Antimicrobial tolerance and its role in the development of resistance: Lessons from enterococci.

Bacteria have developed resistance against every antimicrobial in clinical use at an alarming rate. There is a critical need for more effective use of antimicrobials to both extend their shelf life and prevent resistance from arising. Significantly, antimicrobial tolerance, i.e., the ability to survive but not proliferate during antimicrobial exposure, has been shown to precede the development of bona fide antimicrobial resistance (AMR), sparking a renewed and rapidly increasing interest in this field. As a consequence, problematic infections for the first time are now being investigated for antimicrobial tolerance, with increasing reports demonstrating in-host evolution of antimicrobial tolerance. Tolerance has been identified in a wide array of bacterial species to all bactericidal antimicrobials. Of particular interest are enterococci, which contain the opportunistic bacterial pathogens Enterococcus faecalis and Enterococcus faecium. Enterococci are one of the leading causes of hospital-acquired infection and possess intrinsic tolerance to a number of antimicrobial classes. Persistence of these infections in the clinic is of growing concern, particularly for the immunocompromised. Here, we review current known mechanisms of antimicrobial tolerance, and include an in-depth analysis of those identified in enterococci with implications for both the development and prevention of AMR.

Barriers to genetic manipulation of Enterococci: Current Approaches and Future Directions.

Enterococcus faecalis and Enterococcus faecium are Gram-positive commensal gut bacteria that can also cause fatal infections. To study clinically relevant multi-drug resistant E. faecalis and E. faecium strains, methods are needed to overcome physical (thick cell wall) and enzymatic barriers that limit the transfer of foreign DNA and thus prevent facile genetic manipulation. Enzymatic barriers to DNA uptake identified in E. faecalis and E. faecium include type I, II and IV restriction modification systems and CRISPR-Cas. This review examines E. faecalis and E. faecium DNA defence systems and the methods with potential to overcome these barriers. DNA defence system bypass will allow the application of innovative genetic techniques to expedite molecular-level understanding of these important, but somewhat neglected, pathogens.

Stereochemical Effects on the Antimicrobial Properties of Tetrasubstituted 2,5-Diketopiperazines.

Antimicrobial drug resistance is a looming health crisis facing us in the modern era, and new drugs are urgently needed to combat this growing problem. Synthetic mimics of antimicrobial peptides have recently emerged as a promising class of compounds for the treatment of persistent microbial infections. In the current study, we investigate five cyclic N-alkylated amphiphilic 2,5-diketopiperazines against 15 different strains of bacteria and fungi, including drug-resistant clinical isolates. Several of the 2,5-diketopiperazines displayed activities similar or superior to antibiotics currently in clinical use, with activities coupled to both the cationic and hydrophobic substituents. All possible stereoisomers of the lead peptide were prepared, and the effects of stereochemistry and amphiphilicity were investigated via 1D and 2D NMR spectroscopy, solution dynamics, and membrane interaction modeling. Clear differences in solution structures and membrane interaction potentials explain the differences seen in the bioactivity and physicochemical properties of each stereoisomer.

Optimization of peptide-based inhibitors targeting the HtrA serine protease in Chlamydia: Design, synthesis and biological evaluation of pyridone-based and N-Capping group-modified analogues.

The obligate intracellular bacterium Chlamydia trachomatis (C. trachomatis) is responsible for the most common bacterial sexually transmitted infection and is the leading cause of preventable blindness, representing a major global health burden. While C. trachomatis infection is currently treatable with broad-spectrum antibiotics, there would be many benefits of a chlamydia-specific therapy. Previously, we have identified a small-molecule lead compound JO146 [Boc-Val-Pro-ValP(OPh)2] targeting the bacterial serine protease HtrA, which is essential in bacterial replication, virulence and survival, particularly under stress conditions. JO146 is highly efficacious in attenuating infectivity of both human (C. trachomatis) as well as koala (C. pecorum) species in vitro and in vivo, without host cell toxicity. Herein, we present our continuing efforts on optimizing JO146 by modifying the N-capping group as well as replacing the parent peptide structure with the 2-pyridone scaffold at P3/P2. The drug optimization process was guided by molecular modelling, enzyme and cell-based assays. Compound 18b from the pyridone series showed improved inhibitory activity against CtHtrA by 5-fold and selectivity over human neutrophil elastase (HNE) by 109-fold compared to JO146, indicating that 2-pyridone is a suitable bioisostere of the P3/P2 amide/proline for developing CtHtrA inhibitors. Most pyridone-based inhibitors showed superior anti-chlamydial potency to JO146 especially at lower doses (25 and 50 µM) in C. trachomatis and C. pecorum cell culture assays. Modifications of the N-capping group of the peptidyl inhibitors did not have much influence on the anti-chlamydial activities, providing opportunities for more versatile alterations and future optimization. In summary, we present 2-pyridone based analogues as a new generation of non-peptidic CtHtrA inhibitors, which hold better promise as anti-chlamydial drug candidates.

