Persistent gram-negative bloodstream infection increases the risk of recurrent bloodstream infection with the same species.

The association between persistent gram-negative bloodstream infection (GN-BSI), or ongoing positive cultures, and recurrent GN-BSI has not been investigated. Among 992 adults, persistent GN-BSI was associated with increased recurrent GN-BSI with the same bacterial species and strain (6% vs 2%; p=0.04). Persistent GN-BSI may be a marker of complicated infection.

Female Sex and Mortality in Patients with Staphylococcus aureus Bacteremia: A Systematic Review and Meta-analysis.

Importance: Staphylococcus aureus is the leading cause of death due to bacterial bloodstream infection. Female sex has been identified as a risk factor for mortality in S aureus bacteremia (SAB) in some studies, but not in others. Objective: To determine whether female sex is associated with increased mortality risk in SAB. Data Sources: MEDLINE, Embase, and Web of Science were searched from inception to April 26, 2023. Study Selection: Included studies met the following criteria: (1) randomized or observational studies evaluating adults with SAB, (2) included 200 or more patients, (3) reported mortality at or before 90 days following SAB, and (4) reported mortality stratified by sex. Studies on specific subpopulations (eg, dialysis, intensive care units, cancer patients) and studies that included patients with bacteremia by various microorganisms that did not report SAB-specific data were excluded. Data Extraction and Synthesis: Data extraction and quality assessment were performed by 1 reviewer and verified by a second reviewer. Risk of bias and quality were assessed with the Newcastle-Ottawa Quality Assessment Scale. Mortality data were combined as odds ratios (ORs). Main Outcome and Measures: Mortality at or before 90-day following SAB, stratified by sex. Results: From 5339 studies retrieved, 89 were included (132 582 patients; 50 258 female [37.9%], 82 324 male [62.1%]). Unadjusted mortality data were available from 81 studies (109 828 patients) and showed increased mortality in female patients compared with male patients (pooled OR, 1.12; 95% CI, 1.06-1.18). Adjusted mortality data accounting for additional patient characteristics and treatment variables were available from 32 studies (95 469 patients) and revealed a similarly increased mortality risk in female relative to male patients (pooled adjusted OR, 1.18; 95% CI, 1.11-1.27). No evidence of publication bias was encountered. Conclusions and Relevance: In this systematic review and meta-analysis, female patients with SAB had higher mortality risk than males in both unadjusted and adjusted analyses. Further research is needed to study the potential underlying mechanisms.

In-patient evolution of a high-persister Escherichia coli strain with reduced in vivo antibiotic susceptibility.

Gram-negative bacterial bloodstream infections (GNB-BSI) are common and frequently lethal. Despite appropriate antibiotic treatment, relapse of GNB-BSI with the same bacterial strain is common and associated with poor clinical outcomes and high healthcare costs. The role of persister cells, which are sub-populations of bacteria that survive for prolonged periods in the presence of bactericidal antibiotics, in relapse of GNB-BSI is unclear. Using a cohort of patients with relapsed GNB-BSI, we aimed to determine how the pathogen evolves within the patient between the initial and subsequent episodes of GNB-BSI and how these changes impact persistence. Using Escherichia coli clinical bloodstream isolate pairs (initial and relapse isolates) from patients with relapsed GNB-BSI, we found that 4/11 (36%) of the relapse isolates displayed a significant increase in persisters cells relative to the initial bloodstream infection isolate. In the relapsed E. coli strain with the greatest increase in persisters (100-fold relative to initial isolate), we determined that the increase was due to a loss-of-function mutation in the ptsI gene encoding Enzyme I of the phosphoenolpyruvate phosphotransferase system. The ptsI mutant was equally virulent in a murine bacteremia infection model but exhibited 10-fold increased survival to antibiotic treatment. This work addresses the controversy regarding the clinical relevance of persister formation by providing compelling data that not only do high-persister mutations arise during bloodstream infection in humans but also that these mutants display increased survival to antibiotic challenge in vivo.

