The combination of insulin and linezolid ameliorates Staphylococcus aureus pneumonia in individuals with diabetes via the TLR2/MAPKs/NLRP3 pathway.

Diabetes mellitus (DM) complicated with Staphylococcus aureus (S. aureus) infection lacks effective treatment strategies. In this study, we found that insulin combined with linezolid has potential to deal with the thorny problem. In vitro, our drug sensitivity assay, bacterial growth curve and hemolytic tests showed that a combination of insulin and linezolid exerted good antibacterial and anti-α-hemolysin activity, CCK8 experiment, glucose content and glycogen content determination showed that the combination of insulin and linezolid increased murine macrophage survival rate and reduced the extracellular glucose level of high glucose-treated MH-S cells and intracellular glycogen level, and Western blot showed that the combination inhibited TLR2/MAPKs/NLRP3-related inflammatory pathways in MH-S cells. The results of in vivo experiments showed that the combination therapy stabilized glucose level, remained body weight, ameliorated lung injury including improving pulmonary edema and decreasing lung wet/dry weight ratio, reduced the CFUs and inflammation in the lung tissue in a mouse model of diabetes with S. aureus pneumonia, and inhibited the expression of TLR2, MAPKs and NLRP3 inflammatory pathway. Overall, the combination of insulin and linezolid as autolytic inhibitor exhibited the effects of significant antibacterial and improving glucose level in vitro and in vivo, and also has an anti-inflammation activity via the TLR2/MAPKs/NLRP3 pathway, this paves the way for new treatments for diabetes mellitus complicated with S. aureus infection.

A Hydrazine-Hydrazone Adamantine Compound Shows Antimycobacterial Activity and Is a Probable Inhibitor of MmpL3.

Tuberculosis remains an important cause of morbidity and mortality throughout the world. Notably, an important number of multi drug resistant cases is an increasing concern. This problem points to an urgent need for novel compounds with antimycobacterial properties and to improve existing therapies. Whole-cell-based screening for compounds with activity against Mycobacterium tuberculosis complex strains in the presence of linezolid was performed in this study. A set of 15 bioactive compounds with antimycobacterial activity in vitro were identified with a minimal inhibitory concentration of less than 2 µg/mL. Among them, compound 1 is a small molecule with a chemical structure consisting of an adamantane moiety and a hydrazide-hydrazone moiety. Whole genome sequencing of spontaneous mutants resistant to the compounds suggested compound 1 to be a new inhibitor of MmpL3. This compound binds to the same pocket as other already published MmpL3 inhibitors, without disturbing the proton motive force of M. bovis BCG and M. smegmatis. Compound 1 showed a strong activity against a panel ofclinical strains of M. tuberculosis in vitro. This compound showed no toxicity against mammalian cells and protected Galleria mellonella larvae against M. bovis BCG infection. These results suggest that compound 1 is a promising anti-TB agent with the potential to improve TB treatment in combination with standard TB therapies.

The synthesis and antibacterial activity study of ruthenium-based metallodrugs with a membrane-disruptive mechanism against Staphylococcus aureus.

The wide spread of drug-resistant bacteria, especially methicillin-resistant Staphylococcus aureus (MRSA), poses a tremendous threat to global health. Of particular concern, resistance to vancomycin, linezolid, and daptomycin has already been reported in clinical MRSA strains. New antibacterial agents are urgently needed to overcome this crisis. Here, we designed and synthesized a series of ruthenium-based antibacterial agents via targeting bacterial membrane integrity. Structure-activity relationship studies demonstrated that both the lipophilicity/hydrophilicity ratio and biphenyl group play an important role in elevating the antibacterial activity. To characterize the antibacterial mechanism, we combined scanning electron microscopy, propidium iodide dyeing, and DNA leakage assays. The results demonstrated that Ru2 could destroy the integrity of bacterial cell membranes. In addition, Ru2 can efficiently inhibit biofilm formation and α-hemolysin secretion from Staphylococcus aureus. Finally, in both a mouse skin infection model and a G. mellonella wax worm infection model, Ru2 showed significant antibacterial activity in vivo. Moreover, the Ru2 complex was almost non-toxic. Thus, this work demonstrated that ruthenium-based complexes bearing a biphenyl group are promising agents to combat bacterial infection.

