Diminished in vitro antibacterial activity of oxacillin against clinical isolates of borderline oxacillin-resistant Staphylococcus aureus

Since it is unknown whether β-lactam antimicrobial agents can be used effectively against borderline oxacillin-resistant Staphylococcus aureus (BORSA) with oxacillin MICs ≥4 mg/L, the in vitro bactericidal activity and pharmacodynamic effect of oxacillin against clinical BORSA isolates was evaluated. Time-kill experiments with oxacillin were performed and the results compared with those obtained with vancomycin, daptomycin and linezolid against BORSA with oxacillin MICs ≥4 mg/L and BORSA with oxacillin MICs ≤2 mg/L. Furthermore, the effect of β-lactamase production and plasmid profile analysis were taken into account to clarify responses to oxacillin. Oxacillin killing activity was attenuated against BORSA compared with ATCC 29213 since the pharmacodynamic parameters revealed that the potency of oxacillin was markedly reduced (c. ten-fold) against BORSA with oxacillin MICs ≥4 mg/L. pBORa53-like plasmid-containing BORSA with oxacillin MICs ≤2 mg/L showed markedly more regrowth. In conclusion, oxacillin was non-effective in the eradication of either (i) BORSA with oxacillin MICs ≥4 mg/L or (ii) β-lactamase-hyperproducing BORSA (MICs ≤2 mg/L). Further investigation into β-lactam dosing strategies against different BORSA strains is warranted in order to avoid possible therapy failure.     

高效液相色谱-紫外检测法测定利奈唑胺在体外药效学模型的浓度

目的 建立高效液相色谱-紫外检测法测定利奈唑胺(抗菌药)在国产肉汤基质的药物浓度.方法 MH肉汤样品350 μL,加入15%高氯酸沉淀蛋白,离心后取上清液50μL进样测定.Venusil XBP C_8(4.6 mm×250 mm,5 μm)色谱柱,流动相为水-乙腈(80∶20),流量为1.5 mL·min~(-1),紫外检测波长251nm,室温;用高效液相色谱-紫外检测法测定利奈唑胺浓度.结果 线性范围0.5～40.0 μg·mL~(-1)(γ=0.9996),低、中、高浓度的绝对回收率均大于90%,相对回收率在96%～98%,日内、日间RSD分别小于2%和4%;最低检测浓度为0.5 μg·mL~(-1).结论 该方法准确可靠、操作简便、灵敏度高,适用于体外药效学模型中药物浓度测定.     

高效液相色谱法测定利奈唑胺滴眼液的含量

目的建立测定利奈唑胺滴眼液含量的高效液相色谱方法。方法采用Eclipse XDB-C8柱（4.6 mm×150 mm,5μm）为色谱柱;流动相：水∶乙腈（80∶20,v/v）,柱温50℃,流速1.4 ml/min,检测波长251 nm。结果在0.025～0.8 mg/ml浓度范围内,利奈唑胺峰面积和质量浓度呈良好的线性关系（r=0.999 5）,平均回收率为100.7%,RSD为0.6%,精密度高,耐用性好,样品溶液可以在室温环境下24 h内稳定。结论本方法专属性强,操作简便,结果准确,可用于测定利奈唑胺滴眼液的含量。     

