Combination therapy against vancomycin-resistant enterococci

The therapeutic options for patients infected with vancomycin-resistant enterococci are limited. Optimal therapy for serious enterococcal infections requires the use of synergistic combinations of a cell wall-active agent plus an aminoglycoside. Enterococci have acquired aminoglycoside resistance genes that mediate production of aminoglycoside-modifying enzymes, which eliminate this synergistic bactericidal effect. Traditional therapy has been compromised due to the increasing prevalence of enterococci with beta-lactam, glycopeptide, and high-level gentamicin resistance. Arbekacin, a semi-synthetic aminoglycoside, shows excellent activity against a wide variety of bacteria that produce aminoglycoside modifying enzymes, including AAC(6')-APH(2"). In recent studies, the combination of ampicillin and arbekacin demonstrated inhibitory activity against vancomycin-resistant enterococci, and may prove useful in the treatment of enterococcal infections where treatment options are limited.     

Absence of synergistic activity between ampicillin and vancomycin against highly vancomycin-resistant enterococci.

The emergence of clinical enterococcal isolates resistant to both ampicillin and vancomycin is a cause of great concern, as there are few therapeutic alternatives for treatment of infections caused by such organisms. We evaluated the effects of the combination of ampicillin with vancomycin against vancomycin-resistant clinical enterococcal isolates. Using both the checkerboard technique and time-kill curves, we examined 28 strains of enterococci (17 Enterococcus faecalis and 11 Enterococcus faecium strains) with different levels of resistance to vancomycin. Of these, 15 strains were also highly gentamicin resistant, and 9 demonstrated resistance to ampicillin. Only seven strains of E. faecalis were inhibited synergistically by the combination of vancomycin with ampicillin, and even then, the concentrations of vancomycin at which synergism was demonstrated were above levels achievable in serum. None of the ampicillin-resistant isolates (all E. faecium) were inhibited synergistically at any concentration of the drugs. In no instance was bactericidal synergism observed, and in most cases the combination resulted in less killing than with ampicillin alone. Antagonism was not observed at clinically relevant concentrations. The results of this study suggest that the combination of vancomycin with ampicillin has little to offer against these emerging pathogens.     

Susceptibility patterns of enterococci causing infections

Enterococci are among the common organisms associated with hospital-acquired infections. We examined in vitro activities of different antibiotics to 103 enterococcal isolates. Minimal inhibitory concentrations (MICs) of penicillin G, ampicillin, gentamicin, ciprofloxacin, ofloxacin, levofloxacin, grepafloxacin, trovafloxacin and gemifloxacin were determined by broth microdilution testing method. Among the isolates 71 (69%) were identified as E. faecalis and 32 (31%) as E. faecium. While over 75% of E. faecium isolates were resistant to penicillin and ampicillin, approximately 25% of E. faecalis isolates were resistant to penicillin and ampicillin. None of the E. faecalis and E. faecium isolates were resistant to vancomycin. While 17 (52%) of E. faecium isolates exhibited high-level gentamicin resistance (HLGR), high level streptomycin resistance (HLSR) was detected in 24 (74%) of the isolates. In contrast, HLGR and HLSR rates for E. faecalis were 14 (20%) and 22 (31%), respectively. Both HLGR and HLSR were detected with higher frequency in ampicillin resistant isolates. Among fluoroquinolones, gemifloxacin and trovafloxacin were the most potent antibiotics tested. There was no increase in MIC90 values of the fluoroquinolones in ampicillin resistant isolates in comparison with ampicillin susceptible isolates. Our data suggest newer fluoroquinolones would be good alternative agents to use especially for combination drug therapy where enterococci with ampicillin resistance and HLAR are prevalent.     

