Infections due to vancomycin-resistant Enterococcus faecium resistant to linezolid

Semisynthetic guanidino lipoglycopeptides with potent in vitro and in vivo antibacterial activity

Gram-positive bacterial infections present a major clinical challenge, with methicillin- and vancomycin-resistant strains continuing to be a cause for concern. In recent years, semisynthetic vancomycin derivatives have been developed to overcome this problem as exemplified by the clinically used telavancin, which exhibits increased antibacterial potency but has also raised toxicity concerns. Thus, glycopeptide antibiotics with enhanced antibacterial activities and improved safety profiles are still necessary. We describe the development of a class of highly potent semisynthetic glycopeptide antibiotics, the guanidino lipoglycopeptides, which contain a positively charged guanidino moiety bearing a variable lipid group. These glycopeptides exhibited enhanced in vitro activity against a panel of Gram-positive bacteria including clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant strains, showed minimal toxicity toward eukaryotic cells, and had a low propensity for resistance selection. Mechanistically, guanidino lipoglycopeptides engaged with bacterial cell wall precursor lipid II with a higher binding affinity than vancomycin. Binding to both wild-type d-Ala-d-Ala lipid II and the vancomycin-resistant d-Ala-d-Lac variant was confirmed, providing insight into the enhanced activity of guanidino lipoglycopeptides against vancomycin-resistant isolates. The in vivo efficacy of guanidino lipoglycopeptide EVG7 was evaluated in a S. aureus murine thigh infection model and a 7-day sepsis survival study, both of which demonstrated superiority to vancomycin. Moreover, the minimal to mild kidney effects at supratherapeutic doses of EVG7 indicate an improved therapeutic safety profile compared with vancomycin. These findings position guanidino lipoglycopeptides as candidates for further development as antibacterial agents for the treatment of clinically relevant multidrug-resistant Gram-positive infections.

Enterococci as a One Health indicator of antimicrobial resistance

The rapid increase of antimicrobial-resistant bacteria in humans and livestock is concerning. Antimicrobials are essential for the treatment of disease in modern day medicine, and their misuse in humans and food animals has contributed to an increase in the prevalence of antimicrobial-resistant bacteria. Globally, antimicrobial resistance is recognized as a One Health problem affecting humans, animals, and environment. Enterococcal species are Gram-positive bacteria that are widely distributed in nature. Their occurrence, prevalence, and persistence across the One Health continuum make them an ideal candidate to study antimicrobial resistance from a One Health perspective. The objective of this review was to summarize the role of enterococci as an indicator of antimicrobial resistance across One Health sectors. We also briefly address the prevalence of enterococci in human, animal, and environmental settings. In addition, a 16S RNA gene-based phylogenetic tree was constructed to visualize the evolutionary relationship among enterococcal species and whether they segregate based on host environment. We also review the genomic basis of antimicrobial resistance in enterococcal species across the One Health continuum.

Antibiotic resistance and nanotechnology: A narrative review

The rise of antibiotic resistance poses a significant threat to public health worldwide, leading researchers to explore novel solutions to combat this growing problem. Nanotechnology, which involves manipulating materials at the nanoscale, has emerged as a promising avenue for developing novel strategies to combat antibiotic resistance. This cutting-edge technology has gained momentum in the medical field by offering a new approach to combating infectious diseases. Nanomaterial-based therapies hold significant potential in treating difficult bacterial infections by circumventing established drug resistance mechanisms. Moreover, their small size and unique physical properties enable them to effectively target biofilms, which are commonly linked to resistance development. By leveraging these advantages, nanomaterials present a viable solution to enhance the effectiveness of existing antibiotics or even create entirely new antibacterial mechanisms. This review article explores the current landscape of antibiotic resistance and underscores the pivotal role that nanotechnology plays in augmenting the efficacy of traditional antibiotics. Furthermore, it addresses the challenges and opportunities within the realm of nanotechnology for combating antibiotic resistance, while also outlining future research directions in this critical area. Overall, this comprehensive review articulates the potential of nanotechnology in addressing the urgent public health concern of antibiotic resistance, highlighting its transformative capabilities in healthcare.

Pharmacotherapies for multidrug-resistant gram-positive infections: current options and beyond

INTRODUCTION

Infections due to multidrug-resistant organisms (MDRO) are a serious concern for public health with high morbidity and mortality. Though many antibiotics have been introduced to manage these infections, there are remaining concerns regarding the optimal management of Gram-positive MDROs.

AREAS COVERED

A literature search on the PubMed/Medline database was conducted. We applied no language and time limits for the search strategy. In this narrative review, we discuss the current options for managing Gram-positive MDROs as well as non-traditional antibacterial agents in development.

EXPERT OPINION

Despite their introduction more than 70 years ago, glycopeptides are still the cornerstone in treating Gram-positive infections: all registrative studies of new antibiotics have glycopeptides as control; these studies are designed as not inferior studies, therefore it is almost impossible to give recommendations other than the use of glycopeptides in the treatment of Gram-positive infections. The best evidence on treatments different from glycopeptides comes from post-hoc analysis and meta-analysis. Non-traditional antibacterial agents are being studied to aid in short and effective antibiotic therapies. The use of non-traditional antibacterial agents is not restricted to replacing traditional antibacterial agents with alternative therapies; instead, they should be used in combination with antibiotic therapies.

Characterization of linezolid- and methicillin-resistant coagulase-negative staphylococci in a tertiary hospital in China

BACKGROUND

Recently, linezolid-resistant staphylococci have become an emerging problem worldwide. Understanding the mechanisms of resistance, molecular epidemiology and transmission of linezolid-resistant CoNS in hospitals is very important.

METHODS

The antimicrobial susceptibilities of all isolates were determined by the microdilution method. The resistance mechanisms and molecular characteristics of the strains were determined using whole-genome sequencing and PCR.

RESULTS

All the strains were resistant to oxacillin and carried the mecA gene; 13 patients (36.1%) had prior linezolid exposure. Most S. epidermidis and S. hominis isolates were ST22 and ST1, respectively. MLST typing and evolutionary analysis indicated most linezolid-resistant CoNS strains were genetically related. In this study, we revealed that distinct CoNS strains have different mechanisms of linezolid resistance. Among ST22-type S. epidermidis, acquisition of the T2504A and C2534T mutations in the V domain of the 23 S rRNA gene, as well as mutations in the ribosomal proteins L3 (L101V, G152D, and D159Y) and L4 (N158S), were linked to the development of linezolid resistance. In S. cohnii isolates, cfr, S158Y and D159Y mutations in the ribosomal protein L3 were detected. Additionally, emergence of the G2576T mutation and the cfr gene were major causes of linezolid resistance in S. hominis isolates. The cfr gene, G2576T and C2104T mutations, M156T change in L3 protein, and I188S change in L4 protein were found in S. capitis isolates.

CONCLUSION

The emergence of linezolid-resistant CoNS in the environment is concerning because it involves clonal dissemination and frequently coexists with various drug resistance mechanisms.

Expert opinion on antimicrobial therapies: is there enough scientific evidence to state that targeted therapies outperform non-targeted ones?

INTRODUCTION

Different active and passive strategies have been developed to fight against pathogenic bacteria. Those actions are undertaken to reduce the bacterial burden while minimizing the possibilities to develop not only antimicrobial resistance but also antimicrobial side-effects such as allergic or hypersensitivity reactions.

