Meropenem in cystic fibrosis patients infected with resistant Pseudomonas aeruginosa or Burkholderia cepacia and with hypersensitivity to β-lactam antibiotics

Objective: To assess the efficacy and safety of meropenem, administered on a compassionate basis to 62 cystic fibrosis (CF) patients (age: 24±6 years) with hypersensitivity reactions to β-lactam antibiotics and/or infection by bacteria resistant to other antibiotics.
Methods: Fifty-seven patients were chronically infected with Pseudomonas aeruginosa and 5 with Burkholderia cepacia . In total, 124 courses (1 to 6/patient) of meropenem, 2 g three times a day by intravenous infusion (10 to 15 min) for 14 days, were administered.
Results: During treatment for P. aeruginosa the mean increase in pulmonary function (as a percentage of the predictive values) was 5.6% for FEV₁ (forced expiratory volume in the first second) and 8.6% for FVC (forced vital capacity). C-reactive protein and erythrocyte sedimentation rate (ESR) and leukocyte count decreased significantly. In courses administered for chronic infection with B. cepacia the post treatment FEV₁ and FVC values were higher than the pre-treatment values, and all the inflammatory parameters decreased.
The geometric means of minimal inhibitory concentration (MICs) (μg/mL) for P. aeruginosa ( B. cepacia ) were: tobramycin 6 (59), ciprofloxacin 1.2 (9.7), piperacillin 49 (16.3), ceftazidime 26 (23), aztreonam 26 (35), imipenem 6.4 (not determined) and meropenem 5.1 (4.8). No statistically significant increase in the MICs of meropenem for either pathogen occurred during therapy. Of the 124 courses, 115 were tolerated without any clinical complaint. The following side effects were observed: nausea (0.8%), itching (4%), rash (3.2%), drug fever (1.6%).
Conclusions: Meropenem proved to be a valuable drug in the treatment of CF patients with chronic pulmonary infection with multiresistant P. aeruginosa and B. cepacia and with hypersensitivity reactions to other β-lactam drugs.     

河源地区铜绿假单胞菌碳青霉烯耐药机制分析

目的研究本院铜绿假单胞菌耐碳青霉烯类抗生素的耐药现况及主要耐药机制。方法用E-test方法检测铜绿假单胞菌对哌拉西林、头孢他啶、亚胺培南、美洛培南、庆大霉素、妥布霉素、环丙沙星7种抗生素的最小抑菌浓度,用EDTA双纸片扩散法及三维实验分别对金属酶及AmpC、KPC酶表型进行确证。结果从1 068例致病菌中共分离出108例铜绿假单胞菌,18例是对亚胺培南和/或美罗培南不敏感的菌株,耐药率为16.7%,其中有9例金属酶确证实验阳性,3例为AmpC酶持续高产型菌株,KPC酶确证实验尚没有检测出阳性菌株。结论耐碳青霉烯类铜绿假单胞菌多表现为多重耐药,这是多因素共同作用的结果 。     

Evaluation of the VITEK 2 system for the identification and susceptibility testing of three species of nonfermenting gram-negative rods frequently isolated from clinical samples