Antimicrobial susceptibility and molecular epidemiology of beta-lactamase-producing, aminoglycoside-resistant isolates of Enterococcus faecalis.

beta-Lactamase-producing (BL+), aminoglycoside-resistant (AR) Enterococcus faecalis is endemic in our hospital, having caused widespread colonization and infection. Suitable therapy for infections caused by these organisms has been problematic. We compared the antimicrobial and bactericidal activities, by broth macrodilution and time-kill methods, of several antibiotics, alone and in combination, against BL+, AR isolates of E. faecalis and determined the transmissibility of antibiotic resistance markers. Ampicillin-sulbactam, imipenem, daptomycin, and ciprofloxacin were the most active antibiotics with MICs for 90% of isolates tested of 2, 1, 2, and 1 microgram/ml, respectively, against inocula of 10(3) and 10(5) CFU/ml. Little inoculum effect was noted with imipenem, vancomycin, daptomycin, or ciprofloxacin, while the addition of sulbactam to ampicillin partially inhibited the effect of the increased inoculum. Penicillin-sulbactam and ampicillin-sulbactam combinations in a 2:1 ratio were most frequently bactericidal (greater than or equal to 3-log10-unit decrease in bacterial titers at 24 h for 13 of 20 isolates), followed by daptomycin (8 of 20 isolates) and ciprofloxacin (2 of 20 isolates). Bactericidal activity was not demonstrated for imipenem or teicoplanin. beta-Lactamase production and aminoglycoside resistance were associated with a 60- to 65-MDa plasmid which was easily transferred to a plasmid-free E. faecalis recipient. The 840-bp beta-lactamase gene probe hybridized to purified plasmid DNA from BL+ donor isolates of E. faecalis and transconjugants but not from BL- isolates. Ampicillin-sulbactam and daptomycin (an investigational antibiotic) seem to be reasonable choices for the empiric therapy of presumed enterococcal infections in hospitals in which BL+, AR E. faecalis strains are isolated. Their use should ideally be supported by tests for bactericidal activity.     

Activity of clinafloxacin against multidrug-resistant Enterococcus faecium.

Enterococci resistant to ampicillin, vancomycin, and/or aminoglycosides are a growing clinical problem. We studied the in vitro activity of the new fluoroquinolone clinafloxacin (PD 127,391) against 15 clinical isolates of multidrug-resistant Enterococcus faecium. In kill-kinetic studies, clinafloxacin (1 microgram/ml) was bactericidal against 7 of 12 susceptible isolates, although substantial regrowth occurred in 4 isolates at 48 h. The addition of ampicillin (20 micrograms/ml) resulted in bactericidal activity in all 12 isolates, and no regrowth was seen. For three isolates resistant to clinafloxacin, effective killing was not observed at these concentrations of antibiotics. Clinafloxacin with ampicillin shows promising activity against many of these multiply resistant enterococci.     

临床分离肠球菌对12种抗菌药物耐药性监测

目的 :监测重庆地区 1997— 1998年临床分离肠球菌的耐药性。方法 :采用试管双倍稀释法测定 12种抗菌药物的最低抑菌浓度 (MIC)。结果 :共监测肠球菌 2 4 4株 ,其中 14 4株粪肠球菌、75株屎肠球菌、18株鸟肠球菌、7株鸡肠球菌。结果表明肠球菌对替考拉宁和万古霉素的耐药性最低 ,耐药率分别为 2 .13%和 8.84 % ;肠球菌对青霉素、哌拉西林、氨苄西林、苯唑西林、环丙沙星的耐药性也较低 ,耐药率分别为 9.4 2 %、13.5 2 %、16 .5 5 %、2 5 .85 %、2 6 .14 % ;肠球菌对其他药物的耐药率均大于 5 0 % ,;屎肠球菌对抗菌药物的耐药性明显高于粪肠球菌。结论 :万古霉素及替考拉宁对肠球菌的抗菌活性最高 ;青霉素、氨苄西林、哌拉西林对肠球菌仍具有较稳定的抗菌活性 ,屎肠球菌对抗菌药物的耐药性较粪肠球菌为高 ,临床上已出现了对糖肽类抗生素万古霉素及替考拉宁耐药的肠球菌 ,值得重视。     

