Dissemination of the novel plasmid-mediated beta-lactamase CTX-1, which confers resistance to broad-spectrum cephalosporins, and its inhibition by beta-lactamase inhibitors

Abstract

The novel ,B-lactamase CTX-1 (pl 6.3) encoded on a transferable 84-kilobase plasmid was found in six different bacterial species. It was responsible for a significant decrease in susceptibility towards most penicillins and cephalosporins, except imipenem, temocillin, and' cephalosporins which have a 7-a-methoxy substituent.Synergy between either ampicillin, piperacillin, cefotaxime, ceftazidime, or aztreonam and three D-lactamase inhibitors (clavulanic acid, sulbactam, and YTR 830) was generally found for different strains harboring CTX-1. This enzyme may be related to or derived from the TEM enzyme, since an intragenic probe of the TEM-1 gene hybridized with a fragment of the plasmid carrying CTX-1.Only few plasmid-mediated 1-lactamases able to hydrolyze novel broad-spectrum cephalosporins have been described in Klebsiella pneumoniae, Serratia marcescens, and Klebsiella ozaenae (5, 6). The plasmid-mediated enzyme found in K. ozaenae has been designated SHV-2 by Kliebe et al. (5) and is probably a natural derivative of SHV-1. In this study, we report some characteristics of a novel plasmidmediated P-lactamase, its spectrum of activity, and its inhibition by different ,B-lactamase inhibitors. The enzyme is referred to as CTX-1, the name of an enzyme recently found by Sirot et al. (13) in France in K. pneumoniae. MATERIALS AND METHODSBacterial strains and plasmids. Twenty-three distinct clinical isolates belonging to six bacterial species and harboring the novel plasmid-mediated ,-lactamase CTX-1 were isolated from five patients during a 3-month period in 1986 in the intensive care unit (four patients) and vascular surgery unit (one patient) at Hopital Saint-Joseph in Paris. The detection of CTX-1 was facilitated by the observation of synergy between ceftazidime and clavulanic acid (contained in Augmentin disk) on standard antibiograms. Escherichia coli BM694 (7) was used as recipient for plasmids encoding the different P-lactamases studied.' These included R6K (TEM-1), RP1 (TEM-2), and p453 (SHV-1). SHV-2 was transferred to E. coli BM694 from K. pneumoniae 2144 kindly given by H. Knothe. CTX-1 was transferred after selection on either cefotaxime (2 ,ug/ml) or amikacin (5 ,ug/ml) plus nalidixic acid (20 ,g/ml).Media and antibiotics. Cultures were grown in standard Mueller-Hinton medium broth or on Mueller-Hinton agar. Antimicrobial agents were kindly provided as follows:

Coexistence of SHV-4- and TEM-24-Producing Enterobacter aerogenes Strains before a Large Outbreak of TEM-24-Producing Strains in a French Hospital

“…Nucleotide sequence analysis showed that it differed from the SHV-1 sequence by three substitutions leading to the amino acid replacements Arg3Leu-205, Gly3Ser-238, and Glu3Lys-240 and by two silent mutations at positions 722 (T3C) and 796 (C3G) (positions are numbered in accordance with the coding sequence of SHV-1 [30]). These mutations are identical to those previously described for SHV-4 (22,26), except for the silent mutations.…”

“…The first nosocomial outbreaks caused by ESBL-producing strains occurred in 1985 in France (26,34). Klebsiella pneumoniae was the ESBL-producing enterobacterium most frequently isolated from clinical specimens, but E. aerogenes has recently emerged as an important hospital opportunist.…”

Extended-spectrum beta-lactamases

“…These kinetic constants, however, do not reveal that in terms of specific activity the extended-spectrum enzymes are less active than their parents by a factor of fivefold or more, so that an expanded substrate spectrum is attained at a cost of a reduced catalytic efficiency (20). (7,28) and subsequently has become established in Paris (15,16) (8,19,20,25), except for TEM-7 and SHV-5, for which relative rates at 100 ,uM substrate are shown (10,11). All enzymes had values of sO.1 with cefoxitin or imipenem as the substrate.…”

Long-term investigation of the clonal dissemination of Klebsiella pneumoniae isolates producing extended-spectrum -lactamases in a university hospital

“…They have been responsible for outbreaks, particularly in intensive care units and in chronic care facilities, but have occasionally spread also to medical and surgical wards [7-131. Hospital colonisation by ESBL-producing bacteria can reflect dissemination of a few clones, or the spread of plasmids and resistance genes [13][14][15][16][17][18][19][20][21], facilitated by antibiotic pressure and inadequate infection-control practice [9-10, [22][23][24]. Several outbreaks of nosocomial infections caused by ESBL-producing K. pneumoniae occurred in our hospital between 1988 and 199 1.…”