An in silico approach for understanding the molecular evolution of clinically important metallo-beta-lactamases

Comparison of ERIC carbapenem-resistant Enterobacteriaceae test, BD Phoenix CPO detect panel, and NG-test CARBA 5 for the detection of main carbapenemase types of carbapenem-resistant Enterobacterales

BACKGROUND

This study aimed to assess the performance of three commercial panels, the ERIC Carbapenem-Resistant Enterobacteriaceae Test (ERIC CRE test), the NG-Test CARBA 5 (NG CARBA 5), and the BD Phoenix CPO Detect Panel (CPO panel), for the detection of main types of carbapenemases among carbapenem-resistant Enterobacterales (CRE).

METHODS

We collected 502 isolates of carbapenem-resistant Enterobacterales (CRE) demonstrating intermediate or resistant profiles to at least one carbapenem antibiotic (ertapenem, imipenem, meropenem, or doripenem). Carbapenemase genes and their specific types were identified through multiplex PCR and sequencing methods. Subsequently, the ERIC CRE test, CPO panel, and NG CARBA 5 assay were conducted on these isolates, and the results were compared with those obtained from multiplex PCR.

RESULTS

The results indicated that the ERIC CRE test exhibited an overall sensitivity and specificity of 98.1% and 93.6%, respectively, which were comparable to 99.1% and 90.6% for the NG CARBA 5. However, the CPO panel demonstrated a sensitivity of only 56.2% in identifying Ambler classes, exhibiting the poorest sensitivity for class A. Moreover, while the ERIC CRE test outperformed the NG CARBA 5 in identifying multi-gene isolates with multiple carbapenemase-encoding genes, the CPO panel failed to accurately classify these isolates.

CONCLUSIONS

Our findings support the utilization of the ERIC CRE test as one of the methods for detecting carbapenemases in clinical laboratories. Nonetheless, further optimization is imperative for the CPO panel to enhance its accuracy in determining carbapenemase classification and address limitations in detecting multi-gene isolates.

In silico and In vitro Analysis of Nigella sativa Bioactives Against Chorismate Synthase of Listeria monocytogenes: a Target Protein for Biofilm Inhibition

Listeria monocytogenes have the ability to form biofilms, which aid in the contamination of food and the evasion of antimicrobials. Consumption of L. monocytogenes laden food can promote mild to severe infection in humans and cause serious health issues. Therefore, biofilm development by L. monocytogenes is considered to be a major concern for both healthcare and food safety. This study attempted to target chorismate synthase, an essential protein predicted to be involved in the biofilm pathway. Nigella sativa is renowned for its applications in folk medicine; hence, bioactive ingredients reported were used for molecular docking studies. In the absence of a three-dimensional structure of chorismate synthase from L. monocytogenes, a homology model was generated using the Modeller program. A model with the highest DOPE score was chosen and validated. The reliable model was subjected to docking studies with 30 ligands from N. sativa. From this approach, α-longipinene was unveiled as the best hit. Further in vitro studies demonstrated the antibiofilm potential of α-longipinene against L. monocytogenes. Overall, the study reveals lead molecules from N. sativa as promising antibiofilm agents against L. monocytogenes. Hence, extended investigation with lead molecules will provide sustainable strategies to prevent biofilm-mediated problems due to L. monocytogenes.

Comparative genomics reveals the evolution of antimicrobial resistance in Bacteroides nordii

