1,3-Dioxane-Linked Novel Bacterial Topoisomerase Inhibitors: Expanding Structural Diversity and the Antibacterial Spectrum.

Antibacterial resistance continues its devastation of available therapies. Novel bacterial topoisomerase inhibitors (NBTIs) offer one solution to this critical issue. Two series of amine NBTIs bearing tricyclic DNA-binding moieties as well as amide NBTIs with a bicyclic DNA-binding moiety were synthesized and evaluated against methicillin-resistant Staphylococcus aureus (MRSA). Additionally, these compounds and a series of bicyclic amine analogues displayed high activity against susceptible and drug-resistant Neisseria gonorrhoeae, expanding the spectrum of these dioxane-linked NBTIs.

Sept8/SEPTIN8 involvement in cellular structure and kidney damage is identified by genetic mapping and a novel human tubule hypoxic model.

Chronic kidney disease (CKD), which can ultimately progress to kidney failure, is influenced by genetics and the environment. Genes identified in human genome wide association studies (GWAS) explain only a small proportion of the heritable variation and lack functional validation, indicating the need for additional model systems. Outbred heterogeneous stock (HS) rats have been used for genetic fine-mapping of complex traits, but have not previously been used for CKD traits. We performed GWAS for urinary protein excretion (UPE) and CKD related serum biochemistries in 245 male HS rats. Quantitative trait loci (QTL) were identified using a linear mixed effect model that tested for association with imputed genotypes. Candidate genes were identified using bioinformatics tools and targeted RNAseq followed by testing in a novel in vitro model of human tubule, hypoxia-induced damage. We identified two QTL for UPE and five for serum biochemistries. Protein modeling identified a missense variant within Septin 8 (Sept8) as a candidate for UPE. Sept8/SEPTIN8 expression increased in HS rats with elevated UPE and tubulointerstitial injury and in the in vitro hypoxia model. SEPTIN8 is detected within proximal tubule cells in human kidney samples and localizes with acetyl-alpha tubulin in the culture system. After hypoxia, SEPTIN8 staining becomes diffuse and appears to relocalize with actin. These data suggest a role of SEPTIN8 in cellular organization and structure in response to environmental stress. This study demonstrates that integration of a rat genetic model with an environmentally induced tubule damage system identifies Sept8/SEPTIN8 and informs novel aspects of the complex gene by environmental interactions contributing to CKD risk.

Impact of Daptomycin Dose Exposure Alone or in Combination with ß-Lactams or Rifampin against Vancomycin-Resistant Enterococci in an In Vitro Biofilm Model.

Enterococcus faecium strains are commonly resistant to vancomycin and ß-lactams. In addition, E. faecium often causes biofilm-associated infections and these infections are difficult to treat. In this context, we investigated the activity of dosing regimens using daptomycin (DAP) (8, 10, 12, and 14 mg/kg of body weight/day) alone and in combination with ceftaroline (CPT), ampicillin (AMP), ertapenem (ERT), and rifampin (RIF) against 2 clinical strains of biofilm-producing vancomycin-resistant Enterococcus faecium (VREfm), namely, strains S447 and HOU503, in an in vitro biofilm model. HOU503 harbors common LiaS and LiaR substitutions, whereas S447 lacks mutations associated with the LiaFSR pathway. MIC results demonstrated that both strains were susceptible to DAP and resistant to CPT, AMP, ERT, and RIF. The 168-h pharmacokinetic/pharmacodynamic (PK/PD) CDC biofilm reactor models (simulating human antibiotic exposures) were used with titanium and polyurethane coupons to evaluate the efficacy of antibiotic combinations. DAP 12 and 14 achieved bactericidal activity against S447 but lacked such effect against HOU503. Addition of ERT and RIF enhanced DAP activity, allowing DAP 8 and 10 plus ERT or RIF to produce bactericidal activity against both strains at 168 h. While DAP 8 and 10 plus CPT improved killing, they did not reach bactericidal reduction against S447. Combination of AMP, CPT, ERT, or RIF resulted in enhanced and bactericidal activity for DAP against HOU503 at 168 h. Our data provide further support for the use of combinations of DAP with AMP, ERT, CPT, and RIF in infections caused by biofilm producing VREfm. Further research involving DAP combinations against biofilm-producing enterococci is warranted.

The inhibition of lactoperoxidase catalytic activity through mesna (2-mercaptoethane sodium sulfonate).

