Staphylococcus epidermidis polysaccharide intercellular adhesin induces IL-8 expression in human astrocytes via a mechanism involving TLR2.

Staphylococcus epidermidis is an opportunistic biofilm-forming pathogen associated with neurosurgical device-related meningitis. Expression of the polysaccharide intercellular adhesin (PIA) on its surface promotes S. epidermidis biofilm formation. Here we investigated the pro-inflammatory properties of PIA against primary and transformed human astrocytes. PIA induced IL-8 expression in a dose- and/or time-dependent manner from U373 MG cells and primary normal human astrocytes. This effect was inhibited by depletion of N-acetyl-beta-d-glucosamine polymer from the PIA preparation with Lycopersicon esculentum lectin or sodium meta-periodate. Expression of dominant-negative versions of the TLR2 and TLR4 adaptor proteins MyD88 and Mal in U373 MG cells inhibited PIA-induced IL-8 production. Blocking IL-1 had no effect. PIA failed to induce IL-8 production from HEK293 cells stably expressing TLR4. However, in U373 MG cells which express TLR2, neutralization of TLR2 impaired PIA-induced IL-8 production. In addition to IL-8, PIA also induced expression of other cytokines from U373 MG cells including IL-6 and MCP-1. These data implicate PIA as an important immunogenic component of the S. epidermidis biofilm that can regulate pro-inflammatory cytokine production from human astrocytes, in part, via TLR2.

Poly-N-acetylglucosamine and poly(glycerol phosphate) teichoic acid identification from staphylococcal biofilm extracts using excitation sculptured TOCSY NMR.

We report the successful application of selective excitation sculptured TOCSY NMR (SXS-TOCSY) to identify individual solution components from a heterogeneous system using selectively acquired (1)H NMR spin system patterns. SXS-TOCSY application is illustrated by detection of the simultaneous presence of poly-beta-(1,6)-N-acetylglucosamine (PNAG) and poly(glycerol phosphate) teichoic acid (TA) carbohydrate polymer components in crude biofilm extracts from Staphylococcus epidermidis without the need for further sample purification and component separation. Biofilms are implicated in the barriers for resistance of microbes toward antibiotics and immune responses, therefore efficient rapid detection and quantification of key components are important to assist in the design of a clinical infection response.

Biofilms of clinical strains of Staphylococcus that do not contain polysaccharide intercellular adhesin.

Staphylococcus aureus and coagulase-negative staphylococci, primarily Staphylococcus epidermidis, are recognized as a major cause of nosocomial infections associated with the use of implanted medical devices. The capacity of S. epidermidis to form biofilms, allowing it to evade host immune defence mechanisms and antibiotic therapy, is considered to be crucial in colonizing the surfaces of medical implants and dissemination of infection. It has previously been demonstrated that the biofilm of a model strain S. epidermidis RP62A comprises two carbohydrate-containing moieties, a polysaccharide having a structure of a linear poly-N-acetyl-(1-->6)-beta-D-glucosamine and teichoic acid. In the present paper we show that, unlike this model strain, certain clinical isolates of coagulase-negative staphylococci produce biofilms that do not contain detectable amounts of poly-N-acetyl-(1-->6)-beta-D-glucosamine. In contrast to that of S. epidermidis RP62A, these biofilms are not detached with metaperiodate, while proteinase K causes their partial dispersal.

Carbohydrate-containing components of biofilms produced in vitro by some staphylococcal strains related to orthopaedic prosthesis infections.

The capacity of coagulase-negative staphylococci to colonize implanted medical devices is generally attributed to their ability to produce biofilms. Biofilm of the model strain of Staphylococcus epidermidis RP62A was shown to contain two carbohydrate-containing moieties, a linear poly-beta-(1-->6)-N-acetyl-D-glucosamine (PNAG) and teichoic acid. In the present study, we investigated several biofilm-producing staphylococci isolated from infected orthopaedic implants and characterized the composition of the laboratory-grown biofilms using chemical analysis and 1H nuclear magnetic resonance spectroscopy. Extracellular teichoic acid was produced by all strains studied. Some of the clinical strains were shown to produce biofilms with compositions similar to that of the model strain, containing a varying amount of PNAG. The chemical structure of PNAG of the clinical strains was similar to that previously described for the model strains S. epidermidis RP62A and Staphylococcus aureus MN8m, differing only in the amount of charged groups. Biofilms of the strains producing a substantial amount of PNAG were detached by dispersin B, a PNAG-degrading enzyme, while being unsusceptible to proteinase K treatment. On the other hand, some strains produced biofilms without any detectable amount of PNAG. The biofilms of these strains were dispersed by proteinase K, but not by dispersin B.

