In vitro postantibiotic effect of colistin on multidrug-resistant Acinetobacter baumannii

Infections by multidrug-resistant Acinetobacter baumannii constitute an increasing threat for critically ill patients. Colistin is often the only antimicrobial retaining activity against these strains. The postantibiotic effect (PAE) of colistin was studied on 19 isolates of A. baumannii resistant to ampicillin/sulbactam, ciprofloxacin, and carbapenems with the viable count method. The mean PAEs of 1x MIC and 4x MIC concentrations of colistin on the tested isolates were 3.90 and 4.48 h, respectively, indicating that a modified dosage scheme with increased dosing intervals might retain activity whereas minimizing the incidence of adverse effects.     

In vivo activity of levofloxacin alone or in combination with imipenem or amikacin in a mouse model of Acinetobacter baumannii pneumonia

We evaluated the in vivo activity of levofloxacin alone or in combination with imipenem or amikacin in a mouse model of Acinetobacter baumannii pneumonia using a susceptible strain and one with low-level resistance (MIC/MBC of levofloxacin: 0.06/0.06 and 4/4 mg/L, respectively). As demonstrated previously with other pathogens, the AUC/MIC ratio predicted the efficacy of fluoroquinolones against A. baumannii. This parameter correlated with bactericidal effect and survival. Combination therapy did not enhance the efficacy of levofloxacin.     

采用耳窥镜直视下气管插管法构建小鼠鲍曼不动杆菌肺炎模型

目的建立耳窥镜直视下气管插管法,并采用上述方法构建小鼠鲍曼不动杆菌肺炎模型。方法1采用美国Braintree公司插管工具盒建立在耳窥镜直视下小鼠气管插管方法;2 24只ICR雌性小鼠随机分为正常对照组、免疫缺陷组、免疫缺陷感染组,每组8只,其中免疫缺陷组和免疫缺陷感染组采用环磷酰胺腹腔注射后造成免疫缺陷。3组小鼠在试验当日均按上述方法行气管插管后,免疫缺陷感染组沿气管内插管注射10μL鲍曼不动杆菌(3.2×108 CFU/mL),正常对照组和免疫缺陷组沿气管内插管注射10μL生理盐水;每组小鼠均分别于0h和48 h眼眶后静脉丛取血,观察白细胞、中性粒细胞、淋巴细胞、单核细胞等计数。并在上述时间点各处死4只小鼠,进行小鼠肺组织菌落计数和肺组织病理检查。结果 110只小鼠行耳窥镜直视下气管插管,均获成功,无小鼠插管后死亡。沿气管内插管注射菌液浓度为3.0×108 CFU/mL,气管插管后0h处死小鼠取肺并定量,其菌落计数为2.91×107~5.32×107 CFU/g肺,平均值±标准差为(4.05×107±0.82×107)CFU/g肺,表明该方法重复性好;23组小鼠观察48 h,正常对照组和免疫缺陷组小鼠无死亡,免疫缺陷感染组有2只小鼠死亡(2/8)。与正常对照组比较免疫缺陷组和免疫缺陷感染组小鼠在0h均出现血液白细胞和中性粒细胞计数平均值明显下降(P<0.01);免疫缺陷感染组在感染后即刻(0h)肺内菌量平均值达4.13×107 CFU/g肺,48 h小鼠肺内菌量平均值显著升高达到3.62×1010 CFU/g肺,与0h比较菌量增长近1 000倍(P<0.01),免疫缺陷感染组病理检查结果显示肺组织内局限性肉芽肿形成,肺泡腔内可见脓肿形成。结论采用耳窥镜直视下气管插管法构建小鼠鲍曼不动杆菌肺炎模型操作简便,成功率高,且注射入小鼠肺内的菌量较恒定,试验重复性好,本研究成功构建了小鼠鲍曼不动杆菌肺炎模型。     

