The lack of new antibiotics is among the most critical challenges facing medicine. The problem is particularly acute for Gram-negative bacteria. A novel antibiotic strategy is to target bacterial nutrition and metabolism. The metal gallium can disrupt bacterial iron metabolism as gallium can be taken up by bacteria, and replace iron. Here we performed pre-clinical work and a phase 1 human trial to investigate the antibiotic activity of gallium in people with cystic fibrosis (CF) and chronic Pseudomonas aeruginosa airway infections. We found that CF sputum was iron-limited, and that low micromolar concentrations of gallium inhibited P. aeruginosa growth in CF sputum. Ex vivo experiments indicated that gallium inhibited key iron-dependent enzymes, and increased bacterial sensitivity to oxidants. We also found that gallium resistance developed at low rates, its activity was synergistic with some antibiotics, and it did not affect P. aeruginosa killing by human macrophages. Finally, we tested parenteral gallium in murine lung infections, and in CF patients with chronic P. aeruginosa lung infections and found indications of safety and efficacy. These data represent a small step toward targeting iron metabolism, or other nutritional vulnerabilities of bacteria, to treat human infections.

While much attention has been focused on acquired antibiotic resistance genes, chromosomal mutations may be most important in chronic infections where isolated, persistently infecting lineages experience repeated antibiotic exposure. Here, we used experimental evolution and whole-genome sequencing to investigate chromosomally encoded mutations causing aztreonam resistance in Pseudomonas aeruginosa and characterized the secondary consequences of resistance development. We identified 19 recurrently mutated genes associated with aztreonam resistance. The most frequently observed mutations affected negative transcriptional regulators of the mexAB-oprM efflux system and the target of aztreonam, ftsI. While individual mutations conferred modest resistance gains, high-level resistance (1,024 µg/ml) was achieved through the accumulation of multiple variants. Despite being largely stable when strains were passaged in the absence of antibiotics, aztreonam resistance was associated with decreased in vitro growth rates, indicating an associated fitness cost. In some instances, evolved aztreonam-resistant strains exhibited increased resistance to structurally unrelated antipseudomonal antibiotics. Surprisingly, strains carrying evolved mutations which affected negative regulators of mexAB-oprM (mexR and nalD) demonstrated enhanced virulence in a murine pneumonia infection model. Mutations in these genes, and other genes that we associated with aztreonam resistance, were common in P. aeruginosa isolates from chronically infected patients with cystic fibrosis. These findings illuminate mechanisms of P. aeruginosa aztreonam resistance and raise the possibility that antibiotic treatment could inadvertently select for hypervirulence phenotypes.

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Background Glycopeptides (GPs), lipopeptides (LPs) and lipoglycopeptides (LGPs) are related antimicrobials important for the management of invasive MRSA infections. Cross-resistance among these antibiotics in MRSA is well documented, as is the observation that susceptibility of MRSA to β-lactams increases as susceptibility to GPs and LPs decreases (i.e. the seesaw effect). Efforts to understand the relationship between GP/LP/LGP cross-resistance and the seesaw effect have focused on the PBPs, but the role of lipid metabolism has not been investigated. Objectives Since the cell membrane is structurally and metabolically integrated with the cell wall and anchors associated proteins, including PBPs, we examined the relationship between membrane lipid composition and the phenomena of cross-resistance among GPs/LPs/LGPs and the β-lactam seesaw effect. Methods We selected for daptomycin, vancomycin and dalbavancin resistance using the USA300 strain JE2 and evaluated the resulting mutants by WGS, MS-based lipidomics and antimicrobial susceptibility testing to assess the relationship between membrane composition, cross-resistance, and the seesaw effect. Results We observed cross-resistance to GPs/LPs/LGPs among the selected strains and the seesaw effect against various β-lactams, depending on the PBP targets of the particular β-lactam. We found that modification of membrane composition occurs not only in daptomycin-selected strains, but also vancomycin- and dalbavancin-selected strains. Significantly, we observed that the abundance of most phosphatidylglycerols positively correlates with MICs of GPs/LPs/LGPs and negatively correlates with the MICs of β-lactams. Conclusions These studies demonstrate a major association between membrane remodelling, cross-resistance and the seesaw effect.

Cytokine profiles in amniotic fluid, cord serum, and tracheal aspirate of premature infants suggest a shift toward a proinflammatory state. Cytokines also contribute to the pathogenesis of bronchopulmonary dysplasia (BPD). We hypothesize that the initiating events for BPD are reflected in the placenta and propose that placental expression of cytokines provide a blueprint of events leading to BPD. This is a retrospective, case-controlled study of placental cytokines of premature infants with (n ϭ 49) and without (n ϭ 49) BPD, matched for gender, birth weight, and year of birth at Women and Infants Hospital between 2003 and 2005. Cytokine expression, including IL-6 and IL-10, was determined by immunohistochemistry in membrane rolls, umbilical cords, and placentas. IL-6 was similarly expressed in all tissues of infants with and without BPD. In contrast, anti-inflammatory cytokine IL-10 was less prominent in the placenta of patients with BPD compared with those without BPD. IL-10 expression in the villous trophoblast layer was associated with a reduced odds ratio of developing BPD (adjusted OR 0.08, 95% CI 0.01-0.70, p ϭ 0.02). These results suggest that a placental balance between inflammatory and anti-inflammatory cytokines is crucial to normal lung organogenesis. Importantly, IL-10 seems to be protective against the development of BPD.