A Structurally Characterized Staphylococcus aureus Evolutionary Escape Route from Treatment with the Antibiotic Linezolid.

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterial pathogen that presents great health concerns. Treatment requires the use of last-line antibiotics, such as members of the oxazolidinone family, of which linezolid is the first member to see regular use in the clinic. Here, we report a short time scale selection experiment in which strains of MRSA were subjected to linezolid treatment. Clonal isolates which had evolved a linezolid-resistant phenotype were characterized by whole-genome sequencing. Linezolid-resistant mutants were identified which had accumulated mutations in the ribosomal protein uL3. Multiple clones which had two mutations in uL3 exhibited resistance to linezolid, 2-fold higher than the clinical breakpoint. Ribosomes from this strain were isolated and subjected to single-particle cryo-electron microscopic analysis and compared to the ribosomes from the parent strain. We found that the mutations in uL3 lead to a rearrangement of a loop that makes contact with Helix 90, propagating a structural change over 15 Å away. This distal change swings nucleotide U2504 into the binding site of the antibiotic, causing linezolid resistance. IMPORTANCE Antibiotic resistance poses a critical problem to human health and decreases the utility of these lifesaving drugs. Of particular concern is the "superbug" methicillin-resistant Staphylococcus aureus (MRSA), for which treatment of infection requires the use of last-line antibiotics, including linezolid. In this paper, we characterize the atomic rearrangements which the ribosome, the target of linezolid, undergoes during its evolutionary journey toward becoming drug resistant. Using cryo-electron microscopy, we describe a particular molecular mechanism which MRSA uses to become resistant to linezolid.

Linezolid Metabolism Is Catalyzed by Cytochrome P450 2J2, 4F2, and 1B1.

The oxazolidinone antibacterial linezolid has been in clinical use for over 20 years, yet knowledge of the contributions of specific cytochrome (CYP) 450 enzymes to the metabolic clearance of this drug were mostly unknown. In this investigation, it was revealed that three P450 enzymes that had not been previously explored in linezolid metabolism, CYP2J2, CYP4F2, and CYP1B1, catalyzed the 2-hydroxylation and de-ethyleneation of the morpholine moiety of linezolid. The intrinsic clearance for linezolid metabolism in pooled human liver microsomes was low at 0.51 µL/min/mg protein, consistent with its in vivo clearance in humans, and the KM was high (>200 µM). In recombinant human P450 enzymes, a rank order of intrinsic clearance values for linezolid 2-hydroxylation were CYP2J2 ≫ CYP4F2 > CYP2C8 > CYP1B1 ≈ CYP2D6 ≈ CYP3A4 > CYP1A1 > CYP3A5, with nine other P450 enzymes showing no linezolid metabolism. The effect of selective inhibitors for these eight P450 enzymes on linezolid metabolism in pooled human liver microsomes was evaluated to provide estimates of the relative fractional contributions of these enzymes to linezolid metabolism. These experiments suggest that CYP2J2 and CYP4F2 contribute about 50% each to linezolid hepatic metabolism. It is proposed that the oxidative metabolic clearance of linezolid is primarily catalyzed by these two unusual P450 enzymes and that this explains the lack of observation of meaningful effects of common perpetrators of drug interactions on linezolid pharmacokinetics. SIGNIFICANCE STATEMENT: Linezolid is an important antibacterial drug, but the enzymes involved in its oxidative metabolism were unknown. In this study, evidence is shown that supports an important role for two enzymes not frequently associated with the metabolism of drugs: cytochrome P450 2J2 and cytochrome P450 4F2. These observations offer insight to understand the results of clinical drug-drug interaction studies conducted on linezolid.

Potential activity of Linezolid against SARS-CoV-2 using electronic and molecular docking study.