Bacteroides nordii, is an understudied member of the pathogenic B. fragilis group which comprises several multidrug-resistant (MDR) strains. Thus, it is of great interest to study the genome biology of Bacteroides nordii. However, no detailed study is available that characterized B. nordii at the genetic level and explored its role as a potential pathogen. We isolated an MDR strain viz., B. nordii PGMM4098 from the pus sample and subjected it to whole genome sequencing using Illumina technology. The draft genome was de-novo assembled and annotated, followed by comprehensive comparative genomics analyses using the publicly available genome dataset of B. nordii. The pan-genome analysis revealed the open nature of B. nordii, indicating the continuous accumulation of novel genes in non-core components leading to the emergence of new strains of this species. The thirteen antimicrobial resistance (AMR) genes identified in the genomes of all B. nordii strains were part of the non-core component of the pan-genome. Of these, four AMR genes, nimE, aadS, mef(En2), and ermB/F/G were found to be acquired via the process of horizontal gene transfer (HGT) from anaerobic Bacteroidetes. Importantly, the nimE gene conferring metronidazole resistance was found to be present only in B. nordii PGMM4098, which harbors five other AMR genes encoded in its genome. Of these, nimE (metronidazole resistance), ermB/F/G (macrolide-lincosamide-streptogramin B resistance), and cfxA2/A3 (class A β-lactam resistance) genes were further validated using targeted polymerase chain reaction assay. Notably, these three genes were also found to be under the operation of positive selective pressure suggesting the diversification of these genes, which might lead to the emergence of new MDR strains of B. nordii in the near future. Our study reported and characterized the genome of the first MDR strain of B. nordii and revealed the AMR evolution in this species using a comprehensive comparative genomics approach.

Deciphering the evolution of metallo-β-lactamases: a journey from the test tube to the bacterial periplasm

Understanding the evolution of metallo-β-lactamases (MBLs) is fundamental to deciphering the mechanistic basis of resistance to carbapenems in pathogenic and opportunistic bacteria. Presently, these MBL producing pathogens are linked to high rates of morbidity and mortality worldwide. However, the study of the biochemical and biophysical features of MBLs in vitro provides an incomplete picture of their evolutionary potential, since this limited and artificial environment disregards the physiological context where evolution and selection take place. Herein, we describe recent efforts aimed to address the evolutionary traits acquired by different clinical variants of MBLs in conditions mimicking their native environment (the bacterial periplasm) and considering whether they are soluble or membrane-bound proteins. This includes addressing the metal content of MBLs within the cell under zinc starvation conditions, and the context provided by different bacterial hosts that result in particular resistance phenotypes. Our analysis highlights recent progress bridging the gap between in vitro and in-cell studies.

Enzyme Inhibitors: The Best Strategy to Tackle Superbug NDM-1 and Its Variants

Multidrug bacterial resistance endangers clinically effective antimicrobial therapy and continues to cause major public health problems, which have been upgraded to unprecedented levels in recent years, worldwide. β-Lactam antibiotics have become an important weapon to fight against pathogen infections due to their broad spectrum. Unfortunately, the emergence of antibiotic resistance genes (ARGs) has severely astricted the application of β-lactam antibiotics. Of these, New Delhi metallo-β-lactamase-1 (NDM-1) represents the most disturbing development due to its substrate promiscuity, the appearance of variants, and transferability. Given the clinical correlation of β-lactam antibiotics and NDM-1-mediated resistance, the discovery, and development of combination drugs, including NDM-1 inhibitors, for NDM-1 bacterial infections, seems particularly attractive and urgent. This review summarizes the research related to the development and optimization of effective NDM-1 inhibitors. The detailed generalization of crystal structure, enzyme activity center and catalytic mechanism, variants and global distribution, mechanism of action of existing inhibitors, and the development of scaffolds provides a reference for finding potential clinically effective NDM-1 inhibitors against drug-resistant bacteria.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-β-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-β-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.

Ceftazidime Is the Key Diversification and Selection Driver of VIM-Type Carbapenemases

In recent decades, carbapenems have been considered the last line of antibiotic therapy for Gram-negative bacterial infections. Unfortunately, strains carrying a high diversity of β-lactamases able to hydrolyze carbapenems have emerged in the clinical setting. Among them, VIM β-lactamases have diversified in a bloom of variants. The evolutionary reconstructions performed in this work revealed that, at the end of the 1980s, two independent events involving diversification from VIM-2 and VIM-4 produced at least 25 VIM variants. Later, a third event involving diversification from VIM-1 occurred in the mid-1990s. In a second approach to understanding the emergence of VIM carbapenemases, 44 mutants derived from VIM-2 and VIM-4 were obtained by site-directed mutagenesis based on those positions predicted to be under positive selection. These variants were expressed in an isogenic context. The more-evolved variants yielded increased levels of hydrolytic efficiency toward ceftazidime to a higher degree than toward carbapenems. In fact, an antagonist effect was frequently observed. These results led us to develop an experimental-evolution step. When Escherichia coli strains carrying VIM-2 or VIM-4 were submitted to serial passages at increasing concentrations of carbapenems or ceftazidime, more-efficient new variants (such as VIM-11 and VIM-1, with N165S [bearing a change from N to S at position 165] and R228S mutations, respectively) were only obtained when ceftazidime was present. Therefore, the observed effect of ceftazidime in the diversification and selection of VIM variants might help to explain the recent bloom of carbapenemase diversity, and it also represents another example of the potential universal effect exerted by ceftazidime in the selection of more-efficient β-lactamase variants, as in TEM, CTX-M, or KPC enzymes.

