Emergence of mcr-1 conferred colistin resistance among bacterial isolates from urban sewage water in India

Increased use of colistin, a last resort drug due to failure of carbapenems, has possibly contributed in development and spread of resistance to colistin among Enterobacteriaceae. The colistin belongs to the family of polymyxins, cationic polypeptides, with broad-spectrum activity against Gram-negative bacteria. In this study, we obtained 253 non-duplicate bacterial isolates from sewage water in Delhi and phenotypically screened for colistin resistance. Of the 47 positive isolates, the colistin resistance gene mcr-1 was detected among 5 isolates. Based on 16S ribosomal RNA-based identification, bacterial isolates were found to be Escherichia coli, Aeromonas veronii, and Aeromonas dhakensis. Extended spectrum β-lactamases (ESBL)-resistant determinants CTX-M and TEM were detected in all five mcr-1 positive isolates. On the basis of literature survey, this is the first report of mcr-1 gene from Aeromonas veronii and Aeromonas dhakensis worldwide. Furthermore, mcr-1 gene has not been reported earlier from sewage water in India. Antibiotic susceptibility test of all five isolates against 9 different classes of drugs revealed multidrug-resistant phenotype with high minimum inhibitory concentration values. In vitro transconjugation studies showed successful transfer of mcr-1 and other ESBL-resistant determinants. The occurrence of colistin resistance phenotype conferred by plasmid-based mcr-1 gene in the environment and an ever-increasing list of bacterial isolates is a cause of concern. A comprehensive survey of different water bodies and epidemiological studies are required to assess the risk of dissemination of resistance determinants.

Association of colistin residues and manure treatment with the abundance of mcr-1 gene in swine feedlots

BACKGROUND

The extensive use of colistin in swine production may have contributed to the recent emergence of corresponding mobile resistance gene mcr-1. The use of colistin as a feed additive was banned in China in April 2017.

OBJECTIVES

To examine the occurrence of colistin and dissemination of mcr-1 in swine feedlots before and after the colistin ban and effects of different manure treatments.

METHODS

Environmental samples were collected from swine feedlots before (December 2016) and after (December 2017) the colistin ban. Colistin concentrations were determined by ultra-high performance liquid chromatography coupled to tandem mass spectrometry. The prevalence of mcr-1 were determined by quantitative PCR analysis, while bacterial community composition was investigated by 16S rRNA sequencing.

RESULTS

In 2016, colistin was detected in feed and fresh manure samples at 67 mg/kg and 17 mg/kg, respectively, but was absent from all samples in 2017. In 2016, the relative abundance of mcr-1 in fresh manure was lower than that in solid samples after natural drying, while a higher relative abundance was detected in fresh manure samples compared with biogas slurry samples. A strong correlation between colistin concentration and relative abundance of mcr-1 was observed in fresh manure. The samples collected in 2017 showed a lower relative abundance of mcr-1 compared with those collected in 2016. Bacterial community analysis showed that the abundance of Enterobacteriaceae, which act as a vehicle and reservoir of mcr-1, increased with natural dying but decreased with anaerobic digestion.

CONCLUSIONS

The presence of colistin exerts direct selection pressure for the accumulation of mcr-1 in manure, while the ban on colistin likely halted the dissemination of mcr-1 on pig farms. Anaerobic digestion is an effective waste treatment process for removing mcr-1, which might be mainly driven by the shift in bacterial community structure.

Validation of a colistin plasma concentration breakpoint as a predictor of nephrotoxicity in patients treated with colistin methanesulfonate

Nephrotoxicity limits the effective use of colistin for the treatment of multidrug-resistant Gram-negative bacteria (MDR-GNB) infections. We previously defined a steady-state colistin plasma concentration (C_ss) of 2.42 mg/L that predicted nephrotoxicity at end of treatment (EOT). The objective of this study was to validate this breakpoint in a prospective cohort. This was a multicentre, prospective, observational study conducted at three hospitals with a cohort of patients treated for MDR-GNB infection with colistin methanesulfonate from September 2011 until January 2015. Nephrotoxicity was evaluated at Day 7 and at EOT using the RIFLE criteria. C_ss values were measured and analysed using HPLC. Taking the previously defined breakpoint for colistin concentration as a criterion, patients were divided into two groups (C_ss, ≤2.42 mg/L vs. >2.42 mg/L). Sixty-four patients were included. Seven patients (10.9%) had a C_ss > 2.42 mg/L and were compared with the remaining patients. Bivariate analysis showed that patients with a C_ss > 2.42 mg/L were older and had a significantly higher incidence of nephrotoxicity at Day 7 and EOT. Although not statistically significant, nephrotoxicity occurred earlier in these patients (6.2 days vs. 9.2 days in patients with lower C_ss; P = 0.091). Multivariate analysis of nephrotoxicity showed that C_ss > 2.42 mg/L was the only predictive factor. Nephrotoxicity was more frequent and occurred earlier in patients with colistin plasma concentrations higher than the previously defined breakpoint (2.42 mg/L). Colistin therapeutic drug monitoring should be routinely considered to avoid reaching this toxicity threshold and potential clinical consequences.

