高水平莫匹罗星耐药MRSA体外生物膜形成能力及相关基因检测

目的 了解高水平莫匹罗星耐药甲氧西林耐药金葡菌(MuH MRSA)体外生物膜形成能力及介导生物膜形成相关基因的分布.方法 对分离自上海和浙江省温州地区5所教学医院的803 株临床分离MRSA进行莫匹罗星纸片扩散法检测最低抑菌浓度(MIC),mupA基因PCR扩增筛选MuH MRSA,分光光度计检测MuH MRSA菌株体外生物膜的形成能力,PCR扩增生物膜形成相关基因(icaA、icaD、agr、sarA、sasG、bap和ccpA).结果 共筛选出53株MuH MRSA,其中仅5株(9.4%,5/53)具有体外形成生物膜的能力;基因检测显示,icaD和agr基因存在于全部MuH MRSA菌株中,而icaA、sarA、sasG和ccpA基因则分别存在于83.0%、86.8%、84.9%和92.5%的菌株中,仅有1株细菌携带bap基因.结论 大部分生物膜形成相关基因广泛分布于MuH MRSA菌株中,但仅agr基因可能是该类菌株体外生物膜形成能力的主要影响因素.     

莫匹罗星联合呋喃西林治疗脓疱疮疗效观察

目的:评价莫匹罗星联合呋喃西林治疗脓疱疮疗效及安全性。方法:将67例脓疱疮患者随机分为2组,实验组以莫匹罗星涂患处,且皮损较大处应用呋喃西林溶液湿敷;对照组以红霉素软膏以及碘伏涂患处,3次/d,疗程均1w。结果:实验组与对照组总有效率分别为97.22%、69.69%;痊愈率分别为88.89%、39.39%。经统计学处理,总有效率相比χ2=9.7344(P<0105);痊愈率相比χ2=19.1(P<0101),两者间差异均有统计学意义。结论:莫匹罗星联合呋喃西林治疗脓疱疮疗效确切,且比较安全。     

前列地尔联合西洛他唑、莫匹罗星治疗老年糖尿病足的效果

目的 探讨前列地尔联合西洛他唑、莫匹罗星治疗老年糖尿病足患者的效果.方法 选取2012年1月至2020年1月于南京医科大学附属老年医院住院诊治的糖尿病足老年患者64例,按照纳入和排除标准进行筛选,对符合要求的51例患者的临床资料进行回顾性分析.暴露组20例为前列地尔治疗基础上加用西洛他唑、莫匹罗星,非暴露组31例为单用...     

莫匹罗星联合硫酸镁外敷治疗新生儿静脉炎的效果观察

[目的]观察莫匹罗星联合25%硫酸镁外敷治疗新生儿静脉炎的效果。[方法]将80例静脉炎新生儿随机分为观察组和对照组各40例,对照组出现静脉炎当天给予25%硫酸镁持续湿热敷外加保鲜膜保温,8 h更换1次并做好记录。观察组出现静脉炎当天取适量莫匹罗星软膏外涂患处并轻柔按摩2 min后,再用25%硫酸镁进行持续湿热敷外加保鲜膜保温,8 h更换1次并做好记录。治疗96 h进行疗效观察。[结果]观察组总有效率显著高于对照组（P〈0.01）。[结论]莫匹罗星联合硫酸镁具有协同作用,能有效治疗新生儿静脉输液引起的静脉炎,可缩短住院时间。     

莫匹罗星联合硫酸镁外敷治疗新生儿静脉炎的效果观察

[目的]观察莫匹罗星联合25%硫酸镁外敷治疗新生儿静脉炎的效果。[方法]将80例静脉炎新生儿随机分为观察组和对照组各40例,对照组出现静脉炎当天给予25%硫酸镁持续湿热敷外加保鲜膜保温,8h更换1次并做好记录。观察组出现静脉炎当天取适量莫匹罗星软膏外涂患处并轻柔按摩2min后,再用25%硫酸镁进行持续湿热敷外加保鲜膜保温,8h更换1次并做好记录。治疗96h进行疗效观察。[结果]观察组总有效率显著高于对照组(P0.01)。[结论]莫匹罗星联合硫酸镁具有协同作用,能有效治疗新生儿静脉输液引起的静脉炎,可缩短住院时间。     

预防性外用莫匹罗星对于腹膜透析患者导管出口评分的影响

目的探讨用出口评分（Exit-Site Score,ESS）法评分进行腹膜透析（CAPD）导管出口感染的辅助诊断,观察莫匹罗星治疗对于出口评分的影响。方法选取在上海交通大学附属第一人民医院肾内科行腹膜透析的80例患者,运用横断面调查的方法,采用腹膜透析患者出口评分法来进行评分。对于ESS2～3分者,随机分成两组,一组予以常规的每日清洁,另一组在此基础上进行每日在出口处涂擦莫匹罗星乳膏1个月,再次进行相关的评分。然后对于所有的ESS评分为2～3分的糖尿病患者以及浅表涤纶套距离皮肤较近者（〈1.5cm）,皆采用每日在出口处涂擦莫匹罗星乳膏,累计1个月的治疗,观察其后ESS评分的改善。结果①80例患者中,ESS评分≥4分者有3例,占3%;2～3分者有21例,占26%;ESS评分为0分者40例,占50%,2～3分者平均的评分为（2.7±0.6）分;②治疗组出口处评分经过一个月的治疗,ESS评分≥4分者有1例,以后发展到腹膜炎;2～3分者平均的评分为（2.2±0.5）分,较治疗前明显改善,P〈0.05。与对照组相比,治疗组的ESS评分明显改善,而对照组与治疗前评分无明显的差异;③糖尿病患者与浅表涤纶套离开皮肤较近者（1．5cm）,其ESS评分明显升高,而经过使用抗生素乳膏,ESS评分皆能获得改善。结论本研究提示对ESS评分≥2分者进行莫匹罗星治疗可以明显改善出口评分状况,从而可能影响其腹膜炎的发生。     