Structural elucidation of the extracellular and cell-wall teichoic acids of Staphylococcus aureus MN8m, a biofilm forming strain.

Extracellular teichoic acid, an essential constituent of the biofilm produced by Staphylococcus epidermidis strain RP62A, is also an important constituent of the extracellular matrix of another biofilm producing strain, Staphylococcus aureus MN8m. The structure of the extracellular and cell wall teichoic acids of the latter strain was studied by NMR spectroscopy and capillary electrophoresis-mass spectrometry. Both teichoic acids were found to be a mixture of two polymers, a (1-->5)-linked poly(ribitol phosphate), substituted at the 4-position of ribitol residues with beta-GlcNAc, and a (1-->3)-linked poly(glycerol phosphate), partially substituted with the D-Ala at 2-position of glycerol residue. Such mixture is unusual for S. aureus.

Comparison of two standardisation methods in real-time quantitative RT-PCR to follow Staphylococcus aureus genes expression during in vitro growth.

By real-time quantitative PCR (RTQ-PCR), two different standardisation methods were used to quantify expression of three target genes (RNAII and RNAIII transcripts of agr locus and ica transcript of icaADBC locus): (i) a relative quantification, using a transcript of three housekeeping genes (gyrase A, gyrA; guanylate kinase, gmk and 16S rRNA, 16S) as internal standard, and (ii) an absolute quantification, using cloned sequences of the target genes in known concentrations as external standards. To determine the efficiency and reliability of these two methods, the gene expressions were studied during the growth of a clinical isolate of Staphylococcus aureus. Between 3 and 20 h after inoculation, target gene transcription was analysed using LightCycler Apparatus, LC Data Analysis software and RelQuant software for relative quantification (Roche). For all target genes, the expression profiles obtained with gyrA or gmk as internal standards remained almost identical. However, these profiles varied between each other depending on the standard gene. Due to their important expression variations during growth phases, these two housekeeping genes seem inappropriate to be used as internal standards. The absolute quantification of the three transcripts of interest gave results similar to their relative quantification expressed versus 16S rRNA. Therefore, our study suggests the suitable use of 16S rRNA as internal standard in RTQ-PCR quantification of staphylococcal gene expression during the stationary phase of growth.

Structural elucidation of the extracellular and cell-wall teichoic acids of Staphylococcus epidermidis RP62A, a reference biofilm-positive strain.

The ability to adhere to artificial surfaces and form biofilms is considered as a virulence factor of Staphylococcus epidermidis, one of the major causes of nocosomial infections, especially those related to implanted medical devices. Cell-wall teichoic acid is known to play an important role in biofilm formation of staphylococci. The structure of the cell wall and extracellular teichoic acids of S. epidermidis RP62A, a reference biofilm-positive strain, was studied by NMR spectroscopy and capillary electrophoresis-mass spectrometry. Their structures were found to be a (1-->3)-linked poly(glycerol phosphate), substituted at the 2-position of glycerol residues with alpha-Glc, alpha-GlcNAc, D-Ala and alpha-Glc6Ala. D-Alanyl acylation of a sugar hydroxyl group seems to be a novel structural feature of teichoic acids from staphylococci.

The structure of the carbohydrate backbone of the lipopolysaccharide of Pectinatus frisingensis strain VTT E-79104.

The structure of the carbohydrate backbone of the lipopolysaccharide from Pectinatus frisingensis strain VTT E-79104 was analyzed using chemical degradations, NMR spectroscopy, mass spectrometry, and chemical methods. The LPS contains two major structural variants, differing in the presence or absence of an octasaccharide fragment. The largest structure of the carbohydrate backbone of the LPS, that could be deduced from experimental results, consists of 20 monosaccharides arranged in a nonrepetitive sequence: [carbohydrate structure: see text] where R is H or 4-O-Me-alpha-L-Fuc-(1-2)-4-O-Me-beta-Hep-(1-3)-alpha-GlcNAc-(1-2)-beta-Man-(1-3)-beta-ManNAc-(1-4)-alpha-Gal-(1-4)-beta-Hep-(1-3)-beta-GalNAc-(1- where Hep is a residue of D-glycero-D-galacto-heptose; all monosaccharides have the D-configuration except for 4-O-Me-L-Fuc and L-Ara4N. This structure is architecturally similar to the oligosaccharide system reported previously in P. frisingensis VTT E-82164 LPS, but differs from the latter in composition and also in the size of the outer region.