AREAS COVERED

We have reviewed preclinical results that evidence that targeted antimicrobial therapies outperform non-targeted ones. Active selective targeting against pathogenic bacteria has been achieved through the functionalization of antimicrobials, either alone or encapsulated within micro- or nanocarriers, with various recognition moieties. These moieties include peptides, aptamers, antibodies, carbohydrates, extracellular vesicles, cell membranes, infective agents, and other affinity ligands with specific bacterial tropism. Those selective ligands increase retention and enhance effectiveness reducing the side-effects and the required dose to exert the antimicrobial action at the site of infection.

EXPERT OPINION

When using targeted antimicrobial therapies not only reduced side-effects are observed, but also, compared to the administration of equivalent doses of the non-targeted drugs, a superior efficacy has been demonstrated against planktonic, sessile, and intracellular pathogenic bacterial persisters. The translation of those targeted therapies to subsequent phases of clinical development still requires the demonstration of a reduction in the probabilities for the pathogen to develop resistance when using targeted approaches.

Therapeutics for Vancomycin-Resistant Enterococcal Bloodstream Infections

Vancomycin-resistant enterococci (VRE) are common causes of bloodstream infections (BSIs) with high morbidity and mortality rates. They are pathogens of global concern with a limited treatment pipeline. Significant challenges exist in the management of VRE BSI, including drug dosing, the emergence of resistance, and the optimal treatment for persistent bacteremia and infective endocarditis. Therapeutic drug monitoring (TDM) for antimicrobial therapy is evolving for VRE-active agents; however, there are significant gaps in the literature for predicting antimicrobial efficacy for VRE BSIs. To date, TDM has the greatest evidence for predicting drug toxicity for the three main VRE-active antimicrobial agents daptomycin, linezolid, and teicoplanin. This article presents an overview of the treatment options for VRE BSIs, the role of antimicrobial dose optimization through TDM in supporting clinical infection management, and challenges and perspectives for the future.

Molecular epidemiology of bacteraemic vancomycin-resistant Enterococcus faecium isolates and in vitro activities of SC5005 and other comparators against these isolates collected from a medical centre in northern Taiwan, 2019-2020

OBJECTIVES

The global prevalence of vancomycin-resistant Enterococcus faecium (VREfm) highlights the need for new anti-enterococcal agents. Here, we assessed the molecular epidemiology of clinical VREfm bacteraemic isolates from a medical centre in northern Taiwan in 2019-2020 and to evaluate their susceptibility to last-line antibiotics and a new antimicrobial agent, SC5005.

METHODS

The molecular epidemiology of VREfm was investigated using van genotyping, MLST and PFGE. The susceptibilities of VREfm strains to antibiotics and SC5005 were determined using the agar dilution and broth microdilution methods. The capability of E. faecium to develop resistance to antibiotics and SC5005 was evaluated using frequency of resistance and multipassage resistance assays. The mode of action of SC5005 was assessed by time-kill, bacterial membrane integrity and membrane potential assays.

RESULTS

All 262 VREfm isolates harboured vanA gene, and the most prevalent sequence type was ST17 (51%, n = 134, 84 pulsotypes), followed by ST78 (25%, n = 65, 54 pulsotypes). Additionally, we identified four new STs (ST2101, ST2102, ST2135 and ST2136) and observed the arrival of multidrug-resistant ST1885 in Taiwan. Moreover, SC5005 was effective against all VREfm isolates, including those non-susceptible to last-line antibiotics. SC5005 can disrupt and depolarize the bacterial membrane to kill E. faecium without detectable resistance.

CONCLUSIONS

The findings provide insights into the latest epidemiology and resistance profiles of bacteraemic-causing VREfm in northern Taiwan. Additionally, SC5005 has the potential for development as a new therapeutic to treat VREfm infections.

Antibiotic resistant bacteria: A bibliometric review of literature

Antibiotic-resistant bacteria (ARB) are a serious threat to the health of people and the ecological environment. With this problem becoming more and more serious, more countries made research on the ARB, and the research number has been sharply increased particularly over the past decade. Therefore, it is quite necessary to globally retrace relevant researches on the ARB published from 2010 to 2020. This will help researchers to understand the current research situation, research trends and research hotspots in this field. This paper uses bibliometrics to examine publications in the field of ARB from 2010 to 2020 that were retrieved from the Web of Science (WOS). Our study performed a statistical analysis of the countries, institutions, journals, authors, research areas, author keywords, Essential Science Indicators (ESI) highly cited papers, and ESI hotspots papers to provide an overview of the ARB field as well as research trends, research hotspots, and future research directions in the field. The results showed that the number of related studies is increasing year by year; the USA is most published in the field of ARB; China is the most active in this field in the recent years; the Chinese Acad Sci published the most articles; Sci. Total Environ. published the greatest number of articles; CM Manaia has the most contributions; Environmental Sciences and Ecology is the most popular research area; and "antibiotic resistance," "antibiotics," and "antibiotic resistance genes" were the most frequently occurring author keywords. A citation analysis showed that aquatic environment-related antibiotic resistance is a key research area in this field, while antimicrobial nanomaterial-related research is a recent popular topic.

Detection of an Enterococcus faecium Carrying a Double Copy of the PoxtA Gene from Freshwater River, Italy

Oxazolidinones are valuable antimicrobials that are used to treat severe infections due to multidrug-resistant (MDR) Gram-positive bacteria. However, in recent years, a significant spread of clinically relevant linezolid-resistant human bacteria that is also present in animal and environmental settings has been detected and is a cause for concern. This study aimed to investigate the presence, genetic environments, and transferability of oxazolidinone resistance genes in enterococci from freshwater samples. A total of 10 samples were collected from a river in Central Italy. Florfenicol-resistant enterococci were screened for the presence of oxazolidinone resistance genes by PCR. Enterococcus faecium M1 was positive for the poxtA gene. The poxtA transfer (filter mating and aquaria microcosm assays), localization (S1-PFGE/hybridization), genetic context, and clonality of the isolate (WGS) were analyzed. Two poxtA copies were located on the 30,877-bp pEfM1, showing high-level identity and synteny to the pEfm-Ef3 from an E. faecium collected from an Italian coastal area. The isolate was able to transfer the poxtA to enterococcal recipients both in filter mating and aquaria microcosm assays. This is-to the best of our knowledge-the first detection of an enterococcus carrying a linezolid resistance gene from freshwater in Italy.

Therapeutic drug monitoring status of four common antibiotics: vancomycin, meropenem, linezolid and teicoplanin

Accurate therapeutic drug monitoring (TDM) of vancomycin, meropenem, linezolid and teicoplanin are conducive to developing optimal therapeutic regimes for patients. However, the measurement status of those drugs in different laboratories has not been reported. In this study, four samples including two frozen plasma samples and two lyophilized plasma samples were measured by over 35 laboratories across China. The inter- and intra-laboratory %CV, biases (%) of laboratories and intra- and inter-measurement-system %CV were calculated and analyzed. The short-term stability and homogeneity of those drugs in samples were studied. The results of frozen and lyophilized samples were also compared to determine whether there were significant differences in their matrix effects on various measurement systems. Results showed most laboratories' intra-laboratory %CVs were less than 9% for all drugs, and the mean inter-laboratory %CVs were 18.4%, 86.4%, 19.1% and 37.1% for vancomycin, meropenem, linezolid and teicoplanin measurements, respectively. For vancomycin, the intra-measurement %CV of commercial measurement systems was found to be smaller than that of other measurement systems. For meropenem, linezolid and teicoplanin, the agreement among laboratories using self-developed methods (Liquid chromatography-mass spectrometry [LC-MS] or high-performance liquid chromatography [HPLC]) was not satisfactory as most intra-measurement system CVs% were over 20%. Drugs in lyophilized samples were found to be more stable than in frozen samples, and no obvious differences in matrix effects were found for those two kinds of processed samples on most measurement systems. In conclusion, this study depicted the measurement status of those drugs in clinical laboratories, and found the lyophilized samples were more suitable EQA material for those drugs.

