Pseudomonas aeruginosa isolates from patients with cystic fibrosis: a class of serum-sensitive, nontypable strains deficient in lipopolysaccharide O side chains

Parallel evolution in Pseudomonas aeruginosa over 39,000 generations in vivo

The Gram-negative bacterium Pseudomonas aeruginosa is a common cause of chronic airway infections in individuals with the heritable disease cystic fibrosis (CF). After prolonged colonization of the CF lung, P. aeruginosa becomes highly resistant to host clearance and antibiotic treatment; therefore, understanding how this bacterium evolves during chronic infection is important for identifying beneficial adaptations that could be targeted therapeutically. To identify potential adaptive traits of P. aeruginosa during chronic infection, we carried out global transcriptomic profiling of chronological clonal isolates obtained from 3 individuals with CF. Isolates were collected sequentially over periods ranging from 3 months to 8 years, representing up to 39,000 in vivo generations. We identified 24 genes that were commonly regulated by all 3 P. aeruginosa lineages, including several genes encoding traits previously shown to be important for in vivo growth. Our results reveal that parallel evolution occurs in the CF lung and that at least a proportion of the traits identified are beneficial for P. aeruginosa chronic colonization of the CF lung.

Deadly diseases like AIDS, malaria, and tuberculosis are the result of long-term chronic infections. Pathogens that cause chronic infections adapt to the host environment, avoiding the immune response and resisting antimicrobial agents. Studies of pathogen adaptation are therefore important for understanding how the efficacy of current therapeutics may change upon prolonged infection. One notorious chronic pathogen is Pseudomonas aeruginosa, a bacterium that causes long-term infections in individuals with the heritable disease cystic fibrosis (CF). We used gene expression profiles to identify 24 genes that commonly changed expression over time in 3 P. aeruginosa lineages, indicating that these changes occur in parallel in the lungs of individuals with CF. Several of these genes have previously been shown to encode traits critical for in vivo-relevant processes, suggesting that they are likely beneficial adaptations important for chronic colonization of the CF lung.

Mucoidy, quorum sensing, mismatch repair and antibiotic resistance in Pseudomonas aeruginosa from cystic fibrosis chronic airways infections

Survival of Pseudomonas aeruginosa in cystic fibrosis (CF) chronic infections is based on a genetic adaptation process consisting of mutations in specific genes, which can produce advantageous phenotypic switches and ensure its persistence in the lung. Among these, mutations inactivating the regulators MucA (alginate biosynthesis), LasR (quorum sensing) and MexZ (multidrug-efflux pump MexXY) are the most frequently observed, with those inactivating the DNA mismatch repair system (MRS) being also highly prevalent in P. aeruginosa CF isolates, leading to hypermutator phenotypes that could contribute to this adaptive mutagenesis by virtue of an increased mutation rate. Here, we characterized the mutations found in the mucA, lasR, mexZ and MRS genes in P. aeruginosa isolates obtained from Argentinean CF patients, and analyzed the potential association of mucA, lasR and mexZ mutagenesis with MRS-deficiency and antibiotic resistance. Thus, 38 isolates from 26 chronically infected CF patients were characterized for their phenotypic traits, PFGE genotypic patterns, mutations in the mucA, lasR, mexZ, mutS and mutL gene coding sequences and antibiotic resistance profiles. The most frequently mutated gene was mexZ (79%), followed by mucA (63%) and lasR (39%) as well as a high prevalence (42%) of hypermutators being observed due to loss-of-function mutations in mutL (60%) followed by mutS (40%). Interestingly, mutational spectra were particular to each gene, suggesting that several mechanisms are responsible for mutations during chronic infection. However, no link could be established between hypermutability and mutagenesis in mucA, lasR and mexZ, indicating that MRS-deficiency was not involved in the acquisition of these mutations. Finally, although inactivation of mucA, lasR and mexZ has been previously shown to confer resistance/tolerance to antibiotics, only mutations in MRS genes could be related to an antibiotic resistance increase. These results help to unravel the mutational dynamics that lead to the adaptation of P. aeruginosa to the CF lung.

Genetic adaptation of Pseudomonas aeruginosa during chronic lung infection of patients with cystic fibrosis: strong and weak mutators with heterogeneous genetic backgrounds emerge in mucA and/or lasR mutants

During the chronic lung infection of patients with cystic fibrosis (CF), Pseudomonas aeruginosa can survive for long periods due to adaptive evolution mediated by genetic variation. Hypermutability is considered to play an important role in this adaptive evolution and it has been demonstrated that mutator populations are amplified in the CF lung by hitchhiking with adaptive mutations. Two of the genes that are frequently mutated in isolates from chronic infection are mucA and lasR. Loss-of-function mutations in these genes determine the phenotypic switch to mucoidy and loss of quorum sensing, which are considered hallmarks of chronic virulence. The aims of our study were to investigate (1) the genetic background of the P. aeruginosa subpopulations with non-mutator, weak or strong mutator phenotype and their dynamics during the chronic lung infection, and (2) the time sequence in which the hypermutable, mucoid and quorum-sensing-negative phenotypes emerge during chronic lung infection. For these purposes the sequences of mutS, mutL, uvrD, mutT, mutY and mutM anti-mutator genes as well as of mucA and lasR were analysed in 70 sequential P. aeruginosa isolates obtained from the respiratory secretions of 10 CF patients (one to three isolates per time point). Analysis of the genetic background of the mutator phenotype showed that mutS was the most commonly affected gene followed by mutL in isolates with strong mutator phenotype. The mutT, mutY, mutM genes were affected in isolates with low fold-changes in the mutation frequencies compared to the reference strain PAO1. Isolates with non-mutator, weak or strong mutator phenotype were represented at all time points showing co-existence of these subpopulations, which suggests parallel evolution of the various mutators in the different focal niches of infection in the CF lung. Mutations in mucA and lasR occurred earlier than mutations in the anti-mutator genes, showing that hypermutability is not a prerequisite for the acquisition of mucoidy and loss of quorum sensing, considered hallmarks of chronic virulence. Significantly higher mutation rates and MICs of ceftazidime, meropenem and ciprofloxacin were found for isolates collected late (more than 10 years) during the chronic lung infection compared to isolates collected earlier, which suggests an amplification of the mutator subpopulation by hitchhiking with development of antibiotic resistance. Similar evolutionary pathways concordant with adaptive radiation were observed in different clonal lineages of P. aeruginosa from CF patients.

