A Dual-Mechanism Antibiotic Kills Gram-Negative Bacteria and Avoids Drug Resistance.

The rise of antibiotic resistance and declining discovery of new antibiotics has created a global health crisis. Of particular concern, no new antibiotic classes have been approved for treating Gram-negative pathogens in decades. Here, we characterize a compound, SCH-79797, that kills both Gram-negative and Gram-positive bacteria through a unique dual-targeting mechanism of action (MoA) with undetectably low resistance frequencies. To characterize its MoA, we combined quantitative imaging, proteomic, genetic, metabolomic, and cell-based assays. This pipeline demonstrates that SCH-79797 has two independent cellular targets, folate metabolism and bacterial membrane integrity, and outperforms combination treatments in killing methicillin-resistant Staphylococcus aureus (MRSA) persisters. Building on the molecular core of SCH-79797, we developed a derivative, Irresistin-16, with increased potency and showed its efficacy against Neisseria gonorrhoeae in a mouse vaginal infection model. This promising antibiotic lead suggests that combining multiple MoAs onto a single chemical scaffold may be an underappreciated approach to targeting challenging bacterial pathogens.

Antimicrobial resistance heterogeneity among multidrug-resistant Gram-negative pathogens: Phenotypic, genotypic, and proteomic analysis.

Microbes evolve rapidly by modifying their genomes through mutations or through the horizontal acquisition of mobile genetic elements (MGEs) linked with fitness traits such as antimicrobial resistance (AMR), virulence, and metabolic functions. We conducted a multicentric study in India and collected different clinical samples for decoding the genome sequences of bacterial pathogens associated with sepsis, urinary tract infections, and respiratory infections to understand the functional potency associated with AMR and its dynamics. Genomic analysis identified several acquired AMR genes (ARGs) that have a pathogen-specific signature. We observed that blaCTX-M-15, blaCMY-42, blaNDM-5, and aadA(2) were prevalent in Escherichia coli, and blaTEM-1B, blaOXA-232, blaNDM-1, rmtB, and rmtC were dominant in Klebsiella pneumoniae. In contrast, Pseudomonas aeruginosa and Acinetobacter baumannii harbored blaVEB, blaVIM-2, aph(3'), strA/B, blaOXA-23, aph(3') variants, and amrA, respectively. Regardless of the type of ARG, the MGEs linked with ARGs were also pathogen-specific. The sequence type of these pathogens was identified as high-risk international clones, with only a few lineages being predominant and region-specific. Whole-cell proteome analysis of extensively drug-resistant K. pneumoniae, A. baumannii, E. coli, and P. aeruginosa strains revealed differential abundances of resistance-associated proteins in the presence and absence of different classes of antibiotics. The pathogen-specific resistance signatures and differential abundance of AMR-associated proteins identified in this study should add value to AMR diagnostics and the choice of appropriate drug combinations for successful antimicrobial therapy.

Role of internal loop dynamics in antibiotic permeability of outer membrane porins.

Gram-negative bacteria pose a serious public health concern due to resistance to many antibiotics, caused by the low permeability of their outer membrane (OM). Effective antibiotics use porins in the OM to reach the interior of the cell; thus, understanding permeation properties of OM porins is instrumental to rationally develop broad-spectrum antibiotics. A functionally important feature of OM porins is undergoing open-closed transitions that modulate their transport properties. To characterize the molecular basis of these transitions, we performed an extensive set of molecular dynamics (MD) simulations of Escherichia coli OM porin OmpF. Markov-state analysis revealed that large-scale motion of an internal loop, L3, underlies the transition between energetically stable open and closed states. The conformation of L3 is controlled by H bonds between highly conserved acidic residues on the loop and basic residues on the OmpF ß-barrel. Mutation of key residues important for the loop's conformation shifts the equilibrium between open and closed states and regulates translocation of permeants (ions and antibiotics), as observed in the simulations and validated by our whole-cell accumulation assay. Notably, one mutant system G119D, which we find to favor the closed state, has been reported in clinically resistant bacterial strains. Overall, our accumulated ∼200 µs of simulation data (the wild type and mutants) along with experimental assays suggest the involvement of internal loop dynamics in permeability of OM porins and antibiotic resistance in Gram-negative bacteria.

