OUTER-MEMBRANE PROFILES OF CLONALLY RELATED KLEBSIELLA-PNEUMONIAE ISOLATES FROM CLINICAL-SAMPLES AND ACTIVITIES OF CEPHALOSPORINS AND CARBAPENEMS

Fifteen isolates of Klebsiella pneumoniae producing extended-spectrum beta-lactamases (ESBLs) isolated during a nosocomial outbreak were stu died. The strains belonged to the same clonal type, as shown by pulsed -field gel electrophoretic analysis of chromosomal DNA. All the isolat es were resistant to extended-spectrum cephalosporins, aztreonam, gent amicin, and fluoroquinolones and mere susceptible to carbapenems, tobr amycin, netilmicin, and amikacin, None of the isolates expressed the O mpK36 porin, Eight isolates, for which the MICs of cefoxitin were grea ter than or equal to 64 mu g/ml, showed a diminished level or no expre ssion of a 35-kDa porin, The MICs of meropenem, cefotaxime, and cefpir ome mere three to eight times higher for porin-deficient isolates than for isolates expressing the 35-kDa porin, but the MICs of imipenem in creased two times for porin-deficient isolates compared to those for i solates expressing the porin, This MIC increase reverted to a level si milar to that for the parental strain when porin-deficient isolates we re transformed with the gene coding for the K. pneumoniae porin OmpK36 , It is concluded that the high level of resistance to cefoxitin and t he increase in the MICs of meropenem, cefotaxime, and cefpirome for th e ESBL-producing K. pneumoniae isolates studied are associated with po rin deficiency.