Ionizing groups in lipopolysaccharides of Pseudomonas cepacia in relation to antibiotic resistance

Antiseptics and disinfectants: activity, action, and resistance

Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications. A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine. Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics. This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants. The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants. Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports.

Isolation and characterisation of disodium (4-amino-4-deoxy-beta-L- arabinopyranosyl)-(1-->8)-(D-glycero-alpha-D-talo-oct-2-ulopyranosylona te)- (2-->4)-(methyl 3-deoxy-D-manno-oct-2-ulopyranosid)onate from the lipopolysaccharide of Burkholderia cepacia

A trisaccharide was isolated from the core oligosaccharide in the lipopolysaccharide (LPS) of Burkholderia cepacia GIFU 645 (ATCC 25416, type strain) by methanolysis followed by HPLC and saponification. It was identified by MS, methylation analysis and 1H and 13C NMR spectroscopy as disodium (4-amino-4-deoxy-beta-L-arabinopyranosyl)-(1-->8)-(D-glycero- alpha-D-talo-oct-2-ulopyranosylonate)-(2-->4)-(methyl 3-deoxy-D-manno-oct-2-ulopyranosid)onate. In addition to the trisaccharide derivative, methanolysis gave dimethyl (D-glycero-alpha-D- talo-oct-2-ulopyranosylonate)-(2-->4)-(methyl 3-deoxy-D-manno-oct-2- ulopyranosid)onate in a relative proportion to the trisaccharide of 3:1, indicating a non-stoichiometric (approximately 25%) substitution of the octulosonic acid by 4-amino-4-deoxyarabinose in the LPS.

PmrA-PmrB-regulated genes necessary for 4-aminoarabinose lipid A modification and polymyxin resistance

Antimicrobial peptides are distributed throughout the animal kingdom and are a key component of innate immunity. Salmonella typhimurium regulates mechanisms of resistance to cationic antimicrobial peptides through the two-component systems PhoP-PhoQ and PmrA-PmrB. Polymyxin resistance is encoded by the PmrA-PmrB regulon, whose products modify the lipopolysaccharide (LPS) core and lipid A regions with ethanolamine and add aminoarabinose to the 4' phosphate of lipid A. Two PmrA-PmrB-regulated S. typhimurium loci (pmrE and pmrF) have been identified that are necessary for resistance to polymyxin and for the addition of aminoarabinose to lipid A. One locus, pmrE, contains a single gene previously identified as pagA (or ugd) that is predicted to encode a UDP-glucose dehydrogenase. The second locus, pmrF, is the second gene of a putative operon predicted to encode seven proteins, some with similarity to glycosyltransferases and other complex carbohydrate biosynthetic enzymes. Genes immediately flanking this putative operon are also regulated by PmrA-PmrB and/or have been associated with S. typhimurium polymyxin resistance. This work represents the first identification of non-regulatory genes necessary for modification of lipid A and subsequent antimicrobial peptide resistance, and provides support for the hypothesis that lipid A aminoarabinose modification promotes resistance to cationic antimicrobial peptides.

Regulation of polymyxin resistance and adaptation to low-Mg2+ environments

The PmrA-PmrB two-component system of Salmonella typhimurium controls resistance to the peptide antibiotic polymyxin B and to several antimicrobial proteins from human neutrophils. Amino acid substitutions in the regulatory protein PmrA conferring resistance to polymyxin lower the overall negative charge of the lipopolysaccharide (LPS), which results in decreased bacterial binding to cationic polypeptides and increased bacterial survival within human neutrophils. We have now identified three PmrA-activated loci that are required for polymyxin resistance. These loci were previously shown to be necessary for growth on low-Mg2+ solid media, indicating that LPS modifications that mediate polymyxin resistance are responsible for the adaptation to Mg2+-limited environments. Conditions that promote transcription of PmrA-activated genes--growth in mildly acidic pH and micromolar Mg2+ concentrations--increased survival in the presence of polymyxin over 16,000-fold in a wild-type organism but not in a mutant lacking pmrA. Our experiments suggest that low pH and low Mg2+ concentrations may induce expression of PmrA-activated genes within phagocytic cells and promote bacterial resistance to host antimicrobial proteins. We propose that the LPS is a Mg2+ reservoir and that the PmrA-controlled LPS modifications neutralize surface negative charges when Mg2+ is transported into the cytoplasm during growth in Mg2+-limited environments.

