Chlorocardicin, a monocyclic beta-lactam from a Streptomyces sp. I. Discovery, production and biological activities.

Chlorocardicin is a new monocyclic beta-lactam produced by a Streptomyces sp. It is structurally related to nocardicin A but differs in having a m-chloro substituent on the p-hydroxyphenylglycine unit. The biological activity of chlorocardicin was similar to nocardicin A but the former showed less antagonism in complex media. Moderate in vitro activity was observed against Enterobacteriaceae and Pseudomonas aeruginosa. Chlorocardicin showed low activity against Staphylococcus aureus whereas nocardicin A was inactive. Both compounds were shown to be strongly potentiated by antibiotics that inhibit peptidoglycan biosynthesis and were antagonized by selected L- and D-amino acids.