艾条温灸配合莫匹罗星软膏治疗压疮的疗效

目的 观察艾条温灸配合莫匹罗星软膏治疗压疮的疗效.方法 将40例(49处)压疮患者按随机数字表法分为观察组(20例,27处)和对照组(20例,22处).观察组清洗疮面,使用艾条直接温灸,温灸时间为15～20 min.再用莫匹罗星软膏外涂疮面,外用无菌纱布加压包扎,隔日1次.对照组根据病情清洗疮面后,用无菌纱布加压包扎,隔日1次.2组均用药15 d,观察其疗效.结果 观察组压疮治愈率及总有效率分别为62.9％和96.3％,对照组压疮治愈率及总有效率分别为31.8％和86.3％,2组比较差异均有统计学意义(均P＜0.05).结论 使用艾条温灸配合莫匹罗星软膏外涂治疗压疮见效快、治愈率高,能明显地减轻患者的痛苦.     

贝复新联合莫匹罗星治疗皮肤擦伤疗效观察

[目的]观察贝复新联合莫匹罗星治疗皮肤擦伤的效果。[方法]选取78例急诊科两处以上皮肤擦伤的换药治疗病人,按浅表皮肤损伤、深层皮肤损伤分别随机分为治疗组和对照组,治疗组采用贝复新联合莫匹罗星换药,对照组采用凡士林换药,观察两组疗效。[结果]治疗组痊愈率及总有效率明显高于对照组(P<0.05)。[结论]采用贝复新联合莫匹罗星治疗皮肤擦伤效果优于凡士林换药。     

莫匹罗星在腹部切口感染治疗中的临床价值

目的探讨莫匹罗星在腹部切口感染治疗中的临床价值。方法收集我院普外科2009年1月至2010年1月各种腹部手术后发生切口感染42例,随机分为实验组及对照组。实验组常规清创后涂抹莫匹罗星软膏并凡士林纱条覆盖创面,对照组常规清创后以碘仿纱条填塞伤口。结果对照组患者切口感染治疗时间为9~17 d,平均（10.2±4.7）d,愈合时间23~29 d,平均（25.3±2.7）d。实验组患者切口感染治疗时间为5~8 d,平均（4.7±2.6）d,愈合时间为10~16 d,平均（12.4±2.1）d。两组比较,术后切口感染平均治疗时间和平均愈合时间差异均有统计学意义（P〈0.01）。结论莫匹罗星在术后伤口感染治疗中安全,有效,能明显缩短治疗时间,值得在临床应用中推广。     

Pharmacodynamics of Vancomycin at Simulated Epithelial Lining Fluid Concentrations against Methicillin-Resistant Staphylococcus aureus (MRSA): Implications for Dosing in MRSA Pneumonia