Targeting the outer membrane of gram-negative foodborne pathogens for food safety: compositions, functions, and disruption strategies.

Foodborne pathogens are a major threat to both food safety and public health. The current trend toward fresh and less processed foods and the misuse of antibiotics in food production have made controlling these pathogens even more challenging. The outer membrane has been employed as a practical target to combat foodborne Gram-negative pathogens due to its accessibility and importance. In this review, the compositions of the outer membrane are extensively described firstly, to offer a thorough overview of this target. Current strategies for disrupting the outer membrane are also discussed, with emphasized on their mechanism of action. The disruption of the outer membrane structure, whether caused by severe damage of the lipid bilayer or by interference with the biosynthesis pathway, has been demonstrated to represent an effective antimicrobial strategy. Interference with the outer membrane-mediated functions of barrier, efflux and adhesion also contributes to the fight against Gram-negative pathogens. Their potential for control of foodborne pathogens in the production chain are also proposed. However, it is possible that multiple components in the food matrix may act as a protective barrier against microorganisms, and it is often the case that contamination is not caused by a single microorganism. Further investigation is needed to determine the effectiveness and safety of these methods in more complex systems, and it may be advisable to consider a multi-technology combined approach. Additionally, further studies on outer membranes are necessary to discover more promising mechanisms of action.

In vitro antimicrobial resistance of Escherichia coli, Serratia marcescens, Klebsiella oxytoca, and Klebsiella pneumoniae on Bavarian dairy farms between 2014 and 2022.

The objective of this study was to describe the prevalence of antimicrobial resistance of Escherichia coli, Klebsiella oxytoca, Klebsiellapneumoniae, and Serratiamarcescens from quarter milk samples submitted to the udder health laboratory of the Bavarian Animal Health Services (TGD) in Southern Germany between 2014 and 2022. All samples were tested with the California Mastitis Test and analyzed with a standard microbroth dilution to determine the MIC. The antimicrobials tested were amoxicillin/clavulanate, cefazoline, kanamycin/cefalexin, cefoperazone, cefquinome, and marbofloxacin. Breakpoints were chosen in accordance with the Clinical and Laboratory Standards Institute (CLSI). Over the study period, E. coli, K. oxytoca, and K. pneumoniae showed only few resistances to all antimicrobials tested. For those pathogens MIC 50 and MIC 90 were below breakpoint for all antimicrobials except cefoperazone over the 9 years. A decrease in MIC could be seen for E. coli and K. oxytoca for all of the antimicrobials. While the MIC for K. pneumoniae stayed more stagnant, the prevalence of resistance still decreased overall. Serratiamarcescens isolates were proven intrinsically resistant to amoxicillin/clavulanate and cefazolin, and while in vitro resistances were low for all other antimicrobials tested, S. marcescens tended toward higher MIC for most of the antimicrobials over the years. Over time, there was also an overall increase in the number of isolates for all 4 pathogens per year. Starting 2018 there was a steep increase in the number of isolates particularly from clinical cases. This jump in numbers coincided with a change of the regulation for veterinary drug prescriptions in Germany in 2018 that required, among other things, antimicrobial resistance testing before a change of antibiotics in the course of treatment and the use of critically important antimicrobials. Overall, although the pathogens increased in numbers, the prevalence of their antimicrobial resistance remained low.

Comprehensive Similarity Algorithm and Molecular Dynamics Simulation-Assisted Terahertz Spectroscopy for Intelligent Matching Identification of Quorum Signal Molecules (N-Acyl-Homoserine Lactones).

