Which of these is NOT classified as a type of β-lactam antimicrobial?

The correct choice identifies glycopeptides as not being classified as a type of β-lactam antimicrobial. β-lactam antibiotics are characterized by their β-lactam ring structure, which is crucial for their mechanism of action. This structure allows them to inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins.

Penicillins, cephalosporins, and monobactams all belong to the β-lactam family due to their shared structural features and similar mechanisms of action, primarily the ability to disrupt bacterial cell wall formation.

On the other hand, glycopeptides, such as vancomycin, do not contain a β-lactam ring and work through a different mechanism. They inhibit cell wall synthesis in bacteria by binding to the D-Ala-D-Ala terminal of cell wall precursor units, preventing their incorporation into the growing cell wall. This distinct structure and mechanism clearly separates glycopeptides from β-lactam antibiotics.