Little is known regarding killing activity of vancomycin against methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) in pneumonia since the extent of vancomycin penetration into epithelial lining fluid (ELF) has not been definitively established. We evaluated the impact of the extent of ELF penetration on bacterial killing and resistance by simulating a range of vancomycin exposures (24-h free drug area under the concentration-time curve [ƒAUC₂₄]/MIC) using an in vitro pharmacodynamic model and population-based mathematical modeling. A high-dose, 1.5-g-every-12-h vancomycin regimen according to American Thoracic Society/Infectious Diseases Society of America guidelines (trough concentration, 15 mg/liter) with simulated ELF/plasma penetration of 0, 20, 40, 60, 80, or 100% (ƒAUC₂₄/MIC of 0, 70, 140, 210, 280, or 350) was evaluated against two agr-functional, group II MRSA clinical isolates obtained from patients with a bloodstream infection (MIC = 1.0 mg/liter) at a high inoculum of 10⁸ CFU/ml. Despite high vancomycin exposures and 100% penetration, all regimens up to a ƒAUC₂₄/MIC of 350 did not achieve bactericidal activity. At regimens of ≤60% penetration (ƒAUC₂₄/MIC ≤ 210), stasis and regrowth occurred, amplifying the development of intermediately resistant subpopulations. Regimens simulating ≥80% penetration (ƒAUC₂₄/MIC ≥ 280) suppressed development of resistance. Resistant mutants amplified by suboptimal vancomycin exposure displayed reduced rates of autolysis (Triton X-100) at 72 h. Bacterial growth and death were well characterized by a Hill-type model (r² ≥ 0.984) and a population pharmacodynamic model with a resistant and susceptible subpopulation (r² ≥ 0.965). Due to the emergence of vancomycin-intermediate resistance at a ƒAUC₂₄/MIC of ≤210, exceeding this exposure breakpoint in ELF may help to guide optimal dosage regimens in the treatment of MRSA pneumonia.Nosocomial pneumonia remains a significant cause of morbidity and mortality. Recently the American Thoracic Society and the Infectious Diseases Society of America (ATS/IDSA) (1) proposed vancomycin trough concentrations of 15 to 20 mg/liter for health care- and ventilator-associated (HAP and VAP) methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) pneumonia. This recommendation is derived from evidence suggesting that the vancomycin 24-h area-under-the-concentration-time-curve-to-MIC (AUC/MIC) ratio of ≥350 is predictive of cure in patients with S. aureus pneumonia and recent concerns regarding vancomycin''s antistaphylococcal activity, such as the MIC “creep,” low rate of killing, and increasing reports of treatment failure (14, 26, 31, 32). However, there has been significant debate as to whether high-dose vancomycin is beneficial, since some studies have shown that greater exposure is not correlated with a more favorable hospital outcome and is associated with increased nephrotoxicity in patients receiving high-dose vancomycin regimens (9, 11, 22).Additionally, little is known regarding the degree of penetration of vancomycin into epithelial lining fluid (ELF) from plasma. Although an earlier study by Lamer et al. (19) provided evidence that vancomycin penetrates poorly into ELF (free vancomycin in ELF/plasma was less than 30%), a recent study by G. L. Drusano et al. (7a) suggests that ELF penetration may be higher (free vancomycin in ELF/plasma was approximately 100%). Adding to this discrepancy is the lack of information regarding vancomycin''s killing activity and ability to suppress resistance at clinically achievable concentrations at the site of infection and the relationship between the early physiologic changes in S. aureus that occur due to suboptimal exposure.The objective of this investigation was to simulate human concentration-time profiles of vancomycin in ELF and determine the proclivity toward developing reduced glycopeptide susceptibility, tolerance, and phenotypic alterations using an in vitro pharmacodynamic model of MRSA infection and mathematical modeling.(This work was presented in part at the 47th Annual Meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, September 2007.)     

Mupirocin resistance in Staphylococcus aureus in an Indian hospital

Two hundred Staphylococcus aureus strains collected from an Indian hospital were tested for mupirocin susceptibility using disc diffusion method and E-test. High-level and low-level mupirocin resistance was detected in 10 (5%) and 2 (1%) S. aureus strains, respectively. Pulsed-field gel electrophoresis analysis of the high-level mupirocin-resistant methicillin-resistant S. aureus isolates revealed the presence of 2 clones with the majority of strains belonging to 1 clone, suggesting clonal dissemination.     

Antimicrobial susceptibility and molecular characteristics of 857 methicillin-resistant Staphylococcus aureus isolates from 16 medical centers in Japan (2008-2009): nationwide survey of community-acquired and nosocomial MRSA

This study is a nationwide survey of all clinical methicillin-resistant Staphylococcus aureus (MRSA) isolates, including community-acquired MRSA (CA-MRSA), in Japan. A total of 857 MRSA clinical isolates were collected from the 16 institutions throughout Japan that participated in the survey (2008-2009). The drug susceptibility and staphylococcal cassette chromosome mec (SCCmec) typing and the presence of specific pathogenic genes were evaluated. The isolates comprised SCCmec type II (73.6%), type IV (20%), and type I (6%). The percentage of SCCmec type IV isolates was significantly higher in outpatients than in inpatients. Most of the isolated strains were sensitive to vancomycin (VCM, MIC ≤2 μg/mL), linezolid (MIC ≤4 μg/mL), and teicoplanin (MIC ≤8 μg/mL). Although most strains were sensitive to VCM, the MIC value of VCM for SCCmec type II strains was higher than that for SCCmec type IV strains. Only 4 (2.3%) of 171 SCCmec type IV strains were Panton-Valentine leukocidin (lukS/F-PV)-positive. Thus, this result indicates a unique feature of SCCmec type IV strains in Japan. The information in this study not only is important in terms of local public health but will also contribute to an understanding of epidemic clones of CA-MRSA.     

Spontaneous methicillin-resistant Staphylococcus aureus (MRSA) meningitis

Spontaneous methicillin-resistant Staphylococcus aureus (MRSA) meningitis is extremely rare and has a high mortality rate. We report a case of MRSA meningitis in an otherwise healthy young adult female with no recent trauma or neurosurgical interventions. Despite antibiotics she suffered a vasculitis-induced cerebral vascular ischemic event.     

