DOES HIGH-LEVEL PRODUCTION OF SHV-TYPE PENICILLINASE CONFER RESISTANCE TO CEFTAZIDIME IN ENTEROBACTERIACEAE

We report the isolation of a clinical isolate of Klebsiella pneumoniae that showed resistance to ceftazidime (MIC: 8-mu-g/ml), susceptibility to aztreonam (MIC: 2-mu-g/ml) and cefotaxime (MIC: 0.015-mu-g/ml). A synergistic effect between clavulanic acid and ceftazidime or aztreonam against this strain was also observed. The strain hyperproduced SHV-1 penicillinase (990 U/g) which is encoded by a self-transferable plasmid of at least 150 kb. That the ceftazidime-resistance phenotype could be due to hyperproduction of SHV-1 penicillinase is supported by the study of a spontaneous ceftazidime-resistant mutant in vitro obtained from an Escherichia coli strain containing plasmid p453 encoding the SHV-1. Indeed, this mutant hyperproducing SHV-1 (2200 U/g) was resistant to ceftazidime (MIC: 16-mu-g/ml) and aztreonam (MIC: 8-mu-g/ml) but susceptible to cefotaxime (MIC: 0.03 ng/ml). Clavulanic acid showed a synergistic effect when associated with ceftazidime or aztreonam. In contrast, the hyperproduction of TEM-1 (790 U/g) did not confer a ceftazidime- and aztreonam-resistant phenotype while hyperproduction of both TEM-1 and SHV-1 increased the resistance to amoxycillin/clavulanic acid and to cephalothin.