I have a chicken with foot infection and would like to know the best way to treat it
This sounds like bumblefoot. Bumblefoot is a chronic inflammation of the foot pad and is also referred to as pododermatitis or foot pad dermatitis. It starts out with a small wound to the bottom of the foot which allows bacteria to enter and infection develops. Bumblefoot results in chronic pain making it hard for the chicken to perch and walk around. If left untreated, the infection can spread to the tendons and osteomyelitis arises, along with septic arthritis and, possibly, death.
The best way to deal with bumblefoot is to prevent it. Make sure that your perches don’t have sharp corners or splinters. Wire ends can puncture the foot as well and sharp objects in the litter should be removed. Make sure that they are receiving a good complete diet, especially with regards to vitamin A. Keep the litter dry. Wet litter encourages bacterial growth. If you get a bumblefoot problem, the first thing to do is remove any causes of the problem so that they don’t re-occur.
The next thing to do is a broad spectrum antibiotic in the drinking water. Once you can control the infection, swelling will begin to subside. If not, surgery may be required. Surgery or lancing the wound is the last resort. It will do more damage to the tissue than the original wound. If you need to do surgery, soak the foot in water with Epson salts until the scab becomes soft. Gently pull back the scab and remove the pus. Be careful not to squeeze the pus out or you may damage tissue. Clean out the wound with peroxide and then apply a topical antibiotic. Bandage the wound and keep it as clean as possible. It may be necessary to clean and re-bandage the wound 7-14 days.
The main bacteria of concern is Staphylococcus aureus, which can infect people as well. It is important, therefore, to wear gloves when treating the bird and dispose of the used materials as biological waste.