Analysis and behavior of colistin during anaerobic fermentation

A new analytical method for the determination of colistin in fermenter samples was developed followed by a study on the behavior of this substance during anaerobic fermentation. Analysis of colistin A and B was carried out by liquid chromatography-tandem mass spectrometry. Separation of the analytes was performed on a Security Guard column (4×3mm). Fourteen fermentation tests in batch as well as in continuous reactors were carried out. After 44days of anaerobic digestion of cattle manure, initially spiked with 500mg/kg of colistin sulfate, a considerable decrease of the colistin concentration to less than 1mg/kg could be observed. Furthermore, the daily production of biogas and methane was measured. A correlation between gas production and colistin concentration could not be determined. However, an increase of 10% of the cumulative methane production was observed in those fermenters spiked with an initial bolus of 500mg/kg colistin.

Physicochemical compatibility of nebulizable drug admixtures containing budesonide and colistimethate or hypertonic saline

Knowledge of the physicochemical compatibility of admixtures of nebulizable drugs is an important issue. In this article, the results of our recent study dealing with the compatibility of drug admixtures containing budesonide and colistin methanesulfonate (brand name Colistin CF) or budesonide and 5.85% sodium chloride solution are presented, as well as the up-to-date version of our compatibility table. Admixtures were prepared by mixing 2.0 mL Pulmicort either with 3.0 mL Colistin CF or 4.0 mL 5.85% sodium chloride solution. Test solutions were stored for 24 hours at room temperature under ambient light conditions. Physical compatibility was determined by measuring pH and osmolality. Concentrations of budesonide were measured by a high-performance liquid chromatography assay. The antibiotic activity of colistin methanesulfonate was determined in comparison to standard solutions using a microbiological assay. No loss in drug concentration of budesonide and no change in antibiotic activity of colistin methanesulfonate were detected over a test period of 24 hours. Osmolality remained unchanged in both types of admixtures. In admixtures of budesonide with colistin methanesulfonate, pH increased during the first 4 hours of storage, while in admixtures of budesonide and hypertonic saline pH remained unchanged. No visible changes could be detected. Due to these results admixtures of budesonide and colistin methanesulfonate or 5.85% sodium chloride solution are designated to be compatible, but it is recommended that mixing should take place immediately before administration. Further investigations are needed to determine whether or not drug delivery is affected by mixing the drugs and to ensure simultaneous nebulization is recommendable.

[Determination of polymyxin E1 and polymyxin E2 in polymyxin E sulfate using micellar electrokinetic capillary chromatography]

A method of micellar electrokinetic chromatography capillary (MECC) has been established for separating polymyxins E1 and E2 in polymyxin E sulfate and determining the contents of E1 and E2. Several factors including the running voltage, the type of surfactant, concentrations of Brij-35 (polyoxyethylene glycol dodecyl ether), NaCl solution and acetonitrile, pH of phosphate were investigated. Under the optimum conditions (10 kV running voltage, phosphate buffer solution (0.01 mol/L, pH 4.1) containing 30 mmol/L Brij-35, 5% (v/v) acetonitrile, 0.167 mol/L NaCl), E1 and E2 were separated with the resolution of 1.94. The contents of E1 and E2 in polymyxin E sulfate were 67% and 32%, respectively. As an example, the relative standard deviations of the intra-assay and inter-assay of polymyxin E1 on the plate number and peak area were less than 5%. The method is simple, rapid, accurate, and reproducible.

