Two new monobactam antibiotics produced by a Flexibacter sp. I. Taxonomy,fermentation,isolation and biological properties.

Two new beta-lactam antibiotics, namely SQ 28,502 and SQ 28,503, have been isolated from fermentations of a Flexibacter sp. They are demethoxy monobactams with oligopeptide side chains and have molecular weights of 1,462 and 1,446, respectively. These beta-lactams show a high degree of stability to a variety of beta-lactamases and act as potent irreversible inactivators of P99 beta-lactamase from Enterobacter cloacae. They exhibit weak antibacterial activity.