Linezolid-resistant Strain Research Articles

Genomic epidemiology reveals multiple mechanisms of linezolid resistance in clinical enterococci in China

BackgroundInfections caused by linezolid-resistant enterococci (LRE) are clinically difficult to treat and threaten patient health. However, there is a lack of studies on long time-span LRE strains in China. For this reason, our study comprehensively revealed the resistance mechanisms of LRE strains collected in a Chinese tertiary care hospital from 2011 to 2022.MethodsEnterococcal strains were screened and verified after retrospective analysis of microbial data. Subsequently, 65 LRE strains (61 Enterococcus faecalis and 4 Enterococcus faecium, MIC ≥ 8 µg/ml), 1 linezolid-intermediate Enterococcus faecium (MIC = 4 µg/ml) and 1 linezolid-susceptible Enterococcus faecium (MIC = 1.5 µg/ml) were submitted for whole-genome sequencing (WGS) analysis and bioinformatics analysis.ResultsThe optrA gene was found to be the most common linezolid resistance mechanism in our study. We identified the wild-type OptrA and various OptrA variants in 98.5% of LRE strains (61 Enterococcus faecalis and 3 Enterococcus faecium). We also found one linezolid-resistant Enterococcus faecium strain carried both optrA and cfr(D) gene, while one linezolid-resistant Enterococcus faecium only harbored the poxtA gene. Most optrA genes (55/64) were located on plasmids, with impB-fexA-optrA, impB-fexA-optrA-erm(A), fexA-optrA-erm(A), and fexA-optrA segments. A minority of optrA genes (9/64) were found on chromosomes with the Tn6674-like platform. Besides, other possible linezolid resistance-associated mechanisms (mutations in the rplC and rplD genes) were also found in 26 enterococcal strains.ConclusionsOur study suggested that multiple mechanisms of linezolid resistance exist among clinical LRE strains in China.

Analysis of Pathogenic Bacterial Spectrum, Drug Resistance and Risk Factors for Mortality of Bloodstream Infection in Patients with Hematologic Diseases

To analyze the pathogenic bacterial spectrum, drug resistance, and risk factors associated with multidrug-resistant bacterial infection and mortality in patients with hematologic diseases complicated by bloodstream infections, so as to provide reference for rational drug use and improving prognosis. Positive blood culture specimens of patients with hematologic diseases in two Class A tertiary hospitals of Shanxi province from January 2019 to December 2021 were retrospectively analyzed. Pathogen distribution, drug resistance and outcomes of patients with bloodstream infection were investigated, then the multivariate logistic analysis was performed to analyze the risk factors of multidrug-resistant bacterial infection and factors affecting prognosis. 203 strains of pathogens were identified, mainly Gram-negative bacteria (GNB) (69.46%, 141/203), of which Escherichia coli (E.coli) had the highest incidence (41.13%, 58/141), followed by Klebsiella pneumoniae (20.57%, 29/141) and Pseudomonas aeruginosa (12.77%, 18/141). Extended-spectrum beta-lactamase (ESBL)-producing E.coli and Klebsiella pneumoniae were 46.55% (27/58) and 37.93% (11/29), respectively. Carbapenem-resistant Gram-negative bacteria accounted for 10.64% (15/141). And Gram-positive bacteria accounted for 27.59% (56/203), Staphylococcus epidermidis, Streptococcus pneumoniae, and Staphylococcus aureus were the most frequently isolated pathogen among Gram-positive bacteria (14.29%, 12.50% and 10.71%, respectively), of which methicillin-resistant Staphylococcus aureus accounted for 33.33% (2/6), coagulase-negative staphylococci accounted for 87.50% (7/8), without vancomycin- or linezolid-resistant strain. Additionally, fungi accounted for 2.95% (6/203), all of which were Candida. Multidrug-resistant Gram-negative bacteria (MDR-GNB) accounted for 53.90% (76/141). Duration of neutropenia >14 days was a risk factor for developing MDR-GNB infection. The 30-day all-cause mortality was 10.84%. Multivariate logistic regression analysis showed that the significant independent risk factors for mortality were age≥60 years (P <0.01, OR =5.85, 95% CI: 1.80-19.07) and use of vasopressor drugs (P <0.01, OR =5.89, 95% CI: 1.83-18.94). The pathogenic bacteria of bloodstream infection in patients with hematological diseases are widely distributed, and the detection rate of multidrug-resistant bacteria is high. The clinicians should choose suitable antibiotics according to the results of bacterial culture and antibiotic susceptibility test.