肠球菌属感染临床特点及耐药性研究

目的研究肠球菌属感染的临床特点及其耐药性,指导临床合理使用抗菌药物。方法采用回顾性调查方法对临床分离的924例肠球菌属相关资料进行统计分析。结果临床标本中肠球菌属在尿液中的分布最高,占71.32%;屎肠球菌与粪肠球菌对抗菌药物的耐药率不尽相同,万古霉素耐药菌株逐年增多。肠球菌属引起的院内感染病例占63.42%;60岁以上老年人占64.41%,所有患者均有较严重的基础病。结论肠球菌已是医院感染的重要致病菌,老年及免疫功能低下患者易感,以尿路感染最常见;肠球菌属对多种抗生素耐药,耐万古霉素肠球菌株明显增加。     

儿童肠球菌多重耐药与Ⅰ类整合子的检测

目的了解儿童临床分离肠球菌的耐药特征及其多重耐药与Ⅰ类整合子的相互关系。方法采用琼脂稀释法测定常用抗菌药物对152株肠球菌的最低抑菌浓度（MIC）,用聚合酶链反应（PCR）检测肠球菌Ⅰ类整合子和Ⅰ类整合酶基因。结果屎肠球菌对氨苄西林、阿莫西林-克拉维酸、环丙沙星的耐药率分别为96．8％、95．2％和84．1％,粪肠球菌对上述3种抗菌药物的耐药率分别为23．6％、18．0％和49．4％,屎肠球菌的耐药率明显高于粪肠球菌（P〈0．001）;粪肠球菌中有2株对万古霉素的MIC为8μg/mL,粪肠球菌和屎肠球菌对替考拉宁均敏感。儿童多重耐药肠球菌发生率高达93．7％。屎肠球菌耐药模式以耐氨苄西林、红霉素、环丙沙星、利福平、四环素、高水平庆大霉素6种抗菌药物为主,占屎肠球菌的59％,粪肠球菌以耐四环素、红霉素、利福平、氯霉素、高水平庆大霉素5种抗菌药物为主,占粪肠球菌的26％。全部152株肠球菌未检测到Ⅰ类整合子,仅有5株检测到Ⅰ类整合酶基因。结论儿童肠球菌多重耐药十分严重,儿童肠球菌多重耐药与Ⅰ类整合子和Ⅰ类整合酶基因尚无明显关系。     

Cefepime,piperacillin/tazobactam,gentamicin, ciprofloxacin,and levofloxacin alone and in combination against Pseudomonas aeruginosa

A beta-lactam plus an aminoglycoside is the standard for treating severe Pseudomonas aeruginosa infections. However, the fluoroquinolones are safer and have been widely used as an alternative to the aminoglycosides in this setting. In this study we compared the synergistic activities of piperacillin/tazobactam and cefepime when either drug was combined with gentamicin, ciprofloxacin, or levofloxacin against P. aeruginosa. Susceptibility testing and time-kill curves were performed against 12 clinical isolates of P. aeruginosa. All combinations were bactericidal and retained this activity over the 24 hr period except for piperacillin/tazobactam in combination with levofloxacin or ciprofloxacin against 2 isolates and cefepime in combination with levofloxacin against 1 isolate. None of the combinations were antagonistic. No statistical difference in the frequency of synergy exists between the beta-lactam plus gentamicin (79%) and the beta-lactams plus either ciprofloxacin or levofloxacin combinations (58%, 67%). Furthermore, no differences in synergistic activity were noted between ciprofloxacin combinations (58%) and levofloxacin combinations (67%). In conclusion, the degree of synergy between a beta-lactam plus aminoglycoside and a beta-lactam plus fluoroquinolone seem to be comparable. Furthermore, there is a similar rate of synergy among different fluoroquinolone-based combinations. However, faster killing, less regrowth, and decrease in the development of resistance were seen with the beta-lactam plus aminoglycoside combination.     

