Polymyxin-B-binding sites in the cochlea as demonstrated by polymyxin-B/gold labeling

A polymyxin-B/bovine-serum-albumin/gold complex was used as a probe to detect the binding sites of polymyxin B on thin sections of cochlea embedded in Spurr's resin. The binding sites were found to be mainly located on the stereocilia, the cuticular plate of hair cells, the head plate of Deiters' cells, the tonofilaments in pillar cells and Deiters' cells, fibrous structures in the spiral limbus, the tectorial membrane and the basilar membrane and neural elements such as nerve endings, fibers, and the myelin sheath. The mitochondria, plasma membrane, and chromatin of the nuclei of the cells observed also exhibited binding. Our results suggest that phospholipids, glycoconjugates, cytoskeletal proteins and nucleic acids are responsible for this binding activity.     

Polymyxin-B-binding sites in the cochlea as demonstrated by polymyxin-B/gold labeling

Summary A polymyxin-B/bovine-serum-albumin/gold complex was used as a probe to detect the binding sites of polymyxin B on thin sections of cochlea embedded in Spurr's resin. The binding sites were found to be mainly located on the stereocilia, the cuticular plate of hair cells, the head plate of Deiters' cells, the tonofilaments in pillar cells and Deiters' cells, fibrous structures in the spiral limbus, the tectorial membrane and the basilar membrane and neural elements such as nerve endings, fibers, and the myelin sheath. The mitochondria, plasma mimbrane, and chromatin of the nuclei of the cells observed also exhibited binding. Our results suggest that phospholipids, glycoconjugates, cytoskeletal proteins and nucleic acids are responsible for this binding activity.     

Effect of antibiotics on the human intestinal flora in mice

Antibiotics used during selective decontamination were studied for their effect on the human intestinal flora in mice. Polymyxin B and neomycin were found to eliminate Escherichia coli from the gastrointestinal tract but did not alter total numbers of obligate anaerobes. Neomycin induced an increase of the percentage of gram-negative obligate anaerobes. Cephradine did not affect the numbers of obligate and facultative anaerobes but increased the percentage of gram-negative obligately anaerobic rods in the flora. The selective effect of polymyxin B and neomycin on the flora is accounted for by a relative insusceptibility of the anaerobic flora as compared with E. coli. Low concentrations of polymyxin B and neomycin were detected in caecal supernatants. This was found to be due to strong binding of both antibiotics to the solid fraction of intestinal contents.     

The functional association of polymyxin B with bacterial lipopolysaccharide is stereospecific: studies on polymyxin B nonapeptide

The Gram-negative bacterial endotoxin lipopolysaccharide (LPS) is a major inducer of sepsis. The natural cyclic peptide polymyxin B (PMB) is a potent antimicrobial agent, albeit highly toxic, by virtue of its capacity to neutralize the devastating effects of LPS. However, the exact mode of association between PMB and LPS is not clear. In this study, we have synthesized polymyxin B nonapeptide, the LPS-binding cyclic domain of PMB, and its enantiomeric analogue and studied several parameters related to their interaction with LPS and their capacity to sensitize Gram-negative bacteria toward hydrophobic antibiotics. The results suggest that whereas the binding of the two enantiomeric peptides to E. coli and to E. coli LPS is rather similar, functional association with the bacterial cell is stereospecific. Thus, the L-enantiomer is capable of synergism with the hydrophobic antimicrobial drugs novobiocin and erythromycin, whereas the D-enantiomer is devoid of such activity. The potential of understanding and consequently utilizing the PMB-LPS association for novel, nontoxic PMB-derived drugs is discussed.     

Outer membrane protein H1 of Pseudomonas aeruginosa: purification of the protein and cloning and nucleotide sequence of the gene.

