Have 6 screws+1plate in r foot 6m post lisfranc fusion. Had both mrsa+osteomylitis in r foot. No injury but had sudden severe pain in r foot today?

See doc. Sudden pain after a step may indicate breakage of the metal or a stress reaction in one of your bones. If it cam on over a short time unassociated with walking it could be a recurrence of infection. Sometimes means nothing just breaking up of scar tissue. See your doc sooner than latter if cannot put weight on foot or persists.
Worrisome. Lots of possible reasons: post-traumatic arthritis, hardware pain/ ?Failure, incomplete fusion, re-current infection, just because? Put your brace on, get some crutches, go see your doctor.
Have it evaluate. You may need follow up x-rays to see if you have any bony or hardware issues.