So it’s not specifically the foot that matters? Is it some sort of non lethal maiming you’re going for? Because I’d say go for a heart attack. Disrupting the electrical energy doesn’t require the help of any other entity, which here a population of bacteria is something I would consider as its own entity.
Then you might not know if they Returned to Sender and you have icky magick targeting you in response?
I’d say go back and get your foundation laid, know how to cleanse bad energy and banish unwanted presences. When you get into baneful magick you can start something and you might want to be prepared to handle it.
After that develop your psychic skills so you can read the energy and get feedback on the situation. Then you’re not working blind. Learning tarot does the job too. Some use pendulums.