Overexpression of the divalent cation-regulated outer membrane protein H1 of Pseudomonas aeruginosa is associated with resistance to polymyxin B, aminoglycosides, and EDTA. Protein H1 is believed to act by replacing divalent cations at binding sites on lipopolysaccharide, thereby preventing disruption of the sites and subsequent self-promoted uptake of the antibiotics. Protein H1 purified by two cycles of anion-exchange chromatography was apparently associated with lipopolysaccharide. Lipopolysaccharide-free protein H1 was purified in high yield by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was subjected to N-terminal amino sequencing. Complementary oligodeoxyribonucleotides were used to clone the structural gene for protein H1, oprH, into Escherichia coli. Successful cloning was confirmed by nucleotide sequence analysis. Southern hybridization suggested that oprH was present as a single-copy gene in P. aeruginosa. The deduced amino acid sequence revealed that H1 was a slightly basic polypeptide of 178 residues, with a leader sequence typical of an exported procaryotic protein. It had little similarity, however, to other bacterial surface proteins for which sequence data were available. No expression of protein H1, from its own or the lac promoter, was detected in E. coli. We concluded that, as for some other regulated Pseudomonas genes, expression of oprH, at least under some conditions, is blocked in E. coli.     

Characteristics of lipopolysaccharide interaction with human peripheral-blood monocytes.

The interaction between radioiodinated lipopolysaccharide from Escherichia coli 0111:B4 (125I-LPS) and human peripheral-blood monocytes was studied. The association of 125I-LPS with monocytes at 37 degrees C appeared to depend on binding to the cell membrane with subsequent internalization of the molecule, and was not saturable with time (up to 2 h) or 125I-LPS concentration (up to 10 micrograms/ml). There was no apparent difference in the behaviour of unlabelled LPS and 125I-LPS with respect to monocyte association. 125I-LPS association with monocytes was inhibited by LPS and O-polysaccharide from E. coli 0111:B4 and Salmonella typhi 0901, but not by lipid A or polymyxin B. We propose that the mechanism of human monocyte stimulation by LPS involves polysaccharide-dependent binding to the cell membrane followed by internalization of the LPS molecule. We were unable to demonstrate a specific LPS receptor such as that found on murine B-lymphocytes.     

Effect of polymyxin B on ion permeability of bacterial membranes

Effect of polymyxin B on the movement of K+ and H+ in polymyxin-sensitive cells of E. coli under different metabolic states has been studied. It was shown that polymyxin B induced the efflux of K+, decreased the efflux of H+ and inhibited the consumption of oxygen in bacterial cells. The effect of antibiotic on ion movement was independent of respiratory conditions. It was suggested that polymyxin B increased ion permeability and destroyed lipid-protein interactions of the respiratory chain simultaneously.     

Binding to faeces and influence on human anaerobes of antimicrobial agents used for selective decontamination

The degree of binding of ampicillin, cephradine, co-trimoxazole, gentamicin, nalidixic acid, neomycin, polymyxin B and tobramycin by faecal substance as well as the influence of these antibiotics on human intestinal obligate anaerobes was investigated. In contrast to ampicillin, cephradine, co-trimoxazole and nalidixic acid, the nonabsorbable antibiotics polymyxin B and neomycin were bound to a considerable degree by human faeces. The binding of tobramycin and gentamicin to the solid part of faeces was less effective. The inhibitory effect of co-trimoxazole, gentamicin, nalidixic acid, neomycin, polymyxin B and tobramycin on the human obligate anaerobes was weak as compared with ampicillin and cephradine. Drugs which effectively eliminate Enterobacteriaceae from the gastrointestinal tract and which have a moderate effect on obligate anaerobes, like polymyxin B, are particularly suitable for selective decontamination of the gastrointestinal tract. The strong inactivating binding of aminoglycosides and polymyxin B to faeces accounts for the relatively high oral dose needed for a suitable faecal concentration.     

Deuterium and phosphorus nuclear magnetic resonance studies on the binding of polymyxin B to lipid bilayer-water interfaces

Deuterium and phosphorus NMR methods have been used to study the binding of polymyxin B to the surface of bilayers containing lipids that were deuterated at specific positions in the polar head-group region. The binding of polymyxin B to acidic dimyristoylphosphatidylglycerol (DMPG) membranes induces only small structural distortions of the glycerol head group. The deuterium spin-lattice relaxation times for the different carbon-deuterium bonds in the head group of the same phospholipid are greatly reduced on binding of polymyxin B, indicating a restriction of the motional rate of the glycerol head group. Only very weak interactions were detected between polymyxin B and bilayers of zwitterionic dimyristoylphosphatidylcholine (DMPC). In mixed bilayers of the two phospholipid types, in which either of the two phospholipids was deuterated, the presence of polymyxin B caused a lateral phase separation into DMPG-enriched phospholipid-peptide clusters and a DMPG-depleted phase. Complete phase separation did not occur: peptide-containing complexes with charged phosphatidylglycerol contained substantial amounts of zwitterionic phosphatidylcholine. Exchange of both phospholipid types between complexes and the bulk lipid matrix was shown to be fast on the NMR time scale, with a lifetime for phospholipid-peptide association of less than 1 ms.     