Antibacterial Activity of Ethanolic Extracts Obtained from Roots and Stems of Chelidonium majus L. Against Enterococcus Faecalis Strains

The present study is in vitro research aimed to evaluate the antimicrobial activity of the ethanolic extracts derived from roots and stems of Chelidonium majus L. against two Enterococcus faecalis strains to assess the possible use of this plant in preventing infections caused by this pathogen. Plant materials were harvested from natural habitats on the territory of the Kartuzy district in the Pomeranian province (northern part of Poland). The collected roots and stems were brought into the laboratory for antimicrobial studies. Freshly washed samples were weighed, crushed, and homogenized in 96 % ethanol (in proportion 1:19, w/w) at room temperature. The extracts were then filtered and investigated for their antimicrobial activity. The Enterococcus faecalis (Andrewes and Horder) Schleifer and Kilpper-Balz (ATCC®51299™) and linezolid-resistant Enterococcus faecalis strain locally isolated were used in the current study. The antimicrobial susceptibility testing was done on Muller-Hinton agar by Kirby-Bauer disk diffusion susceptibility test protocol. The results of the current study showed that C. majus possess weak antimicrobial properties against the tested Enterococcus faecalis strains. The ethanolic extracts derived from roots of C. majus collected from rural areas exhibited the maximum antimicrobial activity against linezolid-resistant E. faecalis strain (the mean of inhibition zone diameters was 8.85±0.42 mm) compared to the control samples (7.1 ±0.91 mm). Stem extracts derived from C. majus collected from rural areas showed similar properties against the Enterococcus faecalis (Andrewes and Horder) Schleifer and Kilpper-Balz (ATCC®51299™) strain (8.77 ±1.21 mm) compared to the control samples. Root extracts derived from C. majus collected from urban and rural areas exhibited weak antibacterial ability against linezolid-resistant E. faecalis strains (6.46±0.32 mm and 7.78 ±0.34 mm, respectively), as well as weak antibacterial ability against E. faecalis ATCC®51299™strains (7.9 ±1.08 mm and 7.97±0.85 mm, respectively) compared to the control sample (7.1 ±0.99 mm). The results of this study can induce to provide a new perspective for the use of various Papaveraceae families as medicinal plants to improve the antibacterial responses using other strains. Identification of precise molecular mechanisms responsible for inhibition of bacterial growth by these extracts requires further research.

Analysing pathogenic bacterial spectrum and drug resistance of bloodstream infection in patients with allogeneic hematopoietic stem cell transplantation

目的了解浙江省人民医院异基因造血干细胞移植（allo-HSCT）患者血流感染临床特点、病原菌谱、耐药性及危险因素。方法回顾性分析2014年10月至2019年9月浙江省人民医院血液科210例allo-HSCT患者中发生血流感染的病原学分布、耐药性、感染危险因素及转归。结果210例allo-HSCT患者中49例发生血流感染，共分离出病原菌59株，以革兰阴性菌为主（67.8％），其中以大肠埃希菌最为常见（23.7％），碳青霉烯类耐药革兰阴性菌（CRO）占42.5％；革兰阳性菌占23.7％，未发现万古霉素及利奈唑胺耐药的葡萄球菌株；真菌占8.5％。单因素分析提示血流感染影响因素有性别、移植前疾病状态、预处理方案；多因素分析显示血流感染主要与预处理方案强度有关（OR＝3.043，95％CI 1.236～7.492，P＝0.015）。49例血流感染患者中粒细胞缺乏（粒缺）血流感染占77.6％，非粒缺占22.4％；移植前活动性感染患者发生血流感染占81.0％，移植前无活动性感染患者占16.9％。生存分析结果显示，血流感染患者总生存（OS）时间短于未发生血流感染患者，CRO感染患者比无CRO感染患者OS时间短，粒缺时间>14 d患者OS时间较粒缺时间≤14 d患者短，移植前是否合并活动性感染及感染时是否处于粒缺状态与OS时间无明显相关性。结论本研究提示积极预防耐药菌血流感染、缩短粒缺时间、移植前控制感染、适合的预处理方案，能降低移植死亡率、改善预后。

Genomic Information on Linezolid-Resistant Sequence-Type 398 Livestock-Associated Methicillin-Resistant Staphylococcus aureus Isolated from a Pig.

