Overall mutational scanning unveils the essential active residues for the mechanistic action of MCR-1.

Polymyxins, including colistin and polymyxin B, serve as crucial last-resort antibiotics for managing infections caused by carbapenem-resistant Enterobacterales (CRE). However, the rapid spread of the mobilized colistin resistance gene (mcr-1) challenged the efficacy of treatment by polymyxins. The mcr-1 gene encoded a transmembrane phosphoethanolamine (PEA) transferase enzyme, MCR-1.

Repurposing cetylpyridinium chloride and domiphen bromide as phosphoethanolamine transferase inhibitor to combat colistin-resistant Enterobacterales.

The emergence of plasmid-encoded colistin resistance mechanisms, MCR-1, a phosphoethanolamine transferase, rendered colistin ineffective as last resort antibiotic against severe infections caused by clinical Gram-negative bacterial pathogens. Through screening FDA-approved drug library, we identified two structurally similar compounds, namely cetylpyridinium chloride (CET) and domiphen bromide (DOM), which potentiated colistin activity in both colistin-resistant and susceptible Enterobacterales. These compounds were found to insert their long carbon chain to a hydrophobic pocket of bacterial phosphoethanolamine transferases including MCR-1, competitively blocking the binding of lipid A tail for substrate recognition and modification, resulting in the increase of bacterial sensitivity to colistin.

C-terminal modification of a de novo designed antimicrobial peptide via capping of macrolactam rings.

In this work, by capping a macrolactam ring at the C-terminus of a de novo-designed peptide, namely zp80, we have constructed a small peptide library via the solid phase peptide synthesis for screening. Eight peptides bearing different aspartic acid-rich macrolactam rings but the same linear (IIRR) unit exhibited improved antibacterial activities, hemolytic activity, and selectivity index. Mechanistic studies revealed that they could destroy the integrity of bacterial envelope, leading to cytoplasm leakage and rapid dissipation of membrane potential.

Development of Peptide-based Metallo-β-lactamase Inhibitors as a New Strategy to Combat Antimicrobial Resistance: A Mini-review.

Global dissemination of antimicrobial resistance (AMR) not only poses a significant threat to human health, food security, and social development but also results in millions of deaths each year. In Gram-negative bacteria, the primary mechanism of resistance to β-lactam antibiotics is the production of β-lactamases, one of which is carbapenem-hydrolyzing β-lactamases known as carbapenemases. As a general scheme, these enzymes are divided into Ambler class A, B, C, and D based on their protein sequence homology.

Hydrophobic-hydrophilic Alternation: An effective Pattern to de novo Designed Antimicrobial Peptides.

The antimicrobial peptide (AMP) is a class of molecules that are active against a variety of microorganisms, from bacterial and cancer cells to fungi. Most AMPs are natural products, as part of an organism's own defense system against harmful microbes. However, the growing prevalence of drug resistance has forced researchers to design more promising engineered antimicrobial agents.

Functional and phylogenetic analysis of TetX variants to design a new classification system.

Recently, many TetX variants such as Tet(X3~14) were reported to confer resistance to tigecycline which is a last-resort antibiotic used to treat infections caused by multidrug-resistant bacteria. In this study, we identified essential residues including 329, 339, 340, 350, and 351 in TetX variants that mediated the evolution of the tigecycline-inactive Tet(X2) enzyme to the active forms of Tet(X3) and Tet(X4). Based on their amino acid sequences and functional features, we classified TetX variants into TetX-A class, TetX-B class and TetX-C class.

Unveiling the evolution routes of TEM-type extended-spectrum β-lactamases.

The TEM-1 β-lactamase can only cleave penicillin and the first-generation cephalosporins but it has evolved to become active against second-, third- and fourth-generation drugs. Through sequence analysis of natural TEM variants and those created by mutagenesis experiments, we described two distinct evolution routes of TEM-1 that has generated over 220 enzyme variants. One began with the GlySer alteration and the other originated with the ArgSer substitution.

Structural and mechanistic basis of the high catalytic activity of monooxygenase Tet(X4) on tigecycline.

