Comparison of ciprofloxacin with azlocillin plus tobramycin in the therapy of experimental Pseudomonas aeruginosa endocarditis.

The efficacy of ciprofloxacin (Bay o 9867), a promising new quinolone, was compared with the efficacy of azlocillin plus tobramycin in rabbits with experimentally induced Pseudomonas aeruginosa endocarditis. The MBCs of ciprofloxacin, azlocillin, and tobramycin against the test strain were 0.5, 8, and 4 micrograms/ml respectively. Ciprofloxacin at a concentration of 50 mg/kg or azlocillin at a concentration of 200 mg/kg in combination with tobramycin at a concentration of 5 mg/kg was administered intramuscularly at 8-h intervals for 4 days. Both regimens produced median peak serum bactericidal titers of 1:8. The concentrations of ciprofloxacin, azlocillin, and tobramycin in serum, 1.8 +/- 0.7, 154 +/- 48, and 9.1 +/- 2.4 micrograms/ml (mean +/- standard deviation), respectively, closely approximated concentrations found in humans after accepted dosages. At the end of treatment, the titers of P. aeruginosa were 3.0 +/- 1.6 log10 CFU/g of vegetation (mean +/- standard deviation) for recipients of ciprofloxacin and 3.2 +/- 1.3 log10 CFU/g of vegetation for recipients of azlocillin plus tobramycin. These values compared with control titers of 7.3 +/- 1.6 CFU/g. These data indicate that at the doses used, ciprofloxacin was as effective as azlocillin plus tobramycin in the treatment of P. aeruginosa endocarditis in rabbits. Since the latter drug combination has proven efficacy, ciprofloxacin deserves further evaluation in the therapy of systemic infections in animal models and in humans.     

Activities of tobramycin and azlocillin alone and in combination against experimental osteomyelitis caused by Pseudomonas aeruginosa.

Azlocillin and tobramycin were used alone and in combination in the treatment of chronic osteomyelitis due to Pseudomonas aeruginosa in rabbits. This combination showed in vitro synergy measured by both the checkerboard technique and time-kill curves. A marked inoculum effect was demonstrated in vitro with azlocillin and the infecting strain of P. aeruginosa. The minimal inhibitory concentration of azlocillin, with an inoculum of 10(5) organisms, was 12.5 micrograms/ml; when the inoculum size was increased to 10(7) organisms, the minimal inhibitory concentration rose to more than 500 micrograms/ml. In therapeutic trials, the combination of azlocillin and tobramycin, given for 28 days, was significantly better than either no therapy or azlocillin alone, but was not significantly better than tobramycin alone. Even after 4 weeks of combined therapy with azlocillin and tobramycin, P. aeruginosa was recovered from the bones of 60% of the treated rabbits.     

Mathematical modelling response of Pseudomonas aeruginosa to meropenem

OBJECTIVES: Widespread emergence of resistance to antimicrobial agents is a serious problem. The rate at which new agents are made available clinically is unlikely to keep up with these resistant pathogens, and there is an urgent need to accelerate antimicrobial agent development. We explored the use of mathematical modelling to guide selection of dosing regimens. METHODS: Using time-kill studies data of Pseudomonas aeruginosa over 24 h, we developed a mathematical model to capture the dynamic relationship between a heterogeneous microbial population and meropenem concentrations. The microbial behaviour in response to meropenem over 5 days was predicted via computer simulation and subsequently validated using an in vitro hollow fibre infection model. Three parallel differential equations were used, each characterizing the rate of change of drug concentration, microbial susceptibility and microbial burden of the surviving population over time, respectively. Several model structures were explored; they differed in the adaptation of the microbial population over time. Various fluctuating concentration-time profiles of meropenem were experimentally examined, mimicking human elimination and repeated dosing. RESULTS: Using limited experimental data as inputs, the mathematical model was reasonable in qualitatively predicting microbial response (sustained suppression or regrowth due to resistance emergence) to various pharmacokinetic profiles of meropenem. CONCLUSIONS: Our results suggest that mathematical modelling may be used to predict microbial response to a large number of antimicrobial agent dosing regimens efficiently, and have the potential to be used to guide highly targeted investigation of dosing regimens in pre-clinical studies and clinical trials. The in vivo relevance of the modelling approach warrants further investigations.     

