A compound of formula (I): for use in the prevention or treatment of a bacterial infection wherein: A is either S or Se RA is selected from: wherein: each of Y1, Y2, Y3, Y4 and Y9 is independently selected from CH or N, wherein at least three of Y1, Y2, Y3, Y4 and Y9 is CH V is selected from O, CH-OR01, N-CO2-RC2 or N-RN2 one of Y5, Y6, Y7 and Y8 is selected from CH and N, and the others are CH X is selected from NH, S or O RC1 is selected from O-RO2 or NHRN1 RO1 is selected from H and C1-3 unbranched alkyl RO2 is C1-3 unbranched alkyl RN1 is selected from H and C1-3 unbranched alkyl RN2 is C1-3 unbranched alkyl RC2 is either C1-3 unbranched alkyl or C3-4 branched alkyl RC3 is selected from C1-3 unbranched alkyl and C2H4CO2H RC4 is either H or Me RC5 is either H or Me RC6 represents one or two optional methyl substituents and n is an integer from 2 to 8.