Analysis of acquisition of Pseudomonas aeruginosa gastrointestinal mucosal colonization and horizontal transmission in a murine model

BACKGROUND

Laboratory systems to study bacterial transmission and mucosal colonization leading to infection have not been utilized.

METHODS

We determined whether transmission of various strains of Pseudomonas aeruginosa among individual mice could occur and investigated the properties of such strains in establishing gastrointestinal (GI) mucosal colonization as well as in disseminating systemically after induction of neutropenia.

RESULTS

P. aeruginosa isolates associated with epidemic spread among patients with cystic fibrosis (CF) readily established GI colonization at higher levels than did strains associated with acute infections in patients without CF, and they outcompeted these strains. Colonization was associated with resistance to bile salts. However, epidemic CF isolates did not disseminate after induction of neutropenia and did not induce as much mucosal pathology as did strains that were capable of disseminating.

CONCLUSION

Murine models can be used to study P. aeruginosa transmission and early colonization, and the properties of these strains associated with their known clinical behaviors are mimicked in this setting.

The role of Pseudomonas lipopolysaccharide in cystic fibrosis airway infection

Pseudomonas aeruginosa (PA) is a ubiquitous environmental Gram-negative bacterium found in soil and water. This opportunistic pathogen can cause infections in individuals with impaired phagocytic function, such as those with burns, exposure to chemotherapy, or cystic fibrosis (CF). PA infects the lungs of most individuals with CF, and is associated with severe progressive pulmonary disease that is the major cause of premature death in this disorder. The specific adaptations of PA to the CF airway responsible for bacterial persistence and antibiotic tolerance are not completely understood but may include increased alginate production (i.e., mucoid phenotype), biofilm formation, and specific lipid A modifications. During adaptation to the CF airway, PA synthesizes a variety of lipid A structures that alter host innate immune responses and promote bacterial persistence and chronic infection. The synthesis of specific lipid A structures is attributable to bacterial enzymes that: (1) remove the 3OH-C10:0 acyl chain from the 3-position (PagL); (2) add a C16:0 acyl chain to the 3OH-C10:0 chain at the 3'-position (PagP); (3) add C12:0 and 2OH-C12:0 acyl chains to the 3OH-C12:0 chains at the 2- and 2'-positions (HtrB and LpxO); and (4) add aminoarabinose to phosphate groups at the 1- and 4'-positions (PmrH, PmrF, PmrI, PmrJ, PmrK, and PmrE). These lipid A modifications represent an essential aspect of PA adaptation to the CF airway.

Monoclonal antibody S60-4-14 reveals diagnostic potential in the identification of Pseudomonas aeruginosa in lung tissues of cystic fibrosis patients

The lipopolysaccharide (LPS) of Pseudomonas aeruginosa has been identified to contain an inner-core structure expressing a Pseudomonas-specific epitope. This target structure is characterized by a highly phosphorylated and 7-O-carbamoyl-l-glycero-alpha-d-manno-heptopyranose (CmHep) and was found to be present in all human-pathogenic Pseudomonas species of the Palleroni (RNA)-classification I scheme. We raised and selected the monoclonal antibody S60-4-14 (mAb S60-4-14, subtype IgG1) from mice immunized with heat-killed Pseudomonas bacteria. The epitope of this mAb was found to reside in the inner-core structure of P. aeruginosa and, hence, successfully evaluated for the immunohistochemical detection of P. aeruginosa in formalin- or HOPE-fixed (Hepes-glutamic acid buffer-mediated organic solvent protection effect) and paraffin-embedded human lung tissue slices. Lung specimens, mainly from explanted lungs of cystic fibrosis (CF) patients, as well as P. aeruginosa isolates from patients suffering from CF and patients with extrapulmonar Pseudomonas infections were investigated by PCR, immunohistochemistry, and Western blot analysis with mAb S60-4-14. The results revealed an unequivocal coincidence of PCR and immunohistochemistry. Together with the Western blot results mAb S60-4-14 displays a potential diagnostic tool for the specific identification of P. aeruginosa in infected lungs of CF.

Pseudomonas aeruginosa population structure revisited

At present there are strong indications that Pseudomonas aeruginosa exhibits an epidemic population structure; clinical isolates are indistinguishable from environmental isolates, and they do not exhibit a specific (disease) habitat selection. However, some important issues, such as the worldwide emergence of highly transmissible P. aeruginosa clones among cystic fibrosis (CF) patients and the spread and persistence of multidrug resistant (MDR) strains in hospital wards with high antibiotic pressure, remain contentious. To further investigate the population structure of P. aeruginosa, eight parameters were analyzed and combined for 328 unrelated isolates, collected over the last 125 years from 69 localities in 30 countries on five continents, from diverse clinical (human and animal) and environmental habitats. The analysed parameters were: i) O serotype, ii) Fluorescent Amplified-Fragment Length Polymorphism (FALFP) pattern, nucleotide sequences of outer membrane protein genes, iii) oprI, iv) oprL, v) oprD, vi) pyoverdine receptor gene profile (fpvA type and fpvB prevalence), and prevalence of vii) exoenzyme genes exoS and exoU and viii) group I pilin glycosyltransferase gene tfpO. These traits were combined and analysed using biological data analysis software and visualized in the form of a minimum spanning tree (MST). We revealed a network of relationships between all analyzed parameters and non-congruence between experiments. At the same time we observed several conserved clones, characterized by an almost identical data set. These observations confirm the nonclonal epidemic population structure of P. aeruginosa, a superficially clonal structure with frequent recombinations, in which occasionally highly successful epidemic clones arise. One of these clones is the renown and widespread MDR serotype O12 clone. On the other hand, we found no evidence for a widespread CF transmissible clone. All but one of the 43 analysed CF strains belonged to a ubiquitous P. aeruginosa "core lineage" and typically exhibited the exoS(+)/exoU(-) genotype and group B oprL and oprD alleles. This is to our knowledge the first report of an MST analysis conducted on a polyphasic data set.

