Highly targeted screening system for carbapenem antibiotics.

An improved screening system in a search for carbapenem antibiotics from actinomycetes was developed, involving (1) effective isolation of carbapenem antibiotic producers, (2) favorable cultivation as to antibiotic production and (3) simplified identification of the carbapenem antibiotics: (1) A frequency of isolation of carbapenem antibiotic producers from soils was increased by the use of an amoxicillin/clavulanate-containing medium. As many as 20% of the actinomycetes isolated in this medium were found to be carbapenem antibiotic producers, as compared with 0.6% when conventional media were employed. (2) An agar-surface cultivation on oatmeal - yeast extract - malt extract (OMYM) medium, containing oatmeal, yeast extract, malt extract, glucose and trace elements, was most suitable for the antibiotic production. (3) An agar-diffusion assay for identification of carbapenem antibiotics was developed. Although the carbapenem antibiotics are stable against beta-lactamases, they were hydrolyzed completely with excess amounts of common beta-lactamases. So they could be discriminated from other beta-lactam antibiotics and non-beta-lactam antibiotics by comparison of the susceptibility profiles for such enzymes.