Background: Tigecycline is a tetracycline derivative that constitutes one of the last-resort antibiotics used clinically to treat infections caused by both multiple drug-resistant (MDR) Gram-negative and Gram-positive bacteria. Resistance to this drug is often caused by chromosome-encoding mechanisms including over-expression of efflux pumps and ribosome protection. However, a number of variants of the flavin adenine dinucleotide (FAD)-dependent monooxygenase TetX, such as Tet(X4), emerged in recent years as conferring resistance to tigecycline in strains of Enterobacteriaceae, Acinetobacter sp.

Structural and Functional Characterization of OXA-48: Insight into Mechanism and Structural Basis of Substrate Recognition and Specificity.

Class D β-lactamase OXA-48 is widely distributed among Gram-negative bacteria and is an important determinant of resistance to the last-resort carbapenems. Nevertheless, the detailed mechanism by which this β-lactamase hydrolyzes its substrates remains poorly understood. In this study, the complex structures of OXA-48 and various β-lactams were modeled and the potential active site residues that may interact with various β-lactams were identified and characterized to elucidate their roles in OXA-48 substrate recognition.

Identification of a Novel Metallo-β-Lactamase, VAM-1, in a Foodborne Vibrio alginolyticus Isolate from China.

A multidrug-resistant Vibrio alginolyticus isolate recovered from a shrimp sample with reduced carbapenem susceptibility produced a novel metallo-β-lactamase (MBL), VAM-1. That carbapenemase shared 67% to 70% amino acid identity with several VMB family subclass B1 MBLs, which were recently reported among some marine bacteria including , , and . The gene was located in a novel conjugative plasmid, namely, pC1579, and multiple copies of via an unusual mechanism of gene amplification were detected in pC1579.

An ornithine-rich dodecapeptide with improved proteolytic stability selectively kills gram-negative food-borne pathogens and its action mode on Escherichia coli O157:H7.

Food-borne pathogenic bacteria are dispersed throughout the entire chain of the food industry. However, many food preservatives are limited by poor biocompatibility such as cumulative poisoning. The antimicrobial peptide is increasingly regarded as a promising preservative in food research due to its high bioactivity and low cytotoxicity.

Epidemiological and phylogenetic analysis reveals Flavobacteriaceae as potential ancestral source of tigecycline resistance gene tet(X).

Emergence of tigecycline-resistance tet(X) gene orthologues rendered tigecycline ineffective as last-resort antibiotic. To understand the potential origin and transmission mechanisms of these genes, we survey the prevalence of tet(X) and its orthologues in 2997 clinical E. coli and K.

Chromosomal and Plasmid-Borne Tigecycline Resistance Genes (X3) and (X4) in Dairy Cows on a Chinese Farm.

We isolated 47 strains carrying (X3) and 4 ST767 strains carrying (X4) from 296 rectal swab samples from dairy cows on a Chinese farm. (X3) was located on chromosomes or diverse plasmids, and (X4) was located on IncFIBκ/FIA(HI1)/X1 nontransferable plasmid. The coexistence of (X3) and carbapenemase genes, including and , was detected in 9 spp.

Genetic and Biochemical Characterization of VMB-1, a Novel Metallo-β-Lactamase Encoded by a Conjugative, Broad-Host Range IncC Plasmid from Vibrio spp.

The increasing incidence of phenotypic resistance to carbapenems in recent years is mainly attributed to acquisition of mobile carbapenemase-encoding genetic elements by major bacterial pathogens. Here, a novel carbapenemase known as Vibrio metallo-β-lactamase 1 (VMB-1), which is encoded by a gene (bla ) located in an integron-bearing, highly transmissible IncC type plasmid, namely pVB1796, is identified and characterized, both genetically and functionally. Recovered from a foodborne Vibrio alginolyticus strain that exhibits resistance to all known β-lactam antibiotics, pVB1796 is found to possess a hybrid backbone that exhibits unique features of both type 1 and type 2 IncC elements.

Designed Hexadecapeptides Synergize Glycopeptide Antibiotics Vancomycin and Teicoplanin against Pathogenic via Disruption of Cell Permeability and Potential.

Given the worldwide prevalence of pathogenic drug-resistant bacteria and the slow pace of new antibacterial development, discovering new uses for approved drugs that are outside the scope of the original indication is increasingly becoming an attractive proposition. In this work, seven linear cationic hexadecapeptides were designed, synthesized, and characterized. These amphiphilic peptides are able to transform from the random coil structure in water to α-helix in SDS solution and have only modest bioactivity to limited bacterial strains when used alone.

