Role of the Murein Precursor UDP-
            <i>N</i>
            -Acetylmuramyl-
            <scp>l</scp>
            -Ala-γ-
            <scp>d</scp>
            -Glu-
            <i>meso</i>
            -Diaminopimelic Acid-
            <scp>d</scp>
            -Ala-
            <scp>d</scp>
            -Ala in Repression of β-Lactamase Induction in Cell Division Mutants

Uehara, Tsuyoshi; Park, James T.

doi:10.1128/jb.184.15.4233-4239.2002

Cited by 29 publications

(18 citation statements)

References 38 publications

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“…The consequence of this may be that although the production of the AmpR-activating molecule 1,6-anhydromuropeptide has been blocked, the disruption of PG recycling may not allow the mutant to sustain sufficient cytoplasmic concentrations of UDP-MurNAc pentapeptide to fully repress AmpR. Consistent with this view, the suppression of inducible ␤-lactamase resistance has been observed in cell division mutants that accumulate cytosolic UDP-MurNAc pentapeptide, presumably because increased amounts of the molecule outcompete the incoming anhydromuropeptide inducer and ensure the continued repression of AmpR (45). Regardless, further studies will be required to clarify the precise molecular roles of these inducer and repressor molecules.…”

Section: Discussionsupporting

confidence: 65%

Inactivation of the Glycoside Hydrolase NagZ Attenuates Antipseudomonal β-Lactam Resistance in Pseudomonas aeruginosa

Asgarali

Stubbs

Oliver

et al. 2009

Antimicrob Agents Chemother

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The overproduction of chromosomal AmpC ␤-lactamase poses a serious challenge to the successful treatment of Pseudomonas aeruginosa infections with ␤-lactam antibiotics. The induction of ampC expression by ␤-lactams is mediated by the disruption of peptidoglycan (PG) recycling and the accumulation of cytosolic 1,6-anhydro-N-acetylmuramyl peptides, catabolites of PG recycling that are generated by an N-acetyl-␤-Dglucosaminidase encoded by nagZ (PA3005). In the absence of ␤-lactams, ampC expression is repressed by three AmpD amidases encoded by ampD, ampDh2, and ampDh3, which act to degrade these 1,6-anhydro-Nacetylmuramyl peptide inducer molecules. The inactivation of ampD genes results in the stepwise upregulation of ampC expression and clinical resistance to antipseudomonal ␤-lactams due to the accumulation of the ampC inducer anhydromuropeptides. To examine the role of NagZ on AmpC-mediated ␤-lactam resistance in P. aeruginosa, we inactivated nagZ in P. aeruginosa PAO1 and in an isogenic triple ampD null mutant. We show that the inactivation of nagZ represses both the intrinsic ␤-lactam resistance (up to 4-fold) and the high antipseudomonal ␤-lactam resistance (up to 16-fold) that is associated with the loss of AmpD activity. We also demonstrate that AmpC-mediated resistance to antipseudomonal ␤-lactams can be attenuated in PAO1 and in a series of ampD null mutants using a selective small-molecule inhibitor of NagZ. Our results suggest that the blockage of NagZ activity could provide a strategy to enhance the efficacies of ␤-lactams against P. aeruginosa and other gram-negative organisms that encode inducible chromosomal ampC and to counteract the hyperinduction of ampC that occurs from the selection of ampD null mutations during ␤-lactam therapy.

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Section: Discussionsupporting

confidence: 65%

Inactivation of the Glycoside Hydrolase NagZ Attenuates Antipseudomonal β-Lactam Resistance in Pseudomonas aeruginosa

Asgarali

Stubbs

Oliver

et al. 2009

Antimicrob Agents Chemother

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“…Impairment of PBP2 activity leads to spherical cells in which peptidoglycan is largely confined to the septum (18), which may limit peptidoglycan recycling (72). Consistent with this, the evolved pbpA alleles reduce PBP2 levels while also generating spherical cells.…”

Section: Discussionsupporting

confidence: 49%

Evolution of Penicillin-Binding Protein 2 Concentration and Cell Shape during a Long-Term Experiment withEscherichia coli

et al. 2009

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Peptidoglycan is the major component of the bacterial cell wall and is involved in osmotic protection and in determining cell shape. Cell shape potentially influences many processes, including nutrient uptake as well as cell survival and growth. Peptidoglycan is a dynamic structure that changes during the growth cycle. Penicillinbinding proteins (PBPs) catalyze the final stages of peptidoglycan synthesis. Although PBPs are biochemically and physiologically well characterized, their broader effects, especially their effects on organismal fitness, are not well understood. In a long-term experiment, 12 populations of Escherichia coli having a common ancestor were allowed to evolve for more than 40,000 generations in a defined environment. We previously identified mutations in the pbpA operon in one-half of these populations; this operon encodes PBP2 and RodA proteins that are involved in cell wall elongation. In this study, we characterized the effects of two of these mutations on competitive fitness and other phenotypes. By constructing and performing competition experiments with strains that are isogenic except for the pbpA alleles, we showed that both mutations that evolved were beneficial in the environment used for the long-term experiment and that these mutations caused parallel phenotypic changes. In particular, they reduced the cellular concentration of PBP2, thereby generating spherical cells with an increased volume. In contrast to their fitness-enhancing effect in the environment where they evolved, both mutations decreased cellular resistance to osmotic stress. Moreover, one mutation reduced fitness during prolonged stationary phase. Therefore, alteration of the PBP2 concentration contributed to physiological trade-offs and ecological specialization during experimental evolution.Bacteria in nature must survive multiple stresses and repeated shifts between feast and famine conditions. When Escherichia coli experiences nutritional deprivation, its growth rate decreases sharply and the cells become more spherical and resistant to various other environmental stresses (27). Many of the morphological and physiological changes that occur during entry into "stationary" phase are associated with the cell envelope, especially the cell wall.Peptidoglycan is the major component of the bacterial cell wall, and it affects osmotic stability and cell shape (78). Many of the final steps of peptidoglycan synthesis are catalyzed in the periplasm by the penicillin-binding proteins (PBPs) (40, 82). These enzymes are named for their binding to ␤-lactam antibiotics that inhibit cell wall biosynthesis. Twelve PBPs have been identified so far in E. coli, and they are classified as high-molecular-weight (HMW) and low-molecular-weight (LMW) PBPs. The HMW PBPs assemble both the glycan chain and the peptide cross-links of peptidoglycan and are further divided into class A PBPs (PBP1a, PBP1b, and PBP1c), which are bifunctional enzymes that perform both transglycosylation and transpeptidation functions, and class B PBPs (PBP2 and PBP...