To investigate the mechanism of aquatic pathogens in quorum sensing (QS) and decode the signal transmission of aquatic Gram-negative pathogens, this paper proposes a novel method for the intelligent matching identification of eight quorum signaling molecules (N-acyl-homoserine lactones, AHLs) with similar molecular structures, using terahertz (THz) spectroscopy combined with molecular dynamics simulation and spectral similarity calculation. The THz fingerprint absorption spectral peaks of the eight AHLs were identified, attributed, and resolved using the density functional theory (DFT) for molecular dynamics simulation. To reduce the computational complexity of matching recognition, spectra with high peak matching values with the target were preliminarily selected, based on the peak position features of AHL samples. A comprehensive similarity calculation (CSC) method using a weighted improved Jaccard similarity algorithm (IJS) and discrete Fréchet distance algorithm (DFD) is proposed to calculate the similarity between the selected spectra and the targets, as well as to return the matching result with the highest accuracy. The results show that all AHL molecular types can be correctly identified, and the average quantization accuracy of CSC is 98.48%. This study provides a theoretical and data-supported foundation for the identification of AHLs, based on THz spectroscopy, and offers a new method for the high-throughput and automatic identification of AHLs.

Polymyxin B Plus Aerosolized Colistin vs Polymyxin B Alone in Hospital-acquired Pneumonia ("AEROCOL" Study): A Feasibility Study.

Introduction: In hospital-acquired pneumonia (HAP) due to extensively drug resistant gram-negative pathogens, can treatment with high-dose colistin aerosolization using specific aerosol delivery protocol, improve clinical outcome in addition to systemic polymyxin-B? Materials and methods: In a randomized control trial, invasively ventilated adult ICU patients with HAP in whom clinicians decided to start systemic polypeptide antibiotics, were randomized to receive either intravenous polymyxin-B plus high-dose colistin nebulization (5-MIU 8-hourly) using specific protocol or intravenous polymyxin-B alone. Results: The study was closed early after recruiting 60% of planned patients because of slow rate of recruitment (24 patients in over 30 months). Treatment success (Primary outcome) was nonsignificantly higher in intervention group (63.66 vs 30.77%; p = 0.217). There was higher rate of microbiological cure in intervention group (60 vs 9.09%: p = 0.018). Numerically better secondary outcomes including fever-free days, ventilator- or vasopressor free days at day-7, ICU and hospital mortality also did not reach statistical significance. Two episodes of transient hypoxia were seen during aerosol delivery. However, overall incidences of adverse effects were not different between groups. Conclusion: This study could not confirm superiority of high-dose colistin aerosolization plus systemic polymyxin-B strategy over polymyxin-B alone in treating HAP due to extensive drug resistance (XDR) gram-negative pathogens. How to cite this article: Ghosh S. Polymyxin B Plus Aerosolized Colistin vs Polymyxin B Alone in Hospital-acquired Pneumonia ("AEROCOL" Study): A Feasibility Study. Indian J Crit Care Med 2024;28(8):792-795.

A Lysozyme Murein Hydrolase with Broad-Spectrum Antibacterial Activity from Enterobacter Phage myPSH1140.

Bacteriophages and bacteriophage-derived peptidoglycan hydrolases (endolysins) present promising alternatives for the treatment of infections caused by multidrug resistant Gram-negative and Gram-positive pathogens. In this study, Gp105, a putative lysozyme murein hydrolase from Enterobacter phage myPSH1140 was characterized in silico, in vitro as well as in vivo using the purified protein. Gp105 contains a T4-type lysozyme-like domain (IPR001165) and belongs to Glycoside hydrolase family 24 (IPR002196). The putative endolysin indeed had strong antibacterial activity against Gram-negative pathogens, including E. cloacae, K. pneumoniae, P. aeruginosa, S. marcescens, Citrobacter sp., and A. baumannii. Also, an in vitro peptidoglycan hydrolysis assay showed strong activity against purified peptidoglycans. This study demonstrates the potential of Gp105 to be used as an antibacterial protein to combat Gram-negative pathogens.

Defining the core essential genome of Pseudomonas aeruginosa.

Genomics offered the promise of transforming antibiotic discovery by revealing many new essential genes as good targets, but the results fell short of the promise. While numerous factors contributed to the disappointing yield, one factor was that essential genes for a bacterial species were often defined based on a single or limited number of strains grown under a single or limited number of in vitro laboratory conditions. In fact, the essentiality of a gene can depend on both the genetic background and growth condition. We thus developed a strategy for more rigorously defining the core essential genome of a bacterial species by studying many pathogen strains and growth conditions. We assessed how many strains must be examined to converge on a set of core essential genes for a species. We used transposon insertion sequencing (Tn-Seq) to define essential genes in nine strains of Pseudomonas aeruginosa on five different media and developed a statistical model, FiTnEss, to classify genes as essential versus nonessential across all strain-medium combinations. We defined a set of 321 core essential genes, representing 6.6% of the genome. We determined that analysis of four strains was typically sufficient in P. aeruginosa to converge on a set of core essential genes likely to be essential across the species across a wide range of conditions relevant to in vivo infection, and thus to represent attractive targets for novel drug discovery.

