TRANSFERABLE CLASS-C BETA-LACTAMASES IN ESCHERICHIA-COLI STRAINS ISOLATED IN GREEK HOSPITALS AND CHARACTERIZATION OF 2 ENZYME VARIANTS (LAT-3 AND LAT-4) CLOSELY-RELATED TO CITROBACTER-FREUNDII AMPC BETA-LACTAMASE

Among 2133 isolates of Escherichia coli obtained during 1996 from 10 G reek hospitals, 63 (3%) were resistant to cefoxitin. Typing by ERIC2-P CR indicated that the cefoxitin-resistant (FOXr) isolates were distinc t. beta-Lactamase studies and hybridization experiments showed that mo st strains produced beta-lactamases related to the AmpC chromosomal ce phalosporinase of Citrobacter freundii. The enzymes were encoded by si milar non-self-transmissible plasmids. The bla genes encoding two beta -lactamases (LAT-3 and LAT-4) with isoelectric points 8.9 and 9.4, res pectively, were cloned and sequenced. The deduced amino acid sequences displayed a high degree of homology (>95%) with the AmpC beta-lactama se of C. freundii. The patterns of resistance to beta-lactams of the F OXr E. coli depended on the quantity of class C enzymes and the simult aneous expression of other beta-lactamases. In a few isolates a 36 kDa outer-membrane protein, presumably a porin, was not expressed at dete ctable quantities. These isolates were resistant to cefoxitin, and the ir susceptibility to the other beta-lactams tested was not significant ly decreased.