The crescent evolution of a global pandemic COVID-19 and its respiratory syndrome (SARS-Cov-2) has been a constant concern (Ghosh 2021; Khan et al. 2021; Alazmi and Motwalli 2020; Vargas et al. 2020). The absence of a proven and effective medication has compelled all the scientific community to search for a new drug. The use of known drugs is a faster way to develop new therapies. Molecular docking is a powerful tool (Gao et al. J Mol Model 10: 44-54, 2004; Singh et al. J Mol Model 18: 39-51, 2012; Schulz-Gasch and Stahl J Mol Model 9:47-57, 2003) to study the interaction of potential drugs with SARS-CoV-2, Alsalme et al. (2020) and Sanders et al. (2020) spike protein as a consequence the main goal of this article is to present the result of the study of an interaction between (R and S)-Linezolid with receptor-binding domain (RBD) of SARS-Cov-2 spike protein complexed with human Angiostensin-converting enzyme 2 (ACE2) (6vW1 - from PDB). The Linezolid enantiomers were optimized at B3LYP/6-311++G(2d,p) level of theory. Molecular docking of the system (S)-Linezolid⋯RBD⋯ACE2 and (R)-Linezolid⋯RBD⋯ACE2 was performed, the analysis was made using LigPlot+ and NCIplot software packages, to understand the intermolecular interactions. The UV-Vis and ECD of the complexes - (R and S)-Linezolid⋯RBD⋯ACE2 were performed in two layers with DFT/6-311++G(3df,2p) and DFT/6-31G(d), respectively. The results showed that only the (S)-Linezolid had a stable interaction with - 8.05 kcal.mol- 1, whereas all the R-enantiomeric configurations had positive values of binding energy. The (S)-Linezolid had the same interactions as in the (S)-Linezolid ⋯ Haluarcula morismortui Ribosomal system, where it is well-known the fact that the latter has biological activity. A specific interaction on the fluorine ring justified an attenuation on the ECD signal, in comparison to isolated species. Therefore, some biological activity of (S)-Linezolid with SARS-CoV-2 RBD was expected, indicated by the modification of its ECD signal and justified by a similar interaction in the S-Linezolid⋯Haluarcula marismortui Ribosomal system.

Nafamostat mesilate inhibits linezolid metabolism via its antioxidant effects.

Patients who undergo renal replacement therapy often exhibit a high plasma linezolid concentration. Linezolid is metabolized via oxidation. Nafamostat mesilate has antioxidant effects and is frequently used as an anticoagulant during renal replacement therapy. We aimed to investigate the effect of nafamostat mesilate on plasma linezolid concentration. We examined whether the co-administration of linezolid and nafamostat had any effect on plasma linezolid concentration. Mice were randomly allocated to two groups (n = 18/group): linezolid (100 mg kg-1 , subcutaneous injection) + nafamostat (30 mg kg-1 , intraperitoneal injection) and linezolid + saline. At 5 hours, the linezolid concentration was significantly higher in the linezolid + nafamostat co-administration group than that in the linezolid + saline group (20.6 ± 9.8 vs 3.6 ± 1.2 µg/mL, respectively P < .001). The antioxidant effects of nafamostat may inhibit linezolid metabolism, resulting in the adverse event of high linezolid concentration if both are administered concurrently during renal replacement therapy.

Development of a sensitive LC-MS/MS method for quantification of linezolid and its primary metabolites in human serum.

Linezolid (LZD) is a widely used antimicrobial that is active against a broad range of disease-causing bacteria. Myelosuppression is major treatment-limiting toxicity of LZD that occurs more frequently in patients with renal insufficiency. Quantification of LZD and its two primary metabolites (PNU-142300 and PNU-142586), which undergo significant renal elimination, may support design of improved dosing strategies to mitigate the risk of myelosuppression. In this study, we established the first liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of LZD and its main metabolites in human serum. Proteins in serum samples were precipitated with acetonitrile containing a deuterated internal standard. Chromatographic separation of analytes was performed with Waters X-bridge column (C18, 150 × 4.6 mm, 3.5 µm) at 25 °C and subjected to mass analysis using positive electro-spray ionization. The mobile phase A was water with 0.1% formic acid, and mobile phase B was acetonitrile with 0.1% formic acid at a flow rate of 0.6 mL/min, within a 15 min run time. Standard curves were linear and correlation coefficients (r2) were ≥0.99 for concentration ranges of 0.1-50 µg/mL for LZD and PNU-142300, and 0.1-25 µg/mL for PNU-142586. The inter- and intra-assay precisions were <15% for all analytes in quality control samples, and the accuracies ranged from 97 to 112%. Extraction recoveries ranged from 78 to 103% for all analytes, and there was no significant matrix effect. Samples from 10 patients (5 with renal impairment) were assayed. Mean (SD) LZD, PNU-142300 and PNU-142586 trough concentrations were 19.4(6.8), 11.6(6.8), 25.7(16.4) µg/mL, respectively, in patients with renal impairment. These values were 2.5-, 5.8-, and 6.8-fold higher for LZD, PNU-142300 and PNU-142586, respectively compared to patients without renal impairment. The method was effectively applied in the determination of LZD and its main metabolites in human serum.

