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L-681,217 is a new broad spectrum antibiotic isolated from fermentation broth. The compound is a structurally unique member of the efrotomycin family of growth permittant antibiotics.

Resistant colonies develop with an apparent high frequency in zones of inhibition around fosfomycin filter discs on nutrient agar. The resistance is due, primarily, to loss of the fosfomycin transport system. The resistant colony type usually observed in the inhibition zones seldom arise directly by mutation from a cell sown in the area of the zone of inhibition. Instead, small translucent colonies develop first in the inhibition zone. Within these small translucent colonies, mutational events occur which give rise to the normal resistant type colonies.

Efrotomycin is a narrow spectrum antibiotic. Among the genera tested for susceptibility in vitro it is most active against isolates of Moraxella, Pasteurella, Yersinia, Haemophilus, Streptococcus and Corynebacterium. The drug is as active by oral administration as by the subcutaneous route. Blood levels rise rapidly to high concentrations, after oral dosing, and are prolonged. Two peaks occur which may indicate biliary excretion and reabsorption. Urinary excretion is minimal. The high blood concentrations explain, in part, the in vivo activity against pathogens such as Bordetella bronchiseptica which are relatively insensitive in vitro. Oral activity of efrotomycin is an advantage over the related antibiotics. X-5108 and mocimycin.

Heneicomycin is structurally similar to efrotomycin, mocimycin (kirromycin) and X-5108 (goldinomycin). Comparisons were limited because of the small supplies available. All antibiotics show the same in vitro antibacterial spectrum although some test cultures were less sensitive to efrotomycin. Heneicomycin compared favorably with efrotomycin when given subcutaneously or per os against infections with Moraxella bovis and Streptococcus pyogenes. The raid elimination of heneicomycin observed following oral administration may account for its poor activity against a Bordetella bronchiseptica infection where efrotomycin is effective. It appears more like X-5108 than efrotomycin biologically. The disaccharide on efrotomycin may account for the difference observed.