disclosed are antibiotic cephalosporins of the formula : ## str1 ## wherein the stylized radical attached to the 7 - amino nitrogen of the cephalosporin moiety represents a nitrogen - containing heterocyclic group ; r is , inter alia , hydrogen , alkyl , heterocyclylalkyl , aryl , alkenyl , aralkyl , -- nr 2 , -- or , coor , conr 2 or cn ; a is conventionally known in the cephalosporin art ; and r 2 is h , or loweralkoxyl ; x is o , ch 2 , or nr 7 ( r 7 is , inter alia , hydrogen , alkyl or aralkyl . also disclosed are the pharmaceutically acceptable salt and ester derivatives of i ; processes for the preparation of such compounds , pharmaceutical compositions comprising such compounds ; and methods of treatment comprising administering such compounds and compositions when an antibiotic effect is indicated .