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Improved isolation of Vibrio vulnificus from seawater and sediment with cellobiose-colistin agar.

An improved selective medium, cellobiose-colistin (CC) agar, gave a significantly higher (P < 0.05) isolation rate of Vibrio vulnificus from water and sediment samples than did modified cellobiose-polymyxin B-colistin (mCPC) agar. In a total of 446 alkaline peptone water preenrichments amended with polymyxin B, V. vulnificus was isolated from 154 preenrichments (35%) with mCPC agar and from 179 preenrichments (40%) with CC agar. CC agar gave a higher plating efficiency of V. vulnificus cells than did cellobiose-polymyxin B-colistin (CPC) agar, mCPC agar, or thiosulfate-citrate-bile salts-sucrose (TCBS) agar; the only significant difference was observed with TCBS agar, which gave much lower plating efficiencies than the other selective media. Determination of MICs demonstrated that the concentrations of colistin and polymyxin B in CPC agar inhibit growth of a proportion of V. vulnificus strains.

Agar↗

Bronchoconstriction following nebulised colistin in cystic fibrosis.

Nebulised colistin is regularly used as antipseudomonal therapy in children with cystic fibrosis. We assessed bronchoconstriction in response to nebulised colistin in 58 children. Nebulised colistin significantly reduced FEV(1), MEF(25%), and SaO(2) for 15 minutes. In 20 children the reduction was greater than 10% from baseline FEV(1), and was still at that level in five at 30 minutes. Subjective assessment, baseline FEV(1), and serum IgE were unable to identify susceptible children. It is recommended that children receiving colistin should be carefully assessed for bronchoconstriction.

Administration, Inhalation↗

[In vitro interaction between an ampicillin-colistin combination and ampicillin-resistant Escherichia coli].

In this work, the authors studied in vitro potential interactions between bacteria and antibiotics. Colistin and ampicillin were introduced to ampicillin-resistant Escherichia coli and ampicillin activity was measured. Two layers of agar media were used. The lower layer contained E. coli and colistin. The superficial layer was sown with indicating bacteria (ampicillin-sensitive Proteus mirabilis). Ampicillin activity was evaluated on the upper layer with impregnated disks. By this technique, it was ascertained that ampicillin degradation increased with colistin concentration. In this case, colistin may favour interactions of intracellular beta-lactamases on ampicillin.

Ampicillin↗

Effect of aerosolized colistin on multidrug-resistant Pseudomonas aeruginosa in bronchial secretions of patients without cystic fibrosis.

We performed a limited microbiological study to examine the effect of aerosolized colistin (1 million international units every 8 hours) on the colonization of the respiratory tract with Pseudomonas aeruginosa of five intubated, mechanically ventilated patients in the Intensive Care Unit (ICU). No adverse or side effects of the administered aerosolized colistin were reported. The microbial counts of Pseudomonas aeruginosa prior to the use of aerosolized colistin, as well as during the second, fourth, sixth, and eighth day after the use of the drug were measured. The results of this preliminary study suggest that aerosolized colistin was effective in reducing quickly the microbial counts and eliminating microbial growth of Pseudomonas aeruginosa by the sixth day of use in all studied patients.

Administration, Inhalation↗

Colistin stimulates the activity of neutrophil elastase and Pseudomonas aeruginosa elastase.

Nonantimicrobial effects of antibiotics may contribute to their activity in the treatment of infective airway disease. The aim of this study was to identify antibiotics used for the treatment of infection in cystic fibrosis that may alter the activity of human neutrophil elastase (HNE) and Pseudomonas aeruginosa elastase (PE). The effect of antibiotics on the activity of purified HNE and PE, and HNE in sputum was assessed using colourimetric and fluorescent substrate assays by kinetic measurements, and by examining the interaction of HNE with inhibitors. Ceftazidime, tobramycin, and gentamycin slightly inhibited purified HNE activity whereas erythromycin and colistin significantly stimulated purified HNE and PE (395 and 557%, respectively). However, only colistin increased HNE activity in sputum (+102%) and was therefore studied in more detail. This increase in activity was not due an interference with the specific inhibition of HNE by alpha1-antitrypsin but colistin was found to reverse the inhibitory effects of small molecular weight molecules like heparin. Colistin increases the activity of human neutrophil elastase and Pseudomonas aeruginosa elastase, two proteases that contribute to the pathogenesis of cystic fibrosis airway disease.

Adolescent↗

A randomised clinical trial of nebulised tobramycin or colistin in cystic fibrosis.