One of the objectives recently proposed by the World Health Organization (WHO) Assembly in the global plan on antimicrobial resistance was to improve the understanding and knowledge of antimicrobial resistance. In the present work, we paid attention to the drivers of diversification and selection of new carbapenemases in Gram-negative bacteria, which occupy one of the most critical places in the WHO priority list of antibiotic-resistant microorganisms. Based on evolutionary-reconstruction, site-directed-mutagenesis, and experimental-evolution approaches, we proposed a critical role of ceftazidime exposure in the selection of VIM carbapenemase variants. This surprising finding is also applicable to other β-lactamases, indicating that ceftazidime, and not other antibiotics, might have a universal effect in the diversification of β-lactamases. Our results might help to define future strategies to reconsider the extended use of ceftazidime.

A molecular dynamics study of the complete binding process of meropenem to New Delhi metallo-β-lactamase 1

The mechanism of substrate hydrolysis of New Delhi metallo-β-lactamase 1 (NDM-1) has been reported, but the process in which NDM-1 captures and transports the substrate into its active center remains unknown. In this study, we investigated the process of the substrate entry into the NDM-1 activity center through long unguided molecular dynamics simulations using meropenem as the substrate. A total of 550 individual simulations were performed, each of which for 200 ns, and 110 of them showed enzyme-substrate binding events. The results reveal three categories of relatively persistent and noteworthy enzyme-substrate binding configurations, which we call configurations A, B, and C. We performed binding free energy calculations of the enzyme-substrate complexes of different configurations using the molecular mechanics Poisson-Boltzmann surface area method. The role of each residue of the active site in binding the substrate was investigated using energy decomposition analysis. The simulated trajectories provide a continuous atomic-level view of the entire binding process, revealing potentially valuable regions where the enzyme and the substrate interact persistently and five possible pathways of the substrate entering into the active center, which were validated using well-tempered metadynamics. These findings provide important insights into the binding mechanism of meropenem to NDM-1, which may provide new prospects for the design of novel metallo-β-lactamase inhibitors and enzyme-resistant antibiotics.

An in silico approach to elucidate structure based functional evolution of oxacillinase

Bacterial Oxacillinases (OXAs), genetically being extremely diverse and highly versatile in hydrolyzing antibiotics of different classes, holds utmost significant clinical importance. Hence, to analyze functional evolution of this enzyme, plausible changes in drug profile, affinity and binding stability of different subclasses of OXA with their preferred drugs, viz. penicillin, ceftazidime, imipenem/meropenem were investigated. Maximum-Likelihood dendrogram was constructed and based on tree topology, the least and most divergent variants of each clade were selected. Pocket characterization, enzyme structural stability and mutational effect were analyzed in silico. Modes of interaction of selected OXA variants with respective antibiotics were analyzed by Autodock4.0 and LIGPLOT. Comparative mobility profiling and subsequent ΔG° and Km calculations of representative OXA variants revealed that after RSBL evolution, perhaps, two competitive strategies evolved among the OXA variants. Either loops flanking helix5 gets stabilized or it becomes more flexible. Therefore, while OXA variants (e.g. OXA-2, OXA-32, OXA-23, OXA-133, OXA-24, OXA-25, OXA-51 and OXA-75) with highly stabilized loops flanking helix5 exhibited improved binding stability and affinity towards carbapenems, especially meropenem, OXA variants (e.g. OXA-10, OXA-251, OXA-48 and OXA-247) possessing highly flexibile loops flanking helix5 revealed their catalytic proficiency towards ceftazidime. Moreover, LIGPLOT and PROMALS3D jointly identified ten consensuses/conserved residues, viz. P68, A69, F72, K73, W105, V120, W164, L169, K216 and G218 to be critical for drug hydrolysis. Hence, novel inhibitors could be designed to target these sites.