鲍曼不动杆菌对亚胺培南耐药机制研究

目的了解鲍曼不动杆菌对亚胺培南的耐药性及耐药机制。方法琼脂稀释法对62株鲍曼不动杆菌进行药敏检测,对其中20株亚胺培南耐药的鲍曼不动杆菌进行耐药机制研究。酶三维试验检测ESBLs和AmpC酶,PCR扩增和测序分析检测碳青霉烯酶VIM、IMP、OXA-23和OXA-24,SDS-PAGE方法研究外膜蛋白表达情况,利血平协同抑制试验检测膜外排机制。结果62株鲍曼不动杆菌中,亚胺培南耐药25株,占41%;20株亚胺培南耐药菌中,ESBLs和AmpC酶阳性株分别为10株(50%)和20株(100%),PCR扩增VIM、IMP和OXA-24均阴性;OXA-23基因扩增显示19株(95%)阳性,PCR产物并经序列分析证实为OXA-23;与敏感株相比,部分菌株存在22、29、33kD的外膜蛋白缺失;利血平不能降低亚胺培南对鲍曼不动杆菌的MIC值。结论产OXA-23型β-内酰胺酶是本院鲍曼不动杆菌对亚胺培南耐药的重要原因,产AmpC酶合并外膜蛋白缺失与鲍曼不动杆菌对亚胺培南耐药有密切关系。     

Antibiotic combinations for serious infections caused by carbapenem-resistant Acinetobacter baumannii in a mouse pneumonia model

OBJECTIVES: Successful therapy of carbapenem-resistant Acinetobacter baumannii strains has been reported with colistin, but recently we argued against its use as monotherapy because of the poor results obtained in a mouse pneumonia model. Our aim was to identify antibiotic combinations that were valid therapeutic alternatives in the same model. METHODS: We used two carbapenem-resistant A. baumannii strains (D and E; MICs of imipenem, 8 and 512 mg/L, respectively). MICs of tobramycin, rifampicin and colistin for both strains were 8, 8 and 0.5 mg/L, respectively. RESULTS: In infections caused by strain D, lung bacterial counts (log(10) cfu/g, mean +/- s.d.) were: controls (10.86+/-0.25), imipenem (5.99+/-0.59, P < 0.05 versus controls), and colistin (10.43 +/- 1.09); imipenem + tobramycin was the most active combination (5.46+/-0.62, P < 0.05 versus controls). In infections caused by strain E, results were: controls (10.82+/-0.33), rifampicin (5.62+/-0.26, P < 0.05 versus controls), colistin (8.38+/-1.22, P < 0.05 versus controls), and imipenem (11.01+/-0.2); rifampicin + imipenem (3.79+/-0.99) and rifampicin + tobramycin (3.96+/-0.30) were the most active combinations (P < 0.05); results with rifampicin + colistin (5.59+/-1.17) were similar to those with rifampicin alone. CONCLUSIONS: Our data indicate that imipenem can still be the best alternative for carbapenem-resistant A. baumannii infections with moderate levels of imipenem resistance, preferably combined with aminoglycosides. For strains highly resistant to imipenem, a combination of rifampicin with imipenem, tobramycin or colistin may be useful, if resistance to rifampicin is only moderate.     

耐亚胺培南鲍曼不动杆菌产碳青霉烯酶基因型研究

目的了解安徽省铜陵市人民医院耐亚胺培南鲍曼不动杆菌耐药特性及产碳青霉烯酶基因型。方法用纸片扩散法检测该院2008年1～12月临床分离的31株耐亚胺培南鲍曼不动杆菌对19种常用抗菌药物的敏感性。结果用WHONET5.3软件进行数据统计;应用聚合酶链反应(PCR)检测IMP、VIM-1、VIM-2、SIM-1、OXA-23、OXA-24、OXA-51、OXA-58等碳青霉烯酶基因型。结果 31株耐亚胺培南鲍曼不动杆菌有23株分离自重症监护病房;对19种临床常用抗菌药物除米诺环素耐药率为9.7%、头孢哌酮/舒巴坦为51.6%外,其余都在90.0%以上;碳青霉烯酶基因型检测除1株单产OXA-23型外,其余30株均同时产OXA-23型和OXA-66型碳青霉烯酶。结论该院耐亚胺培南鲍曼不动杆菌在重症监护病房有小范围暴发流行的可能;耐亚胺培南鲍曼不动杆菌对临床常用抗菌药物耐药率极高;同时产OXA-23、OXA-66型碳青霉烯酶可能是其对碳青霉烯类抗菌药物耐药的主要原因。     