住院患者使用利奈唑胺致相关性血小板减少症的危险因素分析

目的 研究住院患者使用利奈唑胺致血小板减少的发生率及危险因素.方法 采用回顾性横断面研究,以解放军总医院2011年1月至2011年5月间使用利奈唑胺的住院患者为研究对象,通过医院信息系统记录患者一般资料、病生理情况、用药情况并动态监测血小板计数变化.定义血小板减少症为低于正常值下限(即血小板计数＜100×109/L),并根据排除标准控制混杂因素,对纳入病例使用利奈唑胺致血小板减少症的观察指标进行逐步逻辑回归筛选危险因素,并绘制ROC曲线预测发生特征.结果 获得用药病例345例,按入排标准纳入有效病例208例,其中男性129(62.02％)例,女性79( 37.98％)例,平均年龄为62.67±18.66(16～ 98)a,用药时间平均为9.68±6.07(3～39)天.使用利奈唑胺致相关性血小板减少症的有59例(28.37％),发生血小板低于正常值或基础值的25％的有106例(50.96％),其中有20人(9.62％)发生了Ⅲ度和Ⅳ度血小板下降,需要输血或输注血小板.单因素分析显示年龄、肌酐清除率、基础血小板值、总胆红素、血清白蛋白对血小板减少症的影响具有统计学意义,逐步逻辑回归多因素分析显示基础血小板值和年龄与血小板减少症密切相关.绘制血ROC曲线Youden指数最大时(0.3855),曲线下面积为0.739时,对应切点的敏感度为62.71％,特异度为75.84％.结论 基础血小板值、年龄是利奈唑胺致相关性血小板减少症的独立危险因素,对基础血小板值≤204×109/L、年龄≥82岁的患者,容易发生明显血小板减少症甚至出血风险,应加强血常规监测频率.低肌酐清除率、低血清白蛋白水平也是发生血小板减少的重要危险因素,提示利奈唑胺致相关性血小板减少症呈浓度依赖性,并与免疫机制相关.此外,可尝试使用ROC曲线筛选预测利奈唑胺相关性血小板减少的风险特征,并在易感人群中调整合适剂量以兼顾有效性和安全性.     

Linezolid- and Multidrug-Resistant Enterococci in Raw Commercial Dog Food,Europe, 2019–2020

We describe enterococci in raw-frozen dog food commercialized in Europe as a source of genes encoding resistance to the antibiotic drug linezolid and of strains and plasmids enriched in antibiotic-resistance and virulence genes in hospitalized patients. Whole-genome sequencing was fundamental to linking isolates from dog food to human cases across Europe.     

A toxicogenomic approach for identifying biomarkers for myelosuppressive anemia in rats

Myelosuppressive anemia is a serious side effect associated with several drugs. Thus, there is an increasing demand for sensitive biomarkers for the early detection of myelosuppressive anemia during toxicological studies. We applied a toxicogenomic approach to identify useful biomarker genes reflecting myelosuppressive anemia in the rat liver. Expression of the hemoglobin beta chain complex (Hbb), aminolevulinic acid synthase 2 (Alas2), and cell division cycle 25 homolog B (Cdc25b) genes changed as a result of anemia induced by the myelosuppressive agents linezolid, cisplatin, and carboplatin, suggesting that these genes may be suitable biomarkers. Moreover, evaluation of perfused and unperfused livers indicated that changes in the expression of these genes originate in circulating reticulocytes in the liver. Erythroid differentiation-associated changes in expression of the Hbb, Alas2, and Cdc25b genes were confirmed in vitro using Friend leukemia cells. In conclusion, our current research provides novel evidence that gene expression in circulating reticulocytes contained in the liver changes dramatically under myelosuppressive conditions. While further large-scale validation studies are needed, our results indicate that the genes we identified might be useful biomarkers for the sensitive detection of myelosuppressive anemia in rats.     

Synthesis and antibacterial activity of substituted oxotriazolylphenyl oxazolidinones