Comparison of Tigecycline and Vancomycin for Treatment of Experimental Foreign-Body Infection Due to Methicillin-Resistant Staphylococcus aureus

Twice-daily 7-day regimens of tigecycline (7 mg/kg) and vancomycin (50 mg/kg) were compared in a rat tissue cage model of chronic foreign-body infection due to methicillin (meticillin)-resistant Staphylococcus aureus strain MRGR3. Subcutaneously administered tigecycline reached levels in tissue cage fluid that were nearly equivalent or slightly superior to the antibiotic MIC (0.5 μg/ml) for strain MRGR3. After 7 days, equivalent, significant reductions in bacterial counts were recorded for tigecycline-treated and vancomycin-treated rats, compared with those for untreated animals.Antimicrobial therapy for foreign-body infections due to Staphylococcus aureus is challenging (38), in particular for multidrug-resistant hospital-associated and community-acquired isolates of methicillin (meticillin)-resistant S. aureus (MRSA) (3, 12, 15, 16). Tigecycline is a novel injectable glycylcycline broad-spectrum antibiotic that demonstrates excellent in vitro and in vivo activity against MRSA and other multiresistant organisms (9, 11, 22, 28, 32) and can overcome both major tetracycline resistance mechanisms, namely ribosomal protection (10, 23) and efflux (4, 27). Tigecycline has shown good activity in various animal models of serious MRSA infections (21, 39, 40), as well as against biofilm-embedded bacteria (14, 26).We previously used a rat tissue cage model of S. aureus chronic foreign-body infections for evaluating a number of antimicrobial agents, namely vancomycin (17), teicoplanin (31), imipenem (30), ceftobiprole (37), daptomycin (29, 35), and several fluoroquinolones (2, 17, 36). This study reports the activity of tigecycline compared to that of the reference anti-MRSA agent vancomycin in a tissue cage model of MRSA chronic foreign-body infection.(This study was presented in part at the 18th European Congress of Clinical Microbiology and Infectious Diseases, Barcelona, Spain, April 2008.)MRSA strain MRGR3, whose properties were previously described (2, 5, 17, 29-31, 36, 37), was used for in vitro and in vivo studies. Strain MRGR3 is resistant to methicillin, gentamicin, erythromycin, tetracycline, and chloramphenicol (17).MICs of freshly prepared (1, 13, 25) tigecycline (Wyeth Research, Collegeville, PA) or vancomycin (Vancocin; Teva Pharma AG, Switzerland) for MRSA strain MRGR3 or quality control S. aureus ATCC 29213 were determined by broth macrodilution in cation-adjusted Mueller-Hinton broth (CAMHB), according to Clinical and Laboratory Standards Institute guidelines (7).The animal protocol used for evaluating the in vivo activities of tigecycline and vancomycin was previously described in detail (17, 37) and approved by the Ethics Committee of the Faculty of Medicine, University of Geneva, and the Veterinary Office of the State of Geneva. Three weeks after subcutaneous implantation of four tissue cages per animal in anesthetized Wistar rats (37), tissue cage fluids were checked for sterility (17).Pilot pharmacokinetic studies were performed using groups of noninfected rats to find an adequate dosing regimen of tigecycline for therapy of tissue cage infections as described previously (37). Tigecycline levels in cage fluids (and blood) were estimated by a microbiological assay (21), with a detection limit of 0.25 μg/ml. To account for protein binding, all plasma or tissue cage fluid samples were diluted with 1 volume of phosphate-buffered saline and assayed in duplicate, with reference to duplicate standard concentrations (0.25 to 8 μg/ml) of tigecycline, in phosphate-buffered saline supplemented with 50% plasma or pooled tissue cage fluids, respectively.Each tissue cage was chronically infected by inoculating 5 × 10⁵ CFU of log-phase MRGR3 (37). Two weeks later, all rats whose cage fluids contained ≥10⁵ CFU/ml received twice-daily doses (by the subcutaneous route for 7 days) of tigecycline (7 mg/kg), vancomycin (50 mg/kg), or no antibiotic (control group). Differences in CFU counts of cage fluid quantitative cultures, performed at day 1 (before treatment) and day 8 (12 h after the last injection of either tigecycline or vancomycin), were expressed as the change in number of log₁₀ CFU/ml (37) and evaluated by one-way analysis of variance and post-analysis of variance pairwise comparisons between individual groups via the Tukey HSD test (http://faculty.vassar.edu/lowry/VassarStats.html), using P values of <0.05 with two-tailed significance levels.Tigecycline resistance was screened by plating 10-fold-diluted cage fluids (100 μl) onto MH agar supplemented with 2 μg/ml tigecycline. No single colony grew on tigecycline-supplemented plates inoculated with 10⁸ CFU of in vitro-grown cultures of strain MRGR3.The MIC of tigecycline in CAMHB for MRSA strain MRGR3 was 0.5 μg/ml, namely at the upper limit of susceptibility breakpoints (7), and was unaffected by supplementation of CAMHB with 50% tissue cage fluid (data not shown). Since