Selection of resistance by piperacillin during Pseudomonas aeruginosa endocarditis

The mechanisms responsible for emergence of resistance during antimicrobial therapy were investigated in isolates obtained from a patient suffering from Pseudomonas aeruginosa endocarditis. The strain was first isolated from blood cultures obtained upon admission of the patient. It was sensitive to piperacillin, ticarcillin and tobramycin. Piperacillin-tobramycin therapy was therefore instituted and led to a rapid improvement of the patient's condition. Unfortunately, the patient subsequently became febrile again and blood cultures continued to yield P. aeruginosa. However, the organism isolated was now resistant to piperacillin and other penicillins tested. Cell-free extracts of the pre- and post-therapy isolates were analyzed for their beta-lactamase activity. The susceptible pre-therapy strain did not produce significant levels of beta-lactamase. In contrast, the post-therapy strain produced high levels of the enzyme. Induction experiments indicated that the production of beta-lactamase was constitutive in the post-therapy isolate. Thus, piperacillin therapy has led to the selection of resistant mutants which produced high levels of beta-lactamase constitutively. This was associated with relapse of the infection and therapeutic failure.     

多重耐药铜绿假单胞菌感染

铜绿假单胞菌广泛分布于土壤、水、植被中,是人体正常定植菌,一般不致病。当人体正常防御体系受损时,如气管插管、留置静脉导管、留置导尿管、中性粒细胞缺乏和免疫抑制状态等,铜绿假单胞菌侵入人体,成为条件致病菌。铜绿假单胞菌可引起包括皮肤软组织感染、肺炎、血流感染在内     

美罗培南个体化治疗慢性阻塞性肺病并发铜绿假单胞菌感染患者的研究

目的：探讨美罗培南个体化治疗慢性阻塞性肺疾病（COPD）并发铜绿假单胞菌感染患者的效果及安全性。方法将COPD并发铜绿假单胞菌感染的患者分成2组（个体化剂量组、标准剂量组）进行治疗,统计分析美罗培南对2组患者的疗效及安全性。结果个体化剂量组患者的美罗培南平均剂量为每12 h（0．86±0．09）g,低于标准剂量组;个体化剂量组治疗的有效率为81．3％,2组间有效率的差异无统计学意义（P＞0．05）。个体化剂量组患者不良反应的发生率低于标准剂量组（P＜0．05）,标准剂量治疗对肾功能有一定损伤,而个体化剂量能减轻美罗培南对肾功能的损伤。结论美罗培南的个体化给药不仅能在保证疗效的前提下提高治疗的安全性,还能降低对肾功能的损害。     

Dynamic interactions of biofilms of mucoid Pseudomonas aeruginosa with tobramycin and piperacillin.

The dynamic interaction of planktonic and biofilm cells of mucoid Pseudomonas aeruginosa with tobramycin and piperacillin was investigated in a chemostat system. The results indicated that planktonic and young biofilm cells of the 2-day-old chemostat culture of P. aeruginosa were susceptible to killing by chemostat-controlled doses of either 250 micrograms of piperacillin per ml plus 5 micrograms of tobramycin per ml or 500 micrograms of piperacillin per ml plus 5 micrograms of tobramycin per ml. Complete eradication of the planktonic and young biofilm cells was observed after exposure of the cells to six chemostat-controlled doses of these antibiotic at 8-h intervals for 7 days. Regrowth of the organism was not observed after the termination of antibiotic therapy on day 7. A different picture was observed when antibiotic treatment was initiated on day 10 after inoculation. Viable old biofilm cells were reduced to approximately 20% after exposure to the chemostat-controlled doses of 500 micrograms of piperacillin per ml plus 5 micrograms of tobramycin per ml. Complete eradication of old biofilm cells could not be achieved, and regrowth of the organism occurred after the termination of antibiotic therapy. These data suggest that young biofilm cells of mucoid P. aeruginosa can be effectively eradicated with the combination of piperacillin and tobramycin, while old biofilm cells are very resistant to these antibiotics and eradication of old biofilm cells is not achievable with the chemostat-controlled doses of piperacillin and tobramycin used in this study.     