VITEK 2 is a new automatic system for the identification and susceptibility testing of the most clinically important bacteria. In the present study 198 clinical isolates, including Pseudomonas aeruginosa (n = 146), Acinetobacter baumannii (n = 25), and Stenotrophomonas maltophilia (n = 27) were evaluated. Reference susceptibility testing of cefepime, cefotaxime, ceftazidime, ciprofloxacin, gentamicin, imipenem, meropenem, piperacillin, tobramycin, levofloxacin (only for P. aeruginosa), co-trimoxazole (only for S. maltophilia), and ampicillin-sulbactam and tetracycline (only for A. baumannii) was performed by microdilution (NCCLS guidelines). The VITEK 2 system correctly identified 91.6, 100, and 76% of P. aeruginosa, S. maltophilia, and A. baumannii isolates, respectively, within 3 h. The respective percentages of essential agreement (to within 1 twofold dilution) for P. aeruginosa and A. baumannii were 89.0 and 88.0% (cefepime), 91.1 and 100% (cefotaxime), 95.2 and 96.0% (ceftazidime), 98.6 and 100% (ciprofloxacin), 88.4 and 100% (gentamicin), 87.0 and 92.0% (imipenem), 85.0 and 88.0% (meropenem), 84.2 and 96.0% (piperacillin), and 97.3 and 80% (tobramycin). The essential agreement for levofloxacin against P. aeruginosa was 86.3%. The percentages of essential agreement for ampicillin-sulbactam and tetracycline against A. baumannii were 88.0 and 100%, respectively. Very major errors for P. aeruginosa (resistant by the reference method, susceptible with the VITEK 2 system [resistant to susceptible]) were noted for cefepime (0.7%), cefotaxime (0.7%), gentamicin (0.7%), imipenem (1.4%), levofloxacin (2.7%), and piperacillin (2.7%) and, for one strain of A. baumannii, for imipenem. Major errors (susceptible to resistant) were noted only for P. aeruginosa and cefepime (2.0%), ceftazidime (0.7%), and piperacillin (3.4%). Minor errors ranged from 0.0% for piperacillin to 22.6% for cefotaxime against P. aeruginosa and from 0.0% for piperacillin and ciprofloxacin to 20.0% for cefepime against A. baumannii. The VITEK 2 system provided co-trimoxazole MICs only for S. maltophilia; no very major or major errors were obtained for co-trimoxazole against this species. It is concluded that the VITEK 2 system allows the rapid identification of S. maltophilia and most P. aeruginosa and A. baumannii isolates. The VITEK 2 system can perform reliable susceptibility testing of many of the antimicrobial agents used against P. aeruginosa and A. baumannii. It would be desirable if new versions of the VITEK 2 software were able to determine MICs and the corresponding clinical categories of agents active against S. maltophilia.     

Performance of Vitek 2 in antimicrobial susceptibility testing of Pseudomonas aeruginosa isolates with different mechanisms of beta-lactam resistance

A total of 78 isolates of Pseudomonas aeruginosa grouped according to the phenotype for ceftazidime and imipenem susceptibility/resistance were used to assess the accuracy of the Vitek 2 system in antimicrobial susceptibility testing. Comparisons were made with a MIC gradient test for piperacillin-tazobactam, ceftazidime, aztreonam, imipenem, meropenem, gentamicin, and ciprofloxacin. For the total of 546 isolate-antimicrobial combinations tested, the category agreement was 83.6%, with 2.0, 1.6, and 12.8% very major, major, and minor errors, respectively. Vitek 2 accuracy was influenced differently by the mechanism responsible for resistance, and interpretation of the results in relation to phenotype could improve the performance of the system.     

Effect of β-lactam antibiotics on the in vitro development of resistance in Pseudomonas aeruginosa

Objective   To investigate whether stepwise selection of resistance mutations may mirror the continued bacterial exposure to antibiotics that occurs in the clinical setting.
Methods   We examined the in vitro development of resistance to a number of commonly used antibiotics (cefepime, cefpirome, ceftazidime, cefotaxime, piperacillin and imipenem) in Pseudomonas aeruginosa , a significant nosocomial pathogen. Stepwise resistance was assessed by serial passage of colonies located nearest to the inhibition zone on antibiotic-containing gradient plates.
Results   The lowest frequencies of spontaneous resistance mutations were found with cefepime and imipenem; these drugs also resulted in the slowest appearance of resistance of spontaneous resistance mutations. In five wild-type P. aeruginosa strains, cefepime-selected isolates required a mean of 30 passages to reach resistance; resistance occurred more rapidly in strains selected with other cephalosporins. P. aeruginosa strains that produced β -lactamase or non-enzymatic resistance generally developed resistance more rapidly than wild-type strains. For most strains, resistance to all antibiotics except imipenem correlated with increased levels of β -lactamase activity. Cross-resistance of cephalosporin-selected resistant mutants to other cephalosporins was common. Cephalosporin-resistant strains retained susceptibility to imipenem and ciprofloxacin.
Conclusions   From our in vitro study, we can conclude that the rate of development of resistance of P. aeruginosa is lower with cefepime compared with other cephalosporines.     