A comparative study of antibodies against proteins extracted from staphylococcal biofilm for the diagnosis of orthopedic prosthesis-related infections in an animal model and in humans.

Staphylococcus aureus and Staphylococcus epidermidis are the microorganisms most frequently seen in periprosthetic infections (PPI) with the capacity of forming biofilm. To find potential antigens for the diagnosis of PPI, the immunogenicity of protein components in biofilm from a model biofilm-positive strain (S. epidermidis RP62A) was investigated. A guinea pig animal model of PPI was developed and sera were obtained. Sera of patients with PPI and those of controls were also collected. Data generated with an enzyme-linked immunosorbent assay showed that there were significantly higher levels of anti-extracellular protein IgG in sera of infected animals than in controls. We also found significantly higher anti-extracellular protein IgG levels in infected patients, compared to the controls; however, receiver operating characteristic curves did not aid in diagnosing PPI.

Recombinant human DNase I decreases biofilm and increases antimicrobial susceptibility in staphylococci.

Extracellular DNA is an adhesive component of staphylococcal biofilms. The aim of this study was to evaluate the antibiofilm activity of recombinant human DNase I (rhDNase) against Staphylococcus aureus and Staphylococcus epidermidis. Using a 96-well microtiter plate crystal-violet binding assay, we found that biofilm formation by S. aureus was efficiently inhibited by rhDNase at 1-4 µg l⁻¹, and preformed S. aureus biofilms were efficiently detached in 2 min by rhDNase at 1 mg l⁻¹. Pretreatment of S. aureus biofilms for 10 min with 10 mg l⁻¹ rhDNase increased their sensitivity to biocide killing by 4-5 log units. rhDNase at 10 mg l⁻¹ significantly inhibited biofilm formation by S. epidermidis in medium supplemented with sub-MICs of antibiotics. We also found that rhDNase significantly increased the survival of S. aureus-infected Caenorhabditis elegans nematodes treated with tobramycin compared with nematodes treated with tobramycin alone. We concluded that rhDNase exhibits potent antibiofilm and antimicrobial-sensitizing activities against S. aureus and S. epidermidis at clinically achievable concentrations. rhDNase, either alone or in combination with antimicrobial agents, may have applications in treating or preventing staphylococcal biofilm-related infections.

Extracellular DNA-dependent biofilm formation by Staphylococcus epidermidis RP62A in response to subminimal inhibitory concentrations of antibiotics.

We measured the ability of Staphylococcus epidermidis to form biofilms in the presence of subminimal inhibitory concentrations (sub-MICs) of vancomycin, tigecycline, linezolid and novobiocin. Six strains that produce different amounts of biofilm were tested. The three strains that produced the highest amounts of biofilm exhibited steady-state or decreased biofilm formation in the presence of sub-MIC antibiotics, whereas the three strains that produced lower amounts of biofilm exhibited up to 10-fold-increased biofilm formation in the presence of sub-MIC antibiotics. In two of the inducible strains (9142 and 456a), antibiotic-induced biofilm formation was inhibited by dispersin B, an enzyme that degrades poly-N-acetylglucosamine (PNAG) biofilm polysaccharide. In the third inducible strain (RP62A), dispersin B inhibited biofilm formation in response to sub-MIC vancomycin, but not to sub-MIC tigecycline. In contrast, DNase I efficiently inhibited biofilm formation by strain RP62A in response to sub-MIC tigecycline and vancomycin. DNase I had no effect on antibiotic-induced biofilm formation in strains 9142 and 456a. Our findings indicate that antibiotic-induced biofilm formation in S. epidermidis is both strain- and antibiotic-dependent and that S. epidermidis RP62A utilizes an extracellular DNA-dependent mechanism to form biofilms in response to sub-MIC antibiotics.

Characteristics of the biofilm matrix and its role as a possible target for the detection and eradication of Staphylococcus epidermidis associated with medical implant infections.