Occupational attainment and depressive symptoms in young adulthood.

Past studies have shown that various aspects of occupational attainment (unemployment, job instability, low occupational status, and low earnings) are associated with poor mental health, but each of these studies focused on one or two aspects of occupational attainment. Consequently, it remains unclear whether their associations are independent of each other. Further, little is known about whether negative self-assessments of occupational attainment are linked to poor mental health. We sought to overcome these limitations of past research while focusing on depressive symptoms as a mental health outcome and young adulthood as a life stage context. The study analysed U.S. data from the National Longitudinal Study of Adolescent to Adult Health (n = 13,178) using ordinary least square models. The analysis showed that all aspects of occupational attainment were associated with depressive symptoms in the expected directions. Further, unemployment, job instability, and negative self-assessment of career progress showed stronger associations, and those associations were independent of other occupational attainment variables. Overall, the results suggested that understanding the association between occupational attainment and mental health requires close attention to the life stage context.

2-Aminothiazole-4-carboxamides Enhance Readthrough of Premature Termination Codons by Aminoglycosides.

Nonsense mutations introduce a premature termination codon (PTC) and are the underlying cause of multiple rare genetic diseases and cancers. Although certain aminoglycosides bind to eukaryotic ribosomes enabling incorporation of an amino acid at the PTC and formation of full-length protein, they are inefficient and toxic at therapeutic doses. Library screening in assays that measure readthrough at a PTC in the TP53 gene in human HDQ-P1 cells identified six novel 2-aminothiazole-4-carboxamide derivatives that potentiate the PTC readthrough (PTCR) efficiency of G418 when used in combination. The two most potent compounds incorporated a 4-indazole motif on the 2-aminothiazole nitrogen and a hydrophobic aryl substituent on the carboxamide nitrogen. These compounds are valuable tools to further investigate the therapeutic potential of aminoglycoside-induced PTCR.

Hemoglobin A1c and retinal arteriolar narrowing in children with type 1 diabetes: the diagnostics of early atherosclerosis risk in kids study.

BACKGROUND/OBJECTIVE: Microvascular alterations play a key role in the development of diabetes complications. Retinal vessel analysis is a unique method to examine microvascular changes in brain-derived vessels. METHODS: Sixty-seven pediatric and adolescent type 1 diabetes patients and 58 healthy control persons (mean age 12.4 ± 2.9 years) underwent non-mydriatic retinal photography of both eyes. Central retinal arteriolar and central retinal venular (CRVE) diameter equivalents as well as the arteriolar-to-venular ratio were calculated using a semiautomated software. All anthropometric and laboratory parameters were measured according to standardized procedures for children. RESULTS: Retinal vessel diameter did not differ between type 1 diabetic children and healthy controls. However, there was an independent association of higher hemoglobin A1c (HbA1c) levels with arteriolar narrowing. Arteriolar narrowing of 5.4 µm was observed with each percent increase in HbA1c. Longer duration of diabetes was associated with wider retinal arterioles. CRVE was not associated with diabetes duration or HbA1c. CONCLUSIONS: Microvascular arteriolar alterations are already present in childhood and may indicate subclinical atherosclerosis and increased risk of diabetes complications later in life. Future research will have to investigate the potential use of retinal vessel diameters for treatment monitoring and guidance of therapy in children.