临床感染肠球菌耐药性等的变迁

目的　对临床分离的肠球菌流行、抗菌药物的耐药与感染性疾病的关系以及变化趋势进行调查和分析。方法　对多年来分离的 60 7株肠球菌 ,用微生物自动分析系统 (AMS)进行鉴定和药物敏感实验 ,并进行综合分析。菌种用半固体营养琼脂 4℃保存 ,复测结果和原测结果 10 0 %吻合。结果　两个时期临床分离的肠球菌都以粪肠球菌、屎肠球菌为主 ,其次为鸟肠球菌和鸡肠球菌 ,但屎肠球菌所占比例有所增加。分离部位 1995～ 1997年脓液标本占首位 ,1999～ 2 0 0 1年痰标本占首位。两个时期药物敏感实验结果显示对所测 9种抗菌药物的耐药率普遍上升 ,对青霉素、氨苄西林、高浓度庆大霉素、高浓度链霉素、四环素的耐药率有统计学差异 ,两个时期都没有发现耐万古霉素的肠球菌 ,两个时期屎肠球菌的耐药率均高于粪肠球菌。结论　由屎肠球菌引起的肠球菌感染在增加 ;由肠球菌引起的呼吸道系统感染在增加 ;肠球菌对各种抗菌药物的耐药率在上升 ;屎肠球菌的耐药严重 ;万古霉素是治疗肠球菌感染的有效药物     

In vitro activity of ciprofloxacin in combination with ceftazidime, aztreonam, and azlocillin against multiresistant isolates of Pseudomonas aeruginosa.

The combinations of ciprofloxacin plus ceftazidime, ciprofloxacin plus aztreonam, and ciprofloxacin plus azlocillin were evaluated for the presence of synergy against multiresistant isolates of Pseudomonas aeruginosa. The frequency of synergy was dependent on antibiotic susceptibilities. If the organism was resistant to ciprofloxacin, synergy was observed in more than 50% of the isolates; however, if the organism was resistant to the beta-lactam (with the exception of ceftazidime), synergy was generally observed in less than 10% of the isolates. Antagonism was not observed with any of the combinations. These results may be helpful in making clinical decisions in treating P. aeruginosa infections.     

Emergence of Streptococcus faecalis isolates with high-level resistance to multiple aminocyclitol aminoglycosides

Isolates of $\text{Streptococcus faecalis}$ were occcasionally found to be resistant to gentamicin concentrations of 500 μg/ml in a microdilution tray. Additional tests were performed with 28 such isolates. They all demonstrated high-level resistance (minimum inhibitory concentration > 2000 μg/ml) to gentamicin, kanamycin, sisomicin, streptomycin, and tobramycin. This high-level aminoglycoside resistance was associated with total resistance to in vitro synergism when each aminoglycoside was combined with ampicillin. In addition to ampicillin-aminoglycoside combinations, ampicillin-vancomycin, ampicillin-rifampin, rifampin-vancomycin, and vancomycin-gentamicin combinations were also tested; all failed to exhibit an in vitro synergistic-bactericidal effect against these enterococci. The emergence of enterococci with high-level resistance to multiple aminoglycosides in this clinical population is a source of grave concern with obvious therapeutic implications in situations such as endocarditis, where an in vitro bactericidal effect is thought to be necessary for a cure. No drug or combination of drugs was found to be bactericidal for these isolates. It is suspected that similar isolates of group D streptococci with high-level resistance to gentamicin may emerge in other institutions but go unrecognized. Surveillance by others for identifying this newly emerging pathogen carrying multiple resistance and a continued search for a satisfactory chemotherapeutic agent(s) are encouraged.     

In vitro activity of RPR 106972 alone and in combination with vancomycin,ampicillin, and gentamicin against multidrug-resistant enterococci

This investigation used checkerboard and time-kill assays to evaluate the in vitro activity of RPR 106972 (45% pristinamycin IB and 55% pristinamycin IIB) alone and in combination with vancomcyin or ampicillin ± gentamicin against multidrug-resistant enterococci. The checkerboard procedure resulted in synergistic or additive effects in 91% of the isolates with the combination of RPR 106972 plus vancomycin versus 68% with RPR 106972 plus ampicillin. The addition of gentamicin to either combination resulted in synergistic or additive results in 100% of the isolates. Inhibitory activity was observed with the time-kill assay with mean change in log₁₀ CFU/mL at 24 h of −0.31 for RPR 106972, 3.3 for vancomycin, −0.46 for RPR 106972 plus vancomycin, and −0.35 for RPR 106972 plus vancomycin and gentamicin. No antagonism was noted with any of the combinations. RPR 106972 demonstrates good inhibitory activity against Enterococcus faecium and may prove useful in the treatment of enterococcal infections.     