Inflammasome-mediated glucose limitation induces antibiotic tolerance in Staphylococcus aureus.

Staphylococcus aureus is a leading human pathogen that frequently causes relapsing infections. The failure of antibiotics to eradicate infection contributes to infection relapse. Host-pathogen interactions have a substantial impact on antibiotic susceptibility and the formation of antibiotic tolerant cells. In this study, we interrogate how a major S. aureus virulence factor, α-toxin, interacts with macrophages to alter the microenvironment of the pathogen, thereby influencing its susceptibility to antibiotics. We find α-toxin-mediated activation of the NLRP3 inflammasome induces antibiotic tolerance. Induction of tolerance is driven by increased glycolysis in the host cells, resulting in glucose limitation and ATP depletion in S. aureus. Additionally, inhibition of NLRP3 activation improves antibiotic efficacy in vitro and in vivo, suggesting that this strategy has potential as a host-directed therapeutic to improve outcomes. Our findings identify interactions between S. aureus and the host that result in metabolic crosstalk that can determine the outcome of antimicrobial therapy.

Antibiotic-induced accumulation of lipid II synergizes with antimicrobial fatty acids to eradicate bacterial populations.

Antibiotic tolerance and antibiotic resistance are the two major obstacles to the efficient and reliable treatment of bacterial infections. Identifying antibiotic adjuvants that sensitize resistant and tolerant bacteria to antibiotic killing may lead to the development of superior treatments with improved outcomes. Vancomycin, a lipid II inhibitor, is a frontline antibiotic for treating methicillin-resistant Staphylococcus aureus and other Gram-positive bacterial infections. However, vancomycin use has led to the increasing prevalence of bacterial strains with reduced susceptibility to vancomycin. Here, we show that unsaturated fatty acids act as potent vancomycin adjuvants to rapidly kill a range of Gram-positive bacteria, including vancomycin-tolerant and resistant populations. The synergistic bactericidal activity relies on the accumulation of membrane-bound cell wall intermediates that generate large fluid patches in the membrane leading to protein delocalization, aberrant septal formation, and loss of membrane integrity. Our findings provide a natural therapeutic option that enhances vancomycin activity against difficult-to-treat pathogens, and the underlying mechanism may be further exploited to develop antimicrobials that target recalcitrant infection.

Persistent Methicillin-Resistant Staphylococcus aureus Bacteremia: Host, Pathogen, and Treatment.

Methicillin-resistant Staphylococcus aureus (MRSA) is a devastating pathogen responsible for a variety of life-threatening infections. A distinctive characteristic of this pathogen is its ability to persist in the bloodstream for several days despite seemingly appropriate antibiotics. Persistent MRSA bacteremia is common and is associated with poor clinical outcomes. The etiology of persistent MRSA bacteremia is a result of the complex interplay between the host, the pathogen, and the antibiotic used to treat the infection. In this review, we explore the factors related to each component of the host-pathogen interaction and discuss the clinical relevance of each element. Next, we discuss the treatment options and diagnostic approaches for the management of persistent MRSA bacteremia.

Clinical and Molecular Analyses of Recurrent Gram-Negative Bloodstream Infections.