New NR5A1 mutations and phenotypic variations of gonadal dysgenesis.

Mutations in NR5A1 have been reported as a frequent cause of 46,XY disorders of sex development (DSD) associated to a broad phenotypic spectrum ranging from infertility, ambiguous genitalia, anorchia to gonadal dygenesis and female genitalia. Here we present the clinical follow up of four 46,XY DSD patients with three novel heterozygous mutations in the NR5A1 gene leading to a p.T40P missense mutation and a p.18DKVSG22del nonframeshift deletion in the DNA-binding domain and a familiar p.Y211Tfs*83 frameshift mutation. Functional analysis of the missense and nonframeshift mutation revealed a deleterious character with loss of DNA-binding and transactivation capacity. Both, the mutations in the DNA-binding domain, as well as the familiar frameshift mutation are associated with highly variable endocrine values and phenotypic appearance. Phenotypes vary from males with spontaneous puberty, substantial testosterone production and possible fertility to females with and without Müllerian structures and primary amenorrhea. Exome sequencing of the sibling's family revealed TBX2 as a possible modifier of gonadal development in patients with NR5A1 mutations.

Lipoprotein-associated phospholipase A2 activity and low-density lipoprotein subfractions after a 2-year treatment with atorvastatin in adolescents with type 1 diabetes.

BACKGROUND: The objective of the study was to assess the effect of atorvastatin on inflammation markers and low-density lipoprotein (LDL) subfractions. METHODS: In a prospective, randomized, double-blind pilot study involving 28 adolescents with type 1 diabetes (T1D), lipoprotein-associated phospholipase A2 (Lp-PLA2) activity, high-sensitivity C-reactive protein (hsCRP), and subfractions of LDL were measured at baseline, after 1 year and 2 years of treatment with atorvastatin (10 mg/day) vs. placebo. RESULTS: For the atorvastatin group, we found posttreatment reductions of Lp-PLA2 activity (p<0.001), LDL cholesterol (p=0.001), non-small dense LDL cholesterol (p<0.001), total cholesterol (p<0.001), and apolipoprotein B (apo B) (p<0.001), whereas small dense LDL cholesterol and hsCRP did not change significantly. CONCLUSIONS: In adolescents with T1D, long-term treatment with atorvastatin is safe and may reduce cardiovascular risk by significant decreases of Lp-PLA2 activity and LDL cholesterol.

Novel small molecules potentiate premature termination codon readthrough by aminoglycosides.

Nonsense mutations introduce premature termination codons and underlie 11% of genetic disease cases. High concentrations of aminoglycosides can restore gene function by eliciting premature termination codon readthrough but with low efficiency. Using a high-throughput screen, we identified compounds that potentiate readthrough by aminoglycosides at multiple nonsense alleles in yeast. Chemical optimization generated phthalimide derivative CDX5-1 with activity in human cells. Alone, CDX5-1 did not induce readthrough or increase TP53 mRNA levels in HDQ-P1 cancer cells with a homozygous TP53 nonsense mutation. However, in combination with aminoglycoside G418, it enhanced readthrough up to 180-fold over G418 alone. The combination also increased readthrough at all three nonsense codons in cancer cells with other TP53 nonsense mutations, as well as in cells from rare genetic disease patients with nonsense mutations in the CLN2, SMARCAL1 and DMD genes. These findings open up the possibility of treating patients across a spectrum of genetic diseases caused by nonsense mutations.

Decrease of small dense LDL and lipoprotein-associated phospholipase A2 due to human growth hormone treatment in short children with growth hormone deficiency and small for gestational age status.

