Compounds of formula (I) and pharmaceutically acceptable salts and in-vivo hydrolysable esters thereof: ##STR1## wherein X is hydrogen or a group NHR.sup.1, wherein R.sup.1 is hydrogen or an amino protecting group, and R is an optionally substituted 5-membered or 6-membered saturated heterocyclic group containing 1 or 2 heteroatoms selected from oxygen, sulphur or nitrogen, are useful in the treatment of bacterial infections in humans and animals.