亚胺培南耐药鲍曼不动杆菌小鼠肺部感染模型建立

目的 建立亚胺培南耐药鲍曼不动杆菌小鼠肺部模型,为泛耐药鲍曼不动杆菌抗感染研究提供实验动物模型.方法 随机选取120只约4周大雄性BALB/C小鼠,平均分成3组:微量气管注射法组、超声雾化法组和滴鼻法组.每组小鼠用甲氨蝶呤化疗降低BALB/C小鼠的免疫力,然后将亚胺培南耐药鲍曼不动杆菌分别用微量气管注射法、超声雾化法、滴鼻法感染免疫力低下和正常的BALB/C小鼠,检测微量气管注射法、超声雾化法、滴鼻法感染的小鼠感染率、死亡率、细菌清除率、肺部病理变化.结果 微量气管注射法、超声雾化法感染免疫力低下的BALB/C小鼠的肺部感染率均为100%(30/30),死亡率分别为100%(10/10),33%(3/10),2组小鼠肺部细菌感染12～24 h后支气管周及肺泡间质内见中性粒细胞、淋巴细胞、巨噬细胞为主的炎症细胞浸润,微量气管注射法感染的小鼠部分肺泡组织结构崩解,肺泡腔内可见脓肿形成及较多细菌集落,超声雾化法感染的小鼠24 h见肺部部分区域存在细胞变性,但支气管及肺泡组织结构基本正常,肺泡壁血管轻度扩张伴淤血,24～48 h后可见支气管和支气管周围变性,部分肺组织血管高度扩张,伴有水肿,48 h后炎症逐渐恢复.滴鼻法感染免疫力低下的BALB/C小鼠的肺部感染不明显,未见小鼠死亡(0/10),肺部无明显病理变化.结论 免疫力低下BALB/C小鼠可以通过微量气管注射法和超声雾化法建立亚胺培南耐药鲍曼不动杆菌肺部感染模型,超声雾化法可以大批量同时操作,简单经济快速,实用性强.亚胺培南耐药鲍曼不动杆菌难以感染免疫力正常小鼠.     

Prevention of rifampicin resistance in Acinetobacter baumannii in an experimental pneumonia murine model, using rifampicin associated with imipenem or sulbactam

OBJECTIVES: To examine the development of rifampicin resistance in multidrug-resistant Acinetobacter baumannii exposed to rifampicin and the prevention of the appearance of rifampicin-resistant mutants when rifampicin is used in association with imipenem or sulbactam. METHODS: A clinical strain of multidrug-resistant A. baumannii was used to examine the frequency of resistance to rifampicin in vivo, in a pneumonia model in immunocompetent C57BL/6 mice. The in vitro and in vivo prevention of the development of resistance to rifampicin was analysed using rifampicin alone or in association with imipenem or sulbactam, in time-kill studies and in the experimental murine pneumonia, respectively. RESULTS: Rifampicin-resistant mutants were found at 48 and 72 h, both in vitro and in vivo, when rifampicin was used alone, with the MIC increasing from 4 to > or =128 mg/L. The in vivo frequency of rifampicin-resistant mutants was 3 x 10(-6). On the contrary, no resistant mutants appeared after 72 h, in vitro or in vivo, when rifampicin was employed in association with imipenem or sulbactam. After six daily passages in rifampicin-free agar plates the resistant mutants maintained the high resistance to rifampicin (> or =128 mg/L). CONCLUSIONS: These results suggest that rifampicin must not be used alone in the treatment of infections caused by multidrug-resistant A. baumannii. In these cases, rifampicin may be used in combination with imipenem or sulbactam, which prevent the development of resistance to rifampicin.     

In vivo efficacies of combinations of beta-lactams, beta-lactamase inhibitors, and rifampin against Acinetobacter baumannii in a mouse pneumonia model.

