Functional Whole Genome Screen of Nutrient-Starved Mycobacterium tuberculosis Identifies Genes Involved in Rifampin Tolerance.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), poses a global health challenge and is responsible for over a million deaths each year. Current treatment is lengthy and complex, and new, abbreviated regimens are urgently needed. Mtb adapts to nutrient starvation, a condition experienced during host infection, by shifting its metabolism and becoming tolerant to the killing activity of bactericidal antibiotics. An improved understanding of the mechanisms mediating antibiotic tolerance in Mtb can serve as the basis for developing more effective therapies. We performed a forward genetic screen to identify candidate Mtb genes involved in tolerance to the two key first-line antibiotics, rifampin and isoniazid, under nutrient-rich and nutrient-starved conditions. In nutrient-rich conditions, we found 220 mutants with differential antibiotic susceptibility (218 in the rifampin screen and 2 in the isoniazid screen). Following Mtb adaptation to nutrient starvation, 82 mutants showed differential antibiotic susceptibility (80 in the rifampin screen and 2 in the isoniazid screen). Using targeted mutagenesis, we validated the rifampin-hypersusceptible phenotype under nutrient starvation in Mtb mutants lacking the following genes: ercc3, moeA1, rv0049, and rv2179c. These findings shed light on potential therapeutic targets, which could help shorten the duration and complexity of antitubercular regimens.

More than magnetic isolation: Dynabeads as strong Raman reporters towards simultaneous capture and identification of targets.

Dynabeads are superparamagnetic particles used for immunomagnetic purification of cells and biomolecules. Post-capture, however, target identification relies on tedious culturing, fluorescence staining and/or target amplification. Raman spectroscopy presents a rapid detection alternative, but current implementations target cells themselves with weak Raman signals. We present antibody-coated Dynabeads as strong Raman reporter labels whose effect can be considered a Raman parallel of immunofluorescent probes. Recent developments in techniques for separating target-bound Dynabeads from unbound Dynabeads makes such an implementation feasible with high specificity. We deploy Dynabeads anti-Salmonella to bind and identify Salmonella enterica, a major foodborne pathogen. Dynabeads present major peaks around 1000 and 1600 cm-1 from aliphatic and aromatic C-C stretching of the polystyrene coating and near 1350 cm-1 from the É£-Fe2O3 and Fe3O4 core, confirmed with electron dispersive X-ray (EDX) imaging. Minor to no contributions are made from the surface antibodies themselves as confirmed by Raman analysis of surface-activated, antibody-free beads. Dynabeads' Raman signature can be measured in dry and liquid samples even at single shot ~30 × 30 µm area imaging using 0.5 s, 7 mW laser acquisition with single and clustered beads providing a 44- and 68-fold larger Raman intensity compared to signature from cells. Higher polystyrene and iron oxide content in clusters yields larger signal intensity and conjugation to bacteria strengthens clustering as a bacterium can bind to more than one bead as observed via transmission electron microscopy (TEM). Our findings shed light on the intrinsic Raman reporter nature of Dynabeads. When combined with emerging techniques for the separation of target-bound Dynabeads from unbound Dynabeads such as using centrifugation through a density media bi-layer, they have potential to demonstrate their dual function for target isolation and detection without tedious staining steps or unique plasmonic substrate engineering, advancing their applications in heterogeneous samples like food, water, and blood.

Functional whole genome screen of nutrient-starved Mycobacterium tuberculosis identifies genes involved in antibiotic tolerance.

Mycobacterium tuberculosis ( Mtb ), the causative agent of tuberculosis (TB), poses a global health challenge and is responsible for over a million deaths each year. Current treatment is lengthy and complex, and new, abbreviated regimens are urgently needed. Mtb adapts to nutrient starvation, a condition experienced during host infection, by shifting its metabolism and becoming tolerant to the killing activity of bactericidal antibiotics. An improved understanding of the mechanisms mediating antibiotic tolerance in Mtb can serve as the basis for developing more effective therapies. We performed a forward genetic screen to identify candidate Mtb genes involved in tolerance to the two key first-line antibiotics, rifampin and isoniazid, under nutrient-rich and nutrient-starved conditions. In nutrient-rich conditions, we found 220 mutants with differential antibiotic susceptibility (218 in the rifampin screen and 2 in the isoniazid screen). Following Mtb adaptation to nutrient starvation, 82 mutants showed differential antibiotic susceptibility (80 in the rifampin screen and 2 in the isoniazid screen). Using targeted mutagenesis, we validated the rifampin-hypersusceptible phenotype under nutrient starvation in Mtb mutants lacking the following genes: ercc3 , moeA1 , rv0049 , and rv2179c . These findings shed light on potential therapeutic targets, which could help shorten the duration and complexity of antitubercular regimens. Importance: Treatment of Mtb infection requires a long course of combination antibiotics, likely due to subpopulations of tolerant bacteria exhibiting decreased susceptibility to antibiotics. Identifying and characterizing the genetic pathways involved in antibiotic tolerance is expected to yield therapeutic targets for the development of novel TB treatment-shortening regimens.

Defining Incidence and Risk Factors for Catheter-Associated Bloodstream Infections in an Outpatient Adult Hematopoietic Cell Transplantation Program.

Allogeneic hematopoietic cell transplantation (HCT) patients are at an increased risk of developing central line-associated bloodstream infections (CLABSIs) due to prolonged periods of myelosuppression, immunosuppression, and indwelling catheter days. CLABSIs are among the most serious complications in HCT recipients and can lead to prolonged hospitalizations, intensive care unit admissions, lengthy antimicrobial therapies, and increased mortality. There is a lack of data regarding the incidence and risk factors associated with the development of CLABSIs in the HCT population undergoing outpatient transplantation. This was a single-center, retrospective analysis of adult patients who underwent allogeneic HCT between July 2012 and July 2016 in an outpatient transplant unit at a tertiary academic medical center. The primary outcome was the cumulative incidence of CLABSIs from the date of central line placement through the first 100 days post-transplantation. Secondary outcomes included risk factors for CLABSI, number of hospitalizations due to CLABSI, mortality rate at 6 months post-transplantation, and the cumulative incidence, speciation, and presence of multidrug resistance in identified microorganisms. Three hundred fifty-nine patients underwent allogeneic HCT at Vanderbilt University Medical Center and 352 were included for analysis. The cumulative incidence of CLABSIs was 9%, with the majority occurring within the first 30 days post HCT (67%). The use of a matched unrelated donor (MUD) and/or haploidentical donor (odds ratio, 3.993; 95% confidence interval [CI], 1.329 to 12.001; P = .0136) and use of an ablative conditioning regimen (odds ratio, 2.394; 95% CI, 1.052 to 5.446; P = .0374) were independently associated with development of a CLABSI on multivariate analysis. The most common organism implicated in CLABSI was Staphylococcus epidermidis (34%). Patients who developed a CLABSI had an almost 5 times higher risk of mortality at 6 months post-transplantation compared with patients who did not develop a CLABSI (hazard ratio, 4.932; 95% CI, 2.463 to 9.878; P < .001). There is a low incidence of CLABSIs in patients undergoing HCT in the outpatient setting. Patients who underwent HCT using a MUD or haploidentical donor and received ablative conditioning were at higher risk for developing CLABSIs. Overall mortality at 6 months post-transplantation was higher in patients who developed a CLABSI. Additional prospective studies are needed to confirm these observations.