Oxazolidinones: mechanisms of resistance and mobile genetic elements involved

The oxazolidinones (linezolid and tedizolid) are last-resort antimicrobial agents used for the treatment of severe infections in humans caused by MDR Gram-positive bacteria. They bind to the peptidyl transferase centre of the bacterial ribosome inhibiting protein synthesis. Even if the majority of Gram-positive bacteria remain susceptible to oxazolidinones, resistant isolates have been reported worldwide. Apart from mutations, affecting mostly the 23S rDNA genes and selected ribosomal proteins, acquisition of resistance genes (cfr and cfr-like, optrA and poxtA), often associated with mobile genetic elements [such as non-conjugative and conjugative plasmids, transposons, integrative and conjugative elements (ICEs), prophages and translocatable units], plays a critical role in oxazolidinone resistance. In this review, we briefly summarize the current knowledge on oxazolidinone resistance mechanisms and provide an overview on the diversity of the mobile genetic elements carrying oxazolidinone resistance genes in Gram-positive and Gram-negative bacteria.

Comparison of Anti-Microbic and Anti-Biofilm Activity Among Tedizolid and Radezolid Against Linezolid-Resistant Enterococcus faecalis Isolates

Background

The emergence and spread of linezolid-resistant Enterococcus faecalis (E. faecalis) have emerged as a serious threat to human health globally. Therefore, this study aims to compare the anti-microbic as well as the anti-biofilm activity of linezolid, tedizolid, and radezolid against linezolid-resistant E. faecalis.

Methods

A total of 2128 E. faecalis isolates were assessed from the First Affiliated Hospital of Wenzhou Medical University from 2011 to 2019. Antibiotic sensitivity was evaluated using the micro broth dilution method. Oxazolidinone-resistant chromosomal and plasmid-borne genes such as cfr, cfr(A), cfr(B), cfr(C), cfr(D), optrA, and poxtA were detected by PCR and then sequenced to detect the presence of mutations in the domain V of the 23S rRNA and the ribosomal proteins L3, L4, and L22. Conjugation experiments were conducted using the broth method. The inhibition and eradication of biofilm were evaluated through crystal violet staining, whereas the efflux pump activities were detected by agar dilution.

Results

Out of 2128 isolated E. faecalis, 71 (3.34%) were linezolid-resistant isolates in which the MICs of tedizolid and radezolid ranged from 1 to 4 μg/mL and 0.5–1 μg/mL, respectively. The MIC₅₀/MIC₉₀ of tedizolid and radezolid were 4 and 8-fold lower than the linezolid, respectively. Out of 71 resistant isolates, 57 (80.28%) carried optrA, 1 (1.41%) carried cfr, 4 (5.63%) carried optrA and cfr, and 6 (8.45%) carried optrA and cfr(D), with no mutations of 23S rRNA gene and ribosomal proteins L3, L4, and L22. Besides, the transfer rate of the optrA, cfr, and cfr(D) was 17.91%, 0% and 0%, respectively. Radezolid showed more effectiveness in eradicating biofilm (8 × MIC). However, tedizolid was more effective than radezolid and linezolid in inhibiting the biofilm formation (1/4 MIC, 1/8MIC, and 1/16MIC). Additionally, in combination with CCCP, the MICs of radezolid in all linezolid-resistant isolates decreased ≥4-fold.

Conclusion

Radezolid showed greater antimicrobial activity than tedizolid and linezolid against linezolid-resistant E. faecalis. However, both tedizolid and radezolid showed differential activity on biofilm inhibition, eradication, and efflux pump compared to linezolid. Thus, our study might bring important clinical value in the application of these drugs for resistant pathogenic strains.

Current Landscape and Future Perspective of Oxazolidinone Scaffolds Containing Antibacterial Drugs

The widespread use of antibiotics has made the problem of bacterial resistance increasingly serious, and the study of new drug-resistant bacteria has become the main direction of antibacterial drug research. Among antibiotics, the fully synthetic oxazolidinone antibacterial drugs linezolid and tedizolid have been successfully marketed and have achieved good clinical treatment effects. Oxazolidinone antibacterial drugs have good pharmacokinetic and pharmacodynamic characteristics and unique antibacterial mechanisms, and resistant bacteria are sensitive to them. This Perspective focuses on reviewing oxazolidinones based on the structural modification of linezolid and new potential oxazolidinone drugs in the past 10 years, mainly describing their structure, antibacterial activity, safety, druggability, and so on, and discusses their structure-activity relationships, providing insight into the reasonable design of safer and more potent oxazolidinone antibacterial drugs.

Linezolid resistance in Enterococcus faecium and Enterococcus faecalis from hospitalized patients in Ireland: high prevalence of the MDR genes optrA and poxtA in isolates with diverse genetic backgrounds

OBJECTIVES

To investigate the prevalence of the optrA, poxtA and cfr linezolid resistance genes in linezolid-resistant enterococci from Irish hospitals and to characterize associated plasmids.

METHODS

One hundred and fifty-four linezolid-resistant isolates recovered in 14 hospitals between June 2016 and August 2019 were screened for resistance genes by PCR. All isolates harbouring resistance genes, and 20 without, underwent Illumina MiSeq WGS. Isolate relatedness was assessed using enterococcal whole-genome MLST. MinION sequencing (Oxford Nanopore) and hybrid assembly were used to resolve genetic environments/plasmids surrounding resistance genes.

RESULTS

optrA and/or poxtA were identified in 35/154 (22.7%) isolates, the highest prevalence reported to date. Fifteen isolates with diverse STs harboured optrA only; one Enterococcus faecium isolate harboured optrA (chromosome) and poxtA (plasmid). Seven Enterococcus faecalis and one E. faecium harboured optrA on a 36 331 bp plasmid with 100% identity to the previously described optrA-encoding conjugative plasmid pE349. Variations around optrA were also observed, with optrA located on plasmids in five isolates and within the chromosome in three isolates. Nine E. faecium and 10 E. faecalis harboured poxtA, flanked by IS1216E, within an identical 4001 bp region on plasmids exhibiting 72.9%-100% sequence coverage to a 21 849 bp conjugative plasmid. E. faecalis isolates belonged to ST480, whereas E. faecium isolates belonged to diverse STs. Of the remaining 119 linezolid-resistant isolates without linezolid resistance genes, 20 investigated representatives all harboured the G2576T 23S RNA gene mutation associated with linezolid resistance.

CONCLUSIONS

This high prevalence of optrA and poxtA in diverse enterococcal lineages in Irish hospitals indicates significant selective pressure(s) for maintenance.

