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

The overproduction of chromosomal AmpC β-lactamase poses a serious challenge to the successful treatment of Pseudomonas aeruginosa infections with β-lactam antibiotics. The induction of ampC expression by β-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-β-d-glucosaminidase encoded by nagZ (PA3005). In the absence of β-lactams, ampC expression is repressed by three AmpD amidases encoded by ampD, ampDh2, and ampDh3, which act to degrade these 1,6-anhydro-N-acetylmuramyl peptide inducer molecules. The inactivation of ampD genes results in the stepwise upregulation of ampC expression and clinical resistance to antipseudomonal β-lactams due to the accumulation of the ampC inducer anhydromuropeptides. To examine the role of NagZ on AmpC-mediated β-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 β-lactam resistance (up to 4-fold) and the high antipseudomonal β-lactam resistance (up to 16-fold) that is associated with the loss of AmpD activity. We also demonstrate that AmpC-mediated resistance to antipseudomonal β-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 β-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 β-lactam therapy

Smoke exposure, airway symptoms and exhaled nitric oxide in infants: The Generation R study

The effect of pre- and post-natal smoke exposure on exhaled nitric oxide fraction (FeNO) in infants was evaluated and the association between respiratory symptoms and FeNO in the first 2 months of life was investigated. The Generation R study is a population-based, prenatally recruited birth cohort. Exposures were assessed by means of questionnaires prospectively administered during pregnancy and after birth. Successful off-line FeNO measurements during tidal breathing were obtained in 187 infants (median age 6.9 weeks). The association between possible determinants and log FeNO was investigated with multiple linear regression analysis. Infants exposed pre- and post-natally to smoke showed lower FeNO than infants exposed only after birth (geometric mean difference (95% confidence interval) 1.5 (1.0-2.1) ppb) and never-exposed infants (1.4 (1.0-1.8) ppb). FeNO was reduced in infants with severe upper respiratory symptoms compared with infants with nonsevere symptoms (1.6 (1.0-2.4) ppb). Infants with symptoms of the lower respiratory tract had lower FeNO than asymptomatic infants (1.2 (1.0-1.50) ppb). In conclusion, the nature of the association between smoke exposure and exhaled nitric oxide fraction is dependent on timing and intensity of exposure. The occurrence and the severity of respiratory symptoms in the first 2 months of life are associated with lower exhaled nitric oxide fraction. Copyrigh