SurA-like and Skp-like Proteins as Important Virulence Determinants of the Gram Negative Bacterial Pathogens.

In the Gram-negative bacteria, many important virulence factors reach their destination via two-step export systems, and they must traverse the periplasmic space before reaching the outer membrane. Since these proteins must be maintained in a structure competent for transport into or across the membrane, they frequently require the assistance of chaperones. Based on the results obtained for the model bacterium Escherichia coli and related species, it is assumed that in the biogenesis of the outer membrane proteins and the periplasmic transit of secretory proteins, the SurA peptidyl-prolyl isomerase/chaperone plays a leading role, while the Skp chaperone is rather of secondary importance. However, detailed studies carried out on several other Gram-negative pathogens indicate that the importance of individual chaperones in the folding and transport processes depends on the properties of client proteins and is species-specific. Taking into account the importance of SurA functions in bacterial virulence and severity of phenotypes due to surA mutations, this folding factor is considered as a putative therapeutic target to combat microbial infections. In this review, we present recent findings regarding SurA and Skp proteins: their mechanisms of action, involvement in processes related to virulence, and perspectives to use them as therapeutic targets.

Restriction of chronic Escherichia coli urinary tract infection depends upon T cell-derived interleukin-17, a deficiency of which predisposes to flagella-driven bacterial persistence.

Urinary tract infections (UTI) frequently progress to chronicity in infected individuals but the mechanisms of pathogenesis underlying chronic UTI are not well understood. We examined the role of interleukin (IL)-17A in UTI because this cytokine promotes innate defense against uropathogenic Escherichia coli (UPEC). Analysis of UPEC persistence and pyelonephritis in mice deficient in IL-17A revealed that UPEC CFT073 caused infection at a rate higher than the multidrug resistant strain EC958. Il17a-/- mice exhibited pyelonephritis with kidney bacterial burdens higher than those of wild-type (WT) mice. Synthesis of IL-17A in the bladder reflected a combination of γδ-T and TH 17 cell responses. Analysis of circulating inflammatory mediators at 24h postinoculation identified predictors of progression to chronicity, including IL-6 and monocyte chemoattractant protein-1 (MCP-1). Histological analysis identified infiltrating populations of neutrophils, NK cells, and γδ T cells in the bladder, whereas neutrophils predominated in the kidney. Analysis of the contribution of flagella to chronicity using hyper-flagellated and fliC-deficient UPEC in WT and Il17a-/- mice revealed that, in a host that is deficient for the production of IL-17A, flagella contribute to bacterial persistence. These findings show a role for IL-17A in defense against chronic UTI and a contribution of flagella to the pathogenesis of infection.

Local complications of adjunct intrathecal antibiotics for nosocomial meningitis associated with gram-negative pathogens: a meta-analysis.

Direct delivery of antibiotics to the ventricular system offers an alternative for the management of nosocomial meningitis. However, the available literature frequently results in controversial findings regarding its safety. The present meta-analysis aimed at summarizing the risk of local complications after the administration of intraventricular/intrathecal (IVT/IT) antibiotics for the treatment of ventriculitis/meningitis (VM) associated with gram-negative pathogens. We systematically searched the medical literature from 1964 until July 2018, for clinical studies reporting on complications after the index treatment. The quality of the eligible studies was classified as "high," "moderated," and "low" for randomized controlled trials, observational studies, and case series, respectively. The results were summarized as pooled frequencies, estimated by the random- or fixed-effects models, according to the inter-study heterogeneity. The publication bias was visualized in trim-and-fill funnel plots. Τhe analysis included twenty-three primary studies with 229 patients. The overall complication rate was as high as 0.13 (95% CI 0.08; 0.19, I2 = 9%); chemical meningitis and seizures represented the majority of the complications, with an occurrence rate of 0.11 (95% CI 0.07; 0.17, I2 = 0%) and 0.07 (95% CI 0.04; 0.12; I2 = 0%), respectively. The meta-analysis was based on studies of "moderate" and "low" reporting quality, while the publication bias after inspecting of the funnel plots revealed significant asymmetry. The present review denotes the absence of large, high-quality studies in the field. Nevertheless, IVT/IT was associated with moderate morbidity, mainly attributed to chemical meningitis and seizures. Further high-quality studies are still required before this therapeutic modality becomes broadly established.