Chronic infection with Pseudomonas aeruginosa is associated with progressive deterioration in lung function in cystic fibrosis (CF) patients. The purpose of this trial was to assess the efficacy and safety of tobramycin nebuliser solution (TNS) and nebulised colistin in CF patients chronically infected with P. aeruginosa. One-hundred and fifteen patients, aged > or = 6 yrs, were randomised to receive either TNS or colistin, twice daily for 4 weeks. The primary end point was an evaluation of the relative change in lung function from baseline, as measured by forced expiratory volume in one second % predicted. Secondary end points included changes in sputum P. aeruginosa density, tobramycin/colistin minimum inhibitory concentrations and safety assessments. TNS produced a mean 6.7% improvement in lung function (p=0.006), whilst there was no significant improvement in the colistin-treated patients (mean change 0.37%). Both nebulised antibiotic regimens produced a significant decrease in the sputum P. aeruginosa density, and there was no development of highly resistant strains over the course of the study. The safety profile for both nebulised antibiotics was good. Tobramycin nebuliser solution significantly improved lung function of patients with cystic fibrosis chronically infected with Pseudomonas aeruginosa, but colistin did not, in this study of 1-month's duration. Both treatments reduced the bacterial load.

Administration, Inhalation↗

Polymyxin B sulfate and colistin: old antibiotics for emerging multiresistant gram-negative bacteria.

BACKGROUND: Polymyxin B sulfate and colistin, also known as colistimethate, have not been used for many years because less toxic antimicrobials are available. Gram-negative bacteria that are resistant to the aminoglycosides, beta-lactams, and fluoroquinolones are becoming more common. These bacteria are often susceptible to the polymyxins. OBJECTIVE: To present a review of the chemistry, antibacterial spectrum, dosing, pharmacokinetics, toxicity, and indications for polymyxin B sulfate and colistin. DATA SOURCE: A MEDLINE search (1966-1998) of the English-language literature was performed to identify primary literature on the polymyxins. Older citations ( 1949-1965) were identified through the bibliographies of these articles. STUDY SELECTION: All available reports of in vitro antibacterial activity, animal and clinical trials, and case reports were reviewed. DATA SYNTHESIS: The polymyxins are amphipathic molecules that interact with lipopolysaccharide in the bacterial outer membrane. They have potent antiendotoxic properties and antibacterial activity against Pseudomonas aeruginosa and many of the Enterobacteriaceae. Polymyxin B and colistin are usually given at a dose of 1.5-2.5 and 5 mg/kg/d, respectively, in two divided doses. Dosing must be altered in renal failure since the kidney is the primary route of elimination. Distribution into pleural fluid, joints, and cerebrospinal fluid is poor. Toxic effects involve the kidney and central nervous system. The polymyxins are recommended for serious systemic infections caused by gram-negative bacteria that are resistant to other agents. CONCLUSIONS: Polymyxin B sulfate and colistin have a role in the therapy of multidrug-resistant gram-negative bacterial infections.

Anti-Bacterial Agents↗

Safety and tolerability of bolus intravenous colistin in acute respiratory exacerbations in adults with cystic fibrosis.

OBJECTIVE: To assess the safety and tolerability of bolus intravenous doses of colistin during acute respiratory exacerbations in adults with cystic fibrosis and chronic Pseudomonas aeruginosa infection. METHODS: Twelve patients with acute exacerbations of cystic fibrosis were enrolled in a Phase I open-label study. On day 1, patients received three doses of colistin 2 mega-units (160 mg), reconstituted in 50 mL of NaCl 0.9%, by infusion over 30 minutes three times daily. On days 2, 3, and 4, the same dose of colistin was administered by bolus injection three times a day over five minutes after reconstitution in 20, 15, and 10 mL of NaCl 0.9%, respectively. The injection was given by a nurse or physician using a hand-held syringe. If the latter dose was tolerated, it was continued for the remaining eight days of the study. If any dose was not tolerated, treatment reverted to the previously tolerated concentration, which was continued throughout the remainder of the study. RESULTS: No serious adverse events occurred during the course of the trial. Patients without total indwelling venous access systems experienced mild to moderate injection pain. There were no clinically significant changes in renal function. CONCLUSIONS: This study indicates that the administration of bolus intravenous colistin as 2 mega-units (160 mg) in 10 mL of NaCl 0.9% three times a day is safe. It is well-tolerated by patients with total indwelling venous access systems.

Adult↗

Combinations of antimicrobial agents. I. The in vitro sensitivity of 100 strains of Pseudomonas aeruginosa to polymyxin B, colistin, carbenicillin, gentamicin and doxycycline and to various combinations of these antibiotics.