Dynamics of the context-specific translation arrest by chloramphenicol and linezolid.

Chloramphenicol (CHL) and linezolid (LZD) are antibiotics that inhibit translation. Both were thought to block peptide-bond formation between all combinations of amino acids. Yet recently, a strong nascent peptide context-dependency of CHL- and LZD-induced translation arrest was discovered. Here we probed the mechanism of action of CHL and LZD by using single-molecule Förster resonance energy transfer spectroscopy to monitor translation arrest induced by antibiotics. The presence of CHL or LZD does not substantially alter dynamics of protein synthesis until the arrest-motif of the nascent peptide is generated. Inhibition of peptide-bond formation compels the fully accommodated A-site transfer RNA to undergo repeated rounds of dissociation and nonproductive rebinding. The glycyl amino-acid moiety on the A-site Gly-tRNA manages to overcome the arrest by CHL. Our results illuminate the mechanism of CHL and LZD action through their interactions with the ribosome, the nascent peptide and the incoming amino acid, perturbing elongation dynamics.

Bacterial membrane destabilization with cationic particles of nano-silver to combat efflux-mediated antibiotic resistance in Gram-negative bacteria.

AIMS: With the purpose of exploring combinatorial options that could enhance the bactericide efficacy of linezolid against Gram-negative bacteria, we assessed the extent of combination of nano-silver and linezolid. MAIN METHODS: In this study, we selected Escherichia coli MTCC 443 as a model to study the combinatorial effect of nano-silver and linezolid to combat efflux-mediated resistance in Gram-negative bacteria. The acting mechanism of nano-silver on E. coli MTCC 443 was investigated by evaluating interaction of nano-silver with bacterial membrane as well as bacterial surface charge, morphology, intracellular leakages and biological activities of membrane bound respiratory chain dehydrogenase and deoxyribonucleic acids (DNA) of the cells following treatment with nano-silver. KEY FINDINGS: The alternation of zeta potential due to the interaction of nano-silver towards bacterial membrane proteins was correlated with enhancement of membrane permeability, which allows the penetration of linezolid into the cells. In addition, the binding affinity of nano-silver towards bacterial membrane depressed biological activities of membrane bound respiratory chain dehydrogenases and DNA integrity. SIGNIFICANCE: Our findings suggested that nano-silver could not only obstruct the activities of efflux pumps, but also altered membrane integrity at the same time and thus increased the cytoplasmic concentration of the linezolid to the effective level.

Intracellular Accumulation of Linezolid and Florfenicol in OptrA-Producing Enterococcus faecalis and Staphylococcus aureus.

The optrA gene, which confers transferable resistance to oxazolidinones and phenicols, is defined as an ATP-binding cassette (ABC) transporter but lacks transmembrane domains. The resistance mechanism of optrA and whether it involves antibiotic efflux or ribosomal protection remain unclear. In this study, we determined the MIC values of all bacterial strains by broth microdilution, and used ultra-high performance liquid chromatography-tandem quadrupole mass spectrometry to quantitatively determine the intracellular concentrations of linezolid and florfenicol in Enterococcus faecalis and Staphylococcus aureus. Linezolid and florfenicol both accumulated in susceptible strains and optrA-carrying strains of E. faecalis and S. aureus. No significant differences were observed in the patterns of drug accumulation among E. faecalis JH2-2, E. faecalis JH2-2/pAM401, and E. faecalis JH2-2/pAM401+optrA, but also among S. aureus RN4220, S. aureus RN4220/pAM401, and S. aureus RN4220/pAM401+optrA. ANOVA scores also suggested similar accumulation conditions of the two target compounds in susceptible strains and optrA-carrying strains. Based on our findings, the mechanism of optrA-mediated resistance to oxazolidinones and phenicols obviously does not involve active efflux and the OptrA protein does not confer resistance via efflux like other ABC transporters.