Review: Lipopolysaccharide biosynthesis in Pseudomonas aeruginosa

Pseudomonas aeruginosa causes serious nosocomial infections, and an important virulence factor produced by this organism is lipopolysaccharide (LPS). This review summarizes knowledge about biosynthesis of all three structural domains of LPS - lipid A, core oligosaccharide, and O polysaccharides. In addition, based on similarities with other bacterial species, this review proposes new hypothetical pathways for unstudied steps in the biosynthesis of P. aeruginosa LPS. Lipid A biosynthesis is discussed in relation to Escherichia coli and Salmonella, and the biosyntheses of core sugar precursors and core oligosaccharide are summarised. Pseudomonas aeruginosa attaches a Common Polysaccharide Antigen and O-Specific Antigen polysaccharides to lipid A-core. Both forms of O polysaccharide are discussed with respect to their independent synthesis mechanisms. Recent advances in understanding O-polysaccharide biosynthesis since the last major review on this subject, published nearly a decade ago, are highlighted. Since P. aeruginosa O polysaccharides contain unusual sugars, sugar-nucleotide biosynthesis pathways are reviewed in detail. Knowledge derived from detailed studies in the O5, O6 and O11 serotypes is applied to predict biosynthesis pathways of sugars in poorly-studied serotypes, especially O1, O4, and O13/O14. Although further work is required, a full understanding of LPS biosynthesis in P. aeruginosa is almost within reach.

Biosynthesis of UDP-GlcNAc(3NAc)A by WbpB, WbpE, and WbpD: enzymes in the Wbp pathway responsible for O-antigen assembly in Pseudomonas aeruginosa PAO1

The B-band O-antigen of the lipopolysaccharide found in the opportunistic pathogen Pseudomonas aeruginosa PAO1 (serotype O5) comprises a repeating trisaccharide unit that is critical for virulence and protection from host defense systems. One of the carbohydrates in this repeating unit, the rare diacetylated aminuronic acid derivative 2,3-diacetamido-2,3-dideoxy-beta-d-mannuronic acid (ManNAc(3NAc)A), is thought to be produced by five enzymes (WbpA, WbpB, WbpE, WbpD, and WbpI) in a stepwise manner starting from UDP-GlcNAc. Although the genes responsible for the biosynthesis of this sugar are known, only two of the five encoded proteins (WbpA and WbpI) have been thoroughly investigated. In this report, we describe the cloning, overexpression, purification, and biochemical characterization of the three central enzymes in this pathway, WbpB, WbpE, and WbpD. Using a combination of capillary electrophoresis, RP-HPLC, and NMR spectroscopy, we show that WbpB and WbpE are a dehydrogenase/aminotransferase pair that converts UDP-GlcNAcA to UDP-GlcNAc(3NH(2))A in a coupled reaction via a unique NAD(+) recycling pathway. In addition, we confirm that WbpD catalyzes the acetylation of UDP-GlcNAc(3NH(2))A to give UDP-GlcNAc(3NAc)A. Notably, WbpA, WbpB, WbpE, WbpD, and WbpI can be combined in vitro to generate UDP-ManNAc(3NAc)A in a single reaction vessel, thereby providing supplies of this complex glycosyl donor for future studies of lipopolysaccharide assembly. This work completes the biochemical characterization of the enzymes in this pathway and provides novel targets for potential therapeutics to combat infections with drug resistant P. aeruginosa strains.

Genetic and biochemical analyses of the Pseudomonas aeruginosa Psl exopolysaccharide reveal overlapping roles for polysaccharide synthesis enzymes in Psl and LPS production

Exopolysaccharides contribute significantly to attachment and biofilm formation in the opportunisitc pathogen Pseudomonas aeruginosa. The Psl polysaccharide, which is synthesized by the polysaccharide synthesis locus (psl), is required for biofilm formation in non-mucoid strains that do not rely on alginate as the principal biofilm polysaccharide. In-frame deletion and complementation studies of individual psl genes revealed that 11 psl genes, pslACDEFGHIJKL, are required for Psl production and surface attachment. We also present the first structural analysis of the psl-dependent polysaccharide, which consists of a repeating pentasaccharide containing d-mannose, d-glucose and l-rhamnose: [See text]. In addition, we identified the sugar nucleotide precursors involved in Psl generation and demonstrated the requirement for GDP-d-mannose, UDP-d-glucose and dTDP-l-rhamnose in Psl production and surface attachment. Finally, genetic analyses revealed that wbpW restored Psl production in a pslB mutant and pslB promoted A-band LPS synthesis in a wbpW mutant, indicating functional redundancy and overlapping roles for these two enzymes. The structural and genetic data presented here provide a basis for further investigation of the Psl proteins and potential roles for Psl in the biology and pathogenesis of P. aeruginosa.

Pseudomonas aeruginosa microevolution during cystic fibrosis lung infection establishes clones with adapted virulence

RATIONALE

During long-term lung infection in patients with cystic fibrosis (CF), Pseudomonas aeruginosa strains develop mutations leading to clonal expansion. This microevolution is believed to be correlated with a reduced virulence.