Structural studies of the O-specific side-chain of lipopolysaccharide from Burkholderia gladioli pv. gladioli strain NCPPB 1891

A polymeric fraction (the O-antigenic side-chain) has been isolated from the lipopolysaccharide of Burkholderia gladioli pv. gladioli strain NCPPB 1891 after mild acid hydrolysis. The components of the polymer and their molar proportions were L-Rha (1), D-Gal (1), D-Man (1), and O-acetyl (1). By means of chemical degradations and NMR studies, the repeating unit of the polymer was shown to be a linear trisaccharide of the structure shown. [formula: see text]

Structure of the O-specific polysaccharide from Burkholderia vietnamiensis strain LMG 6998

The putative O-specific polymer containing D-mannose and L-rhamnose was isolated from the lipopolysaccharide obtained from cells walls of Burkholderia vietnamiensis strain LMG 6998. NMR and degradative studies showed that the polymer has a linear trisaccharide repeating-unit of the structure shown. The same polymer carrying an O-acetyl group at position 3 of the 4-substituted mannose residue has previously been found as the O antigen in the related species Burkholderia cepacia serogroup J. [formula: see text]

Characterization of lipopolysaccharides of polymyxin-resistant and polymyxin-sensitive Klebsiella pneumoniae O3

Lipopolysaccharides isolated from the polymyxin-resistant Klebsiella pneumoniae O3 mutant OM-5 and its polymyxin-sensitive parent LEN-1 were analyzed for chemical composition, and their lipid A portions were structurally characterized. The lipopolysaccharide of OM-5 contained approximately five times more 4-amino-4-deoxy-L-arabinopyranose than that of LEN-1. Other saccharide and phosphate components exhibited no significant differences. Structural characterization, including analyses by phosphorus magnetic resonance spectroscopy and by fast atom bombardment mass spectrometry, revealed a novel type of lipid A. In the OM-5 lipopolysaccharide, both phosphates of lipid A were almost totally present as phosphodiesters with 4-amino-4-deoxy-L-arabinopyranose. In the sensitive-type LEN-1 lipid A, the extent of this substitution was much lower, especially in the glycosidically linked phosphate. Phosphate in these K. pneumoniae lipopolysaccharides was almost exclusively found in lipid A. These results show that cationic substituents of phosphates of lipid A play a decisive role in determining polymyxin reactivity. OM-5 was also found to contain a large proportion of heptaacyl lipid A, which represented only a small fraction of lipid A in LEN-1.

Structure of the O-specific polysaccharide from Burkholderia pickettii strain NCTC 11149

A polymeric fraction (the putative O antigen) has been isolated from the lipopolysaccharide of the type strain of Burkholderia pickettii. The components of the polymer and their molar proportions were: L-rhamnose (3), 2-acetamido-2-deoxy-D-glucose (1), and O-acetyl (1). By means of NMR studies and chemical degradations, the basic repeating-unit of the polymer was identified as a linear tetrasaccharide of the structure shown. The O-acetyl group is probably located at position 2 of the 3-substituted alpha-L-Rha p. Similar polymers constitute O antigens in the related species Burkholderia solanacearum.

Nucleotide sequence analysis of a gene from Burkholderia (Pseudomonas) cepacia encoding an outer membrane lipoprotein involved in multiple antibiotic resistance

Antibiotic-resistant Burkholderia (Pseudomonas) cepacia is an important etiologic agent of nosocomial and cystic fibrosis infections. The primary resistance mechanism which has been reported is decreased outer membrane permeability. We previously reported the cloning and characterization of a chloramphenicol resistance determinant from an isolate of B. cepacia from a patient with cystic fibrosis that resulted in decreased drug accumulation. In the present studies we subcloned and sequenced the resistance determinant and identified gene products related to decreased drug accumulation. Additional drug resistances encoded by the determinant include resistances to trimethoprim and ciprofloxacin. Sequence analysis of a 3.4-kb subcloned fragment identified one complete and one partial open reading frame which are homologous with two of three components of a potential antibiotic efflux operon from Pseudomonas aeruginosa (mexA-mexB-oprM). On the basis of sequence data, outer membrane protein analysis, protein expression systems, and a lipoprotein labelling assay, the complete open reading frame encodes an outer membrane lipoprotein which is homologous with OprM. The partial open reading frame shows homology at the protein level with the C terminus of the protein product of mexB. DNA hybridization studies demonstrated homology of an internal mexA probe with a larger subcloned fragment from B. cepacia. The finding of multiple antibiotic resistance in B. cepacia as a result of an antibiotic efflux pump is surprising because it has long been believed that resistance in this organism is caused by impermeability to antibiotics.