Combined effects of meropenem and aminoglycosides on Pseudomonas aeruginosa in vitro

To investigate combinations of antibiotics against Pseudomonas aeruginosa, the in vitro effects of combinations of meropenem with each of three aminoglycosides, arbekacin, amikacin and netilmicin, were evaluated using an agar dilution chequerboard technique. The combinations of meropenem and aminoglycosides were effective against almost all P. aeruginosa strains tested, which included meropenem-resistant strains. Increased synergic effects were observed in combinations that included arbekacin or amikacin. None of the combinations had an antagonistic effect. Most of the synergic and additive effects were achieved at clinically relevant concentrations.     

Optimal meropenem concentrations to treat multidrug-resistant Pseudomonas aeruginosa septic shock

A patient with septic shock due to extensively drug resistant (XDR) Pseudomonas aeruginosa was cured by optimizing the meropenem (MEM) regimen to obtain at least 40% of the time between two administrations in which drug levels were four times higher than the MIC of the pathogen. As the standard drug dose did not achieve these optimal concentrations, the MEM regimen was progressively increased up to 12 g/day (3 g every 6 h in a 3-h extended infusion), which eventually resulted in sepsis resolution. High MEM dosage may represent a valuable therapeutic option for infection due to multidrug-resistant (MDR) strains, and drug monitoring would allow rapid regimen adjustment in clinical practice.     

Resistance of artificial biofilms of Pseudomonas aeruginosa to imipenem and tobramycin

Viable cells of Pseudomonas aeruginosa were entrapped in alginate gel layers and incubated in a minimal glucose (15 g/L)-yeast extract (2 g/L)-salt medium to form artificial biofilm-like structures. After cultivation for 2 days, the biomass distribution inside the polymer was highly heterogeneous. The cell number reached approximately 1011 cells/g gel in the outer regions of the gel structures whereas the inner areas were less colonized (c. 10(8) cells g/gel). Killing of immobilized organisms by imipenem and tobramycin were compared with free-cell experiments (inoculum c. 10(9) cells/mL). Sessile-like bacteria displayed a higher resistance to the two antibiotics used alone or in combination than did suspended cells. Exposure for 10 h to 20 x MIC imipenem and 15 x MIC tobramycin reduced the number of viable immobilized bacteria to 0.3% and 3%, respectively, of the initial cell population, whereas these antibiotic concentrations were much more efficient (bactericidal) against free-cell cultures (5 log kill in 6 h). A synergic effect of tobramycin and imipenem was detected on bacterial suspensions but not on biofilm-like structures. Effective diffusivity measurements showed that the diffusion of imipenem in the alginate layer was not hindered. A slight but significant enhancement of beta-lactamase induction in immobilized cells as compared with their suspended counterparts was insufficient to explain the high resistance of sessile-like bacteria.     

