Antibacterial compounds of the formula ##STR1## in which R.sub.1 is a cyclic or secondary acyclic amino group which independently has antibacterial activity;R.sub.2 is hydrogen, lower alkoxy, lower alkylthio or formamido;R.sub.3 is hydrogen or an organic group bonded through carbon, oxygen, sulfur or nitrogen;R.sub.4 is an electronegative acidic group; or R.sub.3 and R.sub.4 together form a heterocycle; andR.sub.5 is hydrogen or lower alkyl, except when R.sub.3 and R.sub.4 form a heterocycle, in which case R.sub.5 is hydrogen only; and methods of using same.