BACKGROUND: The causes and clinical characteristics of recurrent gram-negative bacterial bloodstream infections (GNB-BSI) are poorly understood. METHODS: We used a cohort of patients with GNB-BSI to identify clinical characteristics, microbiology, and risk factors associated with recurrent GNB-BSI. Bacterial genotyping (pulsed-field gel electrophoresis [PFGE] and whole-genome sequencing [WGS]) was used to determine whether episodes were due to relapse or reinfection. Multivariable logistic regression was used to identify risk factors for recurrence. RESULTS: Of the 1423 patients with GNB-BSI in this study, 60 (4%) had recurrent GNB-BSI. Non-White race (odds ratio [OR], 2.35; 95% confidence interval [CI], 1.38-4.01; P = .002), admission to a surgical service (OR, 2.18; 95% CI, 1.26-3.75; P = .005), and indwelling cardiac device (OR, 2.73; 95% CI, 1.21-5.58; P = .009) were associated with increased risk for recurrent GNB-BSI. Among the 48 patients with recurrent GNB-BSI whose paired bloodstream isolates underwent genotyping, 63% were due to relapse (30 of 48) and 38% were due to reinfection (18 of 48) based on WGS. Compared with WGS, PFGE correctly differentiated relapse and reinfection in 98% (47 of 48) of cases. Median time to relapse and reinfection was similar (113 days; interquartile range [IQR], 35-222 vs 174 days; IQR, 69-599; P = .13). Presence of a cardiac device was associated with relapse (relapse: 7 of 27, 26%; nonrelapse: 65 of 988, 7%; P = .002). CONCLUSIONS: In this study, recurrent GNB-BSI was most commonly due to relapse. PFGE accurately differentiated relapse from reinfection when compared with WGS. Cardiac device was a risk factor for relapse.

Association of Follow-up Blood Cultures With Mortality in Patients With Gram-Negative Bloodstream Infections: A Systematic Review and Meta-analysis.

Importance: Obtaining follow-up blood cultures (FUBCs) in patients with Staphylococcus aureus bloodstream infection (BSI) is standard practice, although its utility in patients with gram-negative bacterial BSI (GN-BSI) is unclear. Objective: To examine whether obtaining FUBCs is associated with decreased mortality (key question [KQ] 1) and whether positive vs negative FUBCs are associated with increased mortality (KQ2). Data Sources: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science, and gray literature were searched from inception to March 11, 2022. Study Selection: Two investigators used predefined eligibility criteria to independently screen titles, abstracts, and relevant full texts. Randomized clinical trials or observational studies that matched or statistically adjusted for differences in, at minimum, level of acute illness between patients in the intervention (eg, FUBCs obtained) and control (eg, FUBCs not obtained) groups were included in primary analyses. Articles published in languages other than English were excluded. Data Extraction and Synthesis: Data abstraction and quality assessments were performed by one investigator and verified by a second investigator. Risk of bias was assessed with the Newcastle-Ottawa Scale. Effect sizes were pooled using random-effects models. The study followed the Meta-analysis of Observational Studies in Epidemiology (MOOSE) reporting guideline. Main Outcomes and Measures: Mortality before hospital discharge or up to 30 days from the index blood culture. Results: From 3495 studies, 15 were included (all nonrandomized). In the 5 studies (n = 4378 patients) that met criteria for the KQ1 primary analysis, obtaining FUBCs was associated with decreased mortality (hazard ratio, 0.56; 95% CI, 0.45-0.71). For KQ2, 2 studies met criteria for the primary analysis (ie, matched or statistically adjusted for differences in patients with positive vs negative FUBCs), so an exploratory meta-analysis of all 9 studies that investigated KQ2 (n = 3243 patients) was performed. Positive FUBCs were associated with increased mortality relative to negative blood cultures (odds ratio, 2.27; 95% CI, 1.54-3.34). Limitations of the literature included a lack of randomized studies and few patient subgroup analyses. Conclusions and Relevance: In this systematic review and meta-analysis, obtaining FUBCs in patients with GN-BSI was associated with decreased mortality. The benefit of FUBCs may stem from identification of patients with positive FUBCs, which was a poor prognostic marker.

The Appalachian Career Training in Oncology (ACTION) Program: Preparing Appalachian Kentucky High School and Undergraduate Students for Cancer Careers.

