cephalosporin ARO:0000032 antibiotic_resistance Cephalosporins are a class of beta-lactam antibiotics, containing the beta-lactam ring fused with a dihydrothiazolidine ring. Together with cephamycins they belong to a sub-group called cephems. Cephalosporin are bactericidal, and act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls. The peptidoglycan layer is important for cell wall structural integrity, especially in Gram-positive organisms. beta-lactam antibiotic