Disclosed are novel carbapenem derivatives characterized by a 2-substituent of the formula ##STR1## in which A represents cyclopentylene, cyclohexylene or C.sub.2 -C.sub.6 alkylene optionally substituted by one or more C.sub.1 -C.sub.4 alkyl groups; R.sup.5 represents either (a) an optionally substituted aliphatic, cycloaliphatic, cycloaliphatic-aliphatic, aryl, araliphatic, heteroaryl, heteroaraliphatic, heterocyclyl or heterocyclyl-aliphatic radical or (b) a divalent phenylene or C.sub.1 -C.sub.4 alkylene group joined to the ##STR2## ring so as to form a bridged polycyclic group; and ##STR3## represents a quaternized nitrogen-containing non-aromatic heterocycle. Such derivatives are useful as potent antibacterial agents.