Deposition and transport of linezolid mediated by a synthetic surfactant Synsurf® within a pressurized metered dose inhaler: a Calu-3 model.

BACKGROUND: Previous studies in our laboratory demonstrated that a synthetic peptide containing lung surfactant enhances the permeability of chemical compounds through bronchial epithelium. The purpose of this study was to test two formulations of Synsurf® combined with linezolid as respirable compounds using a pressurized metered dose inhaler (pMDI). METHODS: Aerosolization efficiency of the surfactant-drug microparticles onto Calu-3 monolayers as an air interface culture was analyzed using a Next Generation Impactor™. RESULTS: The delivered particles and drug dose showed a high dependency from the preparation that was aerosolized. Scanning electron microscopy imaging allowed for visualization of the deposited particles, establishing them as liposomal-type structures (diameter 500 nm to 2 µm) with filamentous features. CONCLUSION: The different surfactant drug combinations allow for an evaluation of the significance of the experimental model system, as well as assessment of the formulations providing a possible noninvasive, site-specific, delivery model via pMDI.

Dissemination of linezolid-dependent, linezolid-resistant Staphylococcus epidermidis clinical isolates belonging to CC5 in German hospitals.

Objectives: Linezolid-resistant Staphylococcus epidermidis (LRSE) and linezolid-dependent ST22 strains have been shown to predominate in tertiary care facilities all over Greece. We report herein the dissemination of ST22 but also ST2, ST5 and ST168 linezolid-dependent LRSE clones in four unrelated German hospitals. Methods: Fourteen LRSE clinical isolates recovered during 2012-14 from five distantly located German hospitals were tested by for MIC determination broth microdilution and Etest, PCR/sequencing for cfr and for mutations in 23S rRNA, rplC, rplD and rplV genes, MLST, PFGE and growth curves without and with linezolid at 16 and 32 mg/L. Results: Most (11, 78.6%) isolates had linezolid MICs >256 mg/L. Five isolates carried the cfr gene. Eight isolates belonged to ST22, two isolates each to ST168 and ST2 and one isolate each to ST5 and ST23. Ten isolates [seven belonging to ST22 and one to each of ST2, ST5 and ST168; all these STs belong to clonal complex (CC) 5] exhibited linezolid-dependent growth, growing significantly faster in linezolid-containing broth. Four isolates were non-dependent (one belonging to each of ST22, ST2, ST23 and ST168). Four isolates came from three different hospitals, whereas four and six isolates were recovered during outbreaks of LRSE in two distinct hospitals. Conclusions: The multi-clonal dissemination of CC5 linezolid-dependent LRSE throughout German hospitals along with the clonal expansion of ST22 linezolid-dependent LRSE in Greek hospitals is of particular concern. It is plausible that this characteristic is inherent and provides a selective advantage to CC5 LRSE under linezolid pressure, contributing to their dissemination throughout hospitals in these countries.

Linezolid in liver failure: exploring the value of the maximal liver function capacity (LiMAx) test in a pharmacokinetic pilot study.

