NEW MATERIAL:The compound of formula I [R1 is acyl; R2 is (esterified) carboxyl; R3 is H, lower alkyl or cyano; R4 is H or lower alkyl; R3 and R4 may together form a 2-3C methylene chain; R5 is H or lower alkyl; A is bivalent (substituted) aromatic heterocyclic group bonded to the adjacent S through C; Y is bond, S, O, NH, CONH or NHCO; Z is bond or NH; m is 0-4; n is 0-6].

EXAMPLE: 3-[(2-Amidinomethylthio-1,3,4-thiadiazol-5-yl)thiomethyl]-7β-[2-(2- aminothiazol-4-yl)-(Z)-2-hydroxyiminoacetamido]-3-cephem-4-carboxylic acid.

USE: An antibacterial agent against Gram-positive bacteria and Gram-negative bacteria.

PREPARATION: A compound of formula II (R11 is OH, acyloxy or halogen) or its salt is made to react with a compound of formula III.