Compounds of the formula (I), or a pharmaceutically-acceptable salt, or an in-vivo-hydrolysable ester thereof, ##STR00001## and compounds as shown in (I) wherein C is for example ##STR00002## wherein A and B are independently selected from ##STR00003## R.sub.2a to R.sub.3b are independently selected from hydrogen and fluorine; R.sub.1a and R.sub.1b are independently selected from, for example, hydroxy, --NHC(.dbd.W)R.sub.4, ##STR00004## wherein W is O or S; R.sub.4 is, for example, hydrogen, amino, (1-4C)alkyl; HET-1 is, for example, a C-linked 5-membered heteroaryl ring; HET-2 is, for example, an N-linked 5-membered, fully or partially unsaturated heterocyclic ring; are useful as antibacterial agents; and processes for their manufacture and pharmaceutical compositions containing them are described.