Performance of commercial methods for linezolid susceptibility testing of Enterococcus faecium and Enterococcus faecalis

BACKGROUND

Linezolid-resistant enterococci (LRE) causing infections that are challenging to treat are rising, highlighting the need for reliable screening of LRE clinical isolates.

OBJECTIVES

To evaluate the ability of the broth microdilution (BMD) method for LRE detection and to assess the performance of seven commercially available techniques for linezolid susceptibility testing.

METHODS

A collection of 100 clinical isolates (80 Enterococcus faecium and 20 Enterococcus faecalis), including 20 optrA-positive isolates, 17 poxtA-positive isolates and 1 optrA/poxtA-positive E. faecium isolate, were studied. MICs were determined after 18 h [Day 1 (D1)] and 42 h [Day 2 (D2)] of incubation and interpreted following EUCAST and CLSI guidelines, which currently provide different interpretative breakpoints. Performance of commercial techniques was compared with BMD results.

RESULTS

MIC50/D1 and MIC50/D2 were both 8 mg/L, while MIC90/D1 and MIC90/D2 were 16 and 32 mg/L, respectively. MICD1 values for poxtA-positive isolates were lower than those for optrA-positive isolates. Proportions of susceptible isolates at D1 and D2 were 48% and 41%, respectively, according to EUCAST breakpoints and 35% and 13%, respectively, according to CLSI criteria (the proportions of isolates categorized as intermediate following CLSI recommendations were 13% and 28% at D1 and D2, respectively). Percentage susceptibility assessed by the commercially available techniques was always higher. The four commercial methods allowing MIC determination provided an overall essential agreement of ≥90% at D1. Categorical agreement and error rates were generally improved at D2.

CONCLUSIONS

Non-automated methods (Sensititre and UMIC) and, to a lesser extent, gradient strip Etest appear to show an acceptable correlation with the BMD reference method for the detection of isolates with low MICs of linezolid after prolonged incubation.

Targeted Therapeutic Strategies in the Battle Against Pathogenic Bacteria

The emergence and rapid spread of antibiotic resistance in pathogenic bacteria constitute a global threat for public health. Despite ongoing efforts to confront this crisis, the pace of finding new potent antimicrobials is far slower than the evolution of drug resistance. The abuse of broad-spectrum antibiotics not only accelerates the formation of resistance but also imposes a burden on the intestinal microbiota, which acts a critical role in human homeostasis. As such, innovative therapeutic strategies with precision are pressingly warranted and highly anticipated. Recently, target therapies have achieved some breakthroughs by the aid of modern technology. In this review, we provide an insightful illustration of current and future medical targeted strategies, including narrow-spectrum agents, engineered probiotics, nanotechnology, phage therapy, and CRISPR-Cas9 technology. We discuss the recent advances and potential hurdles of these strategies. Meanwhile, the possibilities to mitigate the spread of resistance in these approaches are also mentioned. Altogether, a better understanding of the advantages, disadvantages, and mechanisms of action of these targeted therapies will be conducive to broadening our horizons and optimizing the existing antibacterial approaches.

In vitro and in vivo activities of the carbonic anhydrase inhibitor, dorzolamide, against vancomycin-resistant enterococci

Vancomycin-resistant enterococci (VRE) are a serious public health threat and a leading cause of healthcare-associated infections. Bacterial resistance to antibiotics recommended for the treatment of enterococcal infections complicates the management of these infections. Hence, there is a critical need for the discovery of new anti-VRE agents. We previously reported carbonic anhydrase inhibitors (CAIs) as new potent VRE inhibitors. In the present study, the activity of the CAI, dorzolamide was evaluated against VRE both in vitro and in vivo. Dorzolamide exhibited potent activity against a panel of clinical VRE isolates, with minimum inhibitory concentration (MIC) values ranging from 1 µg/mL to 8 µg/mL. A killing kinetics experiment determined that dorzolamide exhibited a bacteriostatic effect against VRE, which was similar to the drug of choice (linezolid). Dorzolamide interacted synergistically with gentamicin against four strains of VRE, and exhibited an additive interaction with gentamicin against six VRE strains, reducing gentamicin’s MIC by several folds. Moreover, dorzolamide outperformed linezolid in an in vivo VRE colonization reduction mouse model. Dorzolamide significantly reduced the VRE burden in fecal samples of mice by 2.9-log₁₀ (99.9%) and 3.86-log₁₀ (99.99%) after 3 and 5 days of treatment, respectively. Furthermore, dorzolamide reduced the VRE count in the cecal (1.74-log₁₀ (98.2%) reduction) and ileal contents (1.5-log₁₀ (96.3%)) of mice, which was superior to linezolid. Collectively, these results indicate that dorzolamide represents a promising treatment option that warrants consideration as a supplement to current therapeutics used for VRE infections.

In Vivo Antibacterial Activity of Acetazolamide

Vancomycin-resistant enterococci (VRE) represent a major public health threat that requires the development of new therapeutics. In the present study, acetazolamide (AZM) was evaluated against enterococci. It inhibited different enterococcal strains tested at clinically achievable concentrations. Moreover, AZM outperformed linezolid, the drug of choice for VRE infections, in two in vivo VRE mouse models-murine colonization-reduction and VRE septicemia. Collectively, these results indicate that AZM warrants consideration as a promising treatment option for VRE infections.

Characterization of oxazolidinone and phenicol resistance genes in non-clinical enterococcal isolates from Korea

OBJECTIVES

To investigate the distribution and genetic characteristics of linezolid-resistant enterococci.

METHODS

Enterococcus faecalis and Enterococcus faecium strains were isolated from pigs, equipment, grounds, and employees of 19 Korean swine farms in 2017. Antimicrobial susceptibility testing was then performed and linezolid resistance genes were detected via PCR. For genetic epidemiological characterization, multilocus sequence typing and whole-genome sequencing data were analysed.

RESULTS

Twenty-eightE. faecalis and five E. faecium strains were isolated from 1026 samples obtained from the 19 farms. Ten sequence types were identified among the E. faecalis strains, of which ST256 (42.9%) and ST86 (25%) were the most abundant. The oxazolidinone and phenicol resistance genes poxtA, optrA, and fexA were detected in isolates of E. faecalis (100%, 85.7%, and 67.9%, respectively) and E. faecium (100%, 60%, and 80%, respectively). The minimum inhibitory concentrations of linezolid in these isolates ranged from 2 mg/L to 12 mg/L. The whole-genome sequencing data indicated that fexA was located upstream of poxtA.

CONCLUSIONS

This is the first study to report the detection of poxtA in isolates that were both susceptible and resistant to linezolid in Korea. These results demonstrate the importance of antimicrobial resistance monitoring programmes, including regular antimicrobial susceptibility testing and resistance gene expression analysis, to facilitate the control of the spread of antibiotic resistance in non-clinical settings in Korea.