The MICs for 100 strains of Pseudomonas aeruginosa were determined for polymyxin B, colistin, carbenicillin, gentamicin and doxycycline and various combinations of these antibiotics. This study was carried out by means of a tube dilution method. Additive actions were observed in the combinations of polymyxin B plus carbenicillin, polymyxin B plus gentamicin, polymyxin B plus doxycycline, carbenicillin plus doxycycline and gentamicin plus doxycycline. A synergistic action was observed for the combinations of colistin plus carbenicillin, colistin plus gentamicin, colistin plus doxycycline and carbenicillin plus gentamicin. In none of the combinations was any antagonistic action encountered. Numerous reasons for using combined antibiotic treatment are listed. The results were obtained exclusively in in vitro investigations.

Carbenicillin↗

Mechanism of colistin-induced neuromuscular depression.

The effect of a high concentration of the antibiotic colistin sulfate on neuromuscular transmission was examined by recording intracellularly from rat diaphragm blocked with tubocurarine chloride. The presynaptic effect of colistin was different from that of neomycin sulfate, which reduces the probability of acetylcholine release: Colistin reduced that the quantum content of the initial and the last 20 end-plate potentials of a train of 40 stimuli without altering the probability of acetylcholine release. The quantum size was reduced, while the frequency of miniature end-plate potentials was unchanged.

Animals↗

Analysis of colistin sulfate by capillary zone electrophoresis with cyclodextrins as additive.

A method for the quantitative analysis of colistin sulfate by capillary zone electrophoresis is described. Since colistin components have five free amino groups, they tend to adsorb onto the capillary wall and cause peak tailing. It was found that triethanolamine (TEA)-phosphate buffer at pH 2.5 was useful to reduce such adsorption. Methyl-beta-cyclodextrin (M-beta-CD) and 2-propanol (IPA) were found necessary for selectivity enhancement. In order to optimize the separation parameters and predict the method robustness, a central composite design was performed including three variables, namely concentration of M-beta-CD, TEA, and IPA. The effects of capillary length and applied voltage on separation were also investigated. The optimal conditions established were: 140 mM TEA-phosphate buffer containing 5 mM M-beta-CD and 6% v/v IPA, a capillary with 55 cm total length (50 microm inner diameter, 47 cm from inlet to detection window) and 24 kV applied voltage. The method was found to be robust when the variables were changed in the following range: 4-6 mM M-beta-CD, 5-7% v/v IPA, and 130-150 mM TEA. Further, the linearity, limit of detection (LOD), and limit of quantitation (LOQ), as well as repeatability for both colistin A and B were examined and three commercial samples were quantitatively analyzed.

1-Propanol↗

Reliability of the colistin disk test in identification of Serratia marcescens and Serratia liquefaciens.

Resistance to polymycin B or E (colistin) in the disk test, which is used as a means of identification, was tested in 43 strains of Serratia marcescens and 26 of Serratia liquefaciens. While all strains had MIC values greater than 32 mg/l for colistin, false susceptibility to both polymyxins was encountered in the 24 h disk test in 9% of Serratia marcescens and 12-96% of Serratia liquefaciens strains, depending on the kind of polymyxin, temperature and duration of incubation. Using colistin disks and incubation at 25 degrees C for 48 h, the percentage of false susceptible results could be minimized.

Colistin↗

Residue determination of two co-administered antibacterial agents--cephalexin and colistin--in calf tissues using high-performance liquid chromatography and microbiological methods.

Residues of two antibacterial agents, cephalexin and colistin, co-administered by intramuscular injection to calves, were quantified in four different tissues (muscle, fat, liver and kidney) by column switching HPLC and by a microbiological method. For cephalexin assay, tissue samples with cephradin as internal standard were homogenized in a 5% trichloroacetic acid solution and filtrates were injected onto a concentration precolumn filled with LiChroprep RP-18 (25-40 microns). A clean-up step was incorporated by flowing a mobile phase (methanol-0.01 M phosphate buffer (pH 3.0); 15:85, v/v) through the enrichment column before elution on a LiChrospher RP-18e (5 microns) column with a methanol-phosphate buffer (30:70, v/v) at a flow rate of 1 ml min-1. Spectrometric detection was at 260 nm. An additional "off-line" washing step of extracts with methylene chloride was operated to achieve higher selectivity in the case of liver and kidney samples. The limit for quantitative assay was 0.045 micrograms g-1 with relative standard deviations in the range 5-8% and recoveries within 70%. For microbiological assay of colistin, samples were homogenized in 0.1 M hydrochloric acid-acetonitrile mixtures (3:1, v/v, for kidney and liver; 3:2, v/v, for fat and muscle). The supernatants were assayed by the cylinder plate method after evaporation to dryness under vacuum. Bordetella bronchiseptica ATCC 4617 was chosen as test organism. After a 3-h diffusion step at room temperature, the medium was incubated at 37 degrees C for 18 h and then the diameter of the growth inhibition zones was measured. Sensitivity reached 0.10-0.15 micrograms g-1. Results from the analysed samples over a 7-28 day period after drug administration show that no cephalexin was found at concentrations higher than the quantitation limit in the four test tissues and that colistin was found in muscle (injection site only) for 15 days and in kidney for 21 days.

