Outer membrane permeability and beta-lactamase stability of dipolar ionic cephalosporins containing methoxyimino substituents

Abstract

Some enteric bacteria, such as Enterobacter cloacae, can develop high-level resistance to broad-spectrum cephalosporins by overproducing their chromosomally encoded type I P-lactamases. This is because these agents are hydrolyzed rapidly at pharmacologically relevant, low (0.1 to 1 ,uM), concentrations, owing to their high affinity for type I enzymes. In contrast, the more recently developed cephalosporins, with quaternarynitrogen-containing substituents at the 3 position, show increased efficacy against ,I-lactamase-overproducing strains and, indeed, have a much lower affinity for type I enzymes. However, the possible contribution of an improved outer membrane permeability in their increased efficacy has not been studied. We found by proteoliposome swelling assays that cefepime, cefpirome, and E-1040 all penetrated the porin channels of Escherichia coli and E. cloacae much more rapidly than did ceftazidime and at least as rapidly as did cefotaxime. Considering that the influx of anionic compounds such as cefotaxime and ceftazidime will be further retarded in intact cells, owing to the Donnan potential, we expect that the newer compounds will penetrate intact cells 2 to 10 times more rapidly than will cefotaxime and ceftazidime. The kinetic parameters of hydrolysis of these agents by E. cloacae P-lactamase showed that at 0.1 ,M, they were hydrolyzed much more slowly than was cefotaxime and at about the same rate as or a lower rate than was ceftazidime. The combination of these two effects explains nearly quantitatively why these newer agents are more effective against some of the 3-lactamase-overproducing gram-negative bacteria.Conventional assays showed that many of the more recently developed cephalosporins, such as cefoxitin, cefuroxime, and the broad-spectrum cephalosporins, including cefotaxime and ceftazidime, were totally resistant to hydrolysis by commonly encountered ,-lactamases, including the type I or class C chromosomally encoded P-lactamases of members of the family Enterobacteriaceae (for an example, see reference 18). Nevertheless, the widespread use of these agents was followed by the emergence of resistant mutant strains of organisms such as Enterobacter cloacae, Serratia marcescens, and Pseudomonas aeruginosa which constitutively produced high levels of type I ,-lactamases (15). This puzzling finding led to the proposal that the resistance was due to nonhydrolytic substrate binding by ,-lactamase molecules (15,20,21,24).Vu and Nikaido (22) concluded, however, from quantitative considerations of outer membrane permeability and the number of P-lactamase molecules present in the cell, that such a nonhydrolytic trapping mechanism cannot explain the high level of resistance found in E. cloacae strains overproducing the type I P-lactamase. Furthermore, Livermore (8) and Vu and Nikaido (22) pointed out that conventional P-lactam hydrolysis assays with very high (0

Effects of Inoculum and β-Lactamase Activity in AmpC- and Extended-Spectrum β-Lactamase (ESBL)-Producing Escherichia coli and Klebsiella pneumoniae Clinical Isolates Tested by Using NCCLS ESBL Methodology

“…In general, cefepime had lower MICs than ceftazidime, cefotaxime, and cefpodoxime, but similar k cat values were observed for the extended-spectrum ␤-lactams. This may be due to increased permeability of cefepime into members of the family Enterobacteriaceae (17). However, inoculum effects in ESBL-producing Klebsiella spp.…”

β-Lactams and β-Lactamase Inhibitors: An Overview

“…These agents have diminished activity against staphylococci and enterococci compared to earlier cephalosporins, but have more potent activity against Gram-negative organisms. Cefepime tends to have lower MICs against enteric bacteria than the other expanded-spectrum cephalosporins, attributed to greater penetration through the OmpF outermembrane porin protein (Nikaido et al 1990;Bellido et al 1991). Cefotaxime and ceftriaxone are often used to treat susceptible streptococcal infections; all can be used to treat serious infections caused by enteric bacteria if the organisms test susceptible.…”

Molecular, Antigenic, and Functional Analyses of Omp2b Porin Size Variants of Brucella spp

“…They create a controlled permeability of the outer membrane toward small hydrophilic solutes such as sugars that are otherwise not allowed to diffuse through the outer membrane (for a review, see references 21, 22, and 24). In a sense, porins are the Achilles' heel of this protective barrier, since they can act as receptors for bacteriophage and colicins (13), surface-exposed antigens (37), complement-binding sites (29), and the gate of entry for some antibiotics (27,28). In some pathogenic bacteria, such as Neisseria gonorrhoeae, porin sequence variations between serotypes are well described and probably allow successive infection by different serotypes presenting different surface-exposed epitopes (20).…”