Immunomodulatory clarithromycin treatment of experimental sepsis and acute pyelonephritis caused by multidrug-resistant Pseudomonas aeruginosa

Clarithromycin was administered intravenously to 55 rabbits to evaluate its effect on experimental sepsis caused by multidrug-resistant Pseudomonas aeruginosa. Acute pyelonephritis was induced after ligation of the right ureter and injection of 10(8) CFU of the test isolate per kg of body weight into the renal pelvis. The animals were divided into six groups: group A, controls; group B, rabbits that received one intravenous dose of 80 mg of clarithromycin per kg concomitantly with bacterial challenge; group C, rabbits that received two doses of clarithromycin, the second one of which was given 2 h after the first one; group D, rabbits that received 15 mg of amikacin per kg; group E, rabbits that received one dose of clarithromycin and amikacin; and group F, rabbits that received two doses of clarithromycin and amikacin. Serum endotoxin levels were estimated by the QCL-1000 Limulus amoebocyte lysate assay, tumor necrosis factor alpha (TNF-alpha) levels were measured by a bioassay, and malondialdehyde (MDA) levels were measured by the thiobarbiturate assay. Viable bacterial counts in various tissue samples were also assessed. The mean survival times of the animals in groups A, B, C, D, E, and F were 4.50, 7.69, 4.07, 4.55, 11.55, and 11.60 days, respectively (P = 0.033 for group D versus group F, P = 0.006 for group D versus group E, P = not significant for group B versus group E, P = 0.042 for group C versus group F). Serum endotoxin levels were similar between groups at all sampling times; TNF-alpha and MDA levels in groups B, C, E, and F decreased significantly over follow-up. The numbers of viable bacterial cells in the infected kidney were similar among the groups; those in the liver, spleen, lungs, and mesenteral lymph nodes were significantly decreased in groups B, E, and F compared to those in groups A and D. It is concluded that a prolongation of survival in animals with experimental sepsis caused by multidrug-resistant P. aeruginosa was achieved after coadministration of clarithromycin and amikacin and that the increased survival was probably attributable to the immunomodulatory properties of clarithromycin.     

Fosfomycin enhances the active transport of tobramycin in Pseudomonas aeruginosa

Elevated levels of mucins present in bronchiectatic airways predispose patients to bacterial infections and reduce the effectiveness of antibiotic therapies by directly inactivating antibiotics. Consequently, new antibiotics that are not inhibited by mucins are needed to treat chronic respiratory infections caused by Pseudomonas aeruginosa and Staphylococcus aureus. In these studies, we demonstrate that fosfomycin synergistically enhances the activity of tobramycin in the presence of mucin. The bactericidal killing of a novel 4:1 (wt/wt) combination of fosfomycin-tobramycin (FTI) is superior (>9 log(10) CFU/ml) relative to its individual components fosfomycin and tobramycin. Additionally, FTI has a mutation frequency resulting in an antibiotic resistance >3 log(10) lower than for fosfomycin and 4 log(10) lower than for tobramycin for P. aeruginosa. Mechanistic studies revealed that chemical adducts are not formed, suggesting that the beneficial effects of the combination are not due to molecular modification of the components. FTI displayed time-kill kinetics similar to tobramycin and killed in a concentration-dependent fashion. The bactericidal effect resulted from inhibition of protein biosynthesis rather than cell wall biosynthesis. Studies using radiolabeled antibiotics demonstrated that tobramycin uptake was energy dependent and that fosfomycin enhanced the uptake of tobramycin in P. aeruginosa in a dose-dependent manner. Lastly, mutants resistant to fosfomycin and tobramycin were auxotrophic for specific carbohydrates and amino acids, suggesting that the resistance arises from mutations in specific active transport mechanisms. Overall, these data demonstrate that fosfomycin enhances the uptake of tobramycin, resulting in increased inhibition of protein synthesis and ultimately bacterial killing.     

