Extended-Spectrum β-Lactamase Producing Strains ofEnterobacter cloacaeTransferring Resistance to Cefotaxime and Ceftazidime

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Abstract
Transferability of ceftazidime resistance and of extended-spectrum beta-lactamase (ESBL) production was recorded in three strains of Enterobacter cloacae from Frankfurt University Clinics. All three strains were resistant to rifampicin, carbenicillin, cephaloridine, cefotaxime, ceftazidime, aztreonam, imipenem and meropenem. They transferred directly determinants of resistance to carbenicillin and cephaloridine to Escherichia coli K-12 No. 185 nal+ recipient strain. All transconjugant colonies also contained determinants of resistance to cefotaxime, ceftazidime and aztreonam. In the second cycle of transfers, determinants of resistance to carbenicillin, cephaloridine, cefotaxime, ceftazidime and aztreonam were transferred en bloc to the recipient Escherichia coli K-12 No. 3110 rif+ indicating that the "transfer factor" (tra+) mediating the process of conjugational transfer had also been co-transferred. Double-disk diffusion test showed the same pattern of production of ESBLs both in original strains and in transconjugants. Transfer of cefotaxime, ceftazidime and aztreonam was accompanied by the transfer of ESBL production.