Application of a validated method in the stability study of colistin sulfate and methylparaben in a veterinary suspension formulation by high-performance liquid chromatography with a diode array detector

A methodology following International Cooperation on Harmonization for Veterinary Products (VICH) guidelines for the stability evaluation of colistin sulfate in a nonaqueous suspension pharmaceutical dosage form for veterinary use (via their drinking water) is described. This method monitors the percentage of colistin sulfate during the stability study of the preparation in drinking water and establishes the shelf life of the final product by a new high-performance liquid chromatography method which was developed and validated for the simultaneous determination of colistin sulfate [colistin A (Polymixin E1) and colistin B (Polymixin E2)] and methylparaben (Nipagin) using a diode array detector (DAD). The method uses a Kromasil C18 column and isocratic elution. The mobile phase consisted of an acetonitrile-sodium sulfate anhydrous solution (25 + 75) pumped at a flow rate of 1.5 mL/min. The DAD was set at 215 nm. The validation study was carried out according to the VICH guidelines in order to prove that the new analytical method meets the reliability characteristics, which include the fundamental criteria for validation: selectivity, linearity, precision, accuracy, and sensitivity. The method was applied during the quality control or stability studies of the suspension dosage form in order to quantify the drug (colistin) and preservative, and proved to be suitable for rapid and reliable quality control.

Detection of residual bacitracin A, colistin A, and colistin B in milk and animal tissues by liquid chromatography tandem mass spectrometry

Liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS) was applied to the determination of residual bacitracin A, colistin A, and colistin B in milk and animal tissue samples. Prior to instrumental analysis, samples were subjected to acid extraction followed by solid-phase cleanup using Strata-X cartridges. Mass spectral acquisitions were performed under selective multiple reaction monitoring (MRM) mode at m/z 199 and 670 from triply charged precursors of bacitracin A (m/z 475); m/z 385 and 379 from triply charged precursors of colistin A (m/z 391); and m/z 380 and 374 from triply charged precursors of colistin B (m/z 386). Method precision was evaluated from spike recovery of samples fortified at concentrations corresponding to 2/5 of the maximum residue limits (MRLs) for each of the analytes under study. Intra-day and inter-day variations were found to range from 90.9 to 104% with relative standard deviation (RSD) <6.5%, and from 90.1 to 106% with RSD <9.1%, respectively. Limits of quantification (LOQs) were defined as the spiking concentrations at 2/5 MRL, and limits of detection (LODs) were 10-47 microg kg(-1) for bacitracin A, 1-16 microg kg(-1) for colistin A, and 6-14 microg kg(-1) for colistin B in milk and animal tissues. The presented method has good precision and high sensitivity and was applied as a fast screening protocol and a quantitative tool for monitoring of the concerned polypeptides in foods as part of a surveillance program.

Dynamic ultrasound-assisted extraction of colistin from feeds with on-line pre-column derivatization and liquid chromatography-fluorimetric detection

A dynamic ultrasound-assisted extraction (UAE) method with on-line pre-column derivatization/high performance liquid chromatography (HPLC) and fluorimetric detection is proposed for the analysis of colistin in feed. A flow injection manifold is used for the development of the extraction and derivatization steps and for interfacing them with the separation/detection step, thus providing an on-line approach with the advantage of minimum sample handling. The derivatization was performed with ortho-phthaldialdehyde and 2-mercaptoethanol. The optimum conditions for colistin extraction and formation of the fluorescent derivative have been obtained by experimental design methodology. The use of a high-intensity probe sonication makes UAE an expeditious (7 min versus > 1 h) and efficient (93.1-98.2% versus 87.5-94% of recovery) alternative as compared with extraction using an ultrasonic bath. The within-laboratory reproducibility and repeatability, expressed as percentage of relative standard deviation, were 5.2 and 5.8, respectively.

Hyphenation of liquid chromatography to ion trap mass spectrometry to identify minor components in polypeptide antibiotics

The application of liquid chromatography-ion trap mass spectrometry for the characterization of linear and cyclic polypeptide antibiotics was investigated. The aim was on-line identification of impurities in those antibiotic complexes without recourse to time-consuming isolation and purification procedures. Hyphenated techniques, such as liquid chromatography coupled to mass spectrometry, are ideally suited for this purpose. Characterization was performed with an ion trap mass spectrometer offering MS(n) capability; this enables more structural information to be obtained. Liquid chromatography in combination with ion trap mass spectrometry was successfully applied for the characterization of impurities in gramicidin, polymyxin B, polymyxin E, and bacitracin and the study of the degradation products of polymyxins B and E.