Characteristics of linezolid-resistant Enterococcus faecalis isolates from broiler breeder farms

Linezolid is an oxazolidinone class antibiotic used for treatment infections caused by various multidrug-resistant gram-positive pathogens including enterococci. However, recently, linezolid-resistant isolates in animals are considered as a human health hazard. In a broiler operation system, antimicrobial resistance can be transferred to the environment and commercial broiler via the fecal-oral route. Therefore, this study was conducted to investigate the prevalence and characteristics of linezolid-resistant Enterococcus faecalis (E. faecalis) from broiler parent stock in a broiler operation system. Among 297 E. faecalis isolates from 85 flocks in 8 broiler breeder farms, the prevalence of chloramphenicol- and linezolid-resistant isolates was 0 to 12.1% and 0 to 8.0%, respectively; however, there were no significant differences between farms. Therefore, a total of 14 (4.7%) chloramphenicol- and/or linezolid-resistant E. faecalis showed resistance to 7 or more antimicrobial classes. The drug-resistance gene optrA, which can confer resistance to linezolid, tedizolid, and phenicols, was found in 8 (2.69%) isolates, and 7 (2.36%) of the 8 optrA-positive isolates co-carried the phenicol exporter gene fexA. However, E. faecalis isolates from 3 of 8 broiler breeder farms only carried the optrA and/or fexA genes. As linezolid is one of the last antimicrobial treatments of choice for multidrug-resistant gram-positive pathogens including E. faecalis, the presence of antibiotic-resistant E. faecalis in broiler breeder farms should be monitored to prevent the introduction of linezolid-resistant strains to the food chain.

Hospital outbreak of linezolid-resistant and vancomycin-resistant ST80 Enterococcus faecium harbouring an optrA-encoding conjugative plasmid investigated by whole-genome sequencing

BACKGROUND

Linezolid is an antibiotic used to treat infections caused by multi-drug-resistant Gram-positive bacteria. Linezolid resistance in enterococci has been reported with increasing frequency, with a recent rise in resistance encoded by optrA, poxtA or cfr.

AIM

To investigate a hospital outbreak of linezolid- and vancomycin-resistant Enterococcus faecium (LVREfm) using whole-genome sequencing (WGS).

METHODS

Thirty-nine VREfm from patient screening (19 isolates, 17 patients) and environmental sites (20 isolates) recovered in October 2019 were investigated. Isolates were screened using polymerase chain reaction for optrA, poxtA and cfr, and underwent Illumina MiSeq WGS. Isolate relatedness was assessed using E. faecium core genome multi-locus sequence typing (cgMLST). One LVREfm underwent MinION long-read WGS (Oxford Nanopore Technologies) and hybrid assembly with MiSeq short-read sequences to resolve an optrA-encoding plasmid.

FINDINGS

Twenty isolates (51.3%) were LVREfm and optrA-positive, including the LVREfm from the index patient. A closely related cluster of 28 sequence type (ST) 80 isolates was identified by cgMLST, including all 20 LVREfm and eight linezolid-susceptible VREfm, with an average allelic difference of two (range 0-10), indicating an outbreak. Nineteen (95%) LVREfm harboured a 56,684-bp conjugative plasmid (pEfmO_03). The remaining LVREfm exhibited 44.1% sequence coverage to pEfmO_03. The presence of pEfmO_03 in LVREfm and the close relatedness of the outbreak cluster isolates indicated the spread of a single strain. The outbreak was terminated by enhanced infection prevention and control (IPC) and environmental cleaning measures, ceasing ward admissions and ward-dedicated staff.

CONCLUSION

WGS was central in investigating an outbreak of ST80 LVREfm. The rapid implementation of enhanced IPC measures terminated the outbreak.

Urea Derivatives in Modern Drug Discovery and Medicinal Chemistry

The urea functionality is inherent to numerous bioactive compounds, including a variety of clinically approved therapies. Urea containing compounds are increasingly used in medicinal chemistry and drug design in order to establish key drug-target interactions and fine-tune crucial drug-like properties. In this perspective, we highlight physicochemical and conformational properties of urea derivatives. We provide outlines of traditional reagents and chemical procedures for the preparation of ureas. Also, we discuss newly developed methodologies mainly aimed at overcoming safety issues associated with traditional synthesis. Finally, we provide a broad overview of urea-based medicinally relevant compounds, ranging from approved drugs to recent medicinal chemistry developments.

Synthesis and antibacterial evaluation of novel oxazolidinone derivatives containing a piperidinyl moiety

In this article, a series of novel oxazolidinone derivatives containing a piperidinyl moiety was designed and synthesized. Their antibacterial activities were measured against S. aureus, MRSA, MSSA, LREF and VRE by MIC assay. Most of them exhibited potent activity against Gram-positive pathogens comparable to linezolid. Among them, compound 9h exhibited comparable activity with linezolid against human MAO-A for safety evaluation and showed moderate metabolism in human liver microsome. The most promising compound 9h, which showed remarkable antibacterial activity against S. aureus, MRSA, MSSA, LREF and VRE pathogens with MIC value of 0.25-1 μg/mL, was an interesting candidate for further investigation.

Incorporation of a chiral gem-disubstituted nitrogen heterocycle yields an oxazolidinone antibiotic with reduced mitochondrial toxicity

gem-Disubstituted N-heterocycles are rarely found in drugs, despite their potential to improve the drug-like properties of small molecule pharmaceuticals. Linezolid, a morpholine heterocycle-containing oxazolidinone antibiotic, exhibits significant side effects associated with human mitochondrial protein synthesis inhibition. We synthesized a gem-disubstituted linezolid analogue that when compared to linezolid, maintains comparable (albeit slightly diminished) activity against bacteria, comparable in vitro physicochemical properties, and a decrease in undesired mitochondrial protein synthesis (MPS) inhibition. This research contributes to the structure-activity-relationship data surrounding oxazolidinone MPS inhibition, and may inspire investigations into the utility of gem-disubstituted N-heterocycles in medicinal chemistry.

A Case Report on Isolation of Linezolid- and Vancomycin-resistant Enterococcus faecium Species from Cerebrospinal Fluid of a Patient Suffering from Ventriculoperitoneal Shunt-associated Meningitis

Vancomycin-resistant enterococci (VRE) are one of the most common nosocomial infections. Linezolid has been used to treat such infections extensively. Over time there have been reports where linezolid resistance in enterococci has been documented. This is the first report from Pakistan where linezolid- and vancomycin-resistant Enterococcus faecium was isolated from cerebrospinal fluid (CSF) sample from infected ventriculoperitoneal (VP) shunt.

From Phenylthiazoles to Phenylpyrazoles: Broadening the Antibacterial Spectrum toward Carbapenem-Resistant Bacteria

The narrow antibacterial spectrum of phenylthiazole antibiotics was expanded by replacing central thiazole with a pyrazole ring while maintaining its other pharmacophoric features. The most promising derivative, compound 23, was more potent than vancomycin against multidrug-resistant Gram-positive clinical isolates, including vancomycin- and linezolid-resistant methicillin-resistant Staphylococcus aureus (MRSA), with a minimum inhibitory concentration (MIC) value as low as 0.5 μg/mL. Moreover, compound 23 was superior to imipenem and meropenem against highly pathogenic carbapenem-resistant strains, such as Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli. In addition to the notable biofilm inhibition activity, compound 23 outperformed both vancomycin and kanamycin in reducing the intracellular burden of both Gram-positive and Gram-negative pathogenic bacteria. Compound 23 cleared 90% of intracellular MRSA and 98% of Salmonella enteritidis at 2× the MIC. Moreover, preliminary pharmacokinetic investigations indicated that this class of novel antibacterial compounds is highly metabolically stable with a biological half-life of 10.5 h, suggesting a once-daily dosing regimen.