Investigation of osmotically stable spheroplasts from two strains of Escherichia coli ML-35, W7-M5.

Osmotically stable spheroplasts were produced from Escherichia coli ML-35 and W7-M5 using either 1 min exposure to polymyxin B or 10 min exposure to Tris/EDTA, followed by 1 to 3 h incubation with lysozyme. Spheroplast membrane permeability studies were conducted using paired radioactive probes with E. coli ML-35. Experiments with 14C-sucrose-16 kD 3H-dextran indicated that the outer membrane had lost its barrier to 16 kD dextran. Parallel experiments with 81 kD 3H-dextran indicated that the outer membrane was impermeable to the larger dextran. EDTA treated cells also showed outer membrane permeability to 16 kD dextran. Cytoplasmic membrane integrity was confirmed using 14C-sucrose and 3H2O before and after exposure to polymyxin B and EDTA. Scanning electron microscopy showed that a rough surface on polymyxin B produced spheroplasts while Tris/EDTA spheroplasts showed the same smooth surface as control cells.     

Protein kinase C in the nervous system of insects: effects of phorbol esters on cholinergic synapses

Specific high affinity binding sites for phorbol esters have been demonstrated in the nervous tissue of locust. The binding was reduced by the kinase C-inhibitor polymyxin B. Phorbol esters in micromolar concentrations activated protein kinase C in subcellular preparations from locust ganglia. The same concentrations of phorbol esters significantly enhanced the high affinity transport of choline and the release of acetylcholine by locust synaptosomes.     

A DNA-binding protein specific for the early replicated region of the chromosome obtained from Escherichia coli membrane fractions

The binding sites of calf thymus RNA polymerase (B) II, wheat germ RNA polymerase B and of the Escherichia coli RNA polymerase were mapped on the simian virus 40 genome by observation of enzyme-linear DNA complexes by electron microscopy. Three to four major sites and several minor sites are observed for each enzyme; common binding sites for the three enzymes are found in positions 0.17, 0.53 and 0.90 of the viral physical map. Initiation complexes with these enzymes can be stabilized with specific ribodinucleotides and a single ribonucleoside triphosphate. Whereas ApA and ATP greatly enhances the binding of the E. coli enzyme at position 0.17, they stabilize the binding of the eukaryotic enzyme at many sites, some of them located in close proximity of the origin of replication.     

Inhibition of Escherichia coli growth and respiration by polymyxin B covalently attached to agarose beads.

Polymyxin B was attached to agarose beads by stable covalent bonds and the antimicrobial activity of the immobilized peptide was examined. Polymyxin-agarose inhibited the growth of Escherichia coli and Pseudomonas aeruginosa, but not Bacillus subtilis. In addition, the respiration of E. coli, E. coli spheroplasts, and B. subtilis protoplasts was inhibited by immobilized polymyxin, whereas the respiration of B. subtilis was unaffected by polymyxin-agarose. The activity of polymyxin-agarose was not due to the release of free peptide from the derivative. These data indicate that polymyxin can inhibit the growth and respiration of gram-negative bacteria by interacting with the outer surface of these cells. It is proposed that perturbation of outer membrane structure by polymyxin-agarose indirectly affected the selective permeability of the inner membrane and inhibited respiration. The results of this study emphasize the importance of outer membrane structural integrity for the normal functions of gram-negative bacteria.     

Polymyxin B inhibits insulin-induced glucose transporter and IGF II receptor translocation in isolated adipocytes.