Emergence of an Empedobacter falsenii strain harbouring a tet(X)-variant-bearing novel plasmid conferring resistance to tigecycline.

Objectives: To investigate the genomic and phenotypic characteristics of an MDR Empedobacter falsenii strain isolated from a Chinese patient, which was phenotypically resistant to all last-line antibiotics (carbapenems, colistin and tigecycline).

Methods: Species identity was determined by MALDI-TOF MS analysis. The complete genome sequence of the isolate was determined by WGS and the genetic elements conferring antimicrobial resistance were determined.

Structural Insight into the Mechanism of Inhibitor Resistance in CTX-M-199, a CTX-M-64 Variant Carrying the ST Substitution.

The smart design of β-lactamase inhibitors allowed us to combat extended-spectrum β-lactamase (ESBL)-producing organisms for many years without developing resistance to these inhibitors. However, novel resistant variants have emerged recently, and notable examples are the CTX-M-190 and CTX-M-199 variants, which carried a ST amino acid substitution and exhibited resistance to inhibitors such as sulbactam and tazobactam. Using mass spectrometric and crystallographic approaches, this study depicted the mechanisms of inhibitor resistance.

Phenol-Soluble-Modulin-Inspired Amphipathic Peptides Have Bactericidal Activity against Multidrug-Resistant Bacteria.

Phenol-soluble modulins (PSMs) are a large family of cytolytic peptide toxins produced by Staphylococcus aureus. Based on their amino acid sequences, we have constructed a small library of cationic isoleucine-rich peptides for antimicrobial evaluation. Relative to the parent PSMs, peptide zp3 (GIIAGIIIKIKK-NH ) was found to possess greatly improved physicochemical properties (soluble in water) and antibacterial activity (MIC=8 μm for E.

Investigation of synergistic antimicrobial effects of the drug combinations of meropenem and 1,2-benzisoselenazol-3(2H)-one derivatives on carbapenem-resistant Enterobacteriaceae producing NDM-1.

The worldwide prevalence of NDM-1-producing bacteria has drastically undermined the clinical efficacy of the last line antibiotic of carbapenems, prompting a need to devise effective strategy to preserve their clinical value. Our previous studies have shown that ebselen can restore the efficacy of meropenem against a laboratory strain that produces NDM-1. Here we report the construction of a focused compound library of 1,2-benzisoselenazol-3(2H)-one derivatives which comprise a total of forty-six candidate compounds.

Genetic and Functional Characterization of , a Novel Tazobactam and Sulbactam Resistance-Encoding Gene Located in a Conjugative -Bearing IncI2 Plasmid.

We report the genetic and functional characterization of a novel CTX-M-199 β-lactamase, which was encoded by a variant gene found in a conjugative -bearing IncI2 plasmid and exhibited resistance to β-lactamase inhibitors, tazobactam, and sulbactam.

Crystal Structure of Escherichia coli originated MCR-1, a phosphoethanolamine transferase for Colistin Resistance.

MCR-1 is a phosphoethanolamine (pEtN) transferase that modifies the pEtN moiety of lipid A, conferring resistance to colistin, which is an antibiotic belonging to the class of polypeptide antibiotics known as polymyxins and is the last-line antibiotic used to treat multidrug resistant bacterial infections. Here we determined the crystal structure of the catalytic domain of MCR-1 (MCR-1-ED), which is originated in Escherichia coli (E. coli).

A trehalase from Zunongwangia sp.: characterization and improving catalytic efficiency by directed evolution.

Background: Trehalases have potential applications in several fields, including food additives, insecticide development, and transgenic plant. In the present study, we focused on a trehalase from the marine bacterium Zunongwangia sp., which hydrolyzes trehalose to glucose.

Enhanced nematicidal potential of the chitinase pachi from Pseudomonas aeruginosa in association with Cry21Aa.

Nematodes are known to be harmful to various crops, vegetables, plants and insects. The present study reports that, chitin upregulates the activity of chitinase (20%) and nematicidal potential (15%) of Pseudomonas aeruginosa. The chitinase gene (pachi) from P.