tigecycline did not produce a 3-log₁₀ reduction in the number of MRGR3 CFU/ml, it was not considered bactericidal. Nevertheless, supra-MIC levels (1, 2, and 4 μg/ml) of tigecycline produced a 2- to 3-log₁₀ decrease in the number of MRGR3 CFU/ml at 24 h. The vancomycin MIC and minimal bactericidal concentration for strain MRGR3 were 1 and 2 μg/ml, respectively (17).Average tigecycline levels, scored for tissue cage fluids (n = 6) from 0 to 12 h after subcutaneous administration, remained quite constant over time, showing ≤3-fold variations between results at different time points and moderate animal-to-animal differences (Fig. ​(Fig.1).1). A 7-mg/kg twice-daily regimen yielded cage fluid levels of 0.39 to 0.70 μg/ml tigecycline at day 4 and 0.33 to 1.01 μg/ml at day 7, such results thus being nearly equivalent or slightly superior to the antibiotic MIC for MRGR3. Tigecycline plasma levels at 2 h on day 4 were 1.87 ± 0.66 μg/ml, in agreement with other reports (8, 21). A 14-mg/kg twice-daily regimen led to plasma and tissue cage fluid tigecycline levels ca. twofold higher than the 7-mg/kg regimen (Fig. ​(Fig.1).1). Average peak and trough cage fluid levels of vancomycin were previously determined (17) as 12 and 2 μg/ml at 4 and 12 h, respectively.Open in a separate windowFIG. 1.Pharmacokinetic levels of tigecycline in tissue cage fluids of rats on day 4 (open symbols) or day 7 (closed symbols) of therapy every 12 h with 7 mg/kg (○) or 14 mg/kg (▵) of tigecycline. Each value is the mean result of six determinations.At day 1, mean bacterial counts for MRGR3-infected cages were not significantly different (P = 0.65) in controls (6.85 ± 0.19 log₁₀ CFU/ml; n = 28), tigecycline-treated rats (6.92 ± 0.13 log₁₀ CFU/ml; n = 29), or vancomycin-treated rats (6.70 ± 0.18 log₁₀ CFU/ml; n = 27). At day 8, significant (P < 0.01 versus controls) reductions were recorded in bacterial counts in cage fluids of both tigecycline-treated (−0.62 ± 0.17 CFU/ml; n = 29) and vancomycin-treated (−0.76 ± 0.18 log₁₀ CFU/ml; n = 27) rats, whereas the bacterial counts for controls slightly increased (+0.18 ± 0.19 log₁₀ CFU/ml; n = 28) (Fig. ​(Fig.2).2). The reductions in CFU counts for vancomycin-treated and tigecycline-treated rats were not significantly different. Finally, no MRGR3 isolate showing increased tigecycline MIC was observed in any posttherapy cage fluid sample (n = 29). The lack of emergence of MRGR3 derivates with diminished susceptibility to tigecycline is consistent with the difficulty in selecting laboratory-derived, tigecycline-resistant mutants of S. aureus (18), and it contrasts with the emergence of resistant subpopulations during low-dose daptomycin therapy of S. aureus-infected tissue cages (35).Open in a separate windowFIG. 2.Decrease in viable counts of MRSA MRGR3 in tissue cage fluids of rats treated for 7 days with tigecycline or vancomycin.Several studies performed with the rat tissue cage model demonstrated the low initial in vivo response of foreign-body-associated chronic MRSA infections (2, 5, 6, 17, 20, 29-31, 35-37). A much greater reduction of viable MRSA counts in cage fluids requires longer periods of antibiotic therapy (5), as found in clinical situations with foreign-body infections (38). Major pharmacokinetic properties of tigecycline, observed in human and animal studies, are very low plasma levels, long half-lives, and high volumes of distribution indicating extensive tigecycline distribution into the tissues (8, 11, 19, 28, 32, 40). In line with previous observations that showed a requirement for active, preferentially bactericidal, antibiotic levels for obtaining significant reductions of CFU counts in MRSA-infected cage fluids (29, 37), we selected for therapy a twice-daily 7-mg/kg regimen yielding cage fluid tigecycline levels above the MIC for strain MRGR3 for >50% of the dosing interval (32, 33), while minimizing the occurrence of side effects previously observed with higher-dose regimens (39). Our regimen is similar to those required for activity in other animal models of hard-to-treat S. aureus infections, such as endocarditis or osteomyelitis (21, 39), although its relevance to human therapy is not fully defined (32). In addition, the incomplete in vitro killing activity of tigecycline, namely a <3-log₁₀ reduction in number of MRGR3 CFU at 24 h, prevents a pharmacodynamic analysis of tigecycline in vivo activity more detailed than those of previously evaluated bactericidal antibiotics in MRSA-infected cages (29, 37). We can also speculate that other properties of tigecycline, namely its in vivo activity against intracellular, slowly growing, or biofilm-forming bacteria, might significantly contribute to tigecycline activity in MRSA-infected cages (34). Indeed, high intracellular levels of tigecycline were shown to accumulate in human polymorphonuclear neutrophils and prevent growth of phagocytized bacteria (24). Further studies are needed to elucidate the mechanisms of tigecycline activity against hard-to-treat MRSA infections.     

