cases, the immune system can contain these disease-causing agents (pathogens). However, there are times when your immune defenses are low, the pathogen is particularly resistant, or the breakdown of the skin allows microorganisms to easily penetrate vulnerable tissues.

Symptoms of a foot infection are usually mild and easy to treat at home. Others may require more aggressive interventions, including hospitalization for serious and life-threatening complications. In general, there are steps you can take to prevent infection.

Get Medication Information / Brianna Gilmartin

Fungal foot infections

Fungal foot infections are familiar to many of us who may have contracted a foot or toenail infection in a locker room or spa. Pathogenic fungi are especially beneficial and can colonize even intact skin.

The foot, especially between the toes, provides an ideal environment for infection, allowing the roots of the fungus to penetrate moist, softened tissues. All that is needed for infection is foot contact with a wet, contaminated surface .

Fungal foot infections can be persistent and difficult to treat. But they are rarely life threatening .

Athlete's foot (Tinea pedis)

When a rash, itching, and peeling appears between the toes, it is most often associated with a very common condition known as athlete's foot (tinea pedis).

The fungus thrives in humid environments like gyms and saunas and can thrive in sweaty socks and shoes. It is very contagious and can be easily spread through contaminated floors, towels, or clothing. Athlete 's foot can be caused by a number of fungi, including those associated with ringworm .

Most cases can only be identified by symptoms. In more severe or recurrent cases, a microscopic examination of the skin scraping, known as a KOH test , will be helpful.

In mild cases, an over-the- counter antifungal cream or spray can be used. Severe or persistent infections may require an oral antifungal drug such as terbinafine or itraconazole for a period of two to six months .

Toenail fungus (onychomycosis)

Onychomycosis is the term used to describe a fungal infection that usually grows slowly under the toenail. Symptoms include white or yellow discoloration, thickening and peeling of the nail, and separation of the nail from the nail bed.

Onychomycosis often accompanies an athletic foot and is more common in people with weakened immune systems or peripheral vascular disease (characterized by decreased blood flow to the extremities).

The diagnosis can be made by visual evaluation and confirmed with a KOH test. Tissue culture of nail clippings can help identify a specific fungal pathogen .

Onychomycosis is very difficult to treat because most topical creams do not penetrate the nail tissue. Oral antifungal medications generally work best, but it can take six to 12 months for a nail to fully grow. Terbinafine is considered the drug of choice, often supported by itraconazole, another oral antifungal agent .

For fungal toenail infections, oral antifungal medications may be needed.

Bacterial foot infections.

Although a bacterial foot infection is somewhat less common than a fungal infection, it can sometimes become serious and progress from a local infection to a systemic infection (affecting the whole body). Most are caused by tears or abrasions in the skin, often as a result of a penetrating wound.

Bacterial infections under or near the toenail are often the result of an ingrown toenail (onychocryptosis). Even eczema , athlete's foot, or severe sunburn can cause an infection due to damage to the outer layer of the skin ( epidermis ).

Although anyone can get a bacterial foot infection, some people are at higher risk for complications, including:

  • Adults
  • People with diabetes who often have poor circulation in the legs and a reduced ability to fight infection .
  • People with weakened immune systems, such as those with untreated HIV.
  • People undergoing chemotherapy or taking immunosuppressive drugs.

When a bacterial infection occurs, the surrounding skin becomes red, swollen, and painful. There may even be a yellow or greenish discharge in the form of pus. The most common bacterial culprit is Staphylococcus aureus , although other types are associated with certain conditions.

Erythrasma

One type of bacterial infection that is often mistaken for a fungus is erythrasma. Erythrasma is caused by the bacteria Corynebacterium minutissimum and is more common in people with diabetes and obesity.

As with fungi, bacteria settle primarily in skin folds, such as the armpits, under the chest, groin, or between the toes. The infection patches are initially pink, but quickly turn brown and scaly as the skin begins to peel and shed.

Erythrasma can often be diagnosed with an ultraviolet light known as a Wood's lamp, which causes bacteria to glow in an almost fluorescent coral pink light. Erythrasma is best treated with a topical fusidic acid cream or an oral antibiotic such as azithromycin or erythromycin .

Foot abscess

Bacterial foot infections sometimes spread beyond the superficial tissues and fuse into a pus-filled pocket known as an abscess. A foot abscess is usually caused by a puncture wound (such as after an unsterile pedicure) or an infection of the hair follicle. Although abscesses are similar to boils, they involve deeper layers of tissue.

Symptoms include redness, swelling, warmth, pain, and a lump that can arise spontaneously. An abscess can also be accompanied by a mild fever and widespread pain.

While S. aureus is a common culprit, Fusobacterium necrophorum and Arcanobacterium pyogenes are the types most commonly restricted to feet.

Abscesses can often be diagnosed with a physical exam. If necessary, a culture can be done to determine the type of bacteria and help choose the correct antibiotic.

Treatment generally involves draining the abscess with oral and / or topical antibiotics to cure the infection. An over-the-counter pain reliever such as Tylenol (acetaminophen) can be used to relieve pain and fever .

A foot abscess is usually treated with drainage and subsequent treatment with antibiotics.

Cellulitis

Cellulitis is a potentially serious skin complication in which a local bacterial infection begins to spread from the site of the original injury. Cellulite usually begins as a small area of inflammation that spreads rapidly to surrounding tissues, causing swelling, pain, warmth, and characteristic red streaks that move upward from the foot.

The red stripes, known as lymphangitis, indicate that the infection is migrating to the lymph nodes. If this happens, the infection can become systemic and life-threatening. Fever, chills, and body aches are signs of a serious infection.

Cellulite is usually caused by damage to the skin, but it is especially common in people with diabetes or poor circulation. S. aureus and Streptococcus are the most likely causes .

Cellulite is a medical emergency, whether you have a fever or not. If you see a red streak creeping up your foot, seek medical attention as soon as possible.

Uncomplicated cases can be treated with a 5-14 day course of broad-spectrum antibiotics. Severe cases may require hospitalization and IV antibiotics and fluids .

Prophylaxis

Yeast infections of the feet can be prevented by keeping them clean and dry and washing them every day with soap and water. Do not go barefoot in public, do not wear shoes or nail clippers.

Always trim your toenails and change socks and shoes regularly to avoid moisture build-up. If your feet are particularly sweaty and / or prone to yeast infections, use an over-the-counter antifungal foot powder or spray daily .

Bacterial infections can be prevented by keeping the skin intact and clean. If the skin is cut or scraped, it should be washed immediately with soap and water and a sterile bandage applied. If your foot is prone to dryness and cracking, you can apply a petroleum jelly-based foot cream to keep the skin smooth.

In contrast, daily use of prescription or over-the-counter topical antibiotics is not recommended as a preventive measure, as it can eventually lead to antibiotic resistance .

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