Here, we show that mesna (sodium-2-mercaptoethane sulfonate), primarily used to prevent nephrotoxicity and urinary tract toxicity caused by chemotherapeutic agents such as cyclophosphamide and ifosfamide, modulates the catalytic activity of lactoperoxidase (LPO) by binding tightly to the enzyme, functioning either as a one electron substrate for LPO Compounds I and II, destabilizing Compound III. Lactoperoxidase is a hemoprotein that utilizes hydrogen peroxide (H2O2) and thiocyanate (SCN-) to produce hypothiocyanous acid (HOSCN), an antimicrobial agent also thought to be associated with carcinogenesis. Our results revealed that mesna binds stably to LPO within the SCN- binding site, dependent of the heme iron moiety, and its combination with LPO-Fe(III) is associated with a disturbance in the water molecule network in the heme cavity. At low concentrations, mesna accelerated the formation and decay of LPO compound II via its ability to serve as a one electron substrate for LPO compounds I and II. At higher concentrations, mesna also accelerated the formation of Compound II but it decays to LPO-Fe(III) directly or through the formation of an intermediate, Compound I*, that displays characteristic spectrum similar to that of LPO Compound I. Mesna inhibits LPO's halogenation activity (IC50 value of 9.08 µM) by switching the reaction from a 2e- to a 1e- pathway, allowing the enzyme to function with significant peroxidase activity (conversion of H2O2 to H2O without generation of HOSCN). Collectively, mesna interaction with LPO may serve as a potential mechanism for modulating its steady-state catalysis, impacting the regulation of local inflammatory and infectious events.

Breakdown of multiple sclerosis genetics to identify an integrated disease network and potential variant mechanisms.

Genetics of multiple sclerosis (MS) are highly polygenic with few insights into mechanistic associations with pathology. In this study, we assessed MS genetics through linkage disequilibrium and missense variant interpretation to yield a MS gene network. This network of 96 genes was taken through pathway analysis, tissue expression profiles, single cell expression segregation, expression quantitative trait loci (eQTLs), genome annotations, transcription factor (TF) binding profiles, structural genome looping, and overlap with additional associated genetic traits. This work revealed immune system dysfunction, nerve cell myelination, energetic control, transcriptional regulation, and variants that overlap multiple autoimmune disorders. Tissue-specific expression and eQTLs of MS genes implicate multiple immune cell types including macrophages, neutrophils, and T cells, while the genes in neural cell types enrich for oligodendrocyte and myelin sheath biology. There are eQTLs in linkage with lead MS variants in 25 genes including the multitissue eQTL, rs9271640, for HLA-DRB1/DRB5. Using multiple functional genomic databases, we identified noncoding variants that disrupt TF binding for GABPA, CTCF, EGR1, YY1, SPI1, CLOCK, ARNTL, BACH1, and GFI1. Overall, this paper suggests multiple genetic mechanisms for MS associated variants while highlighting the importance of a systems biology and network approach when elucidating intersections of the immune and nervous system.

Evaluation of dalbavancin alone and in combination with ß-lactam antibiotics against resistant phenotypes of Staphylococcus aureus.

Background: Emergence of reduced susceptibility to vancomycin warrants the development of new antimicrobial agents for the treatment of MRSA. We evaluated the activity of dalbavancin, a novel lipoglycopeptide antibiotic, both alone and combined with ß-lactams, in combination MIC testing and time-kill assays against resistant phenotypes of Staphylococcus aureus. Methods: S. aureus isolates included 50 organisms with varying susceptibility patterns. Dalbavancin was tested alone and in combination with five ß-lactams: cefazolin, cefepime, ceftaroline, ertapenem and oxacillin. MIC values of the antibiotics were determined for all isolates. After initial MIC testing, dalbavancin MICs were determined in the presence of 0.5 × MIC of each ß-lactam to determine the effect of each ß-lactam on dalbavancin MIC. Time-kill assays were performed with dalbavancin and ß-lactams tested at 0.5 × MIC for randomly selected organisms representing each MRSA phenotype. Time-kill curves were generated by plotting mean colony counts (log10 cfu/mL) versus time. Results: Dalbavancin MIC50 was 0.0313 mg/L and MIC90 was 0.0625 mg/L. Dalbavancin MICs decreased by zero to greater than five 2-fold dilutions in combination with each ß-lactam. In time-kill assays, dalbavancin was synergistic with cefazolin, cefepime and ertapenem against all strains and the combination of dalbavancin and ceftaroline was synergistic against all but one. The combination of dalbavancin and oxacillin was synergistic against 5/8 strains. Conclusions: Dalbavancin was active against all MRSA strains tested, including heteroresistant vancomycin-intermediate S. aureus, vancomycin-intermediate S. aureus, daptomycin-non-susceptible and linezolid-resistant isolates. The synergy demonstrated against these organisms supports the use of dalbavancin in combination with ß-lactams against resistant phenotypes of S. aureus. Further evaluation is warranted.