The frequent occurrence of sequence-type 398 (ST398) livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in pigs has become a major public health concern owing to the increased zoonotic potential of the pathogen. Recently, a novel oxazolidinone resistance gene, chloramphenicol-florfenicol resistant (cfr), conferring multiresistance phenotypes to phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A (PhLOPSA), has been found among ST398 LA-MRSA strains isolated from pigs. In this study, we report the first in silico genome analysis of a linezolid-resistant ST398 LA-MRSA strain, designated PJFA-521M, recovered from a pig in Korea. Genomic analyses revealed that the presence of the cfr gene was responsible for the observed linezolid resistance in the PJFA-521M strain. Moreover, newer antimicrobial resistance genes, such as the dfrG, aadE, spw, lsa(E), lnu(B), and fexA genes, were found in the PJFA-521M strain. In addition to the genetic elements for antimicrobial resistance, the carriage of various virulence genes for adherence, invasion, and immunomodulation was identified in the genome, especially within several mobile genetic elements (MGEs). The presence of multiple antimicrobial resistance genes and virulence genes on MGEs in the genome of a linezolid-resistant ST398 LA-MRSA should raise awareness regarding the use of other antimicrobial agents in pig farms and may also provide selective pressure for the prevalence of the cfr gene and the associated multidrug-resistant phenotype.

In vitro and in vivo Antibacterial Activity of Linezolid Plus Fosfomycin Against Staphylococcus aureus with Resistance to One Drug.

ObjectiveThe purpose of this study is to assess the in vitro/vivo activities of linezolid plus fosfomycin against Staphylococcus aureus (S. aureus) isolates with varying susceptibility to the study drugs.MethodsThe increasing concentration stepwise method was used to induce S. aureus resistant strains. The in vitro antibacterial activity of linezolid combined with fosfomycin against S. aureus in vitro was studied by time-kill curve and PAE. The transmission electron microscopy (TEM) was employed to observe the cell morphology of bacteria treated with drug, and the changes of cell wall thickness were recorded. The Galleria mellonella infection model was established to demonstrate the in vivo efficacy of linezolid and fosfomycin against S. aureus with varying susceptibility.ResultsThe antibiotic combination showed excellent synergistic or additive effects on the original and the linezolid-resistant strain, but showed indifferent effect for fosfomycin-resistant strain. TEM images showed that fosfomycin alone and in combined could reduce the cell wall thickness of the strains resistant to linezolid and cell lysis, while linezolid increases the cell wall thickness of the strains resistant to fosfomycin. In the Galleria mellonella infection model, the survival rate of the antibiotic combined was improved compared with that of the single drug. There was a good correlation between in vivo efficacy and in vitro susceptibility.ConclusionThe type of interaction expressed in the test combination was highly dependent on fosfomycin resistance.

Whole transcriptome analysis reveals potential novel mechanisms of low-level linezolid resistance in Enterococcus faecalis

Linezolid is an oxazolidinone antibiotic commonly used to treat serious infections caused by vancomycin-resistant enterococcus. Recently, low-level linezolid resistant Enterococcus faecalis strains have emerged worldwide, but the resistant mechanisms remain undefined. Whole-transcriptome profiling was performed on an E. faecalis strain P10748 with low-level linezolid resistance in comparison with a linezolid-susceptible strain 3138 and the standard control strain ATCC29212. The functions of differentially expressed genes (DEGs) were predicted, with some DEGs potentially involved in drug resistance were validated by PCR and quantitative PCR (qPCR). RNA-Seq on three E. faecalis strains generated 1920 unigenes, with 98% of them assigned to various function groups. A total of 150 DEGs were identified in the linezolid resistant strain P10748 compared to the linezolid susceptible strains 3138 and ATCC29212. Functional analysis indicated a significant transcriptomic shift to membrane transportation and biofilm formation in strain P10748, with three significantly up-regulated DEGs predicted to be associated with drug resistance through active efflux pumps and biofilm formation. The existence of these three DEGs was further confirmed by PCR and qPCR. The significant upregulation of genes associated with efflux pumps and biofilm formation in the linezolid resistant strain suggests their roles in low-level resistance to linezolid in E. faecalis.