The effects of various regimens containing combinations of beta-lactams, beta-lactam inhibitor(s), and rifampin were assessed in a recently described mouse model of Acinetobacter baumannii pneumonia (M. L. Joly-Guillou, M. Wolff, J. J. Pocidalo, F. Walker, and C. Carbon, Antimicrob. Agents Chemother. 41:345-351, 1997). Two aspects of the therapeutic response were studied: the kinetics of the bactericidal effect (treatment was initiated 3 h after intratracheal inoculation, and bacterial counts were determined over a 24-h period) and survival (treatment was initiated 8 h after inoculation, and the cumulative mortality rate was assessed on day 5). Two clinical strains were used: a cephalosporinase-producing strain (SAN-94040) and a multiresistant strain (RCH-69). For SAN-94040 and RCH-69, MICs and MBCs (milligrams per liter) were as follows: ticarcillin, 32, 64, 256, and >256, respectively; ticarcillin-clavulanate, 32, 64, and 512, and >512, respectively; imipenem, 0.5, 0.5, 8, and 32, respectively; sulbactam, 0.5, 0.5, 8, and 8, respectively; and rifampin, 8, 8, 4, and 4, respectively. Against SAN-94040, four regimens, i.e., imipenem, sulbactam, imipenem-rifampin, and ticarcillin-clavulanate (at a 25/1 ratio)-sulbactam produced a true bactericidal effect (>/=3-log10 reduction of CFU/g of lung). The best survival rate (i.e., 93%) was obtained with the combination of ticarcillin-clavulanate-sulbactam, and regimens containing rifampin provided a survival rate of >/=65%. Against RCH-69, only regimens containing rifampin and the combination of imipenem-sulbactam had a true bactericidal effect. The best survival rates (>/=80%) were obtained with regimens containing rifampin and sulbactam. These results suggest that nonclassical combinations of beta-lactams, beta-lactamase inhibitors, and rifampin should be considered for the treatment of nosocomial pneumonia due to A. baumannii.     

Rifampicin/imipenem combination in the treatment of carbapenem-resistant Acinetobacter baumannii infections

BACKGROUND: In the setting of a large endemic of Acinetobacter baumannii infections, treatment of those due to carbapenem-resistant strains, susceptible only to colistin, has become a major problem in our hospital during the past years. Successful results have been reported using colistin, but clinical experience with this antibiotic is limited. In our experimental studies using these strains in a mouse pneumonia model, the best results were observed with a combination of rifampicin and imipenem. METHODS: From July 2000 to September 2001, we performed a pilot study with patients suffering from serious infections due to carbapenem-resistant A. baumannii. Patients were treated with a rifampicin/imipenem combination and followed up prospectively. Cultures were repeated during and after treatment, and in vitro activity of rifampicin was monitored. Genotyping of these strains was performed by means of PFGE. RESULTS: Ten patients were selected: four with ventilator-associated pneumonia, and six with other infections (one catheter-related bacteraemia, five surgical infections). Three patients died, two of whom were considered therapeutic failures. In five of the seven patients who were cured, other procedures were also performed such as surgical drainage or catheter removal. In vitro development of high resistance to rifampicin was shown in seven (70%). PFGE demonstrated that initial isolates and high-resistant strains belonged to the same clones. CONCLUSIONS: The results of our study argue against the use of a rifampicin/imipenem combination for the treatment of carbapenem-resistant A. baumannii infections. However, combinations of rifampicin with other antibiotics merit further studies.     

西安地区耐亚胺培南鲍曼不动杆菌的碳青霉烯酶及同源性研究

目的 调查西安地区耐亚胺堵南鲍曼不动杆菌的耐药性,研究其同源性及分子耐药机制.方法 收集西安地区6所三级甲等医院1年间临床分离的非重复鲍曼不动杆菌株146株,采用K-B法进行药敏试验,E试验检测金属酶(MBL),PCR扩增OXA-23,-24,-58,-51 like型及IMP-1型和VIM-2型碳青霉烯酶基因,其阳性产物经测序分析,应用肠杆菌科基因组内重复序列(ERIC)-PCR对菌株进行DNA分型和同源性分析.结果 筛选出对亚胺培南耐药鲍曼不动杆菌(IRAB)非重复株1 5株,其中1株经E试验检测产金属酶,但扩增blaTMP-1,blaVIM-2均阴性,另外14株扩增blaOXA-66均阳性,11株blaUXA-23阳性,1株blaXA 58阳性;ERIC-PCR将15株IRAB分为A型和B型,其中部分菌株的亲缘关系很近,同源性达90%以上.结论 产OXA型碳青霉烯酶是西安地区该菌对亚胺培南耐药的主要原因.其中OXA-23型普遍存在,OXA-58型和OXA-66型基因在国内尚属新型碳青霉烯酶基因型;15株IRAB为2种克隆型,可能存在局部暴发流行.     

