Cephalosporin derivatives of the formula: ##STR1## in which A is a single bond or a radical --CH.sub.2 --, --NH-- or --NHCO--, attached to the 3-position or 4-position of the pyridinio radical, R is a methyl, carboxymethyl, carbamoylmethyl, benzyl or allyl radical, R.sub.a, R.sub.b and R.sub.c are hydrogen atoms, or alternatively R.sub.a is carboxyl and R.sub.b and R.sub.c, which are identical or different, are hydrogen atoms or alkyl radicals, or together form an alkylene radical, and n equals 0 or 1, in their syn form, and also their addition salts with acids, metal salts and addition salts with nitrogen-containing bases are antibacterial agents having a broad spectrum of activity.