Emergence of linezolid-resistant coagulase-negative staphylococci in an intensive care unit

Background The aim of this study was to report the emergence of linezolid-resistant coagulase-negative staphylococci (CoNS) in an intensive care unit. Methods An observational study was conducted in critically ill patients with colonization or infection by linezolid-resistant CoNS between January 2010 and December 2014. We analyzed the epidemiological and clinical features, and the mechanism of resistance to linezolid. We also evaluated the association between the incidence of linezolid-resistant CoNS strains and the consumption of linezolid in the study period. Results During the study period 49 patients had a linezolid-resistant CoNS strain isolated from clinical samples (blood in 42 cases, urine in 6, peritoneal fluid in 1). Molecular study showed a combination of mechanisms of resistance. Most patients were critically ill (APACHE II score = 21.9 ± 8.3) and nearly all had undergone surgery and invasive procedures, and had prior exposure to antibiotics. Linezolid-resistant CoNS were considered to be contaminants in 42 patients and associated with infection in 7 patients, comprising bacteremia and septic shock in most of them. They were successfully treated with glycopeptides or daptomycin. A modest significant correlation was observed between the decrease in linezolid consumption and the lower incidence of resistant isolates. Conclusions Linezolid-resistant CoNS had emerged in critically ill patients with severe underlying diseases and prior antibiotic exposure. Most isolates represented colonization; however, linezolid-resistant CoNS can produce serious infections in critically ill patients. Glycopeptides and daptomycin seem to provide useful alternatives for therapy of these infections. A relationship was found between linezolid consumption and the incidence of linezolid-resistant CoNS strains.

Complete genome sequencing and comparative analysis of the linezolid-resistant Enterococcus faecalis strain DENG1

Genome level analysis of bacterial strains provides information on genetic composition and resistance mechanisms to clinically relevant antibiotics. To date, whole genome characterization of linezolid-resistant Enterococcus faecalis isolated in the clinic is lacking. In this study, we report the entire genome sequence, genomic characteristics and virulence factors of a pathogenic E. faecalis strain, DENG1. Our results showed considerable differences in genomic characteristics and virulence factors compared with other E. faecalis strains (V583 and OG1RF). The genome of this LZD-resistant E. faecalis strain can be used as a reference to study the mechanism of LZD resistance and the phylogenetic relationship of E. faecalis strains worldwide.

Efficacy of Tigecycline Alone and in Combination with Gentamicin in the Treatment of Experimental Endocarditis Due to Linezolid-Resistant Enterococcus faecium

We evaluated the efficacy of tigecycline in a rabbit model of experimental endocarditis caused by a linezolid-resistant clinical strain of Enterococcus faecium. Tigecycline-treated animals had a 2.8-log10-CFU/g reduction in microbial counts in excised vegetations compared with controls. Addition of gentamicin caused a further arithmetical reduction in colony counts. The therapeutic effect was sustained 5 days after completion of treatment, as shown by relapse studies performed in treatment groups.

Vancomycin and Linezolid Resistant Staphylococcus in Hospitalized Children

Background: Staphylococcus aureus is a major cause of serious hospital and community acquired infections, particularly in colonized individuals. Objectives: The study was carried out in a tertiary care center in Tehran, Iran to identify the frequency of hospital acquired methicillin resistant Staphylococcus aureus (HA-MRSA ) colonization and its antibiotic susceptibility pattern and molecular characteristics. Patients and Methods: This point-prevalence study was performed on 631 children who were admitted for at least 48 hours in different wards of Mofid childrens hospital in Tehran, Iran. Samples from anterior nares of these children were taken with sterile swab and cultured. If Staphylococcus aureus (S. aureus) was isolated, methicillin resistance and antibiotic susceptibility pattern were diagnosed according to Center for Disease Control and Prevention (CDC) guidelines of 2011 and Clinical and Laboratory Standards Institute (CLSI), and molecular analysis were determined by minimum inhibitory concentration (MIC) and polymerase chain reaction (PCR) methods. Results: Rate of colonization with S. aureus and methicillin resistant Staphylococcus aureus (MRSA) were 3.2% and 1.1% (1.1% of total and 35% of S. aureus isolates), respectively. All MRSA isolates were susceptible to rifampin and clindamycin. Resistance to vancomycin was reported in six Staphylococcus strains. Resistance to linezolid was detected in 19/20 Staphylococcus. Molecular analysis of isolates showed that all vancomycin resistant S. aureus isolates contained Van A or Van B gene, and 15/19 linezolid resistant strain was positive for chloramphenicol-florfenicol resistant gene ( cfr gene). Conclusions: The rate of MRSA colonization varies in any area, and the knowledge of acquisition risk factors and antibiotic susceptibility pattern are essential in prevention and treatment of MRSA infections. Based on our study, we suggest that clindamycin and rifampin are good choices in empiric treatment of patients suspected to have HA- MRSA infections until results of culture and antibiotic susceptibility pattern are prepared. In respect to the prevalence of linezolid resistance in this study, we suggest avoiding the use of linezolid as empiric therapy in HA-Staphylococcus infection.