In vitro postantibiotic effect following repeated exposure to imipenem, temafloxacin, and tobramycin.

The postantibiotic effect (PAE) following three consecutive 2-h exposures to imipenem, temafloxacin, and tobramycin was determined in Pseudomonas aeruginosa. A PAE and a bactericidal effect were consistently observed for imipenem following each cycle of drug exposure and regrowth. In contrast, the PAE increased with repeated exposure with temafloxacin (1.8 to > 5 h), but disappeared with tobramycin by the third exposure (0.9 to 0 h). These data show that the in vitro PAE may change within a strain following multiple cycles of drug exposure and bacterial regrowth.     

A plasmid-borne blaOXA-58 gene confers imipenem resistance to Acinetobacter baumannii isolates from a Lebanese hospital

We investigated the basis of the carbapenem resistance of 17 multidrug-resistant Acinetobacter baumannii clinical isolates collected from 2004 to 2005 at the Saint George University Hospital in Beirut, Lebanon. A. baumannii isolates were clonally related and were susceptible to colistin and trimethoprim-sulfamethoxazole, susceptible or intermediate to ampicillin-sulbactam and meropenem, and resistant to all other antimicrobials. Conjugation experiments demonstrated that resistance to imipenem could be transferred along with a plasmid containing the carbapenem-hydrolyzing oxacillinase bla_OXA-58 gene. The plasmid that we called pABIR was 29,823 bp in size and showed a novel mosaic structure composed of two origins of replication, four insertion sequence (IS) elements, and 28 open reading frames. The bla_OXA-58 gene was flanked by IS18 and ISAba3 elements at the 5′ and 3′ ends, respectively. The production of the carbapenem-hydrolyzing oxacillinase OXA-58 was apparently the only mechanism for carbapenem resistance in A. baumannii isolates causing the outbreak at the Lebanese Hospital.     

The postantibiotic effect of N-chlorotaurine on Staphylococcus aureus. Application in the mouse peritonitis model.

This study was designed to investigate the delay of regrowth (postantibiotic effect) in the presence of N-chlorotaurine (NCT), an endogenous active N-chlorine compound, of Staphylococcus aureus, strain Smith diffuse. The low reactivity of NCT enabled clear temporal separation of the postantibiotic and killing effect to be defined. Delay of regrowth proved to be dependent both on concentration of NCT, and incubation time. The maximum delay was 3 h. Using the model of lethal staphylococcal peritonitis in mice, in-vivo delay of regrowth of bacteria pretreated with N-chlorotaurine could be demonstrated to correlate with survival. It is concluded that the postantibiotic effect of N-chlorotaurine could be an important factor on decreasing virulence of bacteria. This effect was observed after relatively short incubation times.     

耐碳青霉烯类抗生素鲍曼不动杆菌医院获得性肺炎病例分析

目的了解我院重症监护室(ICU)临床分离的碳青霉烯类抗生素耐药鲍曼不动杆菌(CRAb)医院获得性肺炎(HAP)的流行病学及耐药情况,并探讨ICU中CRAb医院获得性肺炎的危险因素。方法采用纸片扩散法测定鲍曼不动杆菌(Ab)对常用抗菌药物的敏感性,对碳青霉烯类抗生素耐药和敏感(CRAb和CSAb)的HAP患者进行1∶1回顾性病例对照研究。结果①CRAb对大部分抗菌药物的耐药率大于45%,仅对氨苄西林-舒巴坦及头孢哌酮-舒巴坦有较高敏感性(耐药率<20%);与CSAb组相比,CRAb组仅对氨曲南的耐药率进一步上升(P<0.05)。②ICU中CRAb的HAP的独立危险因素是分离出病原菌前14d内接受亚胺培南或美罗培南治疗(OR=6.229)、抗生素使用时间过长(OR=1.067)、APACHEⅡ评分≥20(OR=4.572)以及机械通气时间过长(OR=1.170)。CRAb组及CSAb组的抗生素使用时间分别为(21.87±21.19)d和(8.50±6.00)d(P=0.001),机械通气时间分别为(12.53±11.38)d和(5.67±3.72)d(P=0.013)。结论①2006年7月—2008年6月我院IC...     

