Chromosomal beta-lactamases of Enterobacter cloacae are responsible for resistance to third-generation cephalosporins

Abstract

About 70%o of all Enterobacter cloacae strains tested possessed one of two species-specific 3-lactamases. These enzymes, E. cloacae ,B-lactamase A and E. cloacae ,-lactamase B, with isoelectric points of 8.8 and 7.8, respectively, had the same pH and temperature optima. Both showed similar enzyme kinetics and were inhibited by cloxacillin but not by p-chloromercuribenzoate. E. cloacae 3-lactamase B appeared to be identical with the enzyme of E. cloacae P99. By a mutation in a regulatory gene, inducible enzyme production could be converted into constitutive expression. In E. cloacae, both enzymes did not hydrolyze thirdgeneration cephalosporins, but they were solely responsible for resistance toward these drugs. This was demonstrated by the characterization of Escherichia coli strains expressing an identical resistance pattern after transfer of the corresponding Enterobacter gene.The importance of plasmid-coded 1-lactamases for the resistance of gram-negative bacteria to ,-lactam antibiotics is well established (6-8, 12, 17, 21, 24). In contrast, the contribution of chromosomal lactamases to resistance remains unclear. One exception is Escherichia coli mutants in which constitutive expression of the chromosomal ampC gene contributes to ampicillin resistance (2,3). Recently, however, evidence has begun to accumulate that in certain Enterobacter cloacae strains, the chromosomal ,B-lactamases may play an unexpected role (1, 13,22,23,25,28). These enzymes are typical cephalosporinases which usually can be induced by penicillins and cephalosporins (4,22,23 (25) proposed that thirdgeneration cephalosporins are not inactivated by hydrolysis but by a kind of trapping mechanism, or that other intrinsic factors (13,28) are involved in this process.In this paper we give evidence that (i) there are mainly two chromosomal ,3-lactamases in E.cloacae strains, (ii) that resistance to thirdgeneration cephalosporins arises by mutation to constitutive production of the P-lactamases, and (iii) that these P-lactamases are solely responsible for the resistance. In addition, we provide enzymatic data to characterize these enzymes.MATERIAULS AND METHODS Bacteril sra. A total of 61 cefotaxime-susceptible E. cloacae strains, isolated in 1979 from clinical specimens, were used for the epidemiological study. Five of these strains (E. cloacae 314, 352, 150, 988, and 149)

Chromosomal -lactamase expression and antibiotic resistance in Enterobacter cloacae

“…In particular, thepI 8.4 enzyme exhibited moderate k,,, (40/min) and K , (40 p~) values for cefotaxime, whereas k,,, and K , of this drug for P99 enzyme are about l/min and 1 PM respectively (Bush et al, 1982;Livermore et al, 1986). The PI 8.4 enzyme also differed from the E-2 form of Ia enzyme described by Seeberg et al (1983) and Bush et al (1985), both in its kinetics of activity against cefotaxime, wherein E-2 resembled P99 enzyme, and in the stability of its imipenem complex. Bush et al (1985) reported a half-life of only 0.8 min for the E-2 enzyme-imipenem complex ; considerably less than that observed here for the PI 8.4 enzyme.…”

Gene Mutations Responsible for Overexpression of AmpC β-Lactamase in Some Clinical Isolates ofEnterobacter cloacae

“…The resistance of these bacteria is principally due to constitutive overexpression of chromosomal ampC (which encodes AmpC, a class C ␤-lactamase) (5,33). The ampC gene is located on the chromosome of many gram-negative bacilli and is inducible in the presence of ␤-lactam antibiotics (9).…”

Comparative activity of the penem antibiotic Sch 34343 against Gram-negative and Gram-positive bacteria with special reference to multiresistant strains

“…MICs were not (or only by one dilution) elevated against Citrobacter and Enterobacter strains, highly resistant to third-generation cephalosporins. This behaviour reflects the extreme stability of the drug to /Mactamases, since it has been shown that cephalosporin resistance in such strains is due to chromosomal cephalosporinase (Sanders & Sanders 1983, Seeberg et al, 1983. Sch 34343, thus, together with imipenem, can be considered as potent chemotherapeutic agents in infections caused by Enterobacteriaceae resistant to third-generation cephalosporins and to aztreonam.…”

“…Recent reports have shown that Enterobacteriaceae can become resistant to thirdgeneration cephalosporins by mutation in a chromosomal locus, regulating the production of a cephalosporinase (Seeberg, Tolxdorff-Neutzling & Wiedemann, 1983). The frequency of resistant mutants of this type in clinical isolates is still low (Kayser & Kohler, 1984).…”