OBJECTIVES

We tested this hypothesis in models of lung infection, using mice with different genetic backgrounds.

METHODS

From infected airways of six patients with CF, 25 P. aeruginosa clones were isolated during a period of up to 16.3 years and genotypically and phenotypically characterized. Virulence of the 8 early, 6 intermediate, and 11 late CF isolates and 5 environmental strains was assessed by monitoring acute mortality versus survival and P. aeruginosa chronic persistence versus lung clearance in mice of different genetic backgrounds, including CF mice.

MEASUREMENTS AND MAIN RESULTS

Different patients harbored clonally unrelated strains, but early, intermediate, and late P. aeruginosa isolates from single patients were clonally related, allowing comparative in vivo analysis. Although late isolates were attenuated in causing acute mortality in the mouse models, compared with early and intermediate clonal isolates and environmental strains, they did not differ from early and intermediate clonal isolates in their capacity to establish chronic infection and cause extensive inflammation in the murine respiratory tract.

CONCLUSIONS

Our findings indicate that clonal expansion of P. aeruginosa strains during microevolution within CF lungs leads to populations with altered but not reduced virulence. These P. aeruginosa clones with adapted virulence play a critical role in the pathogenesis of chronic infections and may serve to define virulence determinants as targets for novel therapies.

Efflux unbalance in Pseudomonas aeruginosa isolates from cystic fibrosis patients

Retrospective analysis of 189 nonredundant strains of Pseudomonas aeruginosa sequentially recovered from the sputum samples of 46 cystic fibrosis (CF) patients over a 10-year period (1998 to 2007) revealed that 53 out of 189 (28%) samples were hypersusceptible to the beta-lactam antibiotic ticarcillin (MIC < or = 4 microg/ml) (phenotype dubbed Tic(hs)). As evidenced by trans-complementation and gene inactivation experiments, the mutational upregulation of the efflux system MexXY was responsible for various degrees of resistance to aminoglycosides in a selection of 11 genotypically distinct strains (gentamicin MICs from 2 to 64 microg/ml). By demonstrating for the first time that the MexXY pump may evolve in CF strains, we found that a mutation leading to an F1018L change in the resistance-nodulation-cell division (RND) transporter MexY was able to increase pump-promoted resistance to aminoglycosides, cefepime, and fluoroquinolones twofold. The inactivation of the mexB gene (which codes for the RND transporter MexB) in the 11 selected strains showed that the Tic(hs) phenotype was due to a mutational or functional loss of function of MexAB-OprM, the multidrug efflux system known to contribute to the natural resistance of P. aeruginosa to beta-lactams (e.g., ticarcillin and aztreonam), fluoroquinolones, tetracycline, and novobiocin. Two of the selected strains synthesized abnormally low amounts of the MexB protein, and 3 of 11 strains expressed truncated MexB (n = 2) or MexA (n = 1) polypeptide as a result of mutations in the corresponding genes, while 7 of 11 strains produced wild-type though nonfunctional MexAB-OprM pumps at levels similar to or even higher than that of reference strain PAO1. Overall, our data indicate that while MexXY is necessary for P. aeruginosa to adapt to the hostile environment of the CF lung, the MexAB-OprM pump is dispensable and tends to be lost or inactivated in subpopulations of P. aeruginosa.

Direct interaction between sensor kinase proteins mediates acute and chronic disease phenotypes in a bacterial pathogen

The genome of the opportunistic pathogen Pseudomonas aeruginosa encodes over 60 two-component sensor kinases and uses several (including RetS and GacS) to reciprocally regulate the production of virulence factors involved in the development of acute or chronic infections. We demonstrate that RetS modulates the phosphorylation state of GacS by a direct and specific interaction between these two membrane-bound sensors. The RetS-GacS interaction can be observed in vitro, in heterologous systems in vivo, and in P. aeruginosa. This function does not require the predicted RetS phosphorelay residues and provides a mechanism for integrating multiple signals without cross-phosphorylation from sensors to noncognate response regulators. These results suggest that multiple two-component systems found in a single bacterium can form multisensor signaling networks while maintaining specific phosphorelay pathways that remain insulated from detrimental cross-talk.

Newly introduced genomic prophage islands are critical determinants of in vivo competitiveness in the Liverpool Epidemic Strain of Pseudomonas aeruginosa

Pseudomonas aeruginosa isolates have a highly conserved core genome representing up to 90% of the total genomic sequence with additional variable accessory genes, many of which are found in genomic islands or islets. The identification of the Liverpool Epidemic Strain (LES) in a children's cystic fibrosis (CF) unit in 1996 and its subsequent observation in several centers in the United Kingdom challenged the previous widespread assumption that CF patients acquire only unique strains of P. aeruginosa from the environment. To learn about the forces that shaped the development of this important epidemic strain, the genome of the earliest archived LES isolate, LESB58, was sequenced. The sequence revealed the presence of many large genomic islands, including five prophage clusters, one defective (pyocin) prophage cluster, and five non-phage islands. To determine the role of these clusters, an unbiased signature tagged mutagenesis study was performed, followed by selection in the chronic rat lung infection model. Forty-seven mutants were identified by sequencing, including mutants in several genes known to be involved in Pseudomonas infection. Furthermore, genes from four prophage clusters and one genomic island were identified and in direct competition studies with the parent isolate; four were demonstrated to strongly impact on competitiveness in the chronic rat lung infection model. This strongly indicates that enhanced in vivo competitiveness is a major driver for maintenance and diversifying selection of these genomic prophage genes.

