Allergies in general are one of my areas of interest and I do want to make sure that your vet thoroughly discussed food allergies with you. While some dogs can be allergic to grains it is more common for them to be allergic to the actual protein source in the food. The feet are one of the most common areas effected by food allergies. While the Blue is a good food you want to make sure you are feeding a single protein source food and preferably one that is what we call a novel protein. Novel protein are duck, rabbit, kangaroo, bison. Check the ingredients on the bag because while the food may say one flavor such as beef or chicken Blue normally combines several protein sources in one food. You want to avoid beef, chicken, lamb.
Staph overgrowth is very common in dogs with allergies and this is normally a direct result of itching or licking.
Considering it is his feet this could also be an allergy to things like grass.
To help with over all environmental allergies you can start a dog on local honey. It must be local and raw. Give 1 teaspoon daily. This helps to slowly expose the body to all of the local pollen's allowing the body to build up a natural resistance.
To help now you can try the following
1. Soak the feet twice daily for 5 minutes in a mix of 75% water 25% apple cider vinegar.
2. Use an E collar or socks to prevent licking. If we do not stop the licking he will likely end up with another infection requiring medication.
3. Oral Benadryl can be used at a dose of 1-2mgs per pound of body weight 2-3 times per day, or Zyrtec at a dose of 0.5mgs per pound twice daily.
4. Use either Cortisone spray or ointment on the feet to help stop the itching.
5. Keep a pie pan or dish pan with clean water inside the front door. Every time he goes out rinse his feet when he comes in. This will remove any pollen on his feet in case this is due to a grass allergy.
I hope this helps and he feels better soon.
Please reply back if you have additional questions and I will be happy to continue. If you have no additional questions please take a few moments to provide a rating so that I am compensated by justanswer for assisting you today.