Will bactrim (sulfamethoxazole and trimethoprim) heal an infection of the umbilicus?

Depends. Bactrim (sulfamethoxazole and trimethoprim) is a broad-apectrum antibiotic, meaning that it target many different types of bacteria, including mrsa. It is an adequate first-line drug for skin infections, as long as no other conditions are present. In order to be 100% certain, your would need to know what organism is causing the infection by getting cultures. Do not take any prescription drugs without seeing your physician!