A novel oxidized low-density lipoprotein-binding protein from Pseudomonas aeruginosa

A novel protein, PA0122, has been identified in Pseudomonas aeruginosa and shown to bind to oxidized low-density lipoprotein (Ox-LDL). The PA0122 gene was recognized based on gene expression pattern differences between two strains of P. aeruginosa isolated from the sputum of an individual with cystic fibrosis (CF). There was an approximately eightfold increase in PA0122 expression in the non-mucoid strain 383, compared to that in the mucoid strain 2192. Quantitative real-time RT-PCR (qRT-PCR) supported PA0122 transcript expression differences between strains 383 and 2192 and revealed growth-phase dependence, with the highest level of expression at early stationary phase (OD(600) 1.5). PA0122 encodes a 136 aa 'conserved hypothetical' protein that has similarity to Aspergillus fumigatus Asp-haemolysin, which is an Ox-LDL-binding protein, and possessed a motif that is homologous to the fungal aegerolysin family of proteins. Antibodies produced to purified recombinant PA0122 recognized a 16 kDa protein band in cell lysates as well as in the supernatant fractions of strain 383. The PA0122 protein expression pattern was growth phase-dependent, with maximal production observed at OD(600) 1.5 that was consistent with the PA0122 transcript expression profile. Subcellular fractionation studies revealed differences in the localization of PA0122 between strains 383 and 2192. In 383, PA0122 was observed in the cytoplasm and in membrane fractions. In 2192, PA0122 was found in the cytoplasm but was not detected in membrane fractions. Surface plasmon resonance revealed that recombinant PA0122 binds with high affinity to Ox-LDL and to its major subcomponent, lysophosphatidylcholine, but not to non-oxidized LDL.

[Various typing methods of Pseudomonas aeruginosa strains isolated from cystic fibrosis patients]

Typing methods are essential to understand the epidemiology of bacterial infections. Strain typing is important for the detection of sources or routes of infections, identification between endemic and epidemic strains and prevention of transmission between patients. Some Pseudomonas aeruginosa cystic-fibrosis strains could not be typed with conventional typing methods. Due to the diverse phenotypic nature of P. aeruginosa, phenotyping methods are not discriminatory enough to identify strains belonging to the same genotype. Thus, molecular typing methods are required. These methods should be applied when data from phenotypic typing analysis becomes ambiguous, such as in cystic fibrosis. Molecular typing methods, developed over the past decade, are highly discriminatory in capacity and reproducibility. However, they are more likely applied in specialized laboratories since they are expensive and increase the workload. A reliable and low-cost typing system is required for better defining the epidemiology of this pathogen and designing more rational policies of infection control. Comparison between typing methods will pinpoint the limits and effectiveness of each method and will improve in turn the choice of a nonspecialized laboratory in terms of simplicity, time and cost.

Regulation of lipopolysaccharide O antigen expression in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium that is ubiquitously found in the environment. It is an important opportunistic pathogen in immunocompromised patients and causes life-threatening lung infections in individuals with cystic fibrosis. A prominent virulence factor for many Gram-negative bacteria, including P. aeruginosa, is lipopolysaccharide (LPS), which is an immunodominant antigen located in the outer portion of the outer membrane. P. aeruginosa produces two O antigens that are attached to lipid A + core: a B-band O antigen and an A-band O polysaccharide. The B-band O antigen-repeating unit of LPS is responsible for serotype specificity; strains lacking O antigen have been shown to be less virulent in animal models of infection. What is less well understood is how the O antigen chain length is regulated and why P. aeruginosa and some other bacteria show two preferred O antigen lengths. P. aeruginosa encodes two genes encoding O antigen chain length regulators. These genes, wzz1 and wzz2, influence the expression of the long and very long chain lengths, respectively. The long chain length appears more important for resistance to the action of sera and virulence in a mouse model of infection, while the very long chain length appears to be more sensitive to environmental stress conditions. Studies in other bacteria point to regulation at the level of transcription and complex formation as being involved in determining the O antigen chain length and may provide clues to the regulation in P. aeruginosa.

Airway epithelial control of Pseudomonas aeruginosa infection in cystic fibrosis

Defective expression or function of the cystic fibrosis transmembrane conductance regulator (CFTR) underlies the hypersusceptibility of cystic fibrosis (CF) patients to chronic airway infections, particularly with Pseudomonas aeruginosa. CFTR is involved in the specific recognition of P. aeruginosa, thereby contributing to effective innate immunity and proper hydration of the airway surface layer (ASL). In CF, the airway epithelium fails to initiate an appropriate innate immune response, allowing the microbe to bind to mucus plugs that are then not properly cleared because of the dehydrated ASL. Recent studies have identified numerous CFTR-dependent factors that are recruited to the epithelial plasma membrane in response to infection and that are needed for bacterial clearance, a process that is defective in CF patients hypersusceptible to infection with this organism.

In situ growth rates and biofilm development of Pseudomonas aeruginosa populations in chronic lung infections

The growth dynamics of bacterial pathogens within infected hosts are a fundamental but poorly understood feature of most infections. We have focused on the in situ distribution and growth characteristics of two prevailing and transmissible Pseudomonas aeruginosa clones that have caused chronic lung infections in cystic fibrosis (CF) patients for more than 20 years. We used fluorescence in situ hybridization (FISH) directly on sputum specimens to examine the spatial distribution of the infecting P. aeruginosa cells. Mucoid variants were present in sputum as cell clusters surrounded by an extracellular matrix, whereas nonmucoid variants were present mainly as dispersed cells. To obtain estimates of the growth rates of P. aeruginosa in CF lungs, we used quantitative FISH to indirectly measure growth rates of bacteria in sputum samples (reflecting the in vivo lung conditions). The concentration of rRNA in bacteria isolated from sputa was measured and correlated with the rRNA contents of the same bacteria growing in vitro at defined rates. The results showed that most cells were actively growing with doubling times of between 100 and 200 min, with some growing even faster. Only a small stationary-phase subpopulation seemed to be present in sputa. This was found for both mucoid and nonmucoid variants despite their different organizations in sputum. The results suggest that the bacterial population may be confronted with selection forces that favor optimized growth activities. This scenario constitutes a new perspective on the adaptation and evolution of P. aeruginosa during chronic infections in CF patients in particular and on long-term infections in general.

