Chromosomal  -lactamase expression and antibiotic resistance in Enterobacter cloacae

Abstract

Summary. The activities of P-lactam antibiotics were compared against Enterobacter cloacae clinical isolates and mutants which had inducible, stably-derepressed, and basal expression of a PI 8.4 subtype of the Ia chromosomal P-lactamase. These activities were correlated with the results of studies of the P-lactamase-lability and /?-lactamase-inducer-power of the antibiotics. Cefoxitin and ampicillin were labile, and induced p-lactamase production strongly at concentrations below their MIC values. Consequently, /?-lactamase-inducible and p-lactamase-stably-derepressed organisms were highly resistant (MIC > 256 mg/L) to these antibiotics, whereas enzyme-basal strains and mutants were much more susceptible (MIC 1-16 mg/L). Imipenem also induced p-lactamase production strongly at concentrations below its MIC, but was more stable than ampicillin and cefoxitin. It was active against enzyme-inducible and stably-derepressed organisms at 0-25-0.5 mg/L and against P-lactamase-basal organisms at 0.06-0-25 mg/L. Thus the P-lactamase afforded only very low-level protection against imipenem ; this appeared to be by a non-hydrolytic mechanism, with the enzyme binding to the antibiotic in a relatively stable complex. This complex, which probably was an intermediate in a hydrolytic pathway, was isolated by gelfiltration chromatography and shown to have a breakdown half-life of 47 f 2 min. Cefotaxime, ceftriaxone and mezlocillin were labile to the PI 8.4 P-lactamase but induced p-lactamase production weakly at concentrations below their MIC values. Consequently, P-lactamase-inducible and P-lactamase-basal organisms remained equally susceptible (MIC 0.06-4 mg/L), but stably-derepressed organisms were considerably more resistant (MIC > 64 mg/L) to these antibiotics.

Biochemical-Genetic Characterization and Regulation of Expression of an ACC-1-Like Chromosome-Borne Cephalosporinase from Hafnia alvei

“…Interestingly, its hydrolysis activity was also noticeable against extended-spectrum cephalosporins, mostly against cefpirome (Table 4). Similar activity is not known for any chromosome-or plasmid-borne cephalosporinases (1,10,38,47), and cefpirome hydrolysis activity had not been tested for ACC-1 (6). This result contrasts with the well-accepted knowledge of resistance of cefpirome to hydrolysis by class C enzymes even when they are overproduced (9).…”

“…␤-Lactamase basal level determination and induction assays were performed as described before (40,47) with H. alvei 1, H. alvei 1 DER, H. alvei 1 DER (pNH5), and E. coli MC4100 harboring recombinant plasmids (see Results and Discussion). Induction of ␤-lactamase content was performed for H. alvei cultures and E. coli cultures with imipenem (0.5 g/ml) and cefoxitin (5 g/ml), respectively.…”

“…The inducible biosynthesis of a naturally occurring Bush group 1 ␤-lactamase (Ambler class C [2]) has been reported phenotypically for several enterobacterial species, including Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, Morganella morganii, Providencia stuartii, Serratia marcescens, Yersinia enterocolitica, and H. alvei (10,40,43,44,47). The presence of cephalosporinase in H. alvei may explain its natural phenotype of resistance to aminopenicillins and restrictedspectrum cephalosporins (44).…”

Chromosomal beta-lactamase expression and resistance to beta-lactam antibiotics in Proteus vulgaris and Morganella morganii

“…1-Lactamase production characteristics of the organisms studied in detail, and of mutants derived from them, are listed in Table 1. Stably derepressed mutants were selected from inducible strains on Diagnostic Sensitivity Test agar (Oxoid Ltd., Basingstoke, Hants, United Kingdom) containing cefotaxime (1 or 4 ,ug/ml) by the procedure described previously (24). 1-Lactamase basal mutants (those with low-level uninducible 13-lactamase expression) were derived from the stably derepressed organisms by mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (2 P-Lactamase induction assays.…”

“…1-Lactamase basal mutants (those with low-level uninducible 13-lactamase expression) were derived from the stably derepressed organisms by mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (2 P-Lactamase induction assays. Induction assays were performed by exposure of logarithmic-phase cells to antibiotics in Iso-Sensitest broth (Oxoid) for 4 h, as described previously (24). After induction, the cells were harvested and washed by centrifugation at 5,000 x g and 30°C and then sonicated on ice.…”