The Appalachian Career Training In ONcology or ACTION Program is a National Cancer Institute (NCI) Youth Enjoy Science (YES) research education grant program that recruits and trains early-career undergraduate and high school students from underrepresented, socioeconomically distressed areas of Appalachian Kentucky in cancer research and outreach. The two-year program is a multifaceted experience that includes participation in cross-disciplinary, mentored cancer research projects. In addition to research projects, participants also shadow faculty mentors in clinical medical settings, engage in multiple types of educational activities, and participate in cancer-focused outreach projects within their communities. Participants also engage in peer-to-peer networking and receive career mentorship, training, and coaching. Highlights of program activities include a student-led photovoice project to promote cancer awareness and participant publications including a book featuring participant essays focused on their experiences and thoughts on cancer. Initial impact data show high school participants have a higher than state and county average four-year college-going rate and all undergraduate participants are gaining positive outcomes related to educational and career attainment. This article provides an overview of the significant benefits of the ACTION Program, the program's activities, and highlights from program implementation. Potential impacts of the program and barriers to implementation are also shared.

Vancomycin Heteroresistance and Clinical Outcomes in Bloodstream Infections Caused by Coagulase-Negative Staphylococci.

Coagulase-negative staphylococci (CoNS) are a common etiology of serious and recurrent infections in immunocompromised patients. Although most isolates appear susceptible to vancomycin, a single strain might have a subpopulation of resistant bacteria. This phenomenon is termed heteroresistance and may adversely affect the response to treatment. A retrospective cohort study was performed of pediatric patients with leukemia treated at St. Jude Children's Research Hospital who developed CoNS central line-associated bloodstream infection (CLABSI). Available isolates were sequenced and tested for vancomycin heteroresistance by population analysis profiling. Risk factors for heteroresistance and the association of heteroresistance with treatment failure (death or relapse of infection) or poor clinical response to vancomycin therapy (treatment failure or persistent bacteremia after vancomycin initiation) were evaluated. For 65 participants with CoNS CLABSI, 62 initial isolates were evaluable, of which 24 (39%) were vancomycin heteroresistant. All heteroresistant isolates were of Staphylococcus epidermidis and comprised multiple sequence types. Participants with heteroresistant bacteria had more exposure to vancomycin prophylaxis (P = 0.026) during the 60 days prior to infection. Of the 40 participants evaluable for clinical outcomes, heteroresistance increased the risk of treatment failure (P = 0.012) and poor clinical response (P = 0.001). This effect persisted after controlling for identified confounders. These data indicate that vancomycin heteroresistance is common in CoNS isolates from CLABSIs in pediatric patients with leukemia and is associated with poor clinical outcomes. Validation of these findings in an independent cohort and evaluation of alternative antibiotic therapy in patients with heteroresistant infections have the potential to improve care for serious CoNS infections.

151W monolithic diffraction-limited Yb-doped photonic bandgap fiber laser at ~978nm.

We demonstrate that the strong 4-level Yb emission in a fiber laser can be almost completely suppressed in an Yb all-solid double-clad photonic bandgap fiber, resulting in highly efficient high-power monolithic Yb fiber lasers operating at the 3-level system. We have achieved single-mode continuous wave laser output power of ~151W at ~978nm with an efficiency of 63% with respect to the launched pump power in a practical monolithic fiber laser configuration for the first time. The demonstrated power in this work are setting new records for diffraction-limited double-clad fiber lasers operating at ~978nm.

Highly efficient cladding-pumped single-mode three-level Yb all-solid photonic bandgap fiber lasers.

Efficient cladding-pumped three-level Yb fiber lasers are difficult to achieve due to the competing four-level system and necessary high inversions. We demonstrate an efficiency of ∼62.7% versus a coupled pump, a record for cladding-pumped fiber lasers with a single-pass pump. 84 W at ∼978 nm with ∼1.12M2 was achieved, a record power for flexible fibers. Amplified spontaneous emission was suppressed by >40 dB. The efficiency is quantum-limited ∼94% versus an absorbed pump. This is made possible by the use of a photo-darkening-free Yb phosphosilicate core and recent progress in single-mode large-core all-solid photonic bandgap fiber designs, which provide the necessary large core-to-cladding ratio and suppression of the four-level system.

Efficient 240W single-mode 1018nm laser from an Ytterbium-doped 50/400µm all-solid photonic bandgap fiber.