Use of high-performance liquid chromatography to study the pharmacokinetics of colistin sulfate in rats following intravenous administration

The pharmacokinetics of colistin was investigated using specific high-performance liquid chromatography (HPLC) to measure the concentrations of colistin and colistin A and B in plasma and urine in five rats after administration of an intravenous bolus of 1 mg of colistin sulfate/kg of body weight. There were differences in the pharmacokinetic behaviors of unbound colistin A and B. This is the first report of the use of HPLC to study the pharmacokinetics of colistin and its two major components.

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.

Hyphenated liquid chromatographic method for the determination of colistin residues in bovine tissues

A selective and sensitive high-performance liquid chromatographic (HPLC) method has been developed for the measurement of colistin residues in milk and in four bovine tissues (i.e., muscle, liver, kidney, and fat). The sample treatment consists of protein precipitation using 10% (w/v) trichloroacetic acid, solid-phase purification on C18 cartridges, and precolumn derivatization of colistin with ortho-phthalaldehyde and 2-mercaptoethanol in borate buffer (pH 10.5). This latter step is performed automatically, and the resulting reaction mixture is injected into a switching HPLC system including a precolumn and an analytical column packed with end-capped LiChrospher RP18 (5 microns). Washing the precolumn and final elution onto the analytical column are conducted using acetonitrile-0.01M phosphate buffer (pH 7.0) mixtures with respective proportions of 65:35 and 68:32 (v/v). Detection is carried out by spectrofluorometry (excitation wavelength, 340 nm; emission wavelength, 440 nm). The retention times of the derivatives corresponding to the two main components of colistin (i.e., polymyxins E2 and E1) are approximately 14 and 18 min, respectively. The structural study of the derivatives corresponding to polymyxins E1 and E2 is carried out by HPLC coupled with electrospray mass spectrometry; data obtained confirms that the derivatization process occurs with the five amino groups of the analytes. Selectivity is obtained in the HPLC system versus other coadministered anti-infective drugs (beta-lactams, aminoglycosides, tetracyclines, and sulphonamides) and endogenous compounds. Quantitation is performed using the sum of the peak areas of polymyxin E1 and polymyxin E2 derivatives. Testing linearity affords correlation coefficients greater than 0.990 for calibration curves in the range of 10-500 microL/L for milk, 50-1000 micrograms/kg for muscle and fat, and 100-1000 micrograms/kg for kidney and liver. Relative standard deviation values are less than 10% at a concentration of 25 micrograms/L in milk and 100 micrograms/kg in tissues (six replicates); recoveries are higher than 60%.

Depletion of the residues of colistin and amoxicillin in turkeys following simultaneous subcutaneous administration

The tissue distribution and depletion of colistin and amoxicillin were studied in 84 turkeys dosed subcutaneously on 4 consecutive days with a formulation containing the two drugs at 0.2 ml/kg per day, corresponding to 50 000 IU of colistin sulphate/kg and 20 mg of amoxicillin trihydrate/kg. All the turkeys were killed 1-30 days after the final dose and samples of muscle, liver, kidney and cutaneous-subcutaneous tissues and of the injection site were taken for analysis for colistin and amoxicillin residues. The colistin concentrations in the liver (117.5 +/- 26.0 ng/g) and cutaneous-subcutaneous tissue (100.0 +/- 35.6 ng/g) were higher than those in kidney (92.0 +/- 34.4 ng/g) or muscle (67.5 +/- 16.9 ng/g) 1 day after the final dose. The concentration of this drug then increased for 9-14 days, followed by a slow decrease. The antibiotic was still present at low concentrations in the kidneys of all the treated birds and in the livers of two turkeys 30 days after the end of treatment. Amoxicillin concentrations were greatest in muscle (389.2 +/- 195.0 ng/g) and at the injection sites (440.3 +/- 213.9 ng/g) 1 day after treatment ceased, with a subsequent rapid decline. This drug was undetectable in the livers and kidneys by 10 days after dosing ceased.

Depletion of colistin in eggs following medication of laying hens

The depletion of colistin in eggs was determined separately for the albumen, the yolk and the whole egg after oral and intramuscular administrations of colistin sulphate. Residues were assayed by an agar plate diffusion method with Bordetella bronchoseptica ATCC 4617 as test organism. Colistin residues were not detected after drug administration by the oral route, but could be detected in the yolk until eight days after intramuscular injection. The total amount excreted represented 0.9% of the dose applied.