肠球菌临床感染情况和药物敏感性分析及耐万古霉素肠球菌耐药基因研究

目的分析肠球菌的临床分离情况,研究肠球菌抗菌药物敏感性和耐万古霉素肠球菌（VRE）耐药基因。方法采用VITEK COMPACT分析仪进行菌种鉴定和药敏测定;采用WHONET 5.5进行数据分析;采用PCR、基因测序及序列在线比对检测VRE耐药基因。结果共分离167株菌,屎肠球菌113株,粪肠球菌47株;标本类型前三位分别为尿液（34.1%）、血液（16.8%）和腹水（15.6%）;ICU分离率在临床科室中居首。屎肠球菌对青霉素G、氨苄西林、红霉素、环丙沙星、左氧氟沙星的耐药率高达90%以上,且明显高于粪肠球菌（P〈0.05）。检出11株VRE,携带vanA耐药基因。未发现利奈唑胺耐药株。结论肠球菌总体耐药形势严峻,屎肠球菌的分离率和耐药率高于粪肠球菌,应控制多重耐药株尤其VRE的传播。     

5年肠球菌分布及耐药性变迁分析

目的探讨我院肠球菌的分布及耐药性变化,为临床合理用药提供依据。方法分析5年来从我院住院患者分离出的肠球菌进行分布和耐药性动态分析。结果5年共分离到506株肠球菌,占总感染菌的8％,其中粪肠球菌274株（54．1％）,屎肠球菌225株（44．5％）,主要分离自尿液195株（38．5％）、伤口分泌物132株（26．1％）。屎肠球菌的耐药性比粪肠球菌要高,对红霉素、环丙沙星、青霉素、氨苄西林、左氧氟沙星、利福平及高浓度庚大霉素等的耐药率均〉80％,采发现有β-内酰胺酶阳性菌株,也未发现耐万古霉素菌株。结论肠球菌是我院感染的重要病原菌之一,约占我院感染菌的第七位左右,临床治疗肠球菌应根据药敏结果合理用药。     

The activity in vitro of trospectomycin sulphate (U-63366F) against aminoglycoside-resistant enterococci

Trospectomycin (U-63366F), a 6'-propyl analogue of spectinomycin, was tested against aminoglycoside-resistant enterococci. The MIC90 for Enterococcus faecalis was 4 mg/l and that for E. faecium was 8 mg/l. Trospectomycin alone was not bactericidal for enterococci, with MBC90 4096 mg/l for both E. faecalis and E. faecium. The addition of commercially available polyvalent immunoglobulin decreased significantly both the MICs and the MBCs and the rendered trospectomycin bactericidal for enterococci. Chequerboard titration of a combination of trospectomycin with ampicillin revealed an FIC index of 1.0 for all the isolates tested. Time-kill curves also did not show any enhancement of bactericidal activity of ampicillin when combined with trospectomycin. A combination of ampicillin and gentamicin was synergistic for enterococci under similar experimental conditions. Trospectomycin can be used as a safe alternative to aminoglycosides or beta-lactam antibiotics in enterococcal infection where bactericidal activity is not required, or in the event of serious side effects from these two classes of antibiotics.     

Interactions of ciprofloxacin with clindamycin, metronidazole, cefoxitin, cefotaxime, and mezlocillin against gram-positive and gram-negative anaerobic bacteria.