Comparison of in vitro activities of levofloxacin, ciprofloxacin, ceftazidime, cefepime, imipenem, and piperacillin-tazobactam against aerobic bacterial pathogens from patients with nosocomial infections.

BACKGROUND AND PURPOSE: There is a rapid worldwide emergence of multidrug-resistant pathogens, especially in nosocomial isolates. This study compared the in vitro activities of levofloxacin, ciprofloxacin, ceftazidime, cefepime, imipenem, and piperacillin-tazobactam against 208 aerobic bacterial pathogens that caused 197 nosocomial infections in 184 patients. METHODS: Antimicrobial susceptibility was evaluated by E test in accordance with the guidelines of the National Committee for Clinical Laboratory Standards. RESULTS: Most (140/208, 67%) of the isolates were facultative Gram-negative bacilli. Levofloxacin and ciprofloxacin were the most effective (22/22, 100%) against oxacillin-sensitive Staphylococcus aureus. None of the antibiotics tested were found to be effective (0/25) against oxacillin-resistant S. aureus. Of the 11 isolates of Acinetobacter baumannii that were not pandrug-resistant (PDR), only 9 isolates (9/11, 81%) were sensitive to imipenem and 5 isolates (5/11, 45%) were sensitive to levofloxacin, ciprofloxacin, and ceftazidime. Another 22 isolates of A. baumannii that were PDR were completely resistant to all 6 antibiotics. The majority of isolates of Pseudomonas aeruginosa were sensitive to these 6 antimicrobial agents with 10/11 (91%) sensitive to levofloxacin and ciprofloxacin, 9/11 (83%) sensitive to ceftazidime, cefepime and piperacillin-tazobactam, and 8/11 (75%) sensitive to imipenem. CONCLUSIONS: The majority of the bacterial isolates causing nosocomial infections were found to be sensitive to the 6 antibiotics tested. Bacterial isolates of nosocomial infections that were completely resistant to these 6 antibiotics were PDR A. baumannii, PDR P. aeruginosa, and oxacillin-resistant S. aureus. More potent antimicrobial agents are needed to treat infections caused by PDR A. baumannii and PDR P. aeruginosa.     

Activity of doripenem against extended-spectrum β-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates

The in vitro activity of doripenem was evaluated against a recent collection of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates (201 ESBL-producing Enterobacteriaceae [153 Escherichia coli and 48 Klebsiella pneumoniae] and 201 P. aeruginosa). Comparator agents included amikacin, tobramycin, ciprofloxacin, cefepime, cefotaxime, ceftazidime piperacillin-tazobactam, imipenem, and meropenem. Both doripenem and meropenem inhibited 100% of the ESBL-producing Enterobacteriaceae at ≤0.5 μg/mL. For these isolates, the MIC₉₀ of doripenem (0.12 μg/mL) was 4-fold lower than that of imipenem (0.5 μg/mL). Against P. aeruginosa, the MIC₉₀ of doripenem and meropenem was 2 μg/mL, 4-fold lower than that of imipenem (8 μg/mL). At an MIC of ≤2 μg/mL, doripenem, meropenem, and imipenem inhibited 90.5%, 89.6%, and 82.1% of P. aeruginosa isolates, respectively. Doripenem maintained activity against imipenem-nonsusceptible isolates of P. aeruginosa; at an MIC of ≤4 μg/mL, it inhibited 15 of the 25 isolates with MICs for imipenem of >4 μg/mL. Doripenem is active against ESBL-producing Enterobacteriaceae and P. aeruginosa isolates. Its activity is similar to that of meropenem and slightly better than that of imipenem. The results of this study suggest that doripenem could be an alternative therapeutic agent for infections caused by these organisms.     