Lowering the quantum defect by tandem pumping with fiber lasers at 1018nm was critical for achieving the record 10kW single-mode ytterbium fiber laser. Here we report the demonstration of an efficient directly-diode-pumped single-mode ytterbium fiber laser with 240W at 1018nm. The key for the combination of high efficiency, high power and single-mode at 1018nm is an ytterbium-doped 50µm/400µm all-solid photonic bandgap fiber, which has a practical all-solid design and a pump cladding much larger than those used in previous demonstrations of single-mode 1018nm ytterbium fiber lasers, enabling higher pump powers. Efficient high-power single-mode 1018nm fiber laser is critical for further power scaling of fiber lasers and the all-solid photonic bandgap fiber can potentially be a significant enabling technology.

Large-mode-area fibers operating near single-mode regime.

Lower NA in large-mode-area fibers enables better single-mode operation and larger core diameters. Fiber NA has traditionally been limited to 0.06, mostly due to the control tolerance in the fabrication process. It has been recognized recently that transverse mode instability is a major limit to average power scaling in fiber lasers. One effective method to mitigate this limit is to operate nearer to the single-mode regime. Lower fiber NA is critical in this since it allows relatively larger core diameters which is the key to mitigate the limits imposed by nonlinear effects. We have developed a fabrication process of ytterbium-doped silica glass which is capable of highly accurate refractive index control and sufficient uniformity for LMA fibers. This process is also capable of large-volume production. It is based on a significant amount of post-processing once the fiber preforms are made. We have demonstrated 30/400 and 40/400 LMA fibers with a NA of ~0.028 operating very close to the single-mode regime. The second-order mode cuts off at ~1.2µm and ~1.55µm respectively. We have also studied issues related to bend losses due to the low NA and further optimization of LMA fibers.

Polarizing ytterbium-doped all-solid photonic bandgap fiber with ~1150µm(2) effective mode area.

We demonstrate an Yb-doped polarizing all-solid photonic bandgap fiber for single-polarization and single-mode operation with an effective mode area of ~1150µm(2), a record for all-solid photonic bandgap fibers. The differential polarization mode loss is measured to be >5dB/m over the entire transmission band with a 160nm bandwidth and >15dB/m on the short wavelength edge of the band. A 2.6m long fiber was tested in a laser configuration producing a linearly polarized laser output with a PER value of 21dB without any polarizer, the highest for any fiber lasers based on polarizing fibers.

FabH mutations confer resistance to FabF-directed antibiotics in Staphylococcus aureus.

Delineating the mechanisms for genetically acquired antibiotic resistance is a robust approach to target validation and anticipates the evolution of clinical drug resistance. This study defines a spectrum of mutations in fabH that render Staphylococcus aureus resistant to multiple natural products known to inhibit the elongation condensing enzyme (FabF) of bacterial type II fatty acid synthesis. Twenty independently isolated clones resistant to platensimycin, platencin, or thiolactomycin were isolated. All mutants selected against one antibiotic were cross-resistant to the other two antibiotics. Mutations were not detected in fabF, but the resistant strains harbored missense mutations in fabH. The altered amino acids clustered in and around the FabH active-site tunnel. The mutant FabH proteins were catalytically compromised based on the low activities of the purified enzymes, a fatty acid-dependent growth phenotype, and elevated expression of the fabHF operon in the mutant strains. Independent manipulation of fabF and fabH expression levels showed that the FabH/FabF activity ratio was a major determinant of antibiotic sensitivity. Missense mutations that reduce FabH activity are sufficient to confer resistance to multiple antibiotics that bind to the FabF acyl-enzyme intermediate in S. aureus.

A thioesterase bypasses the requirement for exogenous fatty acids in the plsX deletion of Streptococcus pneumoniae.