In Vitro 24-Hour Time-Kill Studies of Vancomycin and Linezolid in Combination versus Methicillin-Resistant Staphylococcus aureus

Many clinicians are trying unique strategies, including vancomycin and linezolid in combination, for treatment of patients who do not respond to conventional therapy against methicillin (meticillin)-resistant Staphylococcus aureus. In our study, which illustrated in vitro activity only, no synergistic activity was seen when the two agents were combined. Conversely, antagonistic activity occurred in three of five strains when linezolid was added to vancomycin. Our results indicate that vancomycin and linezolid in combination should be avoided.Methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) is a well-known nosocomial pathogen. There is considerable evidence showing that the incidence and possibly the virulence are rising (5, 8, 9, 10). Deep-seated infections are not responding as well to conventional vancomycin therapy (11, 15, 16). There have been case reports of not only vancomycin tolerance but also vancomycin resistance (3). This has an impact on the healthy population, with the growing incidence of community-acquired MRSA, and is of even more concern for the ever-growing number of elderly patients with numerous comorbid conditions, including hospitalized and nursing home patients (4, 6, 7, 17). Numerous alternative regimens are being tested in this era of multidrug-resistant organisms. These regimens include various lengths of treatment as well as combinations of antimicrobial agents. We have observed an increase in the use of linezolid and vancomycin together, with little evidence to support this practice. There is also the potential for overlap when one agent is switched to the other. Vancomycin is a bactericidal agent which inhibits bacterial cell wall synthesis, resulting in cell lysis. Linezolid is a bacteriostatic agent which binds the 50S ribosomal unit and inhibits protein synthesis. Few previous studies show the activity of these two antibiotics in combination. There have been approximately 20 strains of MRSA tested, and of these strains, several have shown no difference in activity while others suggest that linezolid and vancomycin may actually be antagonistic (2, 12, 14, 18). Our investigation was designed to consider additional MRSA isolates in a different geographic region and help provide more evidence about the interaction that vancomycin and linezolid have when used together.In order to start this study, we first obtained five strains of MRSA isolates from blood cultures at Christiana Hospital and tested them to be sure they were different ribotypes. Next, the MICs for each strain were determined using the microdilution technique. The MICs were defined as the lowest concentration of an antimicrobial agent that prevented turbidity when assessed after 24 h of inoculation. MIC determination was repeated twice for consistency, and the average value for all three determinations was used as the final MIC. The MICs were 0.06 μg/ml for vancomycin in all isolates; 0.125 μg/ml for linezolid in isolates 1, 2, 4, and 5; and 0.25 μg/ml for isolate 3.The time-kill study was performed with four concurrent tubes that were run over 24 h. All stock solutions were prepared in accordance with guidelines provided by the Clinical and Laboratory Standards Institute, formerly known as NCCLS (1). Each tube contained Mueller-Hinton broth, with an inoculum of 5 × 10⁶ to 1 × 10⁷ CFU/ml. Tube 1 was antibiotic free and served as the control. Tubes 2 and 3 had linezolid and vancomycin, respectively. Tube 4 contained both linezolid and vancomycin. All tubes were run with all five strains of MRSA separately. Surviving bacteria were counted at 0, 4, 8, and 24 h by subculturing 50-μl serial dilutions (10⁻¹, 10⁻², and 10⁻⁴) of samples in normal saline solution on Mueller-Hinton plates. The above was done at one-fourth, one-half, and two times the MIC for each agent. Bactericidal effect was defined as ≥3 log₁₀ CFU/ml decrease in comparison with the level for the initial inoculum after 24 h of incubation. Synergy was defined as a decrease of ≥2 log₁₀ CFU/ml between the combination and the most active single agent. Antagonism was defined as an increase in the colony count of ≥2 log₁₀ CFU/ml with the combination in comparison with the count obtained with the most active single agent (13). This entire process was repeated for all five strains at one-fourth, one-half, and two times the MIC for each agent alone and in combination.The final data were best delineated at two times the MIC. Figure 1A through E show the macrodilution time-kill curves for all five strains at two times the MIC. These show that for MRSA strains 2, 4, and 5, vancomycin was more effective when used alone than when linezolid was added. In strain number 1, there was no significant difference between each agent alone and combined. In strain number 3, vancomycin alone and linezolid alone were similar in activity. When the two agents were combined, they were less active than either agent alone, although this result was not significant enough to indicate antagonism. No synergistic activity was seen in any of the five strains of MRSA. Three of the five strains exhibited antagonistic activity when linezolid was added to vancomycin. Two of the strains were equivocal. This data set indicates that combination therapy is of no benefit and that vancomycin and linezolid should not be used together for MRSA infections. These results suggest that special attention may need to be given to patients with illnesses such as chronic renal disease when one agent is switched to another since these antibiotics may have altered kinetics or a prolonged half-life. We hypothesize that this antagonism may be due to a reduced ability on the part of vancomycin to bind to cells exposed to linezolid, which is bacteriostatic and decreases protein synthesis.Open in a separate windowFIG. 1.Panels A through E graphically illustrate the results at two times the MIC for each bacterial strain, comparing the activity of vancomycin and linezolid together against that of each antibiotic alone as well as the results for the control group, which did not contain any antibiotics.These results do not account for tissue penetration and metabolism which alter the in vivo activity of these agents when used in combination. There needs to be more data both in vivo and in vitro to demonstrate the interaction between these two agents. These types of combinations as well as new agents will need to be studied as MRSA becomes more resistant and infections become more severe and harder to eradicate.     