Patients in the intensive care unit frequently require antibiotic treatment. Liver impairment poses substantial challenges for dose selection in these patients. The aim of the present pilot study was to assess the novel maximal liver function capacity (LiMAx test) in comparison with conventional liver function markers as covariates of drug clearance in liver failure using linezolid as a model drug. A total of 28 patients with different degrees of liver failure were recruited. LiMAx test as well as plasma, dialysate and urine sampling were performed under linezolid steady-state therapy (600 mg twice daily). NONMEM® was used for a pharmacometric analysis in which the different clearance routes of linezolid were elucidated. Linezolid pharmacokinetics was highly variable in patients with liver failure. The LiMAx score displayed the strongest association with non-renal clearance (CLnon-renal) [ = 4.46∙(body weight/57.9) 0.75∙(LiMAx/221.5)0.388 L/h], which reduced interindividual variability in CLnon-renal from 46.6% to 33.6%, thereby being superior to other common markers of liver function (international normalised ratio, gamma-glutaryl transferase, bilirubin, thrombocytes, alanine aminotransferase, aspartate aminotransferase). For LiMAx < 100 µg/kg/h, 64% of linezolid trough concentrations were above the recommended trough concentration of 8 mg/L, indicating the necessity of therapeutic drug monitoring in these patients. This is the first pilot application of the LiMAx test in a pharmacokinetic (PK) study demonstrating its potential to explain PK variability in linezolid clearance. Further studies with a larger patient collective and further drugs are highly warranted to guide dosing in patients with severe liver impairment.

Structural Basis for Linezolid Binding Site Rearrangement in the Staphylococcus aureus Ribosome.

An unorthodox, surprising mechanism of resistance to the antibiotic linezolid was revealed by cryo-electron microscopy (cryo-EM) in the 70S ribosomes from a clinical isolate of Staphylococcus aureus This high-resolution structural information demonstrated that a single amino acid deletion in ribosomal protein uL3 confers linezolid resistance despite being located 24 Å away from the linezolid binding pocket in the peptidyl-transferase center. The mutation induces a cascade of allosteric structural rearrangements of the rRNA that ultimately results in the alteration of the antibiotic binding site.IMPORTANCE The growing burden on human health caused by various antibiotic resistance mutations now includes prevalent Staphylococcus aureus resistance to last-line antimicrobial drugs such as linezolid and daptomycin. Structure-informed drug modification represents a frontier with respect to designing advanced clinical therapies, but success in this strategy requires rapid, facile means to shed light on the structural basis for drug resistance (D. Brown, Nat Rev Drug Discov 14:821-832, 2015, https://doi.org/10.1038/nrd4675). Here, detailed structural information demonstrates that a common mechanism is at play in linezolid resistance and provides a step toward the redesign of oxazolidinone antibiotics, a strategy that could thwart known mechanisms of linezolid resistance.

Synthesis of Linezolid Metabolites PNU-142300 and PNU-142586 toward the Exploration of Metabolite-Related Events.

Linezolid (1) is an oxazolidinone antibiotic that is partially metabolized in vivo via ring cleavage of its morpholine moiety to mainly form two metabolites, PNU-142300 (2) and PNU-142586 (3). It is supposed that accumulation of 2 and 3 in patients with renal insufficiency may cause thrombocytopenia, one of the adverse effects of linezolid. However, the poor availability of 2 and 3 has hindered further investigation of the clinical significance of the accumulation of these metabolites. In this paper, we synthesized metabolites 2 and 3 via a common synthetic intermediate, 4; this will encourage further exploration of events related to these metabolites and lead to improved clinical use of linezolid.

Loading of atorvastatin and linezolid in ß-cyclodextrin-conjugated cadmium selenide/silica nanoparticles: A spectroscopic study.

The preparation of ß-cyclodextrin-conjugated cadmium selenide-silica nanoparticles, the loading of two drugs viz., Atorvastatin and linezolid in the cyclodextrin cavity, and the fluorescence energy transfer between CdSe/SiO2 nanoparticles and the drugs encapsulated in the cyclodextrin cavity are reported in this paper. IR spectroscopy, X-ray diffractometry, transmission electron microscopy, and particle size analysis by light-scattering experiment were used as the tools of characterizing the size and the crystal system of the nanoparticles. The nanoparticles fall under hexagonal system. The silica-shell containing CdSe nanoparticles were functionalized by reaction with aminoethylamino-ß-cyclodextrin. Fluorescence spectra of the nanoparticles in their free and drug-encapsulated forms were studied. The FÖrster distances between the encapsulated drugs and the CdSe nanoparticles are below 3nm. The change in the FÖrster resonance energy parameters under physiological conditions may aid in tracking the release of drugs from the cavity of the cyclodextrin.