In vitro activity of beta-lactam antibiotics against CTX-M-producing Escherichia coli

Beta-lactam antibiotics have been discussed as options for the treatment of infections caused by multiresistant extended-spectrum beta-lactamase (ESBL)-producing bacteria if the minimum inhibitory concentration (MIC) is low. The objective of this study was to investigate the in vitro activity of different beta-lactam antibiotics against CTX-M-producing Escherichia coli. A total of 198 isolates of E. coli with the ESBL phenotype were studied. Polymerase chain reaction (PCR) amplification of CTX-M genes and amplicon sequencing were performed. The MICs for amoxicillin–clavulanic acid, aztreonam, cefepime, cefotaxime, ceftazidime, ceftibuten, ertapenem, imipenem, mecillinam, meropenem, piperacillin–tazobactam, and temocillin were determined with the Etest. Susceptibility was defined according to the breakpoints of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MIC₅₀ and MIC₉₀ values were calculated. Isolates from CTX-M group 9 showed higher susceptibility to the beta-lactam antibiotics tested than isolates belonging to CTX-M group 1. More than 90% of the isolates belonging to CTX-M group 9 were susceptible to amoxicillin–clavulanic acid, ceftazidime, ceftibuten, piperacillin–tazobactam, and temocillin. The susceptibility was high to mecillinam, being 91%, regardless of the CTX-M group. All isolates were susceptible to imipenem and meropenem, and 99% to ertapenem. This study shows significant differences in susceptibility to different beta-lactam antibiotics among the CTX-M-producing E. coli isolates and a significant difference for many antibiotics tested between the CTX-M-producing groups 1 and 9. The good in vitro activity of other beta-lactam antibiotics compared to carbapenems indicate that clinical studies are warranted in order to examine the potential role of these beta-lactam antibiotics in the treatment of infections caused by multiresistant ESBL-producing E. coli.     

铜绿假单胞菌oprD2基因突变及表达量改变与碳青霉烯类耐药的关系

目的 研究铜绿假单胞菌外膜通道蛋白OprD2的表达减弱或缺失,以及OprD2蛋白自身突变是否会影响铜绿假单胞菌对碳青霉烯类药物的耐药性.方法 收集分离自临床对亚胺培南(IPM)的最低抑菌浓度(MIC)值≥8μg/m1的铜绿假单胞菌共101株,采用肉汤稀释法检测菌株对比阿培南(BPM)、美罗培南(MEM)、帕尼培南(PEM)的MIC值;荧光定量RT-PCR检测铜绿假单胞菌膜通道蛋白oprD2基因的表达量情况;针对oprD2相对表达量正常并对亚胺培南耐药的铜绿假单胞菌,采用普通PCR的方法扩增oprD2全长基因并测序.结果 根据铜绿假单胞菌的OprD2蛋白相对表达量结果,将101株铜绿假单胞菌分成两组,组1为OprD2相对表达量降低组;组2为OprD2相对表达量正常组;组1与组2相比,对IPM、BPM、MEM、PEM的MIC值≥16μg/ml的菌株比例差异均有统计学意义(P＜0.01).组1中,28株同时对4种药物的MIC均≥16 μg/ml,其中有25株的OprD2的相对表达量明显减低(＜0.4);外膜孔蛋白OprD2转录水平与4种碳青霉烯类药物MICs之间呈负相关趋势.组2中,有16株9prD2基因发生突变,按照突变的类型主要分成4组;与PAO1相比,这些菌株对IPM、BPM、MEM、PEM的MIC值有不同程度的增加.结论 OprD2外膜蛋白的表达量减少或缺失是铜绿假单胞菌对亚胺培南耐药的主要机制,可能也与其他3种碳青霉烯类药物耐药有密切关系;铜绿假单胞菌的oprD2基因发生突变,可能会降低铜绿假单胞菌对这儿种碳青霉烯类药物的敏感性.     

Molecular surveillance of European quinolone-resistant clinical isolates of Pseudomonas aeruginosa and Acinetobacter spp. using automated ribotyping

