Compounds of formula ##STR1## wherein R is hydrogen atom or C.sub.1 -C.sub.4 alkyl group optionally substituted from halogen atom or hydroxy group optionally protected, A is a Z, Z--O--C--O-- or Z--C)-- residue, wherein Z is phenylene, naphthylene, heterocyclediyl, C.sub.1 -C.sub.7 alkylene, C.sub.2 -C.sub.4 alkenylene, alkynylene, ##STR2## C.sub.3 -C.sub.8 cycloalkylene, aralkylene radical optionally substituted, and O.sup.(+) represents a group +NR.sub.1 R.sub.2 R.sub.3, wherein R.sub.1, R.sub.2 and R.sub.3 are each either:(i) a optionally substituted alkyl, aralkyl or aryl radical or(ii) R.sub.1 is as defined above under (i) and R.sub.2 and R.sub.3, taken together, represent an optionally substituted or fused heterocyclic radical, or(iii) R.sub.1, R.sub.2 and R.sub.3, taken together, represent an optionally substituted azonia-bicyclo or tricyclo radical, or(iv) R.sub.1, R.sub.2 and R.sub.3, taken together, represent an optionally substituted or fused pyridinium, pyrazinium, pyrazolium or pyridazinium radical, and the pharmaceutically or veterinarily acceptable salts thereof, are disclosed.A method of preparation is also provided. The compounds show high antibacterial activity.