Efficacy of colistin versus beta-lactams,aminoglycosides, and rifampin as monotherapy in a mouse model of pneumonia caused by multiresistant Acinetobacter baumannii

The treatment of life-threatening infections due to carbapenem-resistant Acinetobacter baumannii has become a serious challenge for physicians worldwide. Often, only colistin shows in general good in vitro activity against these carbapenem-resistant strains, but its antibacterial efficacy in comparison with the antibiotics most used in clinical practice is not well known. We studied the efficacy of colistin versus those of imipenem, sulbactam, tobramycin, and rifampin in an experimental pneumonia model with immunocompetent mice. We used three strains of A. baumannii corresponding to the main clones (A, D, and E) involved in the outbreaks of our hospital, with different grades of resistance to imipenem (imipenem MICs of 1, 8, and 512 microg/ml, respectively) and to the other antibiotics. The MIC of colistin was 0.5 microg/ml for the three strains. Reduction of log(10) CFU/g in lung bacterial counts, clearance of bacteremia, and survival versus results with controls were used as parameters of efficacy. Imipenem and sulbactam (Deltalung counts: -5.38 and -4.64 log(10) CFU/ml) showed the highest level of bactericidal efficacy in infections by susceptible and even intermediate strains. Tobramycin and rifampin (-4.16 and -5.15 log(10) CFU/ml) provided good results against intermediate or moderately resistant strains, in agreement with killing curves and pharmacodynamics. On the contrary, colistin showed the weakest antibacterial effect among the antibiotics tested, both in killing curves and in the in vivo model (-2.39 log(10) CFU/ml; P < 0.05). We conclude that colistin did not appear as a good option for treatment of patients with pneumonia due to carbapenem-resistant A. baumannii strains. Other alternatives, including combinations with rifampin, may offer better therapeutic profiles and thus should be studied.     

Use of adjuvants in the treatment of Acinetobacter baumannii

The current antibiotic crisis to treat infections by Acinetobacter baumannii is linked with the increase of antimicrobial resistance and the lack of development of new antimicrobial drugs. For this reason, new alternatives for the treatment and control of infections by A. baumannii are necessary. Several studies have reported the effect of adjuvants to restore the efficacy of existing antimicrobial agents. Herein, we analyzed the main results on the development of adjuvant drugs, as monotherapy or in combination therapy with existing antimicrobial agents, which have shown promising results in vitro and in vivo. However, caution is needed and further extensive in vivo studies have to be performed to confirm the potential use of these adjuvants as true therapeutic alternatives.     

社区获得性鲍曼不动杆菌性肺炎的临床特征及耐药性

目的 探讨社区获得性鲍曼不动杆菌肺炎患者的临床特征及耐药性,增加临床医生对该类肺炎的认识。 方法 纳入哈尔滨医科大学附属第二医院2020年1月-2021年6月呼吸内科病房标本检测为鲍曼不动杆菌,且诊断为社区获得性肺炎的患者44例,进行细菌鉴定及药敏试验,并回顾性分析其临床资料及转归。结果 社区获得性鲍曼不动杆菌肺炎患者多数伴有心脑疾病及慢性肺部疾病史,临床表现主要为咳嗽、咳痰、呼吸困难、发热。肺部CT呈现多形态改变,常见双肺受累。鲍曼不动杆菌呈现出不同程度耐药性,耐药率较高的是β内酰胺类(碳青霉烯类、哌拉西林/他唑巴坦)和喹诺酮类(环丙沙星),其中对碳青霉烯类耐药率高达54.5%。结论 由鲍曼不动杆菌引起的社区获得性肺炎患者以老年人为主,常伴有心脑肺部疾病,重症患者较多,但病死率较低,病原体具有不同程度耐药,需要临床医师关注。