Heteroresistance to cefiderocol in carbapenem-resistant Acinetobacter baumannii in the CREDIBLE-CR study was not linked to clinical outcomes: a post hoc analysis.

IMPORTANCE: The population analysis profiling (PAP) test is considered the "gold standard" method to detect heteroresistance. It exposes bacteria to increasing concentrations of antibiotics at high cell densities to detect any minority resistant subpopulations that might be missed by the low inoculums used for reference susceptibility tests. However, its clinical relevance has not been well established. In the CREDIBLE-CR study, a numerically increased all-cause mortality was observed in the cefiderocol arm relative to the best available therapy arm for patients with Acinetobacter spp. infections. Heteroresistance has independently been proposed by another research group as a potential explanation of the mortality difference. An analysis of the baseline carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex isolates from patients treated with cefiderocol in the CREDIBLE-CR study showed the highest clinical cure rate and the lowest mortality for patients with PAP-heteroresistant isolates compared with PAP-susceptible or PAP-resistant isolates. These findings contradict the abovementioned hypothesis that heteroresistance contributed to the increased mortality.

New boronate drugs and evolving NDM-mediated beta-lactam resistance.

Taniborbactam and xeruborbactam are dual serine-/metallo-beta-lactamase inhibitors (BLIs) based on a cyclic boronic acid pharmacophore that undergo clinical development. Recent report demonstrated that New Delhi metallo-beta-lactamase (NDM)-9 (differs from NDM-1 by a single amino acid substitution, E152K, evolved to overcome Zn (II) deprivation) is resistant to inhibition by taniborbactam constituting pre-existing taniborbactam resistance mechanism. Using microbiological and biochemical experiments, we show that xeruborbactam is capable of inhibiting NDM-9 and propose the structural basis for differences between two BLIs.

Determination of Disk Diffusion and MIC Quality Control Ranges for Nafithromycin (WCK 4873), a New Lactone-Ketolide.

Disk diffusion and MIC quality control (QC) ranges were determined for nafithromycin, a new lactone-ketolide, following the completion of a nine-laboratory, Clinical and Laboratory Standards Institute (CLSI) document M23-defined tier 2 study. Five QC strains consistent with the spectrum of activity of nafithromycin were tested: Staphylococcus aureus ATCC 25923 (disk only), S. aureus ATCC 29213 (broth only), Enterococcus faecalis ATCC 29212 (broth only), Streptococcus pneumoniae ATCC 49619 (disk and broth), and Haemophilus influenzae ATCC 49247 (disk and broth). Nafithromycin disk diffusion QC ranges were determined to be 25 to 31 mm for S. aureus ATCC 25923, 25 to 31 mm for S. pneumoniae ATCC 49619, and 16 to 20 mm for H. influenzae ATCC 49247. Nafithromycin MIC QC ranges were determined to be 0.06 to 0.25 µg/ml for S. aureus ATCC 29213, 0.016 to 0.12 µg/ml for E. faecalis ATCC 29212, 0.008 to 0.03 µg/ml for S. pneumoniae ATCC 49619, and 2 to 8 µg/ml for H. influenzae ATCC 49247. All disk diffusion and MIC QC ranges established in this study were approved by the CLSI Subcommittee on Antimicrobial Susceptibility Testing at their June 2015 meeting and were initially reported in the 2017 M100S document. The QC ranges established in this study should be used for determining the in vitro activity of nafithromycin in phase 2 and phase 3 human clinical trials and subsequently for testing patient isolates and isolates in phase 4 surveillance studies.

Busulfan induces activin A expression in vitro and in vivo: a possible link to venous occlusive disease.

PURPOSE: Hepatic venous occlusive disease is a severe side effect after administration of busulfan before hematopoietic stem cell transplantation. The syndrome is characterized by liver enlargement, fluid retention, jaundice, and weight gain. Endothelial injury has been described as the precipitating factor. The link between busulfan administration and endothelial damage has not been established thus far. METHODS: Complementary deoxyribonucleic acid expression arrays were used to screen for busulfan responsive genes in ECV304 cells. Specific messenger ribonucleic acid and protein levels were examined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Serum samples of 15 pediatric patients with leukemia were analyzed for busulfan and cytokine levels. RESULTS: We identified a member of the transforming growth factor beta superfamily, activin A, to be induced in the human cell line ECV304 after exposure to busulfan in a time- and concentration-dependent manner. Maximum effects were observed at 120 and 168 hours for activin A messenger ribonucleic acid and protein, respectively. Preincubation with the protein kinase C inhibitor bisindolylmaleimide I (10 nmol/L) abolished activin A induction by busulfan (P <.05). Activin receptors were detected in ECV304. Both tissue factor and cyclooxygenase 2 were significantly induced by busulfan (P <.05). In a parallel in vivo study a significant increase in serum activin A concentration was found 4.5 hours after the second dose of busulfan. CONCLUSION: The data demonstrate that busulfan induces activin A both in vitro and in vivo. In view of the multiple targets of activin A (inflammation, proliferation, apoptosis, and coagulation), these findings may be of relevance to our understanding of venous occlusive disease.

Overexpression of glutathione S-transferase A1-1 in ECV 304 cells protects against busulfan mediated G2-arrest and induces tissue factor expression.

1. The antineoplastic drug busulfan is frequently used in preconditioning regimens for bone marrow transplantation. Pharmacokinetics vary tremendously between patients due to extensive metabolism in the liver via conjugation to glutathione catalysed by glutathione S-transferase (GST) A1-1. Since elevated busulfan plasma levels have been reported to be a risk factor for developing veno-occlusive disease (VOD), metabolism of busulfan may play a pivotal role in the induction of VOD. 2. Therefore, we developed a cell model to investigate the influence of busulfan metabolism on its biological effects. GSTA1-1 cDNA was transfected into the cell line ECV 304 and protein expression was demonstrated by Western blotting. Enzymatic activity could be detected by formation of tetrahydrothiophene. Additionally, effects of busulfan treatment on cell cycle and expression of tissue factor have been investigated. 3. A busulfan-induced G2-arrest was reduced in GSTA1-1-transfected cells, which consequently displayed a significantly higher activity of cdc2 kinase (24.1+/-1.5 AU mg(-1) protein) after busulfan treatment compared to controls (14.7+/-2.3 AU mg(-1) protein; P<0.01). Elevated basal expression of tissue factor in GSTA1-1-transfected ECV 304 cells could be 4 fold increased by busulfan treatment. 4. These data demonstrate that ECV 304 cells transfected with GSTA1-1 provide a valuable tool to assess busulfan metabolism in vitro. Furthermore, overexpression of GSTA1-1 leads to a partial protection against cell cycle effects of busulfan and affects tissue factor expression.