The virulence of Staphylococcus epidermidis is related to its capacity to form biofilms. Such biofilm-related infections are extremely difficult to treat and to detect in early stages by the traditional microbiological analyses. The determination of the chemical composition of the extracellular polymeric substances (EPS) of the biofilm matrix, as well as the elucidation of the sensitivity of biofilms to enzymatic degradation should facilitate the development of new therapies against biofilm-related infections. The chemical analyses of EPS had shown qualitative and quantitative variations of their nature, depending on the strains and culture conditions. The poly-N-acetylglucosamine (PNAG) is considered the main component of staphylococcal biofilms. However, certain strains form biofilms without PNAG. In addition to PNAG and proteins, extracellular teichoic acid was identified as a new component of the staphylococcal biofilms. The sensitivity of staphylococcal biofilms to enzymatic treatments depended on their relative chemical composition, and a PNAG-degrading enzyme, in conjunction with proteases, could be an efficient solution to eliminate the staphylococcal biofilms. A detection of specific 'antibiofilm' antibodies in the blood serum of patients could serve as a convenient noninvasive and inexpensive diagnostic tool for the detection of foreign body-associated staphylococcal infections. Used as a coating antigen in the enzyme-linked immunosorbent assay test, PNAG did not sufficiently discriminate healthy individuals from the infected patients.

Effect of berberine on Staphylococcus epidermidis biofilm formation.

Staphylococcus epidermidis is one of the main causes of medical device-related infections owing to its adhesion and biofilm-forming abilities on biomaterial surfaces. Berberine is an isoquinoline-type alkaloid isolated from Coptidis rhizoma (huang lian in Chinese) and other herbs with many activities against various disorders. Although the inhibitory effects of berberine on planktonic bacteria have been investigated in a few studies, the capacity of berberine to inhibit biofilm formation has not been reported to date. In this study, we observed that berberine is bacteriostatic for S. epidermidis and that sub-minimal inhibitory concentrations of berberine blocked the formation of S.epidermidis biofilm. Using viability assays and berberine uptake testing, berberine at a concentration of 15-30mug/mL was shown to inhibit bacterial metabolism. Data from this study also indicated that modest concentrations of berberine (30-45mug/mL) were sufficient to exhibit an antibacterial effect and to inhibit biofilm formation significantly, as shown by the tissue culture plate (TCP) method, confocal laser scanning microscopy and scanning electron microscopy for both S. epidermidis ATCC 35984 and a clinical isolate strain SE243. Although the mechanisms of bacterial killing and inhibition of biofilm formation are not fully understood, data from this investigation indicated a potential application for berberine as an adjuvant therapeutic agent for the prevention of biofilm-related infections.

Poly-N-acetylglucosamine mediates biofilm formation and detergent resistance in Aggregatibacter actinomycetemcomitans.

Clinical isolates of the periodontopathogen Aggregatibacter actinomycetemcomitans form matrix-encased biofilms on abiotic surfaces in vitro. A major component of the A. actinomycetemcomitans biofilm matrix is poly-beta-1,6-N-acetyl-d-glucosamine (PGA), a hexosamine-containing polysaccharide that mediates intercellular adhesion. In this report, we describe studies on the purification, structure, genetics and function of A. actinomycetemcomitans PGA. We found that PGA was very tightly attached to A. actinomycetemcomitans biofilm cells and could be efficiently separated from the cells only by phenol extraction. A. actinomycetemcomitans PGA copurified with LPS on a gel filtration column. (1)H NMR spectra of purified A. actinomycetemcomitans PGA were consistent with a structure containing a linear chain of N-acetyl-d-glucosamine residues in beta(1,6) linkage. Genetic analyses indicated that all four genes of the pgaABCD locus were required for PGA production in A. actinomycetemcomitans. PGA mutant strains still formed biofilms in vitro. Unlike wild-type biofilms, however, PGA mutant biofilms were sensitive to detachment by DNase I and proteinase K. Treatment of A. actinomycetemcomitans biofilms with the PGA-hydrolyzing enzyme dispersin B made them 3 log units more sensitive to killing by the cationic detergent cetylpyridinium chloride. Our findings suggest that PGA, extracellular DNA and proteinaceous adhesins all contribute to the structural integrity of the A. actinomycetemcomitans biofilm matrix.

Neither the presence of ica locus, nor in vitro-biofilm formation ability is a crucial parameter for some Staphylococcus epidermidis strains to maintain an infection in a guinea pig tissue cage model.

