A compound of formula I wherein M is one of the groups M A , M B and M C represented below and either R 1 represents H and, when M is M A , R 2 represents SO 3 H, phosphonooxymethyl or the group L 2A represented below wherein R 2A represents (C 1 -C 4 )alkylamino(C 1 -C 4 )alkyl, [di(C 2 -C 4 )alkylamino]methyl, {(methyl)[(C 2 -C 4 )alkyl]amino}methyl, [di(C 1 -C 4 )alkylamino](C 2 -C 4 )alkyl, morpholin-4-yl-(C 1 -C 4 )alkyl, phosphonooxy(C 1 -C 4 )alkyl, 2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4 )alkyl or [2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl]-(C 1 -C 4 )alkyl, or, when M is M B or M C , R 2 represents PO 3 H 2 , SO 3 H, phosphonooxymethyl or the group L 2BC represented below wherein R 2BC represents (C 1 -C 4 )alkylamino(C 1 -C 4 )alkyl, [di(C 1 -C 4 )alkylamino](C 1 -C 4 )alkyl, morpholin-4-yl-(C 1 -C 4 )alkyl, phosphonooxy(C 1 -C 4 )alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4 )alkyl or [2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl]-(C 1 -C 4 )alkyl, or R 2 represents H and R 1 represents PO 3 H 2 , SO 3 H, phosphonooxymethyl or the group L 1 represented below wherein R 1A represents (C 1 -C 4 )alkylamino(C 1 -C 4 )alkyl, [di(C 1 -C 4 )alkylamino](C 1 -C 4 )alkyl, morpholin-4-yl-(C 1 -C 4 )alkyl, phosphonooxy(C 1 -C 4 )alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4 )alkyl or [2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl]-(C 1 -C 4 )alkyl; it being understood that the molecule is always such that its R 2 group is attached to the oxygen atom of its M A , M B and M C group; or a salt of this compound. M is one of the groups M A , M B and M C represented below and either R 1 represents H and, when M is M A , R 2 represents SO 3 H, phosphonooxymethyl or the group L 2A represented below wherein R 2A represents (C 1 -C 4 )alkylamino(C 1 -C 4 )alkyl, [di(C 2 -C 4 )alkylamino]methyl, {(methyl)[(C 2 -C 4 )alkyl]amino}methyl, [di(C 1 -C 4 )alkylamino](C 2 -C 4 )alkyl, morpholin-4-yl-(C 1 -C 4 )alkyl, phosphonooxy(C 1 -C 4 )alkyl, 2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4 )alkyl or [2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl]-(C 1 -C 4 )alkyl, or, when M is M B or M C , R 2 represents PO 3 H 2 , SO 3 H, phosphonooxymethyl or the group L 2BC represented below wherein R 2BC represents (C 1 -C 4 )alkylamino(C 1 -C 4 )alkyl, [di(C 1 -C 4 )alkylamino](C 1 -C 4 )alkyl, morpholin-4-yl-(C 1 -C 4 )alkyl, phosphonooxy(C 1 -C 4 )alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4 )alkyl or [2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl]-(C 1 -C 4 )alkyl, or R 2 represents H and R 1 represents PO 3 H 2 , SO 3 H, phosphonooxymethyl or the group L 1 represented below wherein R 1A represents (C 1 -C 4 )alkylamino(C 1 -C 4 )alkyl, [di(C 1 -C 4 )alkylamino](C 1 -C 4 )alkyl, morpholin-4-yl-(C 1 -C 4 )alkyl, phosphonooxy(C 1 -C 4 )alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4 )alkyl or [2-(phosphonooxy-(C 1 -C 4 )alkyl)-phenyl]-(C 1 -C 4 )alkyl; it being understood that the molecule is always such that its R 2 group is attached to the oxygen atom of its M A , M B and M C group; or a salt of this compound. <EOS>