Flagellin glycosylation in Pseudomonas aeruginosa PAK requires the O-antigen biosynthesis enzyme WbpO

Pseudomonas aeruginosa PAK (serotype O6) produces a single polar, glycosylated flagellum composed of a-type flagellin. To determine whether or not flagellin glycosylation in this serotype requires O-antigen genes, flagellin was isolated from the wild type, three O-antigen-deficient mutants wbpL, wbpO, and wbpP, and a wbpO mutant complemented with a plasmid containing a wild-type copy of wbpO. Flagellin from the wbpO mutant was smaller (42 kDa) than that of the wild type (45 kDa), or other mutants strains, and exhibited an altered isoelectric point (pI 4.8) when compared with PAK flagellin (pI 4.6). These differences were because of the truncation of the glycan moiety in the wbpO-flagellin. Thus, flagellin glycosylation in P. aeruginosa PAK apparently requires a functional WbpO but not WbpP. Because WbpP was previously proposed to catalyze a metabolic step in the biosynthesis of B-band O-antigen that precedes the action of WbpO, these results prompted us to reevaluate the two-step pathway catalyzed by WbpO and WbpP. Results from WbpO-WbpP-coupled enzymatic assays showed that either WbpO or WbpP is capable of initiating the two-step pathway; however, the kinetic parameters favored the WbpO reaction to occur first, converting UDP-N-acetyl-D-glucosamine to UDP-N-acetyl-D-glucuronic acid prior to the conversion to UDP-N-acetyl-D-galacturonic acid by WbpP. This is the first report to show that a C4 epimerase could utilize UDP-N-acetylhexuronic acid as a substrate.

Quantifying the adhesion and interaction forces between Pseudomonas aeruginosa and natural organic matter

Atomic force microscopy (AFM) was used to characterize interactions between natural organic matter (NOM), and glass or bacteria. Poly(methacrylic acid) (PMA), soil humic Acid (SHA), and Suwannee River humic Acid (SRHA), were adsorbed to silica AFM probes. Adhesion forces (Fadh) for the interaction of organic-probes and glass slides correlated with organic molecular weight (MW), but not with radius of the organic aggregate (R), charge density (Q), or zeta potential (zeta). Two Pseudomonas aeruginosa strains with different lipopolysaccharides (LPS) were chosen: PAO1 (A+B+), whose LPS have common antigen (A-band) + O-antigen (B-band); and mutant AK1401 (A+B-). Fadh between bacteria and organics correlated with organic MW, R, and Q, but not zeta. PAO1 had lower Fadh with silica than NOM, which was attributed to negative charges from the B-band polymers causing electrostatic repulsion. AK1401 adhered stronger to silica than to the organics, perhaps because the absence of the B-band exposed underlying positively charged proteins. DLVO calculations could not explain the differences in the two bacteria or predict qualitative or quantitative trends in interaction forces in these systems. Molecular-level information from AFM studies can bring us closer to understanding the complex nature of bacterial-NOM interactions.

Application of vaccine technology to prevention of Pseudomonas aeruginosa infections

Development of an effective vaccine against the multiple presentations of Pseudomonas aeruginosa infection, including nosocomial pneumonia, bloodstream infections, chronic lung infections in cystic fibrosis patients and potentially sight-threatening keratitis in users of contact lenses, is a high priority. As with vaccine development for any pathogen, key information about the most effective immunologic effectors of immunity and target antigens needs to be established. For P. aeruginosa, although there is a role for cell-mediated immunity in animals following active vaccination, the bulk of the data indicate that opsonically-active antibodies provide the most effective mediators of acquired immunity. Major target antigens include the lipopolysaccharide O-polysaccharides, cell-surface alginate, flagella, components of the Type III secretion apparatus and outer membrane proteins with a potentially additive effect achieved by including immune effectors to toxins and proteases. A variety of active vaccination approaches have the potential for efficacy such as vaccination with purified or recombinant antigens incorporating multiple epitopes, conjugate vaccines incorporating proteins and carbohydrate antigens, and live attenuated vaccines, including heterologous antigen delivery systems expressing immunogenic P. aeruginosa antigens. A diverse range of passive immunotherapeutic approaches are also candidates for effective immunity, with a variety of human monoclonal antibodies described over the years with good preclinical efficacy and some early Phase I and II studies in humans. Finding an effective active and/or passive vaccination strategy for P. aeruginosa infections could be realized in the next 5 to 10 years, but will require that advances are made in the understanding of antigen expression and immune effectors that work in different human tissues and clinical settings, and also require a means to validate that clinical outcomes achieved in Phase III trials represent meaningful advances in management and treatment of P. aeruginosa infections.

Growth phenotypes of Pseudomonas aeruginosa lasR mutants adapted to the airways of cystic fibrosis patients

The opportunistic pathogen Pseudomonas aeruginosa undergoes genetic change during chronic airway infection of cystic fibrosis (CF) patients. One common change is a mutation inactivating lasR, which encodes a transcriptional regulator that responds to a homoserine lactone signal to activate expression of acute virulence factors. Colonies of lasR mutants visibly accumulated the iridescent intercellular signal 4-hydroxy-2-heptylquinoline. Using this colony phenotype, we identified P. aeruginosa lasR mutants that emerged in the airway of a CF patient early during chronic infection, and during growth in the laboratory on a rich medium. The lasR loss-of-function mutations in these strains conferred a growth advantage with particular carbon and nitrogen sources, including amino acids, in part due to increased expression of the catabolic pathway regulator CbrB. This growth phenotype could contribute to selection of lasR mutants both on rich medium and within the CF airway, supporting a key role for bacterial metabolic adaptation during chronic infection. Inactivation of lasR also resulted in increased beta-lactamase activity that increased tolerance to ceftazidime, a widely used beta-lactam antibiotic. Loss of LasR function may represent a marker of an early stage in chronic infection of the CF airway with clinical implications for antibiotic resistance and disease progression.