Nosocomial isolates of Pseudomonas aeruginosa and Acinetobacter spp. exhibit high rates of resistance to antibiotics and are often multidrug resistant. In a previous study (D. Milatovic, A. Fluit, S. Brisse, J. Verhoef, and F. J. Schmitz, Antimicrob. Agents Chemother. 44:1102-1107, 2000), isolates of these species that were resistant to sitafloxacin, a new advanced-generation fluoroquinolone with a high potency and a broad spectrum of antimicrobial activity, were found in high proportion in 23 European hospitals. Here, we investigate the clonal diversity of the 155 P. aeruginosa and 145 Acinetobacter spp. sitafloxacin-resistant isolates from that study by automated ribotyping. Numerous ribogroups (sets of isolates with indistinguishable ribotypes) were found among isolates of P. aeruginosa (n = 34) and Acinetobacter spp. (n = 16), but the majority of the isolates belonged to a limited number of major ribogroups. Sitafloxacin-resistant isolates (MICs > 2 mg/liter, used as a provisional breakpoint) showed increased concomitant resistance to piperacillin, piperacillin-tazobactam, ceftriaxone, ceftazidime, amikacin, gentamicin, and imipenem. The major ribogroups were repeatedly found in isolates from several European hospitals; these isolates showed higher levels of resistance to gentamicin and imipenem, and some of them appeared to correspond to previously described multidrug-resistant international clones of P. aeruginosa (serotype O:12) and Acinetobacter baumannii (clones I and II). Automated ribotyping, when used in combination with more discriminatory typing methods, may be a convenient library typing system for monitoring future epidemiological dynamics of geographically widespread multidrug-resistant bacterial clones.     

MIC determination of fusidic acid and of ciprofloxacin using multidisk diffusion tests

Objective   To investigate the possibility of estimating the MICs of fusidic acid and ciprofloxacin for bacterial isolates using series of antibiotic disk concentrations in diffusion tests, so-called M-tests.
Methods   Thirty Staphylococcus aureus and S. epidermidis strains were tested for fusidic acid susceptibility. Sixty-one clinical isolates of eight bacterial species were tested for ciprofloxacin susceptibility. Disk diffusion was standardized according to the Swedish reference group for antibiotics (SRGA). For fusidic acid, a series of disks (1.5, 5.0, 15, 50 and 150 µg) was used. Ciprofloxacin was applied in four different diffusion sources (1, 3, 10 and 30 µg) on a single strip, the M-strip, and used. True MIC values were determined using the standardized agar dilution method according to the SRGA. Single-strain regression analysis (SRA) was employed to calculate critical concentration equivalents ( Q _zero).
Results   Fusidic acid and ciprofloxacin critical concentrations were determined for the bacterial isolates. The mean conversion factors for Q _zero to yield the true MIC were 2.06 (range 0.34–8.9) for fusidic acid and 2.05 (range 0.37–8.1) for ciprofloxacin. There was a correlation between true MIC values (all MICs expressed as 2 log + 9) and the calculated MIC values ( Q _zero× conversion factor) for both fusidic acid ( R  = 0.9822) and ciprofloxacin ( R  = 0.9696).
Conclusions   MIC values of clinical isolates can be estimated using SRA calculations on zone measurements in disk tests with several concentrations of the antibiotic in diffusion sources.     

Antimicrobial susceptibility of bacteria causing urinary tract infections in Latin American hospitals: results from the SENTRY Antimicrobial Surveillance Program (1997)

Objectives: To evaluate the antimicrobial susceptibility patterns among 469 pathogens isolated as a significant cause of urinary tract infections in 10 Latin American medical centers.
Methods: Consecutively collected isolates were susceptibility tested by broth microdilution methods, and selected isolates were characterized by molecular typing methods.
Results: Escherichia coli and Klebsiella spp. isolates revealed high rates of resistance to broad-spectrum penicillins and to fluoroquinolones. Ceftazidime MICs of ≥2 mg/L, suggesting the production of extended-spectrum β-lactamases (ESBLs), were observed in 37.7% of K. pneumoniae and 8.3% of Escherichia coli isolates. Enterobacter spp. isolates were characterized by high resistance rates to ciprofloxacin (35%) and to ceftazidime (45%), but they generally remained susceptible to cefepime (95% susceptible). Pseudomonas aeruginosa and Acinetobacter spp. were highly resistant to ciprofloxacin and ceftazidime. Imipenem was active against 80% of P. aeruginosa and 93% of Acinetobacter spp. isolates.
Conclusions: Our results demonstrate a high level of resistance to various classes of antimicrobial agents among isolates causing nosocomial urinary tract infections in Latin American hospitals. Clonal dissemination of ESBL-producing K. pneumoniae strains was infrequent.     