Synergy of new C-3 substituted cephalosporins and tobramycin against Pseudomonas aeruginosa and Pseudomonas cepacia

The effects of the combination of E-1040, a new cephalosporin, ceftazidime, cefpirome, or cefepime with tobramycin against 40 Pseudomonas aeruginosa and 16 P. cepacia isolates from cystic fibrosis patients were examined. Synergy fractional inhibitory concentration less than or equal to 0.5 was found against P. aeruginosa when tobramycin was combined with E-1040 32%, cefpirome 32%, cefepime 22%, and ceftazidime 22%. Fifty-two percent of isolates showed an additive response for E-1040, 60% for cefpirome, 45% cefepime, and 55% ceftazidime, p greater than 0.05. The differences were not statistically significant. Synergy was not more likely to be achieved if the isolates were susceptible or resistant to either the aminoglycoside or cephalosporin. None of the E-1040-resistant isolates, all of which were tobramycin-resistant, became susceptible when tested with an aminoglycoside, whereas 15 of 34 cefpirome-resistant, 13 of 30 cefepime-resistant, and seven of 14 ceftazidime-resistant isolates became susceptible. Synergy of aminoglycoside and the cephalosporins against P. cepacia was found for 25% with E-1040, 44% with cefpirome, 38% with cefepime, and 31% with ceftazidime. These differences were not statistically significant.     

Inhaled tobramycin in non-cystic fibrosis patients with bronchiectasis and chronic bronchial infection with Pseudomonas aeruginosa

BACKGROUND: Non-cystic fibrosis (CF) patients with bronchiectasis usually develop chronic bronchial infection with Pseudomonas aeruginosa (PA) that is related to worsening lung function and increased morbidity and mortality. OBJECTIVE: To determine whether direct aerosol delivery of tobramycin to the lower airways may control infection and produce only low systemic toxicity. METHODS: A double-blind, placebo-controlled crossover trial involving 30 patients was conducted to determine the clinical effectiveness and safety of 6-month tobramycin inhalation therapy. Patients received 300 mg of aerosolized tobramycin or placebo twice daily in 2 cycles, each for 6 months, with a one-month washout period. The number of exacerbations, number of hospital admissions, number of hospital admission days, antibiotic use, pulmonary function, quality of life, tobramycin toxicity, density of PA in sputum, emergence of bacterial resistance, and emergence of other opportunistic bacteria were recorded. RESULTS: The number of admissions and days of admission (mean +/- SD) during the tobramycin period (0.15 +/- 0.37 and 2.05 +/- 5.03) were lower than those during the placebo period (0.75 +/-1.16 and 12.65 +/- 21.8) (p < 0.047). A decrease in PA density in sputum was associated with tobramycin administration in the analysis of the first 6-month cycle (p = 0.038). No significant differences were observed in the number of exacerbations, antibiotic use, pulmonary function, and quality of life. The emergence of bacterial resistance and other bacteria did not differ between the 2 periods of study. Inhaled tobramycin was associated with bronchospasm in 3 patients, but not with detectable ototoxicity or nephrotoxicity. CONCLUSIONS: Aerosol administration of high-dose tobramycin in non-CF bronchiectatic patients for endobronchial infection with PA appears to be safe and decreases the risk of hospitalization and PA density in sputum. Nevertheless, pulmonary function and quality of life are not improved, and the risk of bronchospasm is appreciable.     

Activity of meropenem with and without ciprofloxacin and colistin against Pseudomonas aeruginosa and Acinetobacter baumannii

Time-kill synergy studies showed that at 24 h, subinhibitory meropenem and ciprofloxacin concentrations of 0.06 to 128 and 0.03 to 32 microg/ml, respectively, showed synergy against 34/51 Pseudomonas aeruginosa strains; subinhibitory concentrations of meropenem (0.06 to 8 microg/ml) and colistin (0.12 to 1 microg/ml) showed synergy against 13 isolates. Subinhibitory meropenem and ciprofloxacin concentrations of 0.25 to 2 and 0.12 to 16 microg/ml, respectively, showed synergy against 18/52 Acinetobacter baumannii strains at 24 h. Subinhibitory meropenem and colistin concentrations of 0.03 to 64 and 0.06 to 8 microg/ml, respectively, showed synergy against 49 strains at 24 h.