Antibacterial agents can be classified with regard to their structure, mechanism of action, and activity pattern against various types of bacterial pathogens. Which of the following statement(s) is/are true concerning antimicrobial classes?

a. Penicillins and cephalosporins share the compound structure of a b-lactam ring which binds to bacterial division plate proteins

b. Tetracyclines and macrolides such as erythromycin inhibit bacterial ribosomal activity and therefore protein synthesis

d. Sulfonamides and trimethoprim act synergistically to inhibit purine synthesis

Penicillins, cephalosporins, and monobactams possess a b-lactam ring of some type and act to bind bacterial division plate proteins, thus inhibiting cell wall peptidoglycan synthesis and either causing or inducing autolytic bacteriolysis. Because gram-positive and gram-negative bacteria possess different types of division plate proteins, many of these agents exhibit differential activity between these two types of microorganisms. Tetracyclines, chloramphenicol, and macrolides inhibit bacterial ribosomal activity, and thus overall protein synthesis by a variety of different mechanisms. Aminoglycosides act to inhibit protein synthesis and also presumably act on a different target site, a supposition based on the fact that aminoglycosides are bacteriolytic and the other agents are bacteriostatic. Vancomycin inhibits assembly of peptidoglycan polymers, whereas quinolones bind to DNA helicase proteins and inhibit bacterial DNA synthesis. Sulfonamides and trimethoprim act in different mechanisms to inhibit protein synthesis, therefore two agents in combination act synergistically.