Lipopolysaccharides of polymyxin B-resistant mutants of Escherichia coli are extensively substituted by 2-aminoethyl pyrophosphate and contain aminoarabinose in lipid A

Lipopolysaccharides (LPS) of two polymyxin-resistant (pmr) mutants and the corresponding parent strain of Escherichia coli were chemically analysed for composition and subjected to 31P-NMR (nuclear magnetic resonance) for assessment of phosphate substitution. Whereas the saccharide portions, fatty acids, and phosphate contents were similar in wild-type and pmr LPS, the latter contained two- to threefold higher amounts of 2-aminoethanol. The pmr LPS also contained 4-amino-4-deoxy-L-arabinopyranose (L-Arap4N), which is normally not a component of E. coli LPS. This aminopentose has been assigned to be linked to the 4'-phosphate of lipid A. Comparative 31P-NMR analysis of the de-O-acylated LPS of the wild-type and pmr strains revealed that phosphate groups of the pmr LPS were mainly (71-79%) diphosphate diesters, which accounted for only 20% in the wild-type LPS. Diphosphate monoesters were virtually nonexistent in the pmr LPS, whereas they accounted for 42% of all phosphates in wild-type LPS. In the lipid A of the pmr strains, the 4'-phosphate was to a significant degree (35%) substituted by L-Arap4N, whereas in the wild-type LPS the L-ArapN was absent. In the pmr lipid A, 2-aminoethanol was completely substituting the glycosidic pyrophosphate but not the glycosidic monophosphate, forming a diphosphate diester linkage at this position in 40% of lipid A molecules. In the wild-type LPS the glycosidic position of lipid A carried mostly unsubstituted monophosphate and pyrophosphate. Thus the polymyxin resistance was shown to be associated, along with the esterification of the lipid A 4'-monophosphate by aminoarabinose, with extensive esterification of diphosphates in LPS by 2-aminoethanol.

Biological activity of Burkholderia (Pseudomonas) cepacia lipopolysaccharide

Burkholderia cepacia has emerged as an important multiresistant pathogen in cystic fibrosis (CF), associated in 20% of colonised patients with a rapid and fatal decline in lung function. Although knowledge of B. cepacia epidemiology has improved, the mechanisms involved in pathogenesis remain obscure. In this study, B. cepacia lipopolysaccharide (LPS) was assessed for endotoxic potential and the capacity to induce tumour necrosis factor (TNF). LPS preparations from clinical and environmental isolates of B. cepacia and from the closely related species Burkholderia gladioli exhibited a higher endotoxic activity and more pronounced cytokine response in vitro compared to preparations from the major CF pathogen Pseudomonas aeruginosa. This study help to explain the vicious host immune response observed during pulmonary exacerbations in CF patients colonised by B. cepacia and lead to therapeutic advances in clinical management.

Influence of cationic antibiotics on phase behavior of rough-form lipopolysaccharide

The rough-form lipopolysaccharide (LPS) interacted with cationic antibiotic polymyxin B and gramicidin S in solution, and showed altered thermotropic phase behavior and viscoelasticity. The phase behavior was measured by differential scanning calorimetry and quartz crystal microbalance (QCM). Addition of polymyxin B of up to 0.5 mg/mL to the 5.0 mg/mL LPS solution increased gel-to-liquid crystalline phase transition enthalpy (delta H) and raised the transition temperature (tmax). The further addition of polymyxin B reduced the delta H value. Gramicidin S produced a different effect, whereby a minor addition reduced tmax and delta H value of the LPS. The LPS film on the platinum electrode of the QCM indicated a downward shift of resonant frequency and an upward shift of resonant resistance when in contact with the antibiotic solution. An interpretation of these variations is that the LPS on the QCM electrode changed not only film weight, but also viscoelasticity owing to contact with the antibiotic solution. The different effects between the antibiotics between polymyxin B and gramicidin S on the LPS are induced by the difference of the governing effect. Polymyxin B interacts with the LPS electrostatically, whereas gramicidin S interacts by hydrophobic moieties.

Chemical structure of the lipid A component of lipopolysaccharides of the genus Pectinatus