A total of 598 clinical isolates of anaerobic bacteria were tested against ciprofloxacin by the agar dilution technique with 10(5) CFU on Wilkins-Chalgren medium. Selected strains representative of the six major genera of anaerobes relatively resistant to the quinolones were tested for interactions with ciprofloxacin in combination with clindamycin, metronidazole, cefoxitin, cefotaxime, or mezlocillin by using a checkerboard agar dilution technique. Cefotaxime-ciprofloxacin and clindamycin-ciprofloxacin were the most effective combinations, with 16% of all isolates and 44% of the Bacteroides fragilis group isolates responding synergistically to the former combination and 9% of all isolates and 37% of Peptostreptococcus isolates responding synergistically to the latter. Occasional synergy was seen with all other antibiotic combinations except for metronidazole-ciprofloxacin. Likewise, synergism was seen with all groups of anaerobes except for Fusobacterium species. Antagonistic interactions were observed only with a Peptostreptococcus intermedius strain tested against clindamycin-ciprofloxacin. These data suggest that combinations of ciprofloxacin with these agents may be useful for certain resistant anaerobic infections.     

In-vitro synergistic activity of the combination of ampicillin and arbekacin against vancomycin-and high-level gentamicin-resistant Enterococcus faecium with the aph(2")-Id gene

The combination of ampicillin plus arbekacin produced synergistic killing against 8 of 13 vancomycin-, ampicillin-, gentamicin-, and streptomycin-resistant Enterococcus faecium isolates that possess the high-level gentamicin resistance gene, aph(2")-Id. This combination may prove useful in treating infections caused by multiresistant enterococci.     

肠球菌耐药现状调查及抗感染用药探讨

目的了解肠球菌尤其是对万古霉素耐药肠球菌（ＶＲＥ）和庆大霉素高水平耐药（ＨＬＧＲ）肠球菌的耐药状况,指导临床合理用药。方法对北京５家教学医院感染标本中分离出的１６１４株肠球菌,分别进行纸片扩散法药敏试验和β内酰胺酶测试,并以“ＷＨＯＮＥＴ４”软件对试验数据进行分析处理。结果ＶＲＥ和ＨＬＧＲ肠球菌分别占肠球菌感染标本总数的３．４％和５２．６％,产β内酰胺酶的肠球菌占５．８％;对常用抗生素的耐药率,屎肠球菌明显高于粪肠球菌,ＨＬＧＲ株明显高于低耐株;万古霉素和高浓度庆大霉素多重耐药株检出率为０．９％。结论肠球菌对临床常用的８种抗生素以万古霉素最敏感。对不同特征肠球菌感染应采取不同的治疗方案。     

In vitro activities of cefotaxime, vancomycin, quinupristin/dalfopristin, linezolid and other antibiotics alone and in combination against Propionibacterium acnes isolates from central nervous system infections

OBJECTIVES: To evaluate the antibiotic susceptibilities of Propionibacterium acnes isolates from central nervous system (CNS) infections to agents used in current treatment regimens. METHODS: MICs of 16 reference antibiotics were determined by an agar dilution method for 24 consecutive strains of P. acnes isolated from individual patients with intracranial empyema or brain abscess. Bactericidal activities of antibiotics against P. acnes PAN14 were studied at 0.25-2 x MIC using a time-kill method. RESULTS: All of the isolates were resistant to fosfomycin, intermediate or resistant to metronidazole and susceptible to all the other antibiotics tested, except for nine strains, which were intermediate to ofloxacin. Among antibiotics tested alone in time-kill experiments, vancomycin was the most effective drug and exhibited bactericidal activity after 24 h at 1x and 2 x MIC, whereas cefotaxime and ciprofloxacin were bactericidal after 48 h at 2 x MIC. No significant bactericidal activity could be demonstrated with the other antibiotics tested alone. The addition of cefotaxime to vancomycin resulted in bactericidal activity at lower concentrations (0.5 x MIC), whereas synergy was observed between quinupristin/dalfopristin and cefotaxime at 2 x MIC. In contrast, antagonism was observed between cefotaxime and linezolid, and ciprofloxacin and clindamycin. CONCLUSION: Our data suggest that P. acnes isolates causing CNS infections remain highly susceptible to most antibiotics used for the treatment of such infections. Moreover, we showed that cefotaxime, vancomycin and ciprofloxacin possess good bactericidal activities against P. acnes, and that these activities may be enhanced when vancomycin is combined with cefotaxime or when cefotaxime is combined with quinupristin/dalfopristin.