A series of 3-(4'-(2'-alkyl-3'-oxy-1',2',4'-triazolyl)-phenyl)-5-substituted oxazolidinones was designed and synthesized for in vitro antibacterial activity testing against fourteen Gram-negative and six Gram-positive standard organisms. The minimum inhibitory concentration (MIC) was determined by agar dilution at concentrations of 0.10, 0.20, 0.39, 0.78, 1.56, 3.13, 6.25 microg/mL. Different alkyl groups at the 2'-position played an important role in the activity against Gram-positive organisms. (S)-3-(4'-(2'-ethyl-3'-oxy-1',2',4'-triazolyl)-phenyl)-5-acetamidomethyloxazolidinone was active against Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus enteridis and Streptococcus nonhemolyticus, whereas 2'-methyl, 2'-propyl and 2'-n-butyl counterparts did not show activity at 6.25 microg/mL. Modification of the 5-substitutent of oxazolidinones also affected the activity against Gram-positive organisms. (S)-3-(4'-(2'-ethyl-3'-oxy-1',2',4'-triazolyl)-phenyl)-5-acetamidomethyloxazolidinones was approximately two fold more potent than 5-chloroacetamido, 5-dichloroacetamido and 5-trifluoroacetamido counterparts against Streptococcus enteridis. None of these compounds showed growth inhibition against fourteen Gram-negative organisms at 6.25 microg/mL.     

Mitochondrial loss indicates early axonal damage in small fiber neuropathies

Evaluation of nerve fibers in the skin provides a useful tool for the diagnosis of small fiber neuropathies (SFNs). Our aim was to determine whether mitochondria are involved in SFN, indicating early axonal damage. We quantified mitochondrial respiratory chain complex IV (OXPHOS) and axonal (PGP 9.5) fluorescence on skin sections from 32 SFN patients and 14 healthy controls. Also, a group of six patients were recruited before and after 30-day treatment with the mitotoxic antibiotic linezolid. We measured the co-localization of OXPHOS within the intraepidermal and subpapillary dermal axons (PGP-immunoreactive [PGP-ir]). SFN patients with relatively preserved intraepidermal nerve fibers (SFN borderline) showed statistically significant reduction of OXPHOS (50.5 ± 33.9 μm(2) vs. 107.6 ± 81 μm(2) in controls, p < 0.02). A positive correlation was found between both PGP-ir and OXPHOS in controls (Pearson's coefficient r = 0.59, p < 0.001), whereas such correlation was absent in SFN. With respect to baseline measurements, linezolid therapy increased both PGP-ir and OXPHOS, which could be considered an initial compensatory toxic-induced response. This study set out to identify a possible marker of axonal pre-degenerative state in SFN borderline patients.     

Efficacy and safety of linezolid in immunocompromised children with cancer

Background: The aim of this study was to determine the safety, tolerance and efficacy of linezolid for the treatment of infections from Gram‐positive bacteria in immunocompromised children with cancer. Methods: This was a prospective non‐comparative unblinded study in the Hematology/Oncology Unit over a two‐year period, administering linezolid as monotherapy in children with cancer. Results: Seventeen children received linezolid (30 mg/kgr: 3 i.v. per day). Mean duration of linezolid administration was 12.2 days (range, 6–38 days), while the median age of the evaluable patients was 2.2 years (range, 6 months–11.2 years). Primary diagnosis was acute lymphoblastic leukemia (nine patients), brain tumor (three patients), multi‐organ Langerhans cell histiocytosis (two patients), rhabdomyosarcoma, Burkitt's lymphoma and ovarian tumor (one patient each). All patients were in the midst of chemotherapy cycles. Ten out of 17 children had positive blood cultures (methicillin‐resistant Staphylococcus aureus, four patients; vancomycin‐resistant Enterococcus, three patients; penicillin‐resistant Streptococcus pneumoniae, three patients), while seven of the 17 had fever and vancomycin‐resistant Enterococcus in stool cultures. All patients were considered clinically cured after the end of the linezolid regimen (100% efficacy). The main adverse events were thrombocytopenia grade 1–3 and anemia grade 2–3 (four and two patients, respectively). Chemotherapy‐induced myelotoxicity (six patients) was not worsened during linezolid therapy. No bleeding episodes were presented. Self‐limited diarrhea grade 1–2 was presented in four patients (mean duration 2 days). The total adverse event rate was 23.5%; however, there was no premature cessation of linezolid in any patient. Conclusions: Linezolid may be another effective and safe therapy to treat infections from resistant Gram‐positive bacteria in immunocompromised children, even in young ages.