Resistance Selection Studies Comparing the Activity of Razupenem (PTZ601) to Vancomycin and Linezolid against Eight Methicillin-Resistant and Two Methicillin-Susceptible Staphylococcus aureus Strains

Multistep and single-step resistance selection studies were performed with razupenem, linezolid, and vancomycin against 10 methicillin (meticillin)-resistant and -susceptible Staphylococcus aureus strains. After 20 daily subcultures, razupenem yielded only clones with MICs of >4 μg/ml in one strain (8 μg/ml) whose parent''s MIC was already 4 μg/ml. After 18 to 49 passages in 6/10 strains, razupenem MICs rose from 0.016 to 2 μg/ml (parents) to 0.125 to 8 μg/ml (with clones stable after 10 drug-free subcultures). Single-step mutant selection frequencies were similarly low for razupenem and comparators.Staphylococcus aureus is becoming increasingly resistant to antibiotics. Additionally, the majority of methicillin (meticillin)-resistant S. aureus (MRSA) (and also some methicillin-susceptible [MSSA]) strains are resistant to all currently available quinolones (1). Heterogeneous vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus (VISA) strains (1, 5, 7, 8, 11, 12) are increasingly reported, and recently, nine vancomycin-resistant S. aureus (VRSA) strains have been described (1; M. Rybak, personal communication). Two recent papers emphasize the recent spread of VISA strains in Turkey (12) and France (7). Recently, Rybak et al. (11) have indicated, with macro Etest and population analysis testing, that the incidence of hVISA strains has increased over the past 22 years for an overall incidence of 2.2%. Yusof et al. (17) have recently described a double-sided vancomycin/teicoplanin macro Etest strip which accurately differentiates between hVISA and VISA strains. Utilization of this method will increase reports of the incidence of hVISA and VISA strains. As of this time, the pathogenicity of VRSA strains awaits confirmation.The situation has become further complicated by the appearance and rapid spread, especially in the United States, of community-acquired MRSA strains, which are especially virulent possibly by virtue of the production of Panton-Valentine leukocidin (1). Although these strains are currently more drug susceptible than are hospital-acquired strains, this situation will not remain the same, and increased resistance will develop. Additionally, treatment of the community-acquired MRSA strains with glycopeptides will increase the selective pressure leading to nonsusceptibility to vancomycin and teicoplanin. There is therefore an urgent need for nonglycopeptide drugs with which to treat MRSA strains. Recently, we and others have also documented clinical development of daptomycin resistance after daptomycin therapy (8).Razupenem (also formerly known as SM-216601, SMP-601, PZ-601, and PTZ601) (Fig. ​(Fig.1)1) is a new experimental broad-spectrum 2-(4-arylthiazol-2-ylthio)-1β-methylcarbapenem derivative with enhanced activity against gram-positive organisms, including staphylococci, enterococci, and MRSA (9, 10, 14, 15). This study examines the antistaphylococcal activity of razupenem compared to the activities of vancomycin and linezolid, by single- and multistep mutant selection analysis.Open in a separate windowFIG. 1.Chemical structure of razupenem.Ten isolates were tested by multistep and single-step resistance selection analysis. These included eight MRSA strains, comprising two each of MSSA, MRSA, hVISA, VISA, and VRSA isolates. All organisms except VRSA 509 (Michigan) were recent isolates from patients at Hershey Medical Center. Razupenem powder was obtained from Protez Pharmaceuticals, Inc., Malvern, PA.The CLSI standard macrodilution method was used for initial MICs (6). Serial passages were performed daily in Mueller-Hinton broth for each strain in subinhibitory concentrations of all antimicrobials. For each subsequent daily passage, an inoculum was taken from the tube 1 to 2 dilutions below the MIC that matched the turbidity of a growth control tube. This inoculum was used to determine the next MIC. Daily passages (minimum of 14) were performed until a significant increase in MIC (>4-fold) was obtained. Stability of the acquired resistance was determined by MIC determinations after 10 daily passages of the variant on blood agar without antibiotics (3, 4). A stable clone is defined as having an MIC after the drug-free passages within ±1 of the MIC before the drug-free passages. Only for razupenem clones were passages continued for the maximum of 50 days, regardless of MIC, as seen in Table ​Table1.1. For multistep testing, confirmation of parent and resistant clones was done by pulsed-field gel electrophoresis (3, 4).

TABLE 1.

Results of S. aureus multistep resistance selection and daily MIC testing

Antimicrobial activity of daptomycin tested against Gram-positive pathogens collected in Europe,Latin America,and selected countries in the Asia-Pacific Region (2011)

We report the results of the international daptomycin surveillance programs for Europe, Latin America, and selected Asia-Pacific nations. A total of 7948 consecutive Gram-positive organisms of clinical significance were collected in 2011 and susceptibility tested against daptomycin and various comparator agents by Clinical and Laboratory Standards Institute (Clinical and Laboratory Standards Institute. M07-A9. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; approved standard: ninth edition Wayne, PA: CLSI. 2012.; Cubicin Package Insert 2012. Cubist Pharmaceuticals, Inc, Lexington, MA. Available at http://www.cubicin.com/pdf/PrescribingInformation.pdf. Accessed January 1, 2012.) broth microdilution methods. The test medium was adjusted to contain physiological levels of calcium (50 mg/L) when testing daptomycin. Daptomycin exhibited potent activity against methicillin-susceptible and -resistant Staphylococcus aureus overall and for each region (MIC_50/90, 0.25–0.5/0.5 μg/mL), with susceptibility rates at 100.0% in Latin America, Australia/New Zealand, and India, and at 99.9% in Europe. The daptomycin MIC_50/90 for coagulase-negative staphylococci was also at 0.25–0.5/0.5 μg/mL, and only 1 isolate was considered nonsusceptible with a MIC value at 2 μg/mL. Daptomycin was also highly active against Enterococcus faecalis (MIC_50/90, 1/1–2 μg/mL) and E. faecium (MIC_50/90, 2/2 μg/mL for both vancomycin-susceptible and -resistant isolates). All enterococcal isolates were susceptible to daptomycin (MIC, ≤4 μg/mL) and tigecycline. Susceptibility to linezolid for E. faecalis was at 100.0%, while for E. faecium regional susceptibility rates were at 100.0% except in Europe (99.0%). Viridans group streptococci (MIC_50/90, 0.25/1 μg/mL) and β-haemolytic streptococci (MIC_50/90, ≤0.06/0.25 μg/mL) continue to be very susceptible to daptomycin. In summary, the results of this investigation document the high potency and wide spectrum of daptomycin when tested against a large resistance-surveillance collection of Gram-positive pathogens and indicate that daptomycin nonsusceptibility remains rare among indicated species after many years of clinical use worldwide.     