Decreased linezolid uptake in an in vitro-selected linezolid-resistant Staphylococcus epidermidis mutant

The aim of this study was to characterize the mechanism of resistance to linezolid in an in vitro-selected linezolid-resistant Staphylococcus epidermidis mutant. A linezolid-resistant strain of S. epidermidis was selected by serial passages with increasing concentrations of linezolid. The MICs of linezolid, ciprofloxacin, tetracycline, rifampicin, vancomycin, gentamicin, tobramycin, chloramphenicol and oxacillin were determined. The 23S rRNA gene was amplified and sequenced, to search for mutations conferring linezolid resistance. The MIC of linezolid was also determined in the presence of reserpine. Finally, the accumulation of linezolid was measured and quantified by HPLC/UV. The obtained resistant strain had an MIC of linezolid of 64 mg/L and was stable after several passages on blood agar. The MIC measured in the presence of 25 mg/L reserpine, an efflux pump inhibitor, was not altered (MIC of 64 mg/L). The sequence of the 23S rRNA gene showed that the mutation G2576T (Escherichia coli numbering) was not present and no other mutation was found. An analysis of the accumulation of linezolid was performed, comparing the uptake of the resistant strain with that of the susceptible one. This showed that the resistant strain had significantly lower levels of linezolid accumulation than its susceptible parental strain. The mechanism of resistance to linezolid, in this resistant strain, may be related to a decrease in the antimicrobial uptake. This new mechanism of resistance was also related to a little loss of fitness.

Epidemiological Profile of Linezolid‐Resistant Coagulase‐Negative Staphylococci

Surveillance studies have shown that <0.1% of coagulase-negative staphylococci are linezolid resistant; however, at our institution, 4% of such organisms were found to be resistant. We investigated the risk factors for and the epidemiological profile of linezolid-resistant coagulase-negative staphylococci. Susceptibility testing and pulsed-field gel electrophoresis were performed to analyze the genetic relatedness of both linezolid-resistant and linezolid-susceptible isolates. Clinical data were retrieved from medical records, and a case-case-control study was performed to identify unique risk factors for linezolid resistance. Isolates recovered from 25 patients with linezolid-resistant coagulase-negative staphylococci were examined; all but 1 of the isolates were identified as Staphylococcus epidermidis, and all but 1 had a minimum inhibitory concentration of linezolid of >256 microg/mL. Pulsed-field gel electrophoresis showed that 21 (84%) of 25 linezolid-resistant isolates exhibited genetic relatedness, whereas linezolid-susceptible isolates were of diverse clones. Unique, independent predictors of linezolid resistance included receipt of linezolid in the 3 months preceding isolation of the coagulase-negative staphylococci (odds ratio, 20.6; 95% confidence interval, 5.8-73.0). Linezolid-resistant coagulase-negative staphylococci have emerged at our institution and are predominately of a single clone. We believe that the most likely scenario to explain this emergence is that person-to-person spread of linezolid-resistant coagulase-negative staphylococci led to establishment of skin colonization with the strain. Subsequent use of linezolid was followed by selection of the linezolid-resistant strain, which then became the dominant skin flora. The potential for a parallel scenario involving clonal dissemination followed by selection of linezolid-resistant methicillin-resistant Staphylococcus aureus is a real possibility.

First report of a linezolid-resistant vancomycin-resistant Enterococcus faecium strain in Greece.

First report of a linezolid-resistant vancomycin-resistant Enterococcus faecium strain in Greece.