Exacerbations in cystic fibrosis. 1: Epidemiology and pathogenesis

With the improving survival of patients with cystic fibrosis (CF), the clinical spectrum of this complex multisystem disease continues to evolve. One of the most important clinical events for patients with CF in the course of this disease is an acute pulmonary exacerbation. Clinical and microbial epidemiology studies of CF pulmonary exacerbations continue to provide important insight into the course, prognosis and complications of the disease. This review provides a summary of the pathophysiology, clinical epidemiology and microbial epidemiology of a CF pulmonary exacerbation.

Detection of antibodies to Pseudomonas aeruginosa in serum and oral fluid from patients with cystic fibrosis

Cystic fibrosis (CF) patients who are chronically infected withPseudomonas aeruginosamake serum antibodies to bacterial surface LPS as well as other pseudomonas antigens. This study investigated the feasibility of using oral fluid samples for the detection of pseudomonas antibodies in CF patients and compared these results with corresponding serum antibodies. Most strains ofP. aeruginosaproduce two forms of LPS molecule, termed A-band (described as a common antigen) and B-band (O-serotype-specific antigen), apparently bound to a common core oligosaccharide moiety. A-band LPS was demonstrated in 45 out of 49 clinical isolates ofP. aeruginosaby SDS-PAGE and immunoblotting with a specific antibody. Oral fluids were collected from 17 adult CF patients, all of whom were sputum culture positive forP. aeruginosa(13 also provided serum samples), 11 primary ciliary dyskinesia (PCD) patients and 37 healthy volunteers. Antibodies to A-band LPS were detected by immunoblotting in all of the CF patients’ oral fluids but 10 of the volunteer samples gave weak reactions with immunoblotting. Six of the PCD patients gave a weak reaction with A-band antibodies and only one demonstrated antibodies to core LPS. In a quantitative ELISA, 15 of the 17 CF patients’ oral fluids were shown to contain antibodies to A-band LPS, whilst none of the volunteer samples contained antibodies to A-band LPS. All serum samples from the CF patients were positive by both methods. Thus this is a sensitive procedure for the detection of antibodies to A-band LPS ofP. aeruginosain oral fluid and serum from patients with CF.

Pseudomonas aeruginosa lipopolysaccharide: a major virulence factor, initiator of inflammation and target for effective immunity

Pseudomonas aeruginosa is one of the most important bacterial pathogens encountered by immunocompromised hosts and patients with cystic fibrosis (CF), and the lipopolysaccharide (LPS) elaborated by this organism is a key factor in virulence as well as both innate and acquired host responses to infection. The molecule has a fair degree of heterogeneity in its lipid A and O-antigen structure, and elaborates two different outer-core glycoforms, of which only one is ligated to the O-antigen. A close relatedness between the chemical structures and genes encoding biosynthetic enzymes has been established, with 11 major O-antigen groups identified. The lipid A can be variably penta-, hexa- or hepta-acylated, and these isoforms have differing potencies when activating host innate immunity via binding to Toll-like receptor 4 (TLR4). The O-antigen is a major target for protective immunity as evidenced by numerous animal studies, but attempts, to date, to produce a human vaccine targeting these epitopes have not been successful. Newer strategies employing live attenuated P. aeruginosa, or heterologous attenuated bacteria expressing P. aeruginosa O-antigens are potential means to solve some of the existing problems related to making a P. aeruginosa LPS-specific vaccine. Overall, there is now a large amount of information available about the genes and enzymes needed to produce the P. aeruginosa LPS, detailed chemical structures have been determined for the major O-antigens, and significant biologic and immunologic studies have been conducted to define the role of this molecule in virulence and immunity to P. aeruginosa infection.

An intragenic deletion in pilQ leads to nonpiliation of a Pseudomonas aeruginosa strain isolated from cystic fibrosis lung

Deficient motility is one of the characteristic hallmarks observed in Pseudomonas aeruginosa strains that chronically colonize the lungs of cystic fibrosis (CF) patients. Pseudomonas aeruginosa TB is a nonpiliated CF isolate known to be defective in twitching motility. Complementation confirmed a direct link of this phenotype to an intragenic out-of-frame deletion in pilQ (PA5040). Sequence alignment of pilQ derived from TB vs. PAO1 suggests that close direct repeats framing the deletion site may have triggered this mutation. This type of mutation could play a role in the emergence of pathoadaptive mutations of P. aeruginosa in the CF lung habitat.

Genetic adaptation by Pseudomonas aeruginosa to the airways of cystic fibrosis patients

In many human infections, hosts and pathogens coexist for years or decades. Important examples include HIV, herpes viruses, tuberculosis, leprosy, and malaria. With the exception of intensively studied viral infections such as HIV/AIDs, little is known about the extent to which the clonal expansion that occurs during long-term infection by pathogens involves important genetic adaptations. We report here a detailed, whole-genome analysis of one such infection, that of a cystic fibrosis (CF) patient by the opportunistic bacterial pathogen Pseudomonas aeruginosa. The bacteria underwent numerous genetic adaptations during 8 years of infection, as evidenced by a positive-selection signal across the genome and an overwhelming signal in specific genes, several of which are mutated during the course of most CF infections. Of particular interest is our finding that virulence factors that are required for the initiation of acute infections are often selected against during chronic infections. It is apparent that the genotypes of the P. aeruginosa strains present in advanced CF infections differ systematically from those of "wild-type" P. aeruginosa and that these differences may offer new opportunities for treatment of this chronic disease.