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.

Variations in the density of bone cement after centrifugation

Barium sulfate added to bone cement to provide radiopacity has a density about four times greater than that of polymerized radiolucent bone cement. Because centrifugation might make a clinically significant change in the distribution of barium sulfate, this process was studied. Radiolucent and radiopaque Simplex-P bone cement (Howmedica, Inc., Rutherford, New Jersey) were mixed with and without cooling and centrifuged for two or four minutes at 2,000 g or 1,000 g (gravity acceleration). The density of sections of the hardened bone cement was measured using the Archimedes principle. Erythromycin and colistin were added to cement batches to test whether or not centrifugation affected the distribution of antibiotics. Direct and radiographic observation and density measurements (cooled specimens, 2,000 g, p less than 0.01) verified that barium sulfate does accumulate at the bottom of the centrifugation tubes. Thin sections of the bone cement revealed that only larger particles (20-100 micron) of barium sulfate were deposited at the bottom. No evidence of redistribution of antibiotics after centrifugation was seen. It is recommended that Simplex-P bone cement be reformulated to eliminate concern about inhomogeneities that arise from centrifugation. Further, it is recommended that cooled, centrifuged antibiotic cement be used for long-stem revision hip surgery, where longer setting times are necessary, and room temperature cement for "fresh" hip surgery. A total centrifuge time of two minutes with a 2,000 g maximum force is recommended.

Sensitive enzyme immunoassay of colistin and its application to detect residual colistin in rainbow trout tissue

An antibody against colistin (CL), an antibiotic effective for gram-negative bacteria, was produced in rabbits immunized with a colistin-protein conjugate. The conjugate was prepared by a novel and convenient procedure devised to couple an amino group of CL to thiol groups of bovine serum albumin (BSA) introduced by thiol exchange reduction of its disulfide bonds with dithiothreitol, using N-(m-maleimidobenzoyloxy)succinimide (MBS) as a cross-linker. Enzyme labeling of CL with beta-D-galactosidase was performed by utilizing another cross-linker, N-(gamma-maleimidobutyryloxy)succinimide, by means of a convenient labeling method. A double antibody enzyme immunoassay of CL, which could determine as little as 30 ng/mL of CL, was developed using labeled CL and anti-CL antiserum. With this assay, drug levels were easily determined in fish tissue after CL administration. The enzyme immunoassay should provide a useful tool for detection and quantitation of residual drugs in foods and related products.

A sodium-containing polymyxin derived from polymyxin-complex during chromatography

Commercial colistin (polymyxin E)-complex was separated into two major components (colistins A and B) on a preparative scale by HPLC (alkyl bonded silica and aqueous-organic mobile phase containing 0.2 M NaCl-HCl buffer (pH 2.0]. Desalting of the colistins A and B fractions was completed by reversed-phase adsorption and elution using methyl alcohol. In these experiments, it was inadvertently found that prolonged elution with water gave two hydrophilic peptides, which were tentatively named colistins AH and BH, respectively. Further elution with methyl alcohol produced two lipophilic peptides which were named colistins AL and BL. Colistin BH showed higher potency than colistin AH, AL or BL, and it was also effective in vivo. The fatty acid and amino acid composition of colistin BH was identical with that of colistin BL, but colistin BH contained a relatively large amount of nonionic sodium which scarcely responded to the sodium ion-selective electrode of an ion meter; colistin BH had a slightly lower molar extinction coefficient than the colistin BL which contained negligible amount of nonionic sodium. Colistin AH also contained nonionic sodium. Potassium containing colistins could also be derived from colistin-complex. These compounds could not be formed merely by adding sodium chloride or potassium chloride to colistin-complex solution. To obtain the sodium-containing compounds, contact with some hydrophobic stationary phase, such as alkyl-bonded silica or styrene-divinylbenzene copolymer, was necessary. It is postulated that one of the antibacterial mechanisms of polymyxin is associated with its complex-forming action on monovalent cations after contact with the lipid layer of the bacterial outer membrane.