Adipose Tissue↗

Selective oral antimicrobial prophylaxis for the prevention of infection in acute leukaemia-ciprofloxacin versus co-trimoxazole plus colistin. The EORTC-Gnotobiotic Project Group.

230 leukaemic patients were entered into a randomised, prospective, multicentre trial of either ciprofloxacin (1 g/day) or co-trimoxazole (1920 mg/day) plus colistin (800 mg/day) for the prevention of infection during granulocytopenia. Bacteraemia due to resistant gram-negative rods occurred only in the co-trimoxazole-colistin group though both regimens were effective for selective gastrointestinal tract decontamination. However, there were fewer patients without any infective complications (31% vs. 18%: P = 0.02), fewer febrile days [mean (S.D.) 5.9 (1.1) vs. 8.2 (1.4): P = 0.0242], a lower proportion of infective events (0.9 (0.16) vs. 1.2 (0.18): P = 0.005) and fever occurred later (median 19 vs. 14 days: 0.025 less than P less than 0.05) in the co-trimoxazole-colistin group. The choice of prophylactic regimen therefore appears to depend upon whether or not protection against gram-negative infection is required or better systemic prophylaxis overall.

Administration, Oral↗

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.

Acinetobacter baumannii↗

Susceptibility of the Acinetobacter calcoaceticus-A. baumannii complex to imipenem, meropenem, sulbactam and colistin.

The Acinetobacter calcoaceticus-Acinetobacter baumannii complex includes some of the most clinically relevant species of the genus Acinetobacter due to their capacity to cause epidemic nosocomial outbreaks as well as their increasing resistance to antibiotics. Susceptibility of Acinetobacter strains varies greatly depending on origin, thus highlighting the importance of local analyses of susceptibility profiles. Two hundred twenty-one strains of the A. calcoaceticus-A. baumannii complex were identified using biochemical tests and were biotyped. Strain susceptibility to imipenem, meropenem, colistin and sulbactam was studied using agar dilution. Eight different biotypes were found, type 1 accounting for 69.2% of the strains. MIC(50) and MIC(90) to imipenem, meropenem, colistin and sulbactam were 4 and 8 mg/l, 16 and 32 mg/l, 0.5 and 1mg/l, and 8 and 16 mg/l, with susceptibility rates of 64.3, 22.6, 98.2 and 73.8%, respectively. Biotype 1 was the most resistant. A statistically significant difference was observed for the mean MIC of the four predominant biotypes to imipenem, meropenem and sulbactam but not to colistin.

Acinetobacter↗

Evaluation of colistin as an agent against multi-resistant Gram-negative bacteria.

Infections caused by multi-resistant Gram-negative bacteria, particularly Pseudomonas aeruginosa, are increasing worldwide. In patients with cystic fibrosis (CF), resistance in P. aeruginosa to numerous anti-pseudomonal agents is becoming common. The absence since 1995, of new substances active against resistant Gram-negative bacteria, has caused increasing concern. Colistin, an old antibiotic also known as polymyxin E, has attracted more interest recently because of its significant activity against multi-resistant P. aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae, and the low resistance rates to it. Because its use as an anti-pseudomonal agent was displaced by the potentially less toxic aminoglycosides in 1970s, our knowledge of this drug is limited. However, there has been a significant recent increase in the data gathered on colistin, focussing on its chemistry, antibacterial activity, mechanism of action and resistance, pharmacokinetics, pharmacodynamics and new clinical application. It is likely that colistin will be an important antimicrobial option against multi-resistant Gram-negative bacteria, for some years to come.

Acinetobacter baumannii↗

Liquid chromatography-ion trap tandem mass spectrometry for the characterization of polypeptide antibiotics of the colistin series in commercial samples.

A selective reversed-phase liquid chromatography-tandem mass spectrometry method is described for the characterization of related substances in the colistin complex. Mass spectral data were acquired on an LCQ ion trap mass spectrometer equipped with an electrospray ionization probe operated in the positive ion mode. The main advantage of this technique is the characterization of novel related substances without time-consuming isolation and purification procedures. Using this method seven new related substances were partially identified in colistin bulk sample and tablets. Four components were assigned as isomers of the main components of colistin.

Anti-Bacterial Agents↗