The chemical structure of the lipid A components of smooth-type lipopolysaccharides isolated from the type strains of strictly anaerobic beer-spoilage bacteria Pectinatus cerevisiiphilus and Pectinatus frisingensis were analyzed. The hydrophilic backbone of lipid A was shown, by controlled degradation of lipopolysaccharide combined with chemical assays and 31P-NMR spectroscopy, to consist of the common beta 1-6-linked disaccharide of pyranosidic 2-deoxy-glucosamine (GlcN), phosphorylated at the glycosidic position and at position 4'. In de-O-acylated lipopolysaccharide, the latter phosphate was shown to be quantitatively substituted with 4-amino-4-deoxyarabinose, whereas the glycosidically linked phosphate was present as a monoester. Laser-desorption mass spectrometry of free dephosphorylated lipid A revealed that the distal (non-reducing) GlcN was substituted at positions 2' and 3' with (R)-3-(undecanoyloxy)tridecanoic acid, whereas the reducing GlcN carried two unsubstituted (R)-3-hydroxytetradecanoic acids at positions 2 and 3. The lipid A of both Pectinatus species were thus of the asymmetric hexaacyl type. The linkage of lipid A to polysaccharide in the lipopolysaccharide was relatively resistant to acid-catalyzed hydrolysis, enabling the preparation of a dephosphorylated and deacylated saccharide backbone. Methylation analysis of the backbone revealed that position 6' of the distal GlcN of lipid A was the attachment site of the polysaccharide. Despite the quantitative substitution of the lipid A 4'-phosphate by 4-amino-4-deoxyarabinose, which theoretically should render the bacteria resistant to polymyxin, P. cerevisiiphilus was shown to be susceptible to this antibiotic. P. cerevisiiphilus was, however, also susceptibile to vancomycin and bacitracin, indicating that the outer membrane of this bacterium does not act as an effective permeability barrier.

Increased substitution of phosphate groups in lipopolysaccharides and lipid A of the polymyxin-resistant pmrA mutants of Salmonella typhimurium: a 31P-NMR study

De-O-acylated lipopolysaccharides (LPS) of three polymyxin-resistant Salmonella typhimurium pmrA mutants and their parent strains were analysed by 31P-NMR (nuclear magnetic resonance) in order to assess, in relation to polymyxin resistance, the types and degree of substitution of phosphates of the LPS and lipid A. In the pmrA mutant LPS phosphate diesters predominated over phosphate monoesters, whereas the latter were more abundant in the parent wild-type LPS. The increase in the proportion of phosphate diesters was traced to both the core oligosaccharide and the lipid A part. In the latter, the ester-linked phosphate at position 4' was to a large extent (79-88%) substituted with 4-amino-4-deoxy-L-arabinose, whereas in the wild-type LPS the 4'-phosphate was mainly present as monoester. In each LPS, regardless of the pmrA mutation, the glycosidically linked phosphate of lipid A was largely unsubstituted.

Structure of the O9 antigen from Burkholderia (Pseudomonas) cepacia

The O9 antigen of Burkholderia (Pseudomonas) cepacia has the following disaccharide repeating-unit: -->4)-alpha-D-Glcp-(1-->3)-alpha-L-Rhap-(1--> The same unit is present in the O antigens of Serratia marcescens strain S1254 and serogroup O4 (predominantly acetylated at O-2 of rhamnose in the latter case).

Characterization of hemolytic and antifungal substance, cepalycin, from Pseudomonas cepacia

Hemolytic and antifungal substances, cepalycin I and cepalycin II, have been isolated from Pseudomonas cepacia JN106. A large amount of cepalycins were produced by growing the cells on 1% glycerin-nutrient agar medium covered with a cellophane membrane. The cell-washed supernatant was applied to an Amberlite XAD2 column, and cepalycins were eluted with 70% ethanol containing 1mM HCl. Cepalycins were separated by reverse phase HPLC in two fractions which were designated as cepalycin I and cepalycin II. The two cepalycins have indistinguishable UV absorption spectra but have different levels of hemolytic activity relative to the UV absorption. From the inhibition of hemolytic activity of cepalycin by sterols, both cepalycins were suggested to interact with cholesterol in erythrocyte membrane. Such an interaction may contribute to their hemolytic and antifungal activities.

Agents that increase the permeability of the outer membrane

The outer membrane of gram-negative bacteria provides the cell with an effective permeability barrier against external noxious agents, including antibiotics, but is itself a target for antibacterial agents such as polycations and chelators. Both groups of agents weaken the molecular interactions of the lipopolysaccharide constituent of the outer membrane. Various polycations are able, at least under certain conditions, to bind to the anionic sites of lipopolysaccharide. Many of these disorganize and cross the outer membrane and render it permeable to drugs which permeate the intact membrane very poorly. These polycations include polymyxins and their derivatives, protamine, polymers of basic amino acids, compound 48/80, insect cecropins, reptilian magainins, various cationic leukocyte peptides (defensins, bactenecins, bactericidal/permeability-increasing protein, and others), aminoglycosides, and many more. However, the cationic character is not the sole determinant required for the permeabilizing activity, and therefore some of the agents are much more effective permeabilizers than others. They are useful tools in studies in which the poor permeability of the outer membrane poses problems. Some of them undoubtedly have a role as natural antibiotic substances, and they or their derivatives might have some potential as pharmaceutical agents in antibacterial therapy as well. Also, chelators (such as EDTA, nitrilotriacetic acid, and sodium hexametaphosphate), which disintegrate the outer membrane by removing Mg2+ and Ca2+, are effective and valuable permeabilizers.