A new model of bone infection used to evaluate the efficacy of antibiotic-impregnated polymethylmethacrylate cement

An animal model of bone infection was designed for evaluation of the benefits of adding antibiotics to polymethylmethacrylate (PMMA) cement. Femora of New Zealand albino rabbits were exposed at the knee; the medullary canals were entered and the contents aspirated. A known number of bacteria was added to each femur before it was filled with either normal Surgical Simplex P bone cement or Surgical Simplex P antibiotic bone cement. The presence or absence of bone infection was documented by quantitative bacteriologic, roentgenographic, and histologic techniques. Simplex antibiotic bone cement prevented infection, even in the presence of 10(7) bacteria. The effectiveness of the antibiotic bone cement was correlated with the rapid release of high levels of erythromycin (14.1 micrograms/g) and colistin (11.3 micrograms/g) specifically at the site of bacterial contamination.

A method for separating commercial colistin complex into new components: colistins pro-A, pro-B and pro-C

Commercial colistin was separated into three major components as well as lipid components by reversed phase adsorption chromatography on Diaion HP-20 AG, a macroreticular styrene-divinylbenzene copolymer, without any inorganic salts or detergents, in aqueous-organic solvent as mobile phase. These expected components were colistins A, B and C; there were, however, appreciable differences between these components and colistins A, B and C, isolated by countercurrent distribution. The newly isolated components showed slightly higher potency than colistins A, B and C; their molecular weights, as determined by gel permeation chromatography of 2,4-dinitrophenyl derivatives on TSK-GEL G2000H (mobile phase: dimethylformamide), were also slightly higher. Accordingly, they were tentatively named colistins pro-A, pro-B and pro-C. During purification by countercurrent distribution (solvent system: sec-BuOH - n-BuOH - 0.1 N HCl, 30:6:40), colistin pro-A was converted to colistin A. Similarly, colistin pro-B was converted to colistin B, and colistin pro-C to colistin C. Therefore, we concluded that colistins A, B and C are artifacts.

Isolation and characterization of three new polymyxins in polymyxins B and E by high-performance liquid chromatography

Two polymyxin antibiotics, polymyxins B and E (colistin), have been separated analytically into ten to thirteen components on a commercial reversed-phase material by isocratic elution with a mixture of acetonitrile, phosphate/formate and acetate buffer containing sodium sulphate and triethylamine. The analytical system was transferred to a preparative system, using a C18-bonded stationary phase, without extensive impairing of the selectivity. The major components of each product were isolated and characterized by high-performance liquid chromatography, amino acid analysis and identification of the fatty acid. Three components were isolated and characterized for the first time. The fatty acid was also identified in some of the minor components.

Improved high-performance liquid chromatographic method for polypeptide antibiotics and its application to study the effects of treatments to reduce microbial levels in bacitracin powder

Improvements were made in the high-performance liquid chromatographic (HPLC) method to obtain baseline separation of chromatographic peaks of structurally similar polypeptide components in bacitracin. The improved method uses a 30-cm-long stainless-stell column packed with muBondapak C18. The theoretical plates of the column are approximately 140,000 per meter for the bacitracin A peak. The resolution function between bacitracins B1 and B2 and that between bacitracins A and B2 have been improved 418 and 225%, respectively. The components of bacitracin, bacitracins A, B, C, D, E, F, and G, were fractionated by the countercurrent distribution technique. These components, together with Compound X, a compound separated on a carboxymethylcellulose column, and bacitracin F, obtained by degrading bacitracin A sample at neutral pH, were used to identify peaks in the HPLC chromatogram. Effects of processing methods used to reduce microbial contamination levels in bacitracin powders were evaluated. Heat treatment caused a significant loss of antimicrobial activity (35% reduction), bacitracins A, B1, and B2 were reduced by 37, 22, and 21%, respectively. A significant increase (2.8 times) of bacitracin F, an oxidative degradation compound, was show. Irradiation by 60Co at 1.8 Mrad caused no loss of potency nor change in any of the bacitracin components. Ethylene oxide treatment, on the other hand, caused considerable (46%) reduction of potency. Substantial reduction of areas under the peak of bacitracins A, B1, and B2 (50, 24 and 37%, respectively) were noted. The chromatograms showed numerous unresolved peaks around bacitracins A, B1 and B2,; however, no significant increase in the bacitracin F peak, nor appearance of non-UV absorbing peaks were observed. Peptide antibiotics of the polymyxin group, circulin, colistin, and polymyxin, were also analyzed using the muBondapak C18 column with a linear-gradient elution. A UV monitor was used for polymyxin. A moving-wire flame ionization detector was used to monitor circulin and colistin. A sample of polymyxin, circulin, and colistin may be analyzed in less than 20 min of chromatographic time.