Gene essentiality profiling reveals a novel determinant of stresses preventing protein aggregation in Salmonella.

Adaptation to various stresses during infection is important for Salmonella Typhimurium virulence, while the fitness determinants under infection-relevant stress conditions remain unknown. Here, we simulated conditions Salmonella encountered within the host or in the environment by 15 individual stresses as well as two model cell lines (epithelium and macrophage) to decipher the genes and pathways required for fitness. By high-resolution Tn-seq analysis, a total of 1242 genes were identified as essential for fitness under at least one stress condition. The comparative analysis of fitness determinants in 17 stress conditions indicated the essentiality of genes varied in different mimicking host niches. A total of 12 genes were identified as fitness determinants in all stress conditions, including recB, recC, and xseA (encode three exonuclease subunits necessary for DNA recombination repair) and a novel essential fitness gene yheM. YheM is a putative sulfurtransferase subunit that is responsible for tRNA modification, and our results showed that Salmonella lacking yheM accumulated more aggregates of endogenous protein than wild-type. Moreover, we established a scoring scheme for sRNA essentiality analysis and found STnc2080 of unknown function was essential for resistance to LL-37. In summary, we systematically dissected Salmonella gene essentiality profiling and demonstrated the general and specific adaptive requirements in infection-relevant niches. Our data not only provide valuable insights on how Salmonella responds to environmental stresses during infections but also highlight the potential clinical application of fitness determinants in vaccine development.

Fluorescence Turn-On Detection of Ascorbic Acid Using a Self-Assembled Lanthanide Polymer Nanoparticle.

Ascorbic acid (AA), or vitamin C, is an important reactive biological molecule in vivo, and an abnormal level of AA is associated with many diseases. Therefore, the rapid, sensitive, and selective detection of AA levels is of significance in cases of medical assay and diagnosis. Compared with other nanoparticles, lanthanide coordination polymer nanoparticles (Ln-CPs) have been demonstrated as the excellent biomolecule sensing platforms due to their unique optical properties and intrinsic porosities. In this work, the cerium coordination polymer nanoparticles ATP-Ce-Tris were synthesized in a simple and quick way. The synthesized ATP-Ce-Tris nanoparticle shows the characteristic peak of Ce3+ located at 365 nm, which is corresponding to the 4f→5d transition of Ce3+. In the presence of Fe3+, the fluorescence of ATP-Ce-Tris quenched, and the following added ascorbic acid (AA) makes it restoring effectively. Based on this, we constructed a fluorescence probe with excellent sensitivity for AA sensing in a wide linear relationship from 0.05 to 500 µM. The detection limit was as low as 18 nM (signal-to-noise ratio of three), which is one or two orders of magnitude lower than those of reported sensors. The proposed sensing systems also exhibits excellent sensitivity for AA detection in human serum sample, exploiting a valuable platform for AA analysis in clinic diagnostic and drug screening.

Detection of bacteria in stored red cell products using a culture-based bacterial detection system.

BACKGROUND: The Pall eBDS uses oxygen consumption as a surrogate marker for bacterial detection in platelet (PLT) products. This article describes the evaluation of eBDS to detect bacterial contamination in inoculated fresh and stored leukoreduced red cell (RBC) units. STUDY DESIGN AND METHODS: Field studies were conducted at three sites to establish eBDS pouch incubation time and the pass/fail threshold. RBC units were inoculated with each of 12 bacterial species known to cause sepsis at target inocula of either 1 to 15 or 100 colony-forming units (CFUs) per mL. Units were mixed and stored at 2 to 6 degrees C. Samples were taken for culture and eBDS testing weekly from 0 hour to 42 days and incubated for 35 degrees C for 24 to 30, 48, and 72 hours, followed by measurement of percent oxygen content. RESULTS: The studies showed growth of five bacterial species (including Yersinia enterocolitica) in RBC units, while seven bacterial species showed no growth or autosterilized. A pass/fail oxygen threshold of 14.4 percent was determined based on results from noninoculated controls (n = 633) and from inoculated samples (n = 884) after 48 hours of incubation. Detection was 100 percent at all sampling times during refrigerated storage with both 48 and 72 hours of pouch incubation. CONCLUSION: With incubation of eBDS pouches for 48 and 72 hours, 100 percent detection was obtained in 884 samples with bacterial levels of at least 1 CFU per mL, and no false-positive samples were obtained. Based on the bacterial growth patterns, RBC units may be sampled 1 to 3 days after collection for optimal efficacy and read after 48 to 72 hours of incubation of the eBDS sample pouches at 35 degrees C. The Pall eBDS is suited for detection of typical bacterial contaminants in fresh and stored RBCs.