PlsX is an acyl-acyl carrier protein (ACP):phosphate transacylase that interconverts the two acyl donors in Gram-positive bacterial phospholipid synthesis. The deletion of plsX in Staphylococcus aureus results in a requirement for both exogenous fatty acids and de novo type II fatty acid biosynthesis. Deletion of plsX (SP0037) in Streptococcus pneumoniae did not result in an auxotrophic phenotype. The ΔplsX S. pneumoniae strain was refractory to myristic acid-dependent growth arrest, and unlike the wild-type strain, was susceptible to fatty acid synthesis inhibitors in the presence of exogenous oleate. The ΔplsX strain contained longer chain saturated fatty acids imparting a distinctly altered phospholipid molecular species profile. An elevated pool of 18- and 20-carbon saturated fatty acids was detected in the ΔplsX strain. A S. pneumoniae thioesterase (TesS, SP1408) hydrolyzed acyl-ACP in vitro, and the ΔtesS ΔplsX double knockout strain was a fatty acid auxotroph. Thus, the TesS thioesterase hydrolyzed the accumulating acyl-ACP in the ΔplsX strain to liberate fatty acids that were activated by fatty acid kinase to bypass a requirement for extracellular fatty acid. This work identifies tesS as the gene responsible for the difference in exogenous fatty acid growth requirement of the ΔplsX strains of S. aureus and S. pneumoniae.

A gene-derived SNP-based high resolution linkage map of carrot including the location of QTL conditioning root and leaf anthocyanin pigmentation.

BACKGROUND: Purple carrots accumulate large quantities of anthocyanins in their roots and leaves. These flavonoid pigments possess antioxidant activity and are implicated in providing health benefits. Informative, saturated linkage maps associated with well characterized populations segregating for anthocyanin pigmentation have not been developed. To investigate the genetic architecture conditioning anthocyanin pigmentation we scored root color visually, quantified root anthocyanin pigments by high performance liquid chromatography in segregating F2, F3 and F4 generations of a mapping population, mapped quantitative trait loci (QTL) onto a dense gene-derived single nucleotide polymorphism (SNP)-based linkage map, and performed comparative trait mapping with two unrelated populations. RESULTS: Root pigmentation, scored visually as presence or absence of purple coloration, segregated in a pattern consistent with a two gene model in an F2, and progeny testing of F3-F4 families confirmed the proposed genetic model. Purple petiole pigmentation was conditioned by a single dominant gene that co-segregates with one of the genes conditioning root pigmentation. Root total pigment estimate (RTPE) was scored as the percentage of the root with purple color.All five anthocyanin glycosides previously reported in carrot, as well as RTPE, varied quantitatively in the F2 population. For the purpose of QTL analysis, a high resolution gene-derived SNP-based linkage map of carrot was constructed with 894 markers covering 635.1 cM with a 1.3 cM map resolution. A total of 15 significant QTL for all anthocyanin pigments and for RTPE mapped to six chromosomes. Eight QTL with the largest phenotypic effects mapped to two regions of chromosome 3 with co-localized QTL for several anthocyanin glycosides and for RTPE. A single dominant gene conditioning anthocyanin acylation was identified and mapped.Comparative mapping with two other carrot populations segregating for purple color indicated that carrot anthocyanin pigmentation is controlled by at least three genes, in contrast to monogenic control reported previously. CONCLUSIONS: This study generated the first high resolution gene-derived SNP-based linkage map in the Apiaceae. Two regions of chromosome 3 with co-localized QTL for all anthocyanin pigments and for RTPE, largely condition anthocyanin accumulation in carrot roots and leaves. Loci controlling root and petiole anthocyanin pigmentation differ across diverse carrot genetic backgrounds.

Quantitative mode quality characterization of fibers with extremely large mode areas by matched white-light interferometry.

Quantitative mode characterization of fibers with cores much beyond 50µm is difficult with existing techniques due to the combined effects of smaller intermodal group delays and dispersions. We demonstrate, for the first time, a new method using a matched white-light interferometry (MWI) to cancel fiber dispersion and achieve finer temporal resolution, demonstrating ~20fs temporal resolution in intermodal delays, i.e. 6µm path-length resolution. A 1m-long straight resonantly-enhanced leakage-channel fiber with 100µm core was characterized, showing ~55fs/m relative group delay and a ~29dB mode discrimination between the fundamental and second-order modes.