Pharmacodynamic Profile of Tigecycline against Methicillin-Resistant Staphylococcus aureus in an Experimental Pneumonia Model

Tigecycline (TGC) is an extended-spectrum antibiotic with activity against Staphylococcus aureus, including methicillin (meticillin)-resistant S. aureus strains, which are well-recognized pathogens in nosocomial pneumonia. The objective of this study was to characterize the exposure-response relationship for TGC against S. aureus in an immunocompromised BALB/c murine pneumonia model. Six S. aureus isolates were studied, and the TGC MICs for those isolates ranged from 0.125 to 0.5 mg/liter. The pharmacokinetics (PK) of TGC in serum and bronchoalveolar lavage (BAL) fluid were evaluated, as was the level of protein binding of the compound in this murine species. Administration of TGC at 1.56 to 150 mg/kg of body weight/day in single or two to three divided doses was used in the efficacy studies. TGC displayed linear PK and had a mean half-life of 10.9 ± 2.5 h. Efficacy was highly correlated with the area under the free concentration-time curve (fAUC)/MIC (r² = 0.93). The 80% and 50% effective exposure indexes and the stasis exposure index were similar between the isolates (means ± standard deviations, 3.04 ± 1.12, 1.84 ± 1.3, and 1.9 ± 1.5, respectively). Maximal efficacy was predicted at a 2.85-log₁₀-CFU reduction. TGC appeared to accumulate in the interstitial space, as the ratios of the fAUC from 0 to 8 h of epithelial lining fluid to plasma were 7.02, 15.11, and 23.95 for doses of 12.5, 25, and 50 mg/kg, respectively. TGC was highly effective in this murine pneumonia model. In light of current MIC distributions, the fAUC/MIC targets that we defined against S. aureus are readily achievable in humans given conventional doses of TGC.Staphylococcus aureus has long been recognized as an important cause of infection, and the emergence of S. aureus strains with the methicillin (meticillin)-resistant phenotype (methicillin-resistant S. aureus [MRSA]) has further complicated management. Both community-acquired MRSA (CA-MRSA) and hospital-acquired MRSA (HA-MRSA) strains have been associated with severe and difficult-to-treat infections. While the most common site of staphylococcal infection is the skin and skin structures, the surveillance of 8,792 invasive MRSA cases in the United States showed that pneumonia is the second most common clinical manifestation of MRSA infection (13.3% overall; 14% of the strains were CA-MRSA and 28% were HA-MRSA) (9).Tigecycline (TGC) is a broad-spectrum glycylcycline with efficacy against gram-positive and gram-negative bacteria, including drug-resistant bacteria such as MRSA. The MIC₉₀ of TGC against methicillin-susceptible S. aureus (MSSA) and MRSA strains is reported to be ≤0.25 mg/liter (6). TGC is approved by the FDA for use for the treatment of complicated skin and skin structure infections and complicated intra-abdominal infections. Pneumonia is an important clinical manifestation of infection with drug-resistant bacteria; therefore, many in vivo and in vitro studies of TGC for the treatment of lower respiratory infection are ongoing (data available at http://www.clinicaltrialssearch.org/tigecycline_versus_imipenemcilastatin_for_the_treatment_of_subjects_with_nosocomial_pneumonia.html and http://www.medicalnewstoday.com/articles/53035.php).Previously, we demonstrated the efficacy of TGC against Acinetobacter spp. in a murine pneumonia model (10) and against S. aureus in a murine thigh infection model (3). We also found that TGC penetrated well into lung tissue, as displayed by high concentrations in bronchoalveolar (BAL) fluid (4). In the present study, we aimed to explore the exposure-response relationship for TGC against S. aureus in an immunocompromised BALB/c murine pneumonia model.     

Observed Antagonistic Effect of Linezolid on Daptomycin or Vancomycin Activity against Biofilm-Forming Methicillin-Resistant Staphylococcus aureus in an In Vitro Pharmacodynamic Model

Pharmacodynamic activity in antibiotic combinations of daptomycin, vancomycin, and linezolid was investigated in a 48-h in vitro pharmacodynamic model. Using human-simulated free drug concentrations, activity against clinical biofilm-forming methicillin-resistant Staphylococcus aureus isolates was evaluated. Linezolid antagonized vancomycin activity at 24 and 48 h. Linezolid antagonized daptomycin at 24 and 48 h depending on dose and strain. Adding daptomycin increased vancomycin activity at 48 h (P < 0.03). These results may be strain dependent and require further clinical investigation.