Evolution of Resistance among Clinical Isolates of Acinetobacter over a 6-Year Period

 The aim of this report was to study the evolution of susceptibilities of 1532 clinical isolates of Acinetobacter recovered over a period of 6 years. The minimal inhibitory concentrations (MICs) of 15 antimicrobial agents were determined for all the isolates. The respective percentages of resistant strains in the years 1991 and 1996 were as follows: ciprofloxacin, 54.4% and 90.4%; tobramycin, 33% and 71.8%; amikacin, 21% and 83.7%; ampicillin plus sulbactam, 65.7% and 84.1%; ceftazidime, 57.4% and 86.8%; ticarcillin, 70% and 89.4%; trimethoprim plus sulfamethoxazole, 41.1% and 88.9%; and imipenem, 1.3% and 80%. The MIC90s of ciprofloxacin, sparfloxacin, biapenem, meropenem, imipenem, cefepime, cefpirome, and rifampicin against 250 imipenem-resistant Acinetobacter strains were >32, >32, 128, >256, 256, >256, 256, and 16 mg/l, respectively. With serious infections, it was necessary to resort to the use of colistin, the only antibiotic active in vitro.     

Reevaluation of interpretive criteria for Haemophilus influenzae by using meropenem (10-microgram), imipenem (10-microgram), and ampicillin (2- and 10-microgram) disks.

A collection of 300 Haemophilus influenzae clinical strains was used to assess in vitro susceptibility to carbapenems (meropenem, imipenem) by MIC and disk diffusion methods and to compare disk diffusion test results with two potencies of ampicillin disks (2 and 10 micrograms). The isolates included ampicillin-susceptible or- intermediate (167 strains), beta-lactamase-positive (117 strains), and beta-lactamase-negative ampicillin-resistant (BLNAR; 16 strains) organisms. Disk diffusion testing was performed with 10-micrograms meropenem disks from two manufacturers. Meropenem was highly active against H. influenzae strains (MIC50, 0.06 microgram/ml; MIC90, 0.25 microgram/ml; MIC50 and MIC90, MICs at which 50 and 90%, respectively, of strains are inhibited) and was 8- to 16-fold more potent than imipenem (MIC50, 1 microgram/ml; MIC90, 2 micrograms/ml). Five non-imipenem-susceptible strains were identified (MIC, 8 micrograms/ml), but the disk diffusion test indicated susceptibility (zone diameters, 18 to 21 mm). MIC values of meropenem, doxycycline, ceftazidime, and ceftriaxone for BLNAR strains were two- to fourfold greater than those for other strains. The performance of both meropenem disks was comparable and considered acceptable. A single susceptible interpretive zone diameter of > or = 17 mm (MIC, < = or 4 micrograms/ml) was proposed for meropenem. Testing with the 2-micrograms ampicillin disk was preferred because of an excellent correlation between MIC values and zone diameters (r = 0.94) and superior interpretive accuracy with the susceptible criteria at > or = 17 mm (MIC, < or = 1 microgram/ml) and the resistant criteria at < or = 13 mm (MIC, > or = 4 micrograms/ml). Among the BLNAR strains tested, 81.3% were miscategorized as susceptible or intermediate when the 10-micrograms ampicillin disk was used, while the 2-micrograms disk produced only minor interpretive errors (12.5%). Use of these criteria for testing H. influenzae against meropenem and ampicillin should maximize reference test and standardized disk diffusion test performance with the Haemophilus Test Medium. The imipenem disk diffusion test appears compromised and should be used with caution for detecting strains for which imipenem MICs are elevated.     

Evaluation of E-Test for determination of antimicrobial MICs for Pseudomonas aeruginosa isolates from cystic fibrosis patients.