The pathogenesis of Staphylococcus epidermidis is thought to be based on its capacity to colonize medical devices by forming a biofilm. Biofilm formation is in part mediated by the polysaccharide intercellular adhesin (PIA), which is encoded by the icaADBC operon. We have previously investigated in vitro the correlation existing between biofilm formation (B+/-), presence of ica locus (I+/-) and PIA production (P+/-) in some clinical isolates of coagulase-negative staphylococci (CoNS). Here, we used a guinea pig model of subcutaneous implanted tissue cages to assess the implication of B, I and P parameters in the capacity of nine S. epidermidis and one S. carnosus strains to develop and maintain an infection in vivo. Using clinical isolates and a model strain of S. epidermidis, we showed that the "B+, I+, P+" type confers the ability to maintain an infection in vivo. Surprisingly, the opposite type "B-, I-, P-" tested with clinical and commensal isolates, presented infection rates ranging from 25% to 60%. Other clinical isolates having a "B+, I+, P-" type, were not able to cause an infection in the present model. These results showed that, depending on the strains the capacity to colonize the tissue cage might be independent of the ability to form biofilm.

Potential use of poly-N-acetyl-beta-(1,6)-glucosamine as an antigen for diagnosis of staphylococcal orthopedic-prosthesis-related infections.

Staphylococcus aureus and coagulase-negative staphylococci are microorganisms most frequently isolated from orthopedic-implant-associated infections. Their capacity to maintain these infections is thought to be related to their ability to form adherent biofilms. Poly-N-acetyl-beta-(1,6)-glucosamine (PNAG) is an important constituent of the extracellular biofilm matrix of staphylococci. In the present study, we explored the possibility of using PNAG as an antigen for detecting antibodies in the blood sera of patients with staphylococcal orthopedic-prosthesis-associated infections. First, we tested the presence of anti-PNAG antibodies in an animal model, in the blood sera of guinea pigs that developed an implant-associated infection caused by biofilm-forming, PNAG-producing strains of Staphylococcus epidermidis. Animals infected with S. epidermidis RP62A showed levels of anti-PNAG immunoglobulin G (IgG) significantly higher than those of the control group. The comparative study of healthy individuals and patients with staphylococcal prosthesis-related infections showed that (i) relatively high levels of anti-PNAG IgG were present in the blood sera of the healthy control group, (ii) the corresponding levels in the infected patients were slightly but not significantly higher, and (iii) only 1 of 10 patients had a level of anti-PNAG IgM significantly higher than that of the control group. In conclusion, the encouraging results obtained in the animal study could not be readily applied for the diagnosis of staphylococcal orthopedic-prosthesis-related infections in humans, and PNAG does not seem to be an appropriate antigen for this purpose. Further studies are necessary to determine whether the developed enzyme-linked immunosorbent assay method could serve as a complementary test in the individual follow-up treatment of such infections caused by PNAG-producing staphylococci.

Poly-N-acetylglucosamine mediates biofilm formation and antibiotic resistance in Actinobacillus pleuropneumoniae.

Most field isolates of the swine pathogen Actinobacillus pleuropneumoniae form tenacious biofilms on abiotic surfaces in vitro. We purified matrix polysaccharides from biofilms produced by A. pleuropneumoniae field isolates IA1 and IA5 (serotypes 1 and 5, respectively), and determined their chemical structures by using NMR spectroscopy. Both strains produced matrix polysaccharides consisting of linear chains of N-acetyl-D-glucosamine (GlcNAc) residues in beta(1,6) linkage (poly-beta-1,6-GlcNAc or PGA). A small percentage of the GlcNAc residues in each polysaccharide were N-deacetylated. These structures were nearly identical to those of biofilm matrix polysaccharides produced by Escherichia coli, Staphylococcus aureus and Staphylococcus epidermidis. PCR analyses indicated that a gene encoding the PGA-specific glycoside transferase enzyme PgaC was present on the chromosome of 15 out of 15 A. pleuropneumoniae reference strains (serotypes 1-12) and 76 out of 77 A. pleuropneumoniae field isolates (serotypes 1, 5 and 7). A pgaC mutant of strain IA5 failed to form biofilms in vitro, as did wild-type strains IA1 and IA5 when grown in broth supplemented with the PGA-hydrolyzing enzyme dispersin B. Treatment of IA5 biofilms with dispersin B rendered them more sensitive to killing by ampicillin. Our findings suggest that PGA functions as a major biofilm adhesin in A. pleuropneumoniae. Biofilm formation may have relevance to the colonization and pathogenesis of A. pleuropneumoniae in pigs.

Correlation between biofilm formation and production of polysaccharide intercellular adhesin in clinical isolates of coagulase-negative staphylococci.