Pathogenicity of Enterococci

Enterococci are unusually well adapted for survival and persistence in a variety of adverse environments, including on inanimate surfaces in the hospital environment and at sites of infection. This intrinsic ruggedness undoubtedly played a role in providing opportunities for enterococci to interact with other overtly drug-resistant microbes and acquire additional resistances on mobile elements. The rapid rise of antimicrobial resistance among hospital-adapted enterococci has rendered hospital-acquired infections a leading therapeutic challenge. With about a quarter of a genome of additional DNA conveyed by mobile elements, there are undoubtedly many more properties that have been acquired that help enterococci persist and spread in the hospital setting and cause diseases that have yet to be defined. Much remains to be learned about these ancient and rugged microbes, particularly in the area of pathogenic mechanisms involved with human diseases.

Nitroimidazole-containing compounds and their antibacterial and antitubercular activities

Infections especially tuberculosis caused by various bacteria including mycobacteria result in millions of lives every year, but the control of bacterial infections is challenged by the limitation of effective pharmaceuticals against drug-resistant pathogens. Nitroimidazoles belong to a group of nitroheterocyclic compounds that have broad-spectrum activity against a series of organisms such as mycobacteria, anaerobic Gram-positive and Gram-negative bacteria, and some of them have already been used in clinics or under clinical trials for the treatment of infectious diseases. In this review, we made an overview of the recent advances in nitroimidazole-containing compounds with antibacterial and antitubercular activity in the recent 20 years.

Temporal and Geographic Variation in Antimicrobial Susceptibility and Resistance Patterns of Enterococci: Results From the SENTRY Antimicrobial Surveillance Program, 1997-2016

Background

The SENTRY Antimicrobial Surveillance Program was established in 1997 and presently encompasses more than 750 000 bacterial isolates from over 400 medical centers worldwide. Among these pathogens, enterococci represents a prominent cause of bloodstream (BSIs), intra-abdominal (IAIs), skin and skin structure, and urinary tract infections (UTIs). In the present study, we reviewed geographic and temporal trends in Enterococcus species and resistant phenotypes identified throughout the SENTRY Program.

Methods

From 1997 to 2016, a total of 49 491 clinically significant enterococci isolates (15 species) were submitted from 298 medical centers representing the Asia-Pacific (APAC), European, Latin American (LATAM), and North American (NA) regions. Bacteria were identified by standard algorithms and matrix-assisted laser desorption ionization–time of flight mass spectrometry. Susceptibility (S) testing was performed by reference broth microdilution methods and interpreted using Clinical and Laboratory Standards Institute/US Food and Drug Administration and European Committee on Antimicrobial Susceptibility Testing criteria.

Results

The most common Enterococcus species in all 4 regions were Enterococcus faecalis (64.7%) and E. faecium (EFM; 29.0%). Enterococci accounted for 10.7% of BSIs in NA and was most prominent as a cause of IAIs (24.0%) in APAC and of UTIs (19.8%) in LATAM. A steady decrease in the susceptibility to ampicillin and vancomycin was observed in all regions over the 20-year interval. Vancomycin-resistant enterococci (VRE) accounted for more than 8% of enterococcal isolates in all regions and was most common in NA (21.6%). Among the 7615 VRE isolates detected, 89.1% were the VanA phenotype (91.0% EFM) and 10.9% were VanB. Several newer antimicrobial agents demonstrated promising activity against VRE, including daptomycin (99.6–100.0% S), linezolid (98.0%–99.6% S), oritavancin (92.2%–98.3% S), tedizolid (99.5%–100.0% S), and tigecycline (99.4%–100.0% S).

Conclusions

Enterococci remained a prominent gram-positive pathogen in the SENTRY Program from 1997 through 2016. The overall frequency of VRE was 15.4% and increased over time in all monitored regions. Newly released agents with novel mechanisms of action show promising activity against VRE.

Nonribosomal antibacterial peptides that target multidrug-resistant bacteria

This review summarizes the development of nonribosomal antibacterial peptides from untapped sources that target multidrug-resistant bacteria.

Single-dose Intravenous Safety, Tolerability, and Pharmacokinetics and Absolute Bioavailability of LCB01-0371

PURPOSE

LCB01-0371 is a novel broad-spectrum oxazolidinone antibacterial agent under investigation for the treatment of infection by gram-positive pathogens, including methicillin-resistant Staphylococcus aureus. This study evaluated the safety, tolerability, and pharmacokinetics of LCB01-0371 after a single intravenous (IV) infusion and determined its absolute oral bioavailability at a therapeutic dose of 800 mg.

METHODS

This study was conducted in 2 parts. The first part was a single-blind, placebo-controlled, escalating single IV dose study (200, 400, 800, and 1200 mg) of LCB01-0371 via 2 different infusion regimens (250 mL over 60 min or 150 mL over 30 min) in 36 healthy male volunteers. The second part was an open-label, 2-way crossover design study in which 8 subjects were randomly assigned to 1 of 2 sequences of a single oral (800 mg) or IV (400 mg) administration of LCB01-0371. Safety assessments were conducted at regular intervals. Blood and urine were serially sampled, and drug concentrations were measured for up to 24 h to calculate pharmacokinetic parameters.

FINDINGS

LCB01-0371 after IV administration was generally safe and well tolerated up to 800 mg regardless of the infusion regimen. Adverse events were mild, excluding nausea at the highest dose, and resolved spontaneously. After a single IV administration, LCB01-0371 exhibited linear pharmacokinetic properties over the range of 200-800 mg. The elimination t_1/2, volume of distribution, and clearance ranged from 1.48 to 1.68 h, 57.74-76.72 L, and 33.17-43.31 L/h, respectively, and they remained unchanged over the corresponding dose range. C_max, AUC_0-last, and AUC_0-∞ increased in a dose-dependent manner. The dose-normalized total exposure after single PO and IV dosing were equivalent, with 90% CIs of the geometric least squares mean ratio of 86.6%-110% for AUC_0-last and 86.6%-111% for AUC_0-∞. The dose-normalized C_max was not equivalent between oral and IV dosing, with a 90% CI of the geometric least squares mean ratio of 50.0%-105%. The absolute oral bioavailability of LCB01-0371 after a single 800-mg dose was 99.75%.

IMPLICATIONS

After a single IV administration, LCB01-0371 was well tolerated in healthy volunteers at doses up to 800 mg, and it exhibited linear pharmacokinetic properties. The comparable total systemic exposure between IV and oral administration supports the ability to switch administration routes without a need for dose adjustment. ClinicalTrials.gov identifier: NCT02882789.

Risk Factors and Outcomes Associated With Acquisition of Daptomycin and Linezolid-Nonsusceptible Vancomycin-Resistant Enterococcus

Background

Vancomycin-resistant enterococcus (VRE) causes substantial health care–associated infection with increasing reports of resistance to daptomycin or linezolid. We conducted a case–control study reporting 81 cases of daptomycin and linezolid–nonsusceptible VRE (DLVRE), a resistance pattern not previously reported.

Methods

We reviewed VRE isolates from June 2010 through June 2015 for nonsusceptibility to both daptomycin (minimum inhibitory concentration [MIC] > 4) and linezolid (MIC ≥ 4). We matched cases by year to control patients with VRE susceptible to both daptomycin and linezolid and performed retrospective chart review to gather risk factor and outcome data.

