cephalosporin
Cephalosporins are a large, workhorse class of beta-lactam antibiotics, cousins of penicillin but built on a sturdier core. They are organized into numbered generations, each later generation broadening the range of bacteria it can hit — a bit like successive software releases that patch more weaknesses.
Like all beta-lactams, cephalosporins block cell-wall cross-linking by acylating penicillin-binding proteins, killing bacteria by leaving their wall full of holes. Their scaffold is a beta-lactam ring fused to a six-membered dihydrothiazine ring (instead of penicillin's five-membered ring), and chemists tune two side chains to dial in spectrum, stability against beta-lactamases, and pharmacokinetics.
The class began with cephalosporin C, a natural product from the fungus Acremonium (formerly Cephalosporium) — hence the fungal-scaffold origin. The honest trade-off across generations is that broader coverage often comes with more collateral disruption of beneficial bacteria and, for some agents, vulnerability to extended-spectrum beta-lactamases that newer enzymes have evolved.
Ceftriaxone, a third-generation cephalosporin, is a mainstay for serious infections like bacterial meningitis because it penetrates the cerebrospinal fluid.
Later generations trade structure for reach and stability.
Cross-reactivity of allergy between penicillins and cephalosporins is real but lower than once believed; it depends mostly on shared side chains, not the shared beta-lactam core.