We determined the E-Test and National Committee for Clinical Laboratory Standards standardized agar dilution MICs of ceftazidime, ciprofloxacin, piperacillin, and tobramycin for Pseudomonas aeruginosa during tests of 100 rough and mucoid P. aeruginosa isolates from cystic fibrosis patients. The levels of agreement (+/- 1 log2 dilution) between quantitative E-Test and agar dilution MIC results were 80, 97, 73, and 89% for ceftazidime, ciprofloxacin, piperacillin, and tobramycin, respectively. Comparison of the results after converting the MIC data to qualitative categories (susceptible, intermediate, and resistant) yielded levels of agreement of 84, 96, 88, and 93% for the same agents, respectively. Of the 39 qualitative discrepancies, 36 were minor and 3 were very major. We conclude that use of the E-Test is easier and more practical than use of the agar dilution method for most laboratories and that the E-Test furnishes results which are at least as accurate as those obtained by the agar dilution method. However, the higher cost of the E-Test method would likely discourage most laboratories from selecting it over disk diffusion for routine antimicrobial susceptibility testing of P. aeruginosa isolates from cystic fibrosis patients.     

Accuracy of three automated systems (MicroScan WalkAway, VITEK, and VITEK 2) for susceptibility testing of Pseudomonas aeruginosa against five broad-spectrum beta-lactam agents

One hundred recent clinical Pseudomonas aeruginosa isolates were used to assess the quantitative (MIC) and qualitative (susceptibility category) accuracies of the MicroScan WalkAway, VITEK, and VITEK 2 automated susceptibility test systems when five-broad spectrum beta-lactams, aztreonam, cefepime, ceftazidime, imipenem, and piperacillin-tazobactam, were tested. Isolates were selected so that the MICs for the isolates overrepresented the MICs near the breakpoints to assess precisely the agreement between the results obtained with the automated systems and the results obtained by the reference tests. The categorical and MIC results from the automated systems were compared to the consensus result of three reference methods: broth microdilution, agar dilution, and disk diffusion. The consensus categorical testing (susceptibility and resistance) rates were 47 and 27%, respectively, for aztreonam; 59 and 14%, respectively, for cefepime; 44 and 43%, respectively, for ceftazidime; 71 and 19%, respectively, for imipenem; and 50 and 50%, respectively, for piperacillin-tazobactam. All systems tested exhibited a high, unacceptable level of very major (false-susceptible) errors for piperacillin-tazobactam (19 to 27%). Major (false-resistant) error rates were generally acceptable (0 to 3%), but minor error rates were elevated (8 to 32%) for cefepime (VITEK 2 and VITEK) and for aztreonam (all three systems), leading to consistent trends toward false resistance. Manufacturer reevaluation of these automated systems for the testing of selected beta-lactams with current clinical isolates of P. aeruginosa that exhibit contemporary resistance mechanisms would be prudent to minimize the potential for serious reporting errors.     

In vitro activities of tigecycline, ertapenem, isepamicin, and other antimicrobial agents against clinically isolated organisms in Taiwan

This study evaluated the in vitro activities of tigecycline, ertapenem, isepamicin, and other comparators against 861 bacterial isolates recovered from patients treated in three major teaching hospitals in 2003. MICs to antimicrobial agents were determined by the agar dilution method. High rates of oxacillin resistance (58%) in Staphylococcus aureus (60 isolates), and vancomycin resistance (21%) and quinupristin-dalfopristin non-susceptibility (39%) in Enterococcus faecium (34 isolates) were found. Carbapenems had excellent in vitro activities (>or=98% susceptibility) against the 419 isolates of Enterobacteriaceae, with the MIC(50) and MIC(90) of imipenem, meropenem, and ertapenem being 0.25 and 4 mg/L, 0.03 and 0.12 mg/L, and 0.03 and 0.5 mg/L, respectively. For, Pseudomonas aeruginosa (74 isolates) and Burkholderia cepacia (21 isolates), meropenem (MIC(90), 0.25, 2, and 4 mg/L, respectively) had better in vitro activities than imipenem (MIC(90), 8, 4, and 32 mg/L, respectively) and ertapenem (MIC(90), 0.5, >32, and 32 mg/L, respectively). Isepamicin had a similar activity with amikacin against all Enterobacteriaceae, Pseudomonas aeruginosa, B. cepacia, and Acinetobacter baumannii, except for C. freundii isolates in which isepamicin had an eight-fold activity better than amikacin. Tigecycline had excellent in vitro activities against all isolates tested (MIC(90), 相似文献   

Evaluation of the performance of rapid antibiotic susceptibility test results using the disk diffusion directly from the positive blood culture bottles