Results

We identified 81 DLVRE cases. Resistance to both daptomycin and linezolid was more common than resistance to either agent individually. Compared with susceptible VRE, DLVRE was more likely to present as bacteremia without focus (P < 0.01), with DLVRE patients more likely to be immune suppressed (P = .04), to be neutropenic (P = .03), or to have had an invasive procedure in the prior 30 days (P = .04). Any antibiotic exposure over the prior 30 days conferred a 4-fold increased risk for DLVRE (odds ratio [OR], 4.25; 95% confidence interval [CI], 1.43−12.63; P = .01); multivariate analysis implicated daptomycin days of therapy (DOT) over the past year as a specific risk factor (OR, 1.10; 95% CI, 1.01−1.19; P = .03). DLVRE cases had longer hospitalizations (P = .04) but no increased risk for in-hospital death.

Conclusions

DLVRE is an emerging multidrug-resistant pathogen associated with immune suppression, neutropenia, and recent invasive procedure. Prior antibiotic exposure, specifically daptomycin exposure, confers risk for acquisition of DLVRE.

Detection of the Novel optrA Gene Among Linezolid-Resistant Enterococci in Barcelona, Spain

The purpose of this study was to describe the presence of the novel optrA gene among clinical isolates of enterococci in a Spanish teaching hospital (May 2016-April 2017). optrA and cfr genes were screened by PCR in all isolates showing linezolid minimal inhibitory concentration (MIC) ≥4 mg/L. The genetic relatedness of the isolates, the presence of resistance and virulence genes, and the genetic environment of optrA were assessed by whole-genome sequencing (WGS). Six of 1,640 enterococci had linezolid MIC ≥4 mg/L. Among them, the optrA gene was detected in five Enterococcus faecalis isolated from unrelated patients. Although none of them had received linezolid or chloramphenicol, all had antecedents of recent quinolone consumption. WGS analysis revealed the existence of two different genotypes: ST585 and ST474. cfr was not detected in any of the isolates. No mutations were detected among the 23S ribosomal RNA and the ribosomal proteins L3, L4, and L22. Both genotypes also carried genes related to aminoglycoside, lincosamide, macrolide, phenicol, and tetracycline resistance. Detection of optrA in a setting with low linezolid consumption and among patients without antecedents of oxazolidinone therapy is of concern.

Quantitative Proteomics Analysis of Membrane Proteins in Enterococcus faecalis With Low-Level Linezolid-Resistance

Despite increasing reports of low-level linezolid-resistant enterococci worldwide, the mechanism of this resistance remains poorly understood. Previous transcriptome studies of low-level linezolid-resistant Enterococcus faecalis isolates have demonstrated a number of significantly up-regulated genes potentially involved in mediation of drug resistance. However, whether the transcriptome faithfully reflects the proteome remains unknown. In this study, we performed quantitative proteomics analysis of membrane proteins in an E. faecalis isolate (P10748) with low-level linezolid-resistance in comparison with two linezolid-susceptible strains 3138 and ATCC 29212, all of which have been previously investigated by whole transcriptome analysis. A total of 8,197 peptides associated with 1,170 proteins were identified in all three isolates with false discovery rate (FDR) at 1% and P < 0.05. There were 14 significantly up-regulated and 6 significantly down-regulated proteins in strain P10748 compared to strains 3138 and ATCC 29212, which were in general positively correlated with transcription levels revealed in previous transcriptome studies. Our analysis suggests that the low-level linezolid-resistance in E. faecalis is conferred primarily by the ATP-binding cassette protein OptrA through ribosomal protection and, possibly, also by the enterococcal surface protein (Esp) and other proteins through biofilm formation. The genetic transfer of optrA is potentially regulated by the surface exclusion protein Sea1, conjugal transfer protein TraB, replication protein RepA and XRE family transcription regulator protein. This report represents the first investigation of the mechanisms of linezolid-resistance in E. faecalis by a quantitative proteomics approach.

Characterization of Clinical Vancomycin-Resistant Enterococcus faecium Isolated in Eastern Hungary

OBJECTIVES

The aim of our study was to characterize and elicit the genetic relatedness of emerging vancomycin-resistant enterococci (VRE) isolated between 2012 and 2015 at a teaching hospital in Debrecen, Hungary.

RESULTS

Altogether 43 nonduplicate vancomycin-resistant Enterococcus faecium (VREfm) clinical isolates were obtained. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used for species identification. Isolates showed 100% resistance to ampicillin and ciprofloxacin while 81.4% were resistant to gentamicin. PCR analysis revealed the presence of VanB in 40 and VanA in 3 isolates. Among ace, agg, and esp virulence genes only esp was found in seven cases. Modified microtiter-plate test showed 13 weak and 4 moderate biofilm producer isolates. Pulsed-field gel electrophoresis revealed nine pulsotypes. According to multilocus sequence typing all of the tested isolates belonged to clonal complex 17 (CC17).

CONCLUSIONS

We report on the alarming emergence of multidrug-resistant VREfm belonging to CC17 at a tertiary hospital in Eastern Hungary. This is the first report of sequence types 412 and 364 from this region. Although outbreak did not occur the increasing prevalence of VREfm is of concern and dissemination must be prevented with proper infection control measures and regular VRE screening.

Pharmacokinetics, Pharmacodynamics, and Tolerability of Single-Dose Oral LCB01-0371, a Novel Oxazolidinone with Broad-Spectrum Activity, in Healthy Volunteers

LCB01-0371 is a novel oxazolidinone with broad-spectrum activity against Gram-positive pathogens in both in vitro studies and animal infection models. The objectives of this study were to evaluate its safety, tolerability, pharmacokinetics, and pharmacodynamics following single ascending doses. Single oral doses of 600 mg linezolid, a placebo, or LCB01-0371 of between 50 mg and 3,200 mg were tested in 69 healthy male subjects. Blood and urine were sampled, LCB01-0371 concentrations were measured, and the serum inhibitory and bactericidal titers of LCB01-0371 and linezolid were determined. LCB01-0371 was well tolerated up to 2,400 mg. The most common drug-related clinical and laboratory adverse events were nausea with or without vomiting, decreased neutrophil counts, and increased total bilirubin levels. The frequency of adverse events and drug-related adverse events was similar among the treatment groups. The systemic exposure was approximately dose proportional over the range of 50 mg to 800 mg, which includes the anticipated clinical dose. The mean clearance, renal clearance, and volume of distribution were significantly decreased at higher doses (above 800 mg). LCB01-0371 exhibited early bacteriostatic activity against all tested strains except for Streptococcus pneumoniae strains, and the potency of LCB01-0371 at 800 mg was similar to that of linezolid at the therapeutic dose (600 mg). However, LCB01-0371 had less bactericidal activity than linezolid. Taken together, LCB01-0371 was well tolerated, exhibited approximate dose proportionality within the anticipated clinically relevant dose range, and showed bacteriostatic and bactericidal activity comparable to that of linezolid. These results support the further clinical development of LCB01-0371. (This study has been registered at ClinicalTrials.gov under registration no. NCT01554995.).

Genetic Basis of Emerging Vancomycin, Linezolid, and Daptomycin Heteroresistance in a Case of Persistent Enterococcus faecium Bacteremia

Whole-genome sequencing was used to examine a persistent Enterococcus faecium bacteremia that acquired heteroresistance to three antibiotics in response to prolonged multidrug therapy. A comparison of the complete genomes before and after each change revealed the emergence of known resistance determinants for vancomycin and linezolid and suggested that a novel mutation in fabF, encoding a fatty acid synthase, was responsible for daptomycin nonsusceptibility. Plasmid recombination contributed to the progressive loss of vancomycin resistance after withdrawal of the drug.