In isolated adipocytes, polymyxin B inhibited insulin-induced glucose incorporation into lipids in a dose-dependent manner, while polymyxin E, a structurally related antibiotic, was ineffective. To approach the mechanism of this effect, the subcellular distribution of the glucose transporter Glut 4 was investigated. Adipocytes were pretreated without or with polymyxin B before insulin stimulation, subcellular fractionation was performed and Glut 4 was detected by immunodetection. Incubation of adipocytes with polymyxin B prevented the insulin-induced appearance of Glut 4 in the plasma membranes, but did not prevent their decrease from the low-density microsomal fraction. A lower purity of the plasma membrane fractions, a detergent effect of polymyxin B on the membranes or an interference of the substance with the immunodetection of the Glut 4 molecules were excluded. These results suggest that polymyxin B was interfering with the Glut 4 translocation process stimulated by insulin in adipocytes. In a similar fashion, polymyxin B inhibited the insulin-induced increase in IGF II binding to adipocytes. This resulted from a blockade of the appearance of IGF II receptors in the plasma membranes. Since low-molecular-mass GTP-binding proteins have been implicated in the regulation of vesicular trafficking, we have used [alpha-32P]GTP binding to analyze such proteins in adipocyte fractions, after SDS/PAGE and transfer to nitrocellulose. Specific and distinct subsets of GTP-binding proteins were revealed in plasma membrane and low-density microsomal fractions of control adipocytes, whether they were stimulated or not with insulin. Polymyxin B treatment of adipocytes markedly modified the profile of the low-molecular-mass GTP-binding proteins in plasma membranes, but not in low-density microsomal fractions. Our results suggest that polymyxin B was interfering with the exocytotic process of the Glut 4 and IGF II receptor-containing vesicles, perhaps at the fusion step between vesicles and plasma membranes.     

Quantitative Analysis of Polymyxin B Released from Polymyxin B-Treated Dormant Spores of Bacillus subtilis and Relationship between Its Permeability and Inhibitory Effect on Outgrowth

Polymyxin B, one of the cyclic polypeptide antibiotics, binds to the coat of Bacillus subtilis dormant spores and inhibits them from growing after germination. When about 2.8 × 10⁸ cells/ml of polymyxin B-treated dormant spores were incubated in heart infusion broth, 3.6 μg/ml of polymyxin B were released into the liquid medium during germination. Incubation of the same concentration of polymyxin B-treated ones in 100 mM CaCl₂ solution released 4.0 μg/ml of the antibiotic. The effect of various concentrations of polymyxin B on germination, outgrowth and vegetative growth of the dormant spores was investigated; the results showed that concentrations of 4.0 μg/ml and higher of the antibiotic inhibited their outgrowth and vegetative growth after germination. Young vegetative cells were less sensitive to the antibiotic than germinated spores. In addition to these results, immunoelectron microscopy with colloidal gold particles indicated that polymyxin B permeated into the core of the germinated spores and inhibited them from outgrowing.     

USE OF POLYMYXIN B IN A CAPTURE ENZYME IMMUNOASSAY FOR DETECTION OF SALMONELLAE SPP. LIPOPOLYSACCHARIDE

A capture enzyme immunoassay for detection of salmonellae sp. lipopolysaccharide was developed. The assay made use of polymyxin B sulfate, passively attached to a polystyrene matrix, to capture lipopolysaccharide. Bound lipopolysaccharride was then detected with a monoclonal antibody, specific for salmonellae spp. followed by goat antimouse antibody conjugated with horseradish peroxidase.
The analytical sensitivity of the assay was approximately 1 ng/ml of lipopolysaccharide. The results are comparable to those obtained with a competitive enzyme immunoassay previously developed. The sensitivity of the polymyxin B assay decreased to 4–5 ng/ml when the salmonellae spp. lipopolysaccharide was mixed with 1–100 μg/ml of Escherichia coli lipopolysaccharide, while this level of heterogeneous lipopolysaccharide, did not decrease the sensitivity of the competitive enzyme immunoassay.
The polymyxin B capture assay was advantageous in that polymyxin B is a standardized reagent that is relatively inexpensive and does not require extensive preparation or containment facilities. The assay is robust; however, because of the light sensitivity of polymyxin B, its stickiness to other reagents and interference by other lipopolysaccharides, this assay requires careful attention to detail and may therefore be an unsuitable assay for field use.     

Binding sites of E. coli and B. stearothermophilus ribosomal proteins on B stearothermophilus 5S RNA.