PurposeIn this study, we aimed to evaluate the compliance of rapid antibiotic susceptibility test (RAST) and conventional laboratory procedures.MethodsThe RAST was performed directly from the blood cultures of 71 Gram negative bacilli (GNB) and 38 Gram positive cocci (GPC) isolates. The results were evaluated at fourth, sixth and eighth hour. Categorical agreement (CA), very major error (VME), major error (ME) and minor error (mE) were calculated and compared with the results of conventional Vitek-2 system.ResultsCategorical agreement was detected ≥90 in cefotaxime and meropenem at fourth hour in Escherichia coli isolates. An encourage positive CA results were obtained from meropenem, ceftazidime and ciprofloxacin at the fourth hour in Klebsiella pneumoniae isolates. CA was compatible in imipenem, ciprofloxacin, gentamicin, and tobramycin for Pseudomonas aeruginosa at sixth hour. CA was low (<90%) in piperacillin-tazobactam for E. coli and K. pneumoniae, and meropenem in P. aeruginosa isolates. A good CA (≥90) with all tested antibiotics were found at all hours for Acinetobacter baumannii and also very high CA (100%) was detected at sixth and eighth hour in Staphylococcus aureus isolates. CA remained below the standard criteria at fourth hour in vancomycin and high level gentamicin, in addition to imipenem at sixth hours in enterococci isolates. VME and ME were not detected and mE was 12.7% in GNB and 50% in GPC at eighth hour.ConclusionsEUCAST RAST at eighth hour will be beneficial in urgent patients due to their high CA rate, easy preparation, inexpensive, and could be performed with the available equipment and personnel.     

Resistance to antibiotics in clinical isolates of Pseudomonas aeruginosa

OBJECTIVES: To analyse the global resistance to some antibiotics used to treat nosocomial infections by Pseudomonas aeruginosa, specially to carbapenems, and its relationship with the presence of carbapenemases, OXA, VIM and IMP. METHODS: The study included 229 P. aeruginosa isolates from a Hospital in Northern Spain (year 2002). Susceptibility to antimicrobial agents was determined by the analysis of the MIC. Genetic typing was carried out by RAPD-PCR fingerprinting with primer ERIC-2. Genetic experiments to detect class-1 integrons were performed by PCR with primers 5'CS and 3'CS. Detection of carbapenemases was done by phenotypic (Hodge test and DDST) and genotypic methods (PCR with primers for imp, vim1, vim2 and oxa40 genes). RESULTS: 23.9% of isolates were resistant to ceftazidime, 35.9% to cefotaxime, 5.3% to amikacin, 54.9% to gentamicin, 14.6% to imipenem and 6.6% to meropenem. Isolates resistant to imipenem (33) were furtherly tested. Genetic typing didn't show clonal relatedness among the most of the isolates. Class-1 integrons were present in most isolates (sizes 600-1700 bp). Phenotypic methods for carbapenemases showed 5 positive isolates. Genotypic methods showed the presence of two isolates with the oxa40 gene. CONCLUSIONS: Meropenem, amikacin and imipenem were the most active agents to treat infections caused by Pseudomonas aeruginosa. In our study, the presence of carbapenemase enzymes wasn't high. Phenotypic tests cannot be considered as accurate screening tool to detect carbapenemases. This is the fist report of the oxa40 gene in Pseudomonas aeruginosa isolates.     

Doripenem vs meropenem against Pseudomonas and Acinetobacter

Recently, doripenem has been approved for the treatment of nosocomial pneumonia (NP), including ventilator-associated pneumonia (VAP). The E-test was performed to determine the MICs of doripenem and meropenem in 203 endotracheal aspirate isolates that consisted of 140 Acinetobacter calcoaceticus-Acinetobacter baumannii complexes and 63 Pseudomonas aeruginosa. Doripenem showed minimum concentration necessary for inhibition of 50% (MIC 50 ) of P. aeruginosa isolates at 0.38 mg/L which is several times (84.2 times) lower than the corresponding MIC 50 value of >32 mg/L for meropenem. The MIC 50 and MIC 90 were similar for both the drugs against A. baumannii. Thus, P. aeruginosa was consistently more susceptible than the A. baumannii.