Atomic structure and enzymatic insights into the vancomycin-resistant Enterococcus faecalis (V583) alkylhydroperoxide reductase subunit C

The Enterococcus faecalis alkyl hydroperoxide reductase complex (AhpR) with its subunits AhpC (EfAhpC) and AhpF (EfAhpF) are of paramount importance to restore redox homeostasis. Recently, the novel phenomenon of swapping of the catalytic domains of EfAhpF was uncovered. Here, we visualized its counterpart EfAhpC (187 residues) from the vancomycin-resistant E. faecalis (V583) bacterium by electron microscopy and demonstrate, that in contrast to other bacterial AhpCs, EfAhpC forms a stable decamer-ring irrespective of the redox state. The first crystallographic structure (2.8Å resolution) of the C-terminal truncated form (EfAhpC_1-172) confirms the decamer ring and provides new insight into a transition state in-between a fully folded to a locally unfolded conformation in the catalytic center due to redox modulation. Amino acid substitutions of residues in the N- and C-termini as well as the oligomeric interphase of EfAhpC provide information into their structural and enzymatic roles. Mutagenesis, enzymatic and biophysical studies reveal the effect of the unusual existence of four cysteines in EfAhpC, which might optimize the functional adaptation of the E. faecalis enzyme under various physiological conditions.

Phytochemical analysis and antibacterial activities extracts of mangrove leaf against the growth of some pathogenic bacteria

In this study, the effects of water, ethanol, methanol and glycerin at five levels (0, 31.25, 83.33, 125 and 250 ml) were investigated on the efficiency of mangrove leaf extraction using mixture optimal design. The antimicrobial effect of the extracts on Streptococcus pneumoniae, Enterococcus faecium and Klebsiella pneumoniae was evaluated using disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) methods. The mangrove leaf extraction components were identified through gas chromatography/mass spectrometry (GC/MS). Phytochemical analysis (alkaloids, tannins, saponins, flavone and glycosides) were evaluated based on qualitative methods. Antioxidant activity of extracts was measured using 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant potential (FRAP) methods. Maximum antimicrobial effect was observed in Enterococcus faecium and highest resistance against mangrove leaf extract in Enterococcus faecium and Klebsiella pneumoniae, respectively. Increasing concentration of mangrove extracts had a significant effect (p ≤ 0.05) on inhibition zone diameter. The MICs of the mangrove leaf extraction varied from 4 mg/ml to 16 mg/ml. The optimum formulation was found to contain glycerin (0 ml), water (28.22 ml), methanol (59.83 ml) and ethanol (161.95 ml). The results showed that the highest antioxidant activity was related to optimum extract of mangrove leaf and ethanolic extract respectively. The results of phytochemical screening of Avicennia marina leaves extract showed the existence of alkaloids, tannins, saponins, flavone and glycosides. 2-Propenoic acid, 3-phenyl- was the major compound of Avicennia marina. The results of non-significant lack of fit tests, and F value (14.62) indicated that the model was sufficiently accurate. In addition, the coefficient of variations (16.8%) showed an acceptable reproducibility.

The emerging problem of linezolid-resistant enterococci

Enterococcus is a significant pathogen in numerous infections, particularly in nosocomial infections, and is thus a great challenge to clinicians. Linezolid (LNZ), an oxazolidinone antibiotic, is an important therapeutic option for infections caused by Gram-positive bacterial pathogens, especially vancomycin-resistant enterococci. A systematic review was performed of the available literature on LNZ-resistant enterococci (LRE) to characterise these infections with respect to epidemiological, microbiological and clinical features. The results validated the potency of LNZ against enterococcal infections, with a sustained susceptibility rate of 99.8% in ZAAPS and 99.2% in LEADER surveillance programmes. Patients with LRE had been predominantly exposed to LNZ prior to isolation of LRE, with a mean treatment duration of 29.8±48.8days for Enterococcus faecalis and 23.1±21.4days for Enterococcus faecium. Paradoxically, LRE could also develop in patients without prior LNZ exposure. LNZ resistance was attributed to 23S rRNA (G2576T) mutations (51.2% of E. faecalis and 80.5% of E. faecium) as well as presence of the cfr gene (4.7% and 4.8%, respectively), which could transfer horizontally among the strains. In addition to the cfr gene, 32 cases of optrA-positive LRE were identified. Further study is required to determine the prevalence of novel resistance genes. The emergence of LRE thus hampers the treatment of such infections, which warrants worldwide surveillance.

In vitro activity of linezolid alone and combined with other antibiotics against clinical enterococcal isolates

BACKGROUND

The increasing incidence of antimicrobial resistance has led to research on finding new antimicrobial agents or identifying drug combinations with synergistic effects. Enterococcal infections, particularly those associated with vancomycin-resistant enterococci (VREs), are therapeutic problems. Linezolid (LZD), an oxazolidinone antibiotic, shows good activity against Gram-positive bacteria including enterococci. To avoid the emergence of linezolid-resistant subpopulations and achieve enhanced activity or bactericidal effect, the use of combined therapy has been considered.

METHODS

The in vitro activity of LZD in combination with five different antibiotics was evaluated using a microdilution checkerboard method and time-kill study against 12 clinical enterococcus isolates.

RESULTS

With the checkerboard method, LZD plus doxycycline (DX) had the highest frequency among all synergistic combinations. This combination and the one of LZD plus ceftriaxone (CRO) were the most frequent effective combinations against VREs. Time-kill studies using selected synergistic combinations-LZD + DX and LZD + CRO-showed an indifferent interaction. One tested combination of LZD + rifampicin showed antagonism.

CONCLUSIONS

Antagonistic interactions in combinations containing LZD are rare. LZD + DX and LZD + CRO may be beneficial in the treatment of VREs. However, more time-kill studies as well as in vivo experiments are required.

Distribution of optrA and cfr in florfenicol-resistant Staphylococcus sciuri of pig origin

A novel transferable oxazolidinone-phenicol resistance gene, optrA, which confers resistance to linezolid, the next-generation oxazolidinone tedizolid, and also to chloramphenicol and florfenicol, has been identified in enterococcal and staphylococcal species. Here, we investigated the epidemiology of optrA in florfenicol-resistant Staphylococcus spp. isolates of pig origin, and characterized the genetic context of oxazolidinone resistance genes in 20 optrA-positive florfenicol- and methicillin-resistant S. sciuri isolates, 11 (55%) of which also harbored the multi-resistance gene cfr. Pulsed-field gel electrophoresis and direct repeat unit (dru) typing of the 20 optrA-positive S. sciuri isolates revealed 17 patterns and four distinct dru types, respectively. Nine and six different arrangements of the optrA and cfr gene regions, respectively, were identified among the isolates. The arrangements optrA-araC-Tn558 or optrA-ΔTn558 were present in all optrA-positive isolates, and in three of them, ISEnfa5 and cfr were located immediately downstream of optrA. The cfr-carrying segment in eight isolates was similar to the corresponding region of the staphylococcal plasmid pWo28-3, in which the coexistence of cfr and optrA was identified for the first time.