Approximately 10% (89 isolates) of Klebsiella pneumoniae isolated in 1985 from patients in intensive care units in Clermont-Ferrand exhibited a complex resistance phenotype towards antibiotics. They were resistant to amino-, carboxy- and ureidopenicillins, aminoglycosides (except gentamicin), chloramphenicol, sulphonamides, tetracyclines and, most importantly, to cephalosporins (except cefoxitin and latamoxef) and to aztreonam. The metabolic profile of fifty isolates was identical and seven were selected for further study. All the resistance characters in these isolates were transferable to Escherichia coli by conjugation and were lost en bloc after treatment with ethidium bromide. Agarose gel electrophoresis of crude lysates of the wild types and their transconjugants indicated that the multiple resistances were mediated by a 95kb plasmid, pCF04. The seven isolates selected for study and their corresponding transconjugants, constitutively produced a plasmid-mediated beta-lactamase with a pI of 6.3 that was much more active against third-generation cephalosporins than against cephalothin. The substrate profile and the isoelectric-focusing behaviour of this enzyme differed from those of other known plasmid-mediated beta-lactamases, and the enzyme was designated CTX-1. A chromosomally-encoded SHV-1 (PIT-2) penicillinase (pI 7.7) was also present in the seven K. pneumoniae isolates but did not transfer. Resistance to aminoglycosides in the K. pneumoniae isolates was due to synthesis of a 6'-aminoglycoside acetyltransferase type IV. Our data indicate an epidemic of antibiotic multiply-resistant strains of K. pneumoniae producing a new beta-lactamase.

Five plasmid-mediated P-lactamases conferring high-level resistance to ceftazidime were isolated from Klebsiellapneumoniae strains in the same hospital. These enzymes had isoelectric points ranging from 5.3 to 6.5 5.55; 6.0; 5.3; 6.5; 6.3). All isolates and their Escherichia coli transconjugants were highly resistant to amoxicillin (MICs, >4,096 ,ug/ml), piperacillin (64 to 256 ,ug/ml), cephalothin (32 to 256 ,ug/ml), and ceftazidime (32 to 512 ,ig/ml) but remained moderately susceptible to cefotaxime (0.5 to 8 ,ug/ml). Only CAZ-6-and CAZ-7-producing strains were highly resistant to aztreonam (64 to 128 ,ug/ml). All the isolates remained susceptible to moxalactam and imipenem. The reduced activity of piperacillin, cefotaxime, ceftazidime, or aztreonam was restored by 2 ,ug of clavulanate, sulbactam, tazobactam, or brobactam per ml for E. coli producing CAZ-2, CAZ-3, and CAZ-7. Sulbactam had a lower protective effect than other inhibitors for E. coli harboring CAZ-1 and especially CAZ-6. Except for CAZ-1, which was mediated by a 150-kilobase (kb) plasmid (pCFF14), the other ceftazidimases were mediated by plasmids of 85 kb with EcoRI digestion patterns similar to that of pCFF04 encoding CTX-1 ,B-lactamase. A TEM probe hybridized with a 19-kb EcoRI fragment of all these closely related plasmids.Since the outbreak of infections caused by CTX-1-producing Klebsiella pneumoniae and other species of the family Enterobacteriaceae (17, 18), we have observed in the same hospital the advent of several novel extended-spectrum ,B-lactamases in K. pneumoniae isolates. These isolates were markedly more resistant to ceftazidime than to cefotaxime. On the basis of this resistance phenotype, we designated these ,-lactamases ceftazidimases (CAZ).Since the original CAZ-1 (16)-and CAZ-2 (7)-producing strains were isolated in January and July 1987, respectively, three other extended-spectrum ,B-lactamases were identified at the end of 1987: CAZ-3,

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