Pentamidine sensitizes FDA-approved non-antibiotics for the inhibition of multidrug-resistant Gram-negative pathogens.

Pentamidine sensitizes FDA-approved antibiotics to combat Gram-negative pathogens. We screened 1374 FDA-approved non-antibiotics for their ability to be sensitized by pentamidine against Escherichia coli. We identified mitomycin C and mefloquine as potent hits effective against multiple drug-resistant, Gram-negative bacteria. Killing kinetics and an in vivo model with Caenorhabditis elegans (C. elegans) revealed that such combinations produced synergy against colistin-resistant Enterobacter cloacae (E. cloacae). These findings suggest combinations of FDA-approved non-antibiotics, and pentamidine can be repurposed into new antimicrobial agents.

Synthesis and in vitro activity of asymmetric indole-based bisamidine compounds against Gram-positive and Gram-negative pathogens.

A series of new asymmetric bisamidine was designed, synthesized, and tested for their in-vitro antibacterial activity using a range of Gram-positive and Gram-negative pathogens. Most compounds demonstrated powerful antibacterial activity, and interestingly, some displayed better activity against several Gram-negative strains than the lead compound 1. The most potent bisamidine 8l exhibited 4-fold more potent activity against E. coli, K. pneumonia, P. aeruginosa, and C. freundii than compound 1. Especially 8l exhibited a powerful activity against K. pneumonia secreting NDM-1 enzyme with a minimum inhibitory concentration (MIC) of 2 µg/mL, while levofloxacin and vancomycin displayed resistance, with MICs > 128 µg/mL.

The utility of endotracheal aspirate bacteriology in identifying mechanically ventilated patients at risk for ventilator associated pneumonia: a single-center prospective observational study.

BACKGROUND: Ventilator-associated pneumonia (VAP) is a well-known, life-threatening disease that persists despite preventative measures and approved antibiotic therapies. This prospective observational study investigated bacterial airway colonization, and whether its detection and quantification in the endotracheal aspirate (ETA) is useful for identifying mechanically ventilated ICU patients who are at risk of developing VAP. METHODS: 240 patients admitted to 3 ICUs at the Lahey Hospital and Medical Center (Burlington, MA) between June 2014 and June 2015 and mechanically ventilated for > 2 days were included. ETA samples and clinical data were collected. Airway colonization was assessed, and subsequently categorized into "heavy" and "light" by semi-quantitative microbiological analysis of ETAs. VAP was diagnosed retrospectively by the study sponsor according to a pre-specified pneumonia definition. RESULTS: Pathogenic bacteria were isolated from ETAs of 125 patients. The most common species isolated was S. aureus (56.8%), followed by K. pneumoniae, P. aeruginosa, and E. coli (35.2% combined). VAP was diagnosed in 85 patients, 44 (51.7%) with no bacterial pathogen, 18 associated with S. aureus and 18 Gram-negative-only cases, and 5 associated with other Gram-positive or mixed species. A higher proportion of patients who were heavily colonized with S. aureus developed VAP (32.4%) associated with S. aureus compared to those lightly colonized (17.6%). The same tendency was seen for patients heavily and lightly colonized with Gram-negative pathogens (30.0 and 0.0%, respectively). Detection of S. aureus in the ETA preceded S. aureus VAP by approximately 4 days, while Gram-negative organisms were first detected 2.5 days prior to Gram-negative VAP. VAP was associated with significantly longer duration of mechanical ventilation and hospitalization regardless of microbiologic cause when compared to patients who did not develop VAP. CONCLUSIONS: The overall VAP rate was 35%. Heavy tracheal colonization supported identification of patients at higher risk of developing a corresponding S. aureus or Gram-negative VAP. Detection of bacterial ETA-positivity tended to precede VAP.