Evolution of Metallo-β-lactamases: Trends Revealed by Natural Diversity and in vitro Evolution

The production of β-lactamase enzymes is one of the most distributed resistance mechanisms towards β-lactam antibiotics. Metallo-β-lactamases constitute a worrisome group of these kinds of enzymes, since they present a broad spectrum profile, being able to hydrolyze not only penicillins, but also the latest generation of cephalosporins and carbapenems, which constitute at present the last resource antibiotics. The VIM, IMP, and NDM enzymes comprise the main groups of clinically relevant metallo-β-lactamases. Here we present an update of the features of the natural variants that have emerged and of the ones that have been engineered in the laboratory, in an effort to find sequence and structural determinants of substrate preferences. This knowledge is of upmost importance in novel drug design efforts. We also discuss the advances in knowledge achieved by means of in vitro directed evolution experiments, and the potential of this approach to predict natural evolution of metallo-β-lactamases.

Elucidating the Role of Residue 67 in IMP-Type Metallo-β-Lactamase Evolution

Antibiotic resistance in bacteria is ever changing and adapting, as once-novel β-lactam antibiotics are losing their efficacy, primarily due to the production of β-lactamases. Metallo-β-lactamases (MBLs) efficiently inactivate a broad range of β-lactam antibiotics, including carbapenems, and are often coexpressed with other antibacterial resistance factors. The rapid dissemination of MBLs and lack of novel antibacterials pose an imminent threat to global health. In an effort to better counter these resistance-conferring β-lactamases, an investigation of their natural evolution and resulting substrate specificity was employed. In this study, we elucidated the effects of different amino acid substitutions at position 67 in IMP-type MBLs on the ability to hydrolyze and confer resistance to a range of β-lactam antibiotics. Wild-type β-lactamases IMP-1 and IMP-10 and mutants IMP-1-V67A and IMP-1-V67I were characterized biophysically and biochemically, and MICs for Escherichia coli cells expressing these enzymes were determined. We found that all variants exhibited catalytic efficiencies (kcat/Km) equal to or higher than that of IMP-1 against all tested β-lactams except penicillins, against which IMP-1 and IMP-1-V67I showed the highest kcat/Km values. The substrate-specific effects of the different amino acid substitutions at position 67 are discussed in light of their side chain structures and possible interactions with the substrates. Docking calculations were employed to investigate interactions between different side chains and an inhibitor used as a β-lactam surrogate. The differences in binding affinities determined experimentally and computationally seem to be governed by hydrophobic interactions between residue 67 and the inhibitor and, by inference, the β-lactam substrates.

Worldwide dissemination of the NDM-type carbapenemases in Gram-negative bacteria

The emergence of one of the most recently described carbapenemases, namely, the New Delhi metallo-lactamase (NDM-1), constitutes a critical and growingly important medical issue. This resistance trait compromises the efficacy of almost all lactams (except aztreonam), including the last resort carbapenems. Therapeutical options may remain limited mostly to colistin, tigecycline, and fosfomycin. The main known reservoir of NDM producers is the Indian subcontinent whereas a secondary reservoir seems to have established the Balkans regions and the Middle East. Although the spread of bla NDM-like genes (several variants) is derived mostly by conjugative plasmids in Enterobacteriaceae, this carbapenemase has also been identified in P. aeruginosa and Acinetobacter spp. Acinetobacter sp. may play a pivotal role for spreading bla NDM genes for its natural reservoir to Enterobacteriaceae. Rapid diagnostic techniques (Carba NP test) and screening of carriers are the cornerstone to try to contain this outbreak which threatens the efficacy of the modern medicine.