The present disclosure relates to novel &bgr；-lactam compounds of formula (I), their preparation and use. In particular, this disclosure relates to novel &bgr；-lactam compounds which are amidine substituted monobactam derivatives useful as antimicrobial agents and their preparation. The compounds are useful in treating bacterial infections. Examples of compounds that fall within the scope of formula (I) are: (2Z)-2-(2-Amino-1,3-thiazol-4-yl)-2-{ [2-(4-carbamimidoyl-3-hydroxyphenoxy)ethoxy]imino} -N-[(3S)-2,2-dimethyl-4-oxo-1-(sulfooxy)azetidin-3-yl]ethanamide； (2S,3S)-3-{ [(2Z)-2-(2-Amino-1,3-thiazol-4-yl)-2-{ [2-(4-carbamimidoyl-3-hydroxyphenoxy)-ethoxy]imino} acetyl]amino} -2-methyl-4-oxoazetidine-1-sulfonic acid and (2S,3S)-3-{ [(2Z)-2-(2-Amino-1,3-thiazol-4-yl)-2-({ 2-[(6-carbamimidoylpyridin-3-yl)oxy]ethoxy} -imino)acetyl]amino} -2-methyl-4-oxoazetidine-1-sulfonic acid