Ebselen bearing polar functionality: Identification of potent antibacterial agents against multidrug-resistant Gram-negative bacteria.

Antibiotic-resistant bacteria has become one of the greatest challenges to global human health today. Innovative strategies are needed to identify new therapeutic leads to tackle infections of drug-resistant Gram-negative bacteria. We herein synthesize a series of EB analogues to investigate their antibacterial activities. Select polar functionality at N-terminus of EB exhibited higher activities against multi-drug-resistant Gram-negative pathogens, including E. coli, P. aeruginosa and K. pneumoniae. EB analogue 4g and 4i exhibited potent antibacterial activities against E. coli-ESBL (MIC = 1-4 µg/mL) and E. coli producing NDM-1 (MIC = 4-32 µg/mL), which is superior to the traditional antibiotics (cefazolin, imipenem). Furthermore, the time-kill kinetics studies and the inhibition zone tests indicated that analogue 4i effectively and rapidly cause death of E. coli-ESBL and E. coli-NDM-1. Additionally, accumulation assays and SEM images showed that 4i could permeate bacterial membranes, leading to an irregular cell morphology. Importantly, bacterial resistance for analogue 4i was difficult to induce against E. coli-ESBL. EB analogues here reported low cytotoxicity against L-929 cells and mice model in vivo. We believe that EB analogues with polar functionality could play a pivotal role in the development of novel antibacterial agents in eradicating multi-drug-resistant Gram-negative pathogens infections.

Nationwide epidemiology of early-onset sepsis in Israel 2010-2015, time to re-evaluate empiric treatment.

AIM: Early-onset neonatal sepsis (EOS) may lead to significant morbidity and mortality, yet the recommended antimicrobials have not changed for many years. We aimed to optimise EOS treatment by examining EOS pathogens, resistance rates and resistance risk factors. METHODS: A retrospective, nationwide cohort study analysing 2010-2015 EOS data in Israel. RESULTS: The 21 participating centres constitute 92% of the total birth cohort (around 180 000 live births/year). Of 549 EOS neonates (0.57/1000 live births), 306 (56%) and 243 (44%) were full-term and preterm, respectively (0.35 vs. 2.94 per/1000 live births). Gram-negative pathogens predominated, especially in preterms. Escherichia coli and Streptococcus agalactiae were most common pathogens (0.2 and 0.19 per 1000 live births, respectively). In 277 Gram-negatives, 16%, 14%, 8% and 3% were gentamicin-resistant, extended-spectrum beta-lactamase (ESBL)-positive, gentamicin-resistant and ESBL-positive, and amikacin-resistant, respectively; preterms had higher resistance rates. No risk factors for antimicrobial resistance were identified. Mortality was reported in 21% of Gram-negative EOS versus 7% of Gram-positive EOS [OR 3.4 (95% CI 1.8-6.2), p < 0.01]. CONCLUSION: In this nationwide study, EOS was caused predominantly by Gram-negatives, with high gentamicin resistance and ESBL phenotype rates, without identifiable resistance risk factors. As EOS is life-threatening, modification of empiric therapy for amikacin-based regimens should be considered, mainly in preterms.

Increasing the Antimicrobial Activity of Nisin-Based Lantibiotics against Gram-Negative Pathogens.

