Multiply resistant mutants of Enterobacter cloacae selected by beta-lactam antibiotics

Then, R L; Angehrn, Peter

doi:10.1128/aac.30.5.684

Cited by 29 publications

(20 citation statements)

References 24 publications

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“…These results may seem unexpected because other researchers previously reported that the MIC of imipenem either did not change (1,4,6,30) or increased only slightly (25) in porin-deficient mutants of enteric bacteria. However, in contrast to our strains, all of the strains used in these earlier studies produced 3-lactamase at much lower levels: the activities measured by using 0.…”

Section: Resultscontrasting

confidence: 48%

Imipenem- and meropenem-resistant mutants of Enterobacter cloacae and Proteus rettgeri lack porins

Raimondi

Traverso

Nikaido

1991

Antimicrob Agents Chemother

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Carbapenems such as imipenem and meropenem are not rapidly hydrolyzed by commonly occurring Plactamases. Nevertheless, it was possible, by mutagenesis and selection, to isolate mutant strains of Enterobacter cloacae and Proteus rettgeri that are highly resistant to meropenem and imipenem. Two alterations were noted in the E. cloacae mutants. First, the mutant strains appeared to be strongly derepressed in the production of I8-lactamases, which reached a very high level when the strains were grown in the presence of imipenein. Second, these mutants were deficient in the production of nonspecific porins, as judged by the pattern of outer membrane proteins as well as by reconstitution assays of permeability. As with most porindeficient mutants, their cultures were unstable, and their cultivation in the absence of carbapenems rapidly led to an overgrowth of porin-producing revertants. Analysis of the data suggests that the synergism between the lowered outer membrane permeability and the slow but significant hydrolysis of carbapenems by the overproduced enzymes can explain the resistance phenotypes quantitatively, although the possibility of alteration of the target cannot be excluded at present. With P. reffgeri mutants, there was no indication of further derepression of j8-lactamase, but the enzyme hydrolyzed imipenem much more efficiently than the E. cloacae enzyme did. In addition, the major porin was absent in one mutant strain. These results suggest that a major factor for the carbapenem resistance of these enteric bacteria is the porin deficiency, and this conclusion forms a contrast to the situation in Pseudomonas aeruginosa, in which the most prevalent class of imipenem-resistant mutants appears to lack the specific channel protein D2 yet retains the major nonspecific porin F.

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Section: Resultscontrasting

confidence: 48%

Imipenem- and meropenem-resistant mutants of Enterobacter cloacae and Proteus rettgeri lack porins

Raimondi

Traverso

Nikaido

1991

Antimicrob Agents Chemother

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“…Various data do not favor this hypothesis. First, E. cloacae 908S (the wild-type ␤-lactamaseinducible strain) and E. cloacae 908R (the ␤-lactamase-overproducing strain) show the same level of resistance to various non-␤-lactam antibiotics such as chloramphenicol, norfloxacin, nalidixic acid, or erythromycin, and these levels are the same as those observed for Salmonella wild-type strains (24,31). Moreover, the P for benzylpenicillin, a ␤-lactam sensitive to efflux systems, is the same for E. aerogenes 006, the wild-type strain, and E. aerogenes 008-4.…”

Section: Discussionmentioning

confidence: 59%

Method for Estimation of Low Outer Membrane Permeability to β-Lactam Antibiotics

Lakaye

Dubus

Joris

et al. 2002

Antimicrob Agents Chemother

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The outer membrane of gram-negative bacteria plays a major role in ␤-lactam resistance as it slows down antibiotic entry into the periplasm and therefore acts in synergy with ␤-lactamases and efflux systems. Up to now, the quantitative estimation of low outer membrane permeability by the method of Zimmermann and Rosselet was difficult because of the secreted and cell surface-associated ␤-lactamases. The method presented here uses the acylation of a highly sensitive periplasmic penicillin-binding protein (PBP) (BlaR-CTD) to assess the rate of ␤-lactam penetration into the periplasm. The method is dedicated to measurement of low permeability and is only valid when the diffusion rate through the outer membrane is rate limiting. Cytoplasmic membrane associated PBPs do not interfere since they are acylated after the very sensitive BlaR-CTD. This method was used to measure the permeability of ␤-lactamase-deficient strains of Enterobacter cloacae and Enterobacter aerogenes to benzylpenicillin, ampicillin, carbenicillin, cefotaxime, aztreonam, and cephacetrile. Except for that of cephacetrile, the permeability coefficients were equal to or below 10 ؊7 cm/s. For cephacetrile, carbenicillin, and benzylpenicillin, the outer membrane of E. cloacae was 20 to 60 times less permeable than that of Escherichia coli, whereas for cefotaxime, aztreonam, and ampicillin it was, respectively, 400, 1,000, and 700 times less permeable. The permeability coefficient for aztreonam is the lowest ever measured (P ‫؍‬ 3.2 ؋ 10 ؊9 cm/s). Using these values, the MICs for a ␤-lactamase-overproducing strain of E. cloacae were successfully predicted, demonstrating the validity of the method.␤-Lactams are the most potent and widely used antibiotics, and many studies have been devoted to understanding how bacteria increase their resistance to these compounds. Gramnegative resistance results mainly from the interplay between four independent factors: (i) the sensitivity of the target enzymes, the penicillin-binding proteins, (ii) the properties and concentration of the periplasmic ␤-lactamases, (iii) the permeability of the outer membrane and (iv) the efficiency of the active efflux system (12, 26).On this basis, a model which allowed a quantitative prediction of the MICs for gram-negative bacteria was developed and applied with success to Escherichia coli and Enterobacter cloacae (3,5,25). However, as demonstrated by Livermore and Davy (18), this model was not applicable to Pseudomonas aeruginosa, one of the most common opportunistic pathogens. This was due to efflux pumps which also significantly contribute to intrinsic ␤-lactam resistance in P. aeruginosa (15,16,19,22). This was unexpected, because ␤-lactam targets are located outside the cytoplasmic membrane and also because in E. coli this mechanism does not produce such a high and broad level of resistance (21). Li et al., pointed out that the low outer membrane permeability of P. aeruginosa renders this efflux mechanism particularly efficient (15, 16). In fact, while the few permeability coeff...

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“…Minimum inhibitory concentrations (MIC) for antibiotics were determined by agar dilution on Mueller Hinton Agar [9].…”

Section: Methodsmentioning

confidence: 99%

N‐terminal amino acid sequence of the chromosomal dihydrofolate reductase purified from trimethoprim‐resistant Staphylococcus aureus

et al. 1988

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The existence of two distinct dihydrofolate reductases (DHFR) in highly trimethoprim-resistant clinical isolates has been unequivocally demonstrated. The enzymes have been characterized with regard to the affinity for substrates and sensitivity to inhibitors. The chromosomal, trimethoprim-sensitive DHFR was purified to homogeneity by a new simple two-step procedure. Its N-terminal amino acid sequence, determined up to the first 35 amino acids, showed 69% homology with the Escherichia coli DHFR.

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Multiply resistant mutants of Enterobacter cloacae selected by beta-lactam antibiotics

Cited by 29 publications

References 24 publications

Imipenem- and meropenem-resistant mutants of Enterobacter cloacae and Proteus rettgeri lack porins

Imipenem- and meropenem-resistant mutants of Enterobacter cloacae and Proteus rettgeri lack porins

Method for Estimation of Low Outer Membrane Permeability to β-Lactam Antibiotics

N‐terminal amino acid sequence of the chromosomal dihydrofolate reductase purified from trimethoprim‐resistant Staphylococcus aureus

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