Interspecies scaling of excretory amounts using allometry - retrospective analysis with rifapentine, aztreonam, carumonam, pefloxacin, miloxacin, trovafloxacin, doripenem, imipenem, cefozopran, ceftazidime, linezolid for urinary excretion and rifapentine, cabotegravir, and dolutegravir for fecal excretion.

1. Interspecies allometry scaling for prediction of human excretory amounts in urine or feces was performed for numerous antibacterials. Antibacterials used for urinary scaling were: rifapentine, pefloxacin, trovafloxacin (Gr1/low; <10%); miloxacin, linezolid, PNU-142300 (Gr2/medium; 10-40%); aztreonam, carumonam, cefozopran, doripenem, imipenem, and ceftazidime (Gr3/high; >50%). Rifapentine, cabotegravir, and dolutegravir was used for fecal scaling (high; >50%). 2. The employment of allometry equation: Y = aW(b) enabled scaling of urine/fecal amounts from animal species. Corresponding predicted amounts were converted into % recovery by considering the respective human dose. Comparison of predicted/observed values enabled fold difference and error calculations (mean absolute error [MAE] and root mean square error [RMSE]). Comparisons were made for urinary/fecal data; and qualitative assessment was made amongst Gr1/Gr2/Gr3 for urine. 3. Average correlation coefficient for the allometry scaling was >0.995. Excretory amount predictions were largely within 0.75- to 1.5-fold differences. Average MAE and RMSE were within ±22% and 23%, respectively. Although robust predictions were achieved for higher urinary/fecal excretion (>50%), interspecies scaling was applicable for low/medium excretory drugs. 4. Based on the data, interspecies scaling of urine or fecal excretory amounts may be potentially used as a tool to understand the significance of either urinary or fecal routes of elimination in humans in early development.

First report of linezolid dependence in methicillin-resistant Staphylococcus aureus.

Linezolid is used to treat infections caused by methicillin-resistant Staphylococcus aureus (MRSA). We describe the first report of linezolid dependence in MRSA. The strain was isolated from a respiratory sample of a cystic fibrosis patient, and it showed a thymidine-dependent small-colony variant phenotype. The effect was not related to any known mechanisms implicated in S. aureus resistance to linezolid. The clinical significance of this phenomenon needs further investigation.

Linezolid resistance in clinical isolates of Staphylococcus epidermidis from German hospitals and characterization of two cfr-carrying plasmids.

OBJECTIVES: This study was a detailed investigation of Staphylococcus epidermidis clinical isolates exhibiting linezolid resistance. METHODS: Thirty-six linezolid-resistant S. epidermidis from eight German hospitals, including isolates from suspected hospital-associated outbreaks between January 2012 and April 2013, were analysed with respect to their antimicrobial susceptibility and the presence of cfr and/or mutations in the 23S rRNA, rplC, rplD and rplV genes. Relatedness of isolates was estimated by MLST and SmaI macrorestriction analysis. Characterization of cfr plasmids was carried out by means of Illumina sequencing. RESULTS: The MICs of linezolid varied substantially between the isolates. No apparent correlation was detected between the level of resistance, the presence of cfr and ribosomal target site mutations. S. epidermidis isolates from two hospitals were confirmed as clonally related, indicating the spread of the respective clone over a period of 1 year. Next-generation sequencing revealed two different categories of cfr-expressing plasmids, both of them varying in genetic arrangement and composition from previously published cfr plasmids: p12-00322-like plasmids showed incorporation of cfr into a pGO1-like backbone and displayed capabilities for intra- and inter-species conjugational transfer. CONCLUSIONS: To date, linezolid-resistant S. epidermidis have rarely been isolated from human clinical sources in Germany. Here, we describe the emergence and outbreaks of these strains. We detected previously described and novel point mutations in the 23S ribosomal genes. The cfr gene was only present in six isolates. However, this is the first known description of cfr incorporation into conjugative vectors; under selective pressure, these vectors could give reasonable cause for concern.