First, all people that contact the gym should disinfect themselves by washing their hand with soap. It would be better if they could wash their entire body and changes their cloth.
To find the best disinfectant to kill the bacteria you can take a sample and then test it with various disinfectant. The disk with lowest bacteria count will be the most effective disinfectant. Then, you should clean all the room using the chosen disinfectant solution.