Evaluation of Telavancin Alone and Combined with Ceftaroline or Rifampin against Methicillin-Resistant Staphylococcus aureus in an In Vitro Biofilm Model.

Infections caused by biofilm-producing methicillin-resistant Staphylococcus aureus (MRSA) bacteria are challenging due to increasing antibiotic resistance. Synergistic activities of lipopeptides and lipoglycopeptides with ß-lactams have been demonstrated for MRSA, but little is known about biofilm-embedded organisms. Our objective was to evaluate two telavancin (TLV) dosage regimens (7.5 mg/kg of body weight and 10 mg/kg every 24 h [q24h]) alone and in combination with ceftaroline (CPT) (600 mg every 8 h [q8h]) or rifampin (RIF) (450 mg every 12 h [q12h]) against two biofilm-producing MRSA strains (494 and N315). Pharmacokinetic/pharmacodynamic CDC biofilm reactor models with polyurethane coupons were used to evaluate the efficacies of the antibiotic combinations over 72 h. Overall, there were no significant differences observed between the two TLV dosing regimens either alone or in combination with RIF or CPT against these strains. Both TLV dosing regimens and CPT alone demonstrated killing but did not reach bactericidal reduction at 72 h. However, both TLV regimens in combination with RIF demonstrated enhanced activity against both strains, with a rapid decrease in CFU/ml at 4 h that was bactericidal and maintained over the 72-h experiment (-Δ3.75 log10 CFU/ml from baseline; P < 0.0001). Of interest, no enhanced activity was observed for TLV combined with CPT. No development of resistance was observed in any of the combination models. However, resistance to RIF developed as early as 24 h, with MIC values exceeding 32 mg/liter. Our results show that TLV plus RIF displayed therapeutic improvement against biofilm-producing MRSA. These results suggest that TLV at 7.5 and 10 mg/kg q24h are equally effective in eradicating biofilm-associated MRSA strains in vitro.

Impact of cefazolin co-administration with vancomycin to reduce development of vancomycin-intermediate Staphylococcus aureus.

OBJECTIVE: Development of antimicrobial resistance during monotherapy of complicated methicillin-resistant Staphylococcus aureus bacteremia is problematic due to cross-resistance between vancomycin (VAN) and daptomycin, the only approved agents for this condition. Our objective was to demonstrate that development of resistance under conditions of suboptimal VAN (200 mg q 12 h) exposure in S. aureus can be attenuated by addition of cefazolin (CFZ). METHODS: Two strains of S. aureus, 1 methicillin-susceptible Staphylococcus aureus (MSSA) (RN9120) and 1 methicillin-resistant S. aureus (MRSA) (JH1), were evaluated. The organisms were exposed to subtherapeutic VAN concentrations in a 1-compartment pharmacokinetic/pharmacodynamic model combined with recycling in the presence and absence of CFZ. Changes in MIC to glyco/lipopeptides and ß-lactams along with susceptibility to human cathelicidin LL-37 killing were studied. Population analysis profiles (PAPs) were performed to detect changes in VAN heteroresistance. RESULTS: VAN MIC of both organisms increased from 1 to 4 mg/L within 144 h under subtherapeutic VAN exposure. Increase in VAN MIC was associated with increased glyco/lipopeptides MICs. Additionally, increased survival in LL-37 killing assays from 40% to >90% accompanied the increase in VAN MIC. Addition of CFZ prevented the emergence of VAN-intermediate S. aureus. PAPs demonstrated an attenuation of VAN area under the curve shift (reduced organism selection with higher MICs values) when suboptimal VAN exposure was accompanied with CFZ compared to VAN alone (MSSA 17.81 versus 36.027, MRSA -0.35 versus 17.92, respectively). Given the emerging data on the clinical benefits of ß-lactam adjunctive therapy in refractory MRSA bacteremia, additional studies on a larger collection of clinical isolates are needed to establish the utility of VAN plus CFZ for treatment of MRSA bacteremia.

Mesna (2-mercaptoethane sodium sulfonate) functions as a regulator of myeloperoxidase.