The ability to form a biofilm seems to play an essential role in the virulence of coagulase-negative staphylococci (CoNS) by permitting them to cause persistent prosthetic device-related infections. The most clearly characterized component of staphylococcal biofilms is the polysaccharide intercellular adhesin (PIA) encoded by the icaADBC operon. In the present paper, we assess the link between the ability to form a biofilm (Bf+/-), to synthesize PIA (PIA+/-) and the presence of the ica locus (ica+/-). For this purpose, 66 CoNS strains were tested in vitro. Seventy three percent of all strains revealed presence of the ica locus (ica+), and therefore were potentially able to produce PIA and to form a biofilm. However, the characteristics observed indicated that 15% of all strains were biofilm forming without PIA production (Bf+, PIA-, ica+/-) while 8% were PIA producers without biofilm formation (Bf-, PIA+, ica+). On the basis of the obtained data we conclude that (i) PIA synthesis alone is not sufficient to produce a biofilm and (ii) staphylococci can also form a biofilm without producing PIA.

Extracellular carbohydrate-containing polymers of a model biofilm-producing strain, Staphylococcus epidermidis RP62A.

Staphylococcus aureus and coagulase-negative staphylococci, primarily Staphylococcus epidermidis, are recognized as a major cause of nosocomial infections associated with the use of implanted medical devices. It has been established that clinical isolates often produce a biofilm, which is involved in adherence to biomaterials and provides enhanced resistance of bacteria against host defenses and antibiotic treatments. It has been thought that the staphylococcal biofilm contains two polysaccharides, one responsible for primary cell adherence to biomaterials (polysaccharide/adhesin [PS/A]) and an antigen that mediates bacterial aggregation (polysaccharide intercellular adhesin [PIA]). In the present paper we present an improved procedure for preparation of PIA that conserves its labile substituents and avoids contamination with by-products. Based on structural analysis of the polysaccharide antigens and a thorough overview of the previously published data, we concluded that PIA from S. epidermidis is structurally identical to the recently described poly-beta-(1-->6)-N-acetylglucosamine from PS/A-overproducing strain S. aureus MN8m. We also show that another carbohydrate-containing polymer, extracellular teichoic acid (EC TA), is an essential component of S. epidermidis RP62A biofilms. We demonstrate that the relative amounts of extracellular PIA and EC TA produced depend on the growth conditions. Moderate shaking or static culture in tryptic soy broth favors PIA production, while more EC TA is produced in brain heart infusion medium.

Structural characterization of a flavonoid-inducible Pseudomonas aeruginosa A-band-like O antigen of Rhizobium sp. strain NGR234, required for the formation of nitrogen-fixing nodules.

Rhizobium (Sinorhizobium) sp. strain NGR234 contains three replicons, the smallest of which (pNGR234a) carries most symbiotic genes, including those required for nodulation and lipo-chito-oligosaccharide (Nod factor) biosynthesis. Activation of nod gene expression depends on plant-derived flavonoids, NodD transcriptional activators, and nod box promoter elements. Nod boxes NB6 and NB7 delimit six different types of genes, one of which (fixF) is essential for the formation of effective nodules on Vigna unguiculata. In vegetative culture, wild-type NGR234 produces a distinct, flavonoid-inducible lipopolysaccharide (LPS) that is not produced by the mutant (NGRomegafixF); this LPS is also found in nitrogen-fixing bacteroids isolated from V. unguiculata infected with NGR234. Electron microscopy showed that peribacteroid membrane formation is perturbed in nodule cells infected by the fixF mutant. LPSs were purified from free-living NGR234 cultured in the presence of apigenin. Structural analyses showed that the polysaccharide portions of these LPSs are specialized, rhamnose-containing O antigens attached to a modified core-lipid A carrier. The primary sequence of the O antigen is [-3)-alpha-L-Rhap-(1,3)-alpha-L-Rhap-(1,2)-alpha-L-Rhap-(1-]n, and the LPS core region lacks the acidic sugars commonly associated with the antigenic outer core of LPS from noninduced cells. This rhamnan O antigen, which is absent from noninduced cells, has the same primary sequence as the A-band O antigen of Pseudomonas aeruginosa, except that it is composed of L-rhamnose rather than the D-rhamnose characteristic of the latter. It is noteworthy that A-band LPS is selectively maintained on the P. aeruginosa cell surface during chronic cystic fibrosis lung infection, where it is associated with an increased duration of infection.