Final answer:
The ß-lactam ring of penicillin derivatives is the molecular structure targeted and inactivated by ß-lactamases produced by certain bacterial strains.
Step-by-step explanation:
The part of the penicillin derivative molecular structure that is inactivated by bacterial enzymes is the ß-lactam ring. Certain bacteria produce enzymes known as ß-lactamases, which specifically cleave this ring, rendering the penicillin molecule inactive. Methicillin and other penicillin analogs were synthesized to combat strains of bacteria that produce penicillinase, by modifying the side chain to protect the ß-lactam ring from enzymatic destruction, hence providing resistance to ß-lactamase degradation.