The primary binding sites for Bacillus stearothermophilus proteins B-L5 and B-L22 and the Escherichia coli proteins E-L5, E-L18 and E-L25 on B. stearothermophilus 5S RNA were determined by limited ribonuclease digestion of the corresponding 5S RNA-protein complexes. The results obtained in this study are in agreement with our previous experiments in which the binding sites of E. coli and B. stearothermophilus proteins were determined for E. coli 5S RNA and lead to the conclusion that the proteins interact with the most conserved regions of 5S RNA. A comparison of the results obtained in this study with those of other published experiments suggest that the proposed interaction of nucleotides 16-21 with those of 58-63 is facilitated by protein binding to 5S RNA.     

Effect of Polymyxin on the Bacteriophage Receptors of the Cell Walls of Gram-Negative Bacteria

Treatment of gram-negative bacteria with lethal doses of polymyxin B and colistin resulted in the formation of projections of the outer layer of the cell wall. Phages T3, T4, and T7, which use wall lipopolysaccharide as receptors, were specifically prevented from adsorbing to Escherichia coli B cells treated with polymyxin, whereas phages T1, T2, T5, and T6 were not. In the systems of phage P22C-Salmonella typhimurium LT2 and phage C21-S. typhimurium variant SL1069, the phage were prevented from adsorbing to the host cell treated with the antibiotics. Electron microscopic observations show that phage T2 adsorbed irreversibly to the normal smooth surface between the projections on the outer layer caused by the drug treatment. These results indicate that lipopolysaccharide is affected by polymyxin functionally and morphologically, but lipoprotein is not. The purified lipopolysaccharide showed a ribbon-like structure when viewed face on and showed trilamellar structure when viewed edge on. The lipopolysaccharide from E. coli B was irreversibly adsorbed by phages T3, T4, and T7, but not phage T2. Often, phage T4 adsorbed to both sides of the lipopolysaccharide strand at comparable distances. Phage P22C adsorbed through the spikes of the tail-plates to the lipopolysaccharide from S. typhimurium LT2. Lipopolysaccharide which was treated with low doses of the drug (2.5 to 6.25 mug of polymyxin B per ml to 100 mug of lipopolysaccharide per ml) turned into the coiled form and was partially broken down into short segments with coiled form. The loosely coiled lipopolysaccharide retains both its function as the receptor and its trilamellar structure. Treatment with high doses of the drug (12.5 to 25 mug of polymyxin B per ml to 100 mug of lipopolysaccharide per ml) caused the collapse of the trilamellar structure of the strand. These collapsed lipopolysaccharides became flat and fused with each other, making an amorphous mass, and finally they were broken into small collapsed fragments.     

Improvement of modified charcoal-cefoperazone-deoxycholate agar by supplementation with a high concentration of polymyxin B for detection of Campylobacter jejuni and C. coli in chicken carcass rinses

Modified charcoal-cefoperazone-deoxycholate agar (mCCDA) was improved by supplementation with a high concentration of polymyxin B. The ability of the supplemented medium to isolate Campylobacter jejuni and C. coli from chicken carcass rinses was compared to that of Campy-Cefex agar and mCCDA. Modification of mCCDA with increased polymyxin B yielded a significantly (P < 0.05) higher isolation rate and greater selectivity than those achieved using Campy-Cefex agar and mCCDA.     

Mechanism of Polymyxin B Resistance in Proteus mirabilis

The lipids from three types of organisms-a Proteus mirabilis wild type highly resistant to polymyxin B, a polymyxin B-sensitive mutant derived from the wild type, and the wild type grown in the presence of sulfadiazine resulting in phenotypic conversion to polymyxin B sensitivity-were examined to determine the nature of polymyxin B resistance. The phospholipid compositions were nearly identical; each organism contained similar small amounts of N-methyl phosphatidylethanolamine in addition to comparable quantities of phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. the fatty acid compositions were similar in the exponential phase of growth; in the stationary phase, sulfadiazine markedly inhibited the synthesis of cyclopropane fatty acids. Liposomes prepared from the dried lipids of the three types of organisms were extensively and similarly disrupted by the polymyxin. These findings suggest that polymyxin B resistance in P. mirabilis is determined by the cell envelope which prevents access of the antibiotic to the susceptible lipid target sites.