The Remarkable Innate Resistance of Burkholderia bacteria to Cationic Antimicrobial Peptides: Insights into the Mechanism of AMP Resistance.

Gram-negative bacteria belonging to the genus Burkholderia are remarkably resistant to broad-spectrum, cationic, antimicrobial peptides (AMPs). It has been proposed that this innate resistance is related to changes in the outer membrane lipopolysaccharide (OM LPS), including the constitutive, essential modification of outer membrane Lipid A phosphate groups with cationic 4-amino-4-deoxy-arabinose. This modification reduces the overall negative charge on the OM LPS which may change the OM structure and reduce the binding, accumulation, and permeation of cationic AMPs. Similarly, the Gram-negative pathogen Pseudomonas aeruginosa can quickly become resistant to many AMPs by multiple mechanisms, frequently, including activation of the arn operon, which leads, transiently, to the same modification of Lipid A. We recently discovered a set of synthetically evolved AMPs that do not invoke any resistance in P. aeruginosa over multiple passages and thus are apparently not inhibited by aminorabinosylation of Lipid A in P. aeruginosa. Here we test these resistance-avoiding peptides, within a set of 18 potent AMPs, against Burkholderia thailandensis. We find that none of the AMPs tested have measurable activity against B. thailandensis. Some were inactive at concentrations as high as 150 µM, despite all having sterilizing activity at ≤ 10 µM against a panel of common, human bacterial pathogens, including P. aeruginosa. We speculate that the constitutive modification of Lipid A in members of the Burkholderia genus is only part of a broader set of modifications that change the architecture of the OM to provide such remarkable levels of resistance to cationic AMPs.

Optimization of Host Cell-Compatible, Antimicrobial Peptides Effective against Biofilms and Clinical Isolates of Drug-Resistant Bacteria.

Here, we describe the continued synthetic molecular evolution of a lineage of host-compatible antimicrobial peptides (AMP) intended for the treatment of wounds infected with drug-resistant, biofilm-forming bacteria. The peptides tested are variants of an evolved AMP called d-amino acid CONsensus with Glycine Absent (d-CONGA), which has excellent antimicrobial activities in vitro and in vivo. In this newest generation of rational d-CONGA variants, we tested multiple sequence-structure-function hypotheses that had not been tested in previous generations. Many of the peptide variants have lower antibacterial activity against Gram-positive or Gram-negative pathogens, especially variants that have altered hydrophobicity, secondary structure potential, or spatial distribution of charged and hydrophobic residues. Thus, d-CONGA is generally well tuned for antimicrobial activity. However, we identified a variant, d-CONGA-Q7, with a polar glutamine inserted into the middle of the sequence, that has higher activity against both planktonic and biofilm-forming bacteria as well as lower cytotoxicity against human fibroblasts. Against clinical isolates of Klebsiella pneumoniae, innate resistance to d-CONGA was surprisingly common despite a lack of inducible resistance in Pseudomonas aeruginosa reported previously. Yet, these same isolates were susceptible to d-CONGA-Q7. d-CONGA-Q7 is much less vulnerable to AMP resistance in Gram-negative bacteria than its predecessor. Consistent with the spirit of synthetic molecular evolution, d-CONGA-Q7 achieved a critical gain-of-function and has a significantly better activity profile.

Exploring Match Space: How Medical School and Specialty Characteristics Affect Residency Match Geography in the United States.

PURPOSE: To explore how school and specialty characteristics impact the geographic match location of U.S. senior medical students. METHOD: The authors collected student match data between 2018 and 2020 from U.S. MD-granting medical schools and calculated the distance between students' medical schools and residency training programs. They use the term "match space" to describe this distance. Match space was codified on a 5-point ordinal scale by where the student matched: 1 = home institution, 2 = home state, 3 = an adjacent state, 4 = the same or adjacent U.S. Census division (and not adjacent state), and 5 = skipped at least one U.S. Census division. Ordinal logistic regression correlated school and specialty characteristics with match space. RESULTS: During the study period, 26,102 medical students, representing 66 medical schools from 28 states, matched in 23 specialties. Fifty-nine percent of students were from public institutions, and 27% of schools ranked in the top 40 of National Institutes of Health (NIH) research funding. The match space was higher for students graduating from private institutions (odds ratio [OR] 1.14; 95% confidence interval [CI], 1.06 to 1.22) and matching into more competitive specialties (OR 1.07; 95% CI, 1 to 1.14). The match space was lower for students graduating from top NIH-funded institutions (OR 0.89; 95% CI, 0.85 to 0.94) and from schools with a higher percentage of in-state matriculants (OR 0.75; 95% CI, 0.72 to 0.77). CONCLUSIONS: School characteristics such as region, public/private designation, NIH funding, and percentage of in-state students were associated with residency match geography. Matching into more competitive specialties also showed a marginal increase in match distance. These findings suggest that a student's choice of specialty and medical school may impact subsequent geographic placement for residency training, which should be considered by students and residency programs alike.