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“…In an Escherichia coli mpl mutant, a 1.7-fold decrease in the level of the UDP-MurNAc-pentapeptide pool was observed compared to the wild type (23). In Citrobacter freundii, in vitro transcription assays demonstrated that this murein precursor acts as a repressing ligand for AmpR (57). It has been suggested that a similar situation might occur in P. aeruginosa (32,40).…”

Section: Resultsmentioning

confidence: 86%

Genetic Determinants Involved in the Susceptibility of Pseudomonas aeruginosa to β-Lactam Antibiotics

Álvarez-Ortega

Wiegand

Olivares

et al. 2010

Antimicrob Agents Chemother

159

138

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The resistome of P. aeruginosa for three ␤-lactam antibiotics, namely, ceftazidime, imipenem, and meropenem, was deciphered by screening a comprehensive PA14 mutant library for mutants with increased or reduced susceptibility to these antimicrobials. Confirmation of the phenotypes of all selected mutants was performed by Etest. Of the total of 78 confirmed mutants, 41 demonstrated a reduced susceptibility phenotype and 37 a supersusceptibility (i.e., altered intrinsic resistance) phenotype, with 6 mutants demonstrating a mixed phenotype, depending on the antibiotic. Only three mutants demonstrated reduced (PA0908) or increased (glnK and ftsK) susceptibility to all three antibiotics. Overall, the mutant profiles of susceptibility suggested distinct mechanisms of action and resistance for the three antibiotics despite their similar structures. More detailed analysis indicated important roles for novel and known ␤-lactamase regulatory genes, for genes with likely involvement in barrier function, and for a range of regulators of alginate biosynthesis.Pseudomonas aeruginosa is an important opportunistic pathogen and a leading cause of nosocomial infections (32,41) and is the major cause of morbidity and mortality among individuals affected by cystic fibrosis (CF) (33). Infections caused by this opportunistic pathogen are difficult to eradicate due to its high intrinsic resistance to different classes of antibiotics. Treatment of patients is further complicated by the emergence of multidrug resistance arising principally from mutations, but also through acquisition of plasmids with antibiotic resistance determinants (32, 41).␤-Lactam antibiotics are among the main antibiotics currently used in anti-pseudomonal therapy (18,56). The killing mechanism of ␤-lactams is initiated by binding to cell wall transpeptidases (penicillin-binding proteins [PBPs]), thus blocking an important step in peptidoglycan biosynthesis (59). This family of antibiotics includes penicillins, cephalosporins, monobactams, and carbapenems. Resistance to ␤-lactams commonly results from drug inactivation by ␤-lactamases, drug extrusion through efflux pumps, changes in outer membrane permeability, and modification of PBPs (46). However, recent publications have demonstrated that a myriad of genetic determinants modulate susceptibility to antibiotics, aside from those responsible for typical antibiotic resistance mechanisms, like the ones described above (8,16,19,52), especially when one considers mutations causing modest changes in the MIC (e.g., 2-fold). Furthermore, ␤-lactam antibiotics are known to affect global gene expression, suggesting that the response to these drugs entails many different genes (1, 6).To identify novel genetic determinants involved in susceptibility to ␤-lactams, we screened a comprehensive P. aeruginosa mutant library (31) for changes in the MICs of imipenem and meropenem (carbapenems) and ceftazidime (a cephalosporin). Our findings demonstrated that mutations in a broad array of genes belonging to different functional fami...

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Role of the Murein Precursor UDP- N -Acetylmuramyl- l -Ala-γ- d -Glu- meso -Diaminopimelic Acid- d -Ala- d -Ala in Repression of β-Lactamase Induction in Cell Division Mutants

Cited by 29 publications

References 38 publications

Inactivation of the Glycoside Hydrolase NagZ Attenuates Antipseudomonal β-Lactam Resistance in Pseudomonas aeruginosa

Inactivation of the Glycoside Hydrolase NagZ Attenuates Antipseudomonal β-Lactam Resistance in Pseudomonas aeruginosa

Evolution of Penicillin-Binding Protein 2 Concentration and Cell Shape during a Long-Term Experiment withEscherichia coli

Genetic Determinants Involved in the Susceptibility of Pseudomonas aeruginosa to β-Lactam Antibiotics

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