Compounds of formula (IA) or (IB) have antibacterial activity: wherein W is ═CH— or ═N—; Ri and R2 are independently selected from hydrogen, fluoro and chloro, provided that Ri and R2 are not each hydrogen when W is ═CH—; n is 0 or 1; X is —O—, —S—, or —CH2—; and Q is (i) a phenyl radical, a naphthyl radical, a monocyclic carbocyclic or heteroaryl radical having 3 to 6 ring atoms, or a bicyclic heteroaryl radical having 5 to 10 ring atoms, any of which radicals being optionally substituted; or (ii) an optionally substituted C1-C6 alkyl, C2-C6 alkenyl, or C2-C6 alkynyl radical, which may optionally be interrupted by —O—, —S—, —S(O)—, —S(O2)—, —NH—, —N(CH3)—, —N(CH2CH3)—, —C—K═Oh or —C(═O)—O—.