Complex Responses to Hydrogen Peroxide and Hypochlorous Acid by the Probiotic Bacterium Lactobacillus reuteri.

Inflammatory diseases of the gut are associated with increased intestinal oxygen concentrations and high levels of inflammatory oxidants, including hydrogen peroxide (H2O2) and hypochlorous acid (HOCl), which are antimicrobial compounds produced by the innate immune system. This contributes to dysbiotic changes in the gut microbiome, including increased populations of proinflammatory enterobacteria (Escherichia coli and related species) and decreased levels of health-associated anaerobic Firmicutes and Bacteroidetes The pathways for H2O2 and HOCl resistance in E. coli have been well studied, but little is known about how commensal and probiotic bacteria respond to inflammatory oxidants. In this work, we have characterized the transcriptomic response of the anti-inflammatory, gut-colonizing Gram-positive probiotic Lactobacillus reuteri to both H2O2 and HOCl. L. reuteri mounts distinct but overlapping responses to each of these stressors, and both gene expression and survival were strongly affected by the presence or absence of oxygen. Oxidative stress response in L. reuteri required several factors not found in enterobacteria, including the small heat shock protein Lo18, polyphosphate kinase 2, and RsiR, an L. reuteri-specific regulator of anti-inflammatory mechanisms.IMPORTANCE Reactive oxidants, including hydrogen peroxide and hypochlorous acid, are antimicrobial compounds produced by the immune system during inflammation. Little is known, however, about how many important types of bacteria present in the human microbiome respond to these oxidants, especially commensal and other health-associated species. We have now mapped the stress response to both H2O2 and HOCl in the intestinal lactic acid bacterium Lactobacillus reuteri.

Risk Factors for Readmission after Shock Wave Lithotripsy for Urinary Stones.

INTRODUCTION: Cost saving measures have put an increased emphasis on reducing complications and rehospitalization. We analyzed the rate of readmission and presentation to emergency departments within 90 days of shock wave lithotripsy to identify prognostic risk factors for this outcome. METHODS: We retrospectively reviewed patients who underwent shock wave lithotripsy at our institution from January 2011 to May 2013 using the Modulith® SLX-F2 lithotripter for solitary ureteral or renal stones 2.0 cm or smaller. The primary outcome was readmission or presentation to the emergency department within 90 days. Secondary end points included stone-free rates at 30 and 90 days. Univariate and multivariate logistic regression analyses were performed to identify risk factors for primary and secondary outcomes. RESULTS: The study population consisted of 307 patients with renal and 270 with ureteral stones. Mean stone size was 9.2 mm. The 90-day readmission rate was 11.6%. Of analyzed metrics only urgency of procedure predicted readmission. Among patients who were readmitted renal colic was the most common chief complaint (67%), followed by infection (10%) and postoperative hematoma or hematuria (7.5%). Stone-free rates were 57% and 78% at 30 and 90 days, respectively. Stone size and nonurgent shock wave lithotripsy status predicted stone-free status. CONCLUSIONS: The 90-day readmission rate following shock wave lithotripsy was 11.6%. Urgency of shock wave lithotripsy was predictive of this outcome. Stone centers should monitor their readmission rates following shock wave lithotripsy to establish national standards and guide decision making when considering other endourological methods if these outcomes are considered unacceptable.

The effects of changes in the World Health Organization's International Classification of Diseases on suicide rates in 71 countries, 1950-1999.

The World Health Organization (WHO) provides annual mortality statistics from 1950 onward based on the International Classification of Diseases (ICD). In this paper we evaluate the effects of ICD form revisions on suicide rates for 71 countries. The changes between ICD-6, ICD-7, ICD-8, and ICD-9 did not have an overall effect on reported suicide rates. The transitions to ICD-8 and ICD-9 were, however, associated with country-specific changes in the suicide rate in some countries. The change from ICD-9 to ICD-10 was associated with an overall change of -.73 suicides per 100,000 inhabitants. It is recommended that researchers using the WHO mortality data for longitudinal cross-national studies control for the ICD form used at different time points.