Lantibiotics are ribosomally synthesized and posttranslationally modified antimicrobial compounds containing lanthionine and methyl-lanthionine residues. Nisin, one of the most extensively studied and used lantibiotics, has been shown to display very potent activity against Gram-positive bacteria, and stable resistance is rarely observed. By binding to lipid II and forming pores in the membrane, nisin can cause the efflux of cellular constituents and inhibit cell wall biosynthesis. However, the activity of nisin against Gram-negative bacteria is much lower than that against Gram-positive bacteria, mainly because lipid II is located at the inner membrane, and the rather impermeable outer membrane in Gram-negative bacteria prevents nisin from reaching lipid II. Thus, if the outer membrane-traversing efficiency of nisin could be increased, the activity against Gram-negative bacteria could, in principle, be enhanced. In this work, several relatively short peptides with activity against Gram-negative bacteria were selected from literature data to be fused as tails to the C terminus of either full or truncated nisin species. Among these, we found that one of three tails (tail 2 [T2; DKYLPRPRPV], T6 [NGVQPKY], and T8 [KIAKVALKAL]) attached to a part of nisin displayed improved activity against Gram-negative microorganisms. Next, we rationally designed and reengineered the most promising fusion peptides. Several mutants whose activity significantly outperformed that of nisin against Gram-negative pathogens were obtained. The activity of the tail 16 mutant 2 (T16m2) construct against several important Gram-negative pathogens (i.e., Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter aerogenes) was increased 4- to 12-fold compared to that of nisin. This study indicates that the rational design of nisin can selectively and significantly improve its outer membrane-permeating capacity as well as its activity against Gram-negative pathogens.IMPORTANCE Lantibiotics are antimicrobial peptides that are highly active against Gram-positive bacteria but that have relatively poor activity against most Gram-negative bacteria. Here, we modified the model lantibiotic nisin by fusing parts of it to antimicrobial peptides with known activity against Gram-negative bacteria. The appropriate selection of peptidic moieties that could be attached to (parts of) nisin could lead to a significant increase in its inhibitory activity against Gram-negative bacteria. Using this strategy, hybrids that outperformed nisin by displaying 4- to 12-fold higher levels of activity against relevant Gram-negative bacterial species were produced. This study shows the power of modified peptide engineering to alter target specificity in a desired direction.

Design, solid-phase synthesis and evaluation of enterobactin analogs for iron delivery into the human pathogen Campylobacter jejuni.

The human enteropathogen Campylobacter jejuni, like many bacteria, employs siderophores such as enterobactin for cellular uptake of ferric iron. This transport process has been shown to be essential for virulence and presents an attractive opportunity for further study of the permissiveness of this pathway to small-molecule intervention and as inspiration for the development of synthetic carriers that may effectively transport cargo into Gram-negative bacteria. In this work, we have developed a facile and robust microscale assay to measure growth recovery of C. jejuni NCTC 11168 in liquid culture as a result of ferric iron uptake. In parallel, we have established the solid-phase synthesis of catecholamide compounds modeled on enterobactin fragments. Applying these methodological developments, we show that small synthetic iron chelators of minimal dimensions provide ferric iron to C. jejuni with equal or greater efficiency than enterobactin.

Effect of prior receipt of antibiotics on the pathogen distribution and antibiotic resistance profile of key Gram-negative pathogens among patients with hospital-onset urinary tract infections.

BACKGROUND: This retrospective cohort study characterized the impact of prior antibiotic exposure on distribution and nonsusceptibility profiles of Gram-negative pathogens causing hospital-onset urinary tract infections (UTI). METHODS: Hospital patients with positive urine culture for Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and other Enterobacteriaceae ≥3 days after hospital admission were included. Assessment outcomes included the distribution of bacteria in urine cultures, antibiotic susceptibility patterns, and the effect of prior antibiotic exposure, defined as 0, 1, or ≥2 prior antibiotics, on the distribution and antibiotic susceptibility profiles of the Gram-negative organisms. RESULTS: The most commonly isolated pathogens from 5574 unique UTI episodes (2027 with and 3547 without prior antibiotic exposure) were E. coli (49.5%), K. pneumoniae (17.1%), and P. aeruginosa (8.2%). P. aeruginosa was significantly more commonly isolated in patients with ≥2 prior antibiotic exposures (12.6%) compared with no exposure (8.2%; p = 0.036) or 1 prior exposure (7.9%; p = 0.025). Two or more prior antibiotic exposures were associated with slightly higher incidences of fluoroquinolone nonsusceptibility, multidrug resistance, and extended-spectrum ß-lactamase phenotype compared with 0 or 1 exposure, suggesting an increased risk for resistant Gram-negative pathogens among hospital patients with urinary tract infections occurring ≥3 days after admission. CONCLUSIONS: Clinicians should critically assess prior antibiotic exposure when selecting empirical therapy for patients with hospital-onset urinary tract infections caused by Gram-negative pathogens.