Myeloperoxidase (MPO), an abundant protein in neutrophils, monocytes, and macrophages, is thought to play a critical role in the pathogenesis of various disorders ranging from cardiovascular diseases to cancer. We show that mesna (2-mercaptoethanesulfonic acid sodium salt), a detoxifying agent, which inhibits side effects of oxazaphosphorine chemotherapy, functions as a potent inhibitor of MPO; modulating its catalytic activity and function. Using rapid kinetic methods, we examined the interactions of mesna with MPO compounds I and II and ferric forms in the presence and absence of chloride (Cl-), the preferred substrate of MPO. Our results suggest that low mesna concentrations dramatically influenced the build-up, duration, and decay of steady-state levels of Compound I and Compound II, which is the rate-limiting intermediate in the classic peroxidase cycle. Whereas, higher mesna concentrations facilitate the porphyrin-to-adjacent amino acid electron transfer allowing the formation of an unstable transient intermediate, Compound I*, that displays a characteristic spectrum similar to Compound I. In the absence of plasma level of chloride, mesna not only accelerated the formation and decay of Compound II but also reduced its stability in a dose depend manner. Mesna competes with Cl-, inhibiting MPO's chlorinating activity with an IC50 of 5µM, and switches the reaction from a 2e- to a 1e- pathway allowing the enzyme to function only with catalase-like activity. A kinetic model which shows the dual regulation through which mesna interacts with MPO and regulates its downstream inflammatory pathways is presented further validating the repurposing of mesna as an anti-inflammatory drug.

Dynamics of extended-spectrum cephalosporin resistance in pathogenic Escherichia coli isolated from diseased pigs in Quebec, Canada.

The aim of this study was to investigate the evolution with time of ceftiofur-resistant Escherichia coli clinical isolates from pigs in Québec, Canada, between 1997 and 2012 with respect to pathotypes, clones and antimicrobial resistance. Eighty-five ceftiofur-resistant E. coli isolates were obtained from the OIE (World Organisation for Animal Health) Reference Laboratory for Escherichia coli. The most prevalent pathovirotypes were enterotoxigenic E. coli (ETEC):F4 (40%), extraintestinal pathogenic E. coli (ExPEC) (16.5%) and Shiga toxin-producing E. coli (STEC):F18 (8.2%). Susceptibility testing to 15 antimicrobial agents revealed a high prevalence of resistance to 13 antimicrobials, with all isolates being multidrug-resistant. blaCMY-2 (96.5%) was the most frequently detected ß-lactamase gene, followed by blaTEM (49.4%) and blaCTX-M (3.5%). Pulsed-field gel electrophoresis (PFGE) applied to 45 representative E. coli isolates revealed that resistance to ceftiofur is spread both horizontally and clonally. In addition, the emergence of extended-spectrum ß-lactamase-producing E. coli isolates carrying blaCTX-M was observed in 2011 and 2012 in distinct clones. The most predominant plasmid incompatibility (Inc) groups were IncFIB, IncI1, IncA/C and IncFIC. Resistance to gentamicin, kanamycin and chloramphenicol as well as the frequency of blaTEM and IncA/C significantly decreased over the study period, whereas the frequency of IncI1 and multidrug resistance to seven antimicrobial categories significantly increased. These findings reveal that extended-spectrum cephalosporin-resistant porcine E. coli isolates in Québec belong to several different clones with diverse antimicrobial resistance patterns and plasmids. Furthermore, blaCMY-2 was the major ß-lactamase gene in these isolates. From 2011, we report the emergence of blaCTX-M in distinct clones.

Impact of medicated feed along with clay mineral supplementation on Escherichia coli resistance to antimicrobial agents in pigs after weaning in field conditions.

The aim of this study was to examine changes in antimicrobial resistance (AMR) phenotype and virulence and AMR gene profiles in Escherichia coli from pigs receiving in-feed antimicrobial medication following weaning and the effect of feed supplementation with a clay mineral, clinoptilolite, on this dynamic. Eighty E. coli strains isolated from fecal samples of pigs receiving a diet containing chlortetracycline and penicillin, with or without 2% clinoptilolite, were examined for antimicrobial resistance to 15 antimicrobial agents. Overall, an increased resistance to 10 antimicrobials was observed with time. Supplementation with clinoptilolite was associated with an early increase but later decrease in blaCMY-2, in isolates, as shown by DNA probe. Concurrently, a later increase in the frequency of blaCMY-2 and the virulence genes iucD and tsh was observed in the control pig isolates, being significantly greater than in the supplemented pigs at day 28. Our results suggest that, in the long term, supplementation with clinoptilolite could decrease the prevalence of E. coli carrying certain antimicrobial resistance and virulence genes.