Penicillins and cephalosporins of the formula ##STR1## wherein A is phenyl, 4-hydroxyphenyl, cyclohexyl, cyclohene-1-yl, cyclohexa-1,4-diene-1-yl, 2-thienyl, 3-thienyl, 2-furyl, 3-furyl or 3,4-disubstituted phenyl, where the substituents, which may be identical to or different from each other, are each chlorine, hydroxyl or methoxy;R.sub.1 is an unsubstituted or substituted 5- or 6-membered heterocycle comprising carbon atoms and 1 to 4, preferably 1 to 2, identical or different heteroatoms such as oxygen, sulfur or nitrogen;n is 0 or 1;X is ##STR2## D is hydrogen, hydroxyl, acetoxy, aminocarbonyloxy, pyridinium, aminocarbonyl-pyridinium or S-Het, where Het is 1-methyl-tetrazol-5-yl, tetrazol-5-yl, 3-methyl-1,2,4-thiadiazol-5-yl, 1,2,4-triadiazol-5-yl, 1,3,4-thiadiazol-5-yl, 2-methyl-1,3,4-thiadiazol-5-yl, 2-methylamino-1,3,4-thiadiazol-5-yl, 2-dimethylamino-1,3,4-thiadiazol-5-yl, 2-formylamino-1,2,4-thiadiazol-5-yl, 2-acetylamino-1,3,4-thiadiazol-5-yl, 2-methyl-1,3,4-oxadiazol-5-yl, 1,2,3-triazol-4-yl or 1,2,4-triazol-3-yl; andE is hydrogen or a protective group which is easily removable in nitro or in vivo, especially an ester-forming group which can be removed under mild conditions by hydrogenation or hydrolysis or other treatments, or an ester-forming group which can easily be split off in the living organism;and, when E is hydrogen, their non-toxic, pharmacologically acceptable salts thereof, such as their alkali metal or alkaline earth metal salts, especially the sodium, potassium, magnesium or calcium salts; their ammonium salts; or their organic amine salts, especially the triethylamine or dicyclohexylamine salts. The compounds are useful as antibiotics.