BACKGROUND: Growth hormone deficiency (GHD) and small for gestational age (SGA) status are associated with cardiovascular risks. We therefore, investigated antiatherogenic effects of growth hormone (GH). METHODS: Subfractions of low-density lipoprotein (LDL) and high-density lipoprotein (HDL), lipoprotein-associated phospholipase A2 (Lp-PLA2), and high-sensitivity C-reactive protein (hsCRP) were measured at baseline, after 8 and 52 weeks of GH treatment in 51 short children born SGA (n=33) or with GHD (n=18). RESULTS: The overall group showed post-treatment reductions of LDL cholesterol (LDL-C) (p=0.016), small-dense LDL cholesterol (sdLDL-C, p<0.001), Lp-PLA2 (p<0.001), and hsCRP (p=0.005), but increase of HDL2a cholesterol (HDL2a-C, p=0.025). SGA children revealed significant correlations between Lp-PLA2 and LDL-C and sdLDL-C both before and after GH, significant reductions of sdLDL-C, Lp-PLA2, hsCRP, and an increase of HDL2a-C. GHD children showed the same lipid responses, though not significantly. CONCLUSIONS: Children with GHD or born SGA may benefit from GH by growth acceleration and reduction of cardiovascular long-term risks.

Osteochondral glenoid allograft for biologic resurfacing of the glenoid: biomechanical comparison of novel design concepts.

INTRODUCTION: Biologic resurfacing of the glenoid has hitherto failed to adequately restore the geometry and biology of the glenoid. We hypothesised that a new concept for a press-fit osteochondral allograft glenoid replacement would restore the anatomic geometry of the glenoid, with primary stability guaranteed by the construct through press-fit fixation alone. MATERIAL AND METHODS: Five sawbone models of human scapulae and 5 models using sheep scapulae were prepared for testing of 3 different interface designs (cross, rectangle, and dovetail). Micromotion at the graft interface was assessed in response to 1000 cycles of 30 N shear and 100 N compressive load, and maximal craniocaudal force was determined under 500 N compressive load. RESULTS: In sawbones, mean (range) micromotion ranged from 38 (13-88) µm for cross to 208 (89-335) µm for rectangle, and decreased to 29 (21-57) µm for cross to 104 (34-127) µm for rectangle after 1000 cycles of applied shear force. In sheep bone, the mean (range) of micromotion was 15 (9-22) µm for dovetail to 51 (10-503) µm for cross and decreased to 15 (10-20) µm for dovetail to 44 (24-199) µm for cross; after 1000 cycles with the rectangle design, it decreased from 32 (25-217) µm to 16 (9-143) µm. DISCUSSION: Despite biomechanical differences, in vitro allograft stability was generally adequate for all tested designs, particularly after the graft was allowed to "seat" by repetitive loading. While various geometries are potentially candidates for press-fitting a glenoid allograft to a host scapula, a rectangular interface between graft and host provided a favorable combination of both technical feasibility and biomechanical reliability. CONCLUSION: The concept of an osteochondral glenoid allograft for glenoid reconstruction is technically feasible and demonstrates adequate primary stability in vitro.

Exposure to furosemide as the strongest risk factor for nephrocalcinosis in preterm infants.

BACKGROUND: The objective of this study was to determine which of the many risk factors for nephrocalcinosis (NC) in preterm infants are most relevant. METHODS: In 55 neonates born before 32 completed weeks of gestation, parameters relevant to NC were analyzed. Median birthweight was 1010 g (range 500-2070 g). Fifteen (27%) asymptomatic children had ultrasonographic NC. RESULTS: In multivariate analysis the strongest independent risk factor was furosemide therapy above 10 mg per kg bodyweight cumulative dose, with a 48-fold increased risk of NC (odds ratio confidence interval 4.0-585, P < 0.01). The risk of NC was 1.65-fold higher per 100 g lower weight (1.07-2.56, P= 0.02) and 4.5-fold higher per mmol/l of urinary calcium concentration (1.14-17.7, P= 0.03). Many other risk factors were only significant in univariate analysis (gestational age, mechanical ventilation, infection, broncho-pulmonary dysplasia, blood transfusions, intraventricular hemorrhage, surfactant therapy, vasopressors, phenobarbital or caffeine, duration of hospital stay), indicating an indirect effect only. Other parameters of calcium and phosphate homeostasis were not significant, possibly due to standardized supplementation. CONCLUSION: We suggest that in preterm infants, furosemide should be prescribed with caution and close monitoring of calcium excretions is advisable. Some guidelines for infant respiratory distress syndrome now favor calcium-sparing thiazides if diuretics are considered.