Adaptations of Pseudomonas aeruginosa to the cystic fibrosis lung environment can include deregulation of zwf, encoding glucose-6-phosphate dehydrogenase

Cystic fibrosis (CF) patients are highly susceptible to chronic pulmonary disease caused by mucoid Pseudomonas aeruginosa strains that overproduce the exopolysaccharide alginate. We showed here that a mutation in zwf, encoding glucose-6-phosphate dehydrogenase (G6PDH), leads to a approximately 90% reduction in alginate production in the mucoid, CF isolate, P. aeruginosa FRD1. The main regulator of alginate, sigma-22 encoded by algT (algU), plays a small but demonstrable role in the induction of zwf expression in P. aeruginosa. However, G6PDH activity and zwf expression were higher in FRD1 strains than in PAO1 strains. In PAO1, zwf expression and G6PDH activity are known to be subject to catabolite repression by succinate. In contrast, FRD1 zwf expression and G6PDH activity were shown to be refractory to such catabolite repression. This was apparently not due to a defect in the catabolite repression control (Crc) protein. Such relaxed control of zwf was found to be common among several examined CF isolates but was not seen in other strains of clinical and environmental origin. Two sets of clonal isolates from individual CF patient indicated that the resident P. aeruginosa strain underwent an adaptive change that deregulated zwf expression. We hypothesized that high-level, unregulated G6PDH activity provided a survival advantage to P. aeruginosa within the lung environment. Interestingly, zwf expression in P. aeruginosa was shown to be required for its resistance to human sputum. This study illustrates that adaptation to the CF pulmonary environment by P. aeruginosa can include altered regulation of basic metabolic activities, including carbon catabolism.

Exopolysaccharides from Burkholderia cenocepacia inhibit neutrophil chemotaxis and scavenge reactive oxygen species

Bacteria belonging to the Burkholderia cepacia complex are important opportunistic pathogens in compromised hosts, particularly patients with cystic fibrosis or chronic granulomatous disease. Isolates of B. cepacia complex may produce large amounts of exopolysaccharides (EPS) that endow the bacteria with a mucoid phenotype and appear to facilitate bacterial persistence during infection. We showed that EPS from a clinical B. cenocepacia isolate interfered with the function of human neutrophils in vitro; it inhibited chemotaxis and production of reactive oxygen species (ROS), both essential components of innate neutrophil-mediated host defenses. These inhibitory effects were not due to cytotoxicity or interference with intracellular calcium signaling. EPS also inhibited enzymatic generation of ROS in cell-free systems, indicating that it scavenges these bactericidal products. B. cenocepacia EPS is structurally distinct from Pseudomonas aeruginosa alginate, yet they share the capacity to scavenge ROS and inhibit chemotaxis. These properties could explain why the two bacterial species resist clearance from the infected cystic fibrosis lung.

Proteome analysis reveals adaptation ofPseudomonas aeruginosa to the cystic fibrosis lung environment

Pseudomonas aeruginosa is known for the chronic lung colonization of cystic fibrosis (CF) patients in addition to eye, ear and urinary tract infections. With the underlying disease CF patients are predisposed to P. aeruginosa chronic lung infection, which leads to morbidity and mortality. In this study, we compared the protein expression profile of a CF lung-adapted P. aeruginosa strain C with that of the burn-wound isolate PAO. Differentially expressed proteins from the whole-cell, membrane, periplasmic as well as extracellular fraction were identified. The whole-cell proteome of strain C showed down-regulation of several proteins involved in amino acid metabolism, fatty acid metabolism, energy metabolism and adaptation leading to a highly distinct proteome pattern for strain C in comparison to PAO. Analysis of secreted proteins by strain C compared to PAO revealed differential expression of virulence factors under non-inducing conditions. The membrane proteome of strain C showed modulation of the expression of porins involved in nutrient and antibiotic influx. The proteome of the periplasmic space of strain C showed retention of elastase despite that the equal amounts were secreted by strain C and PAO. Altogether, our results elucidate adaptive strategies of P. aeruginosa towards the nutrient-rich CF lung habitat during the course of chronic colonization.

Cystic fibrosis lung disease: genetic influences, microbial interactions, and radiological assessment

Cystic fibrosis (CF) is a multiorgan disease caused by mutation of the CF transmembrane conductance regulator (CFTR) gene. Obstructive lung disease is the predominant cause of morbidity and mortality; thus, most efforts to improve outcomes are directed toward slowing or halting lung-disease progression. Current therapies, such as mucolytics, airway clearance techniques, bronchodilators, and antibiotics, aim to suppress airway inflammation and the processes that stimulate it, namely, retention and infection of mucus plaques at the airway surface. New approaches to therapy that aim to ameliorate specific CFTR mutations or mutational classes by restoring normal expression or function are being investigated. Because of its sensitivity in detecting changes associated with early airway obstruction and regional lung disease, high-resolution CT (HRCT) complements pulmonary function testing in defining disease natural history and measuring response to both conventional and experimental therapies. In this review, perspectives on the genetics and microbiology of CF provide a context for understanding the increasing importance of HRCT and other imaging techniques in assessing CF therapies.

Microcolony formation: a novel biofilm model of Pseudomonas aeruginosa for the cystic fibrosis lung

Pseudomonas aeruginosa colonizing the lung of cystic fibrosis patients is responsible for a decline in health and poor prognosis for these patients. Once established, growth of P. aeruginosa in microcolonies makes it very difficult to eradicate the organisms by antimicrobial treatment. An artificial sputum medium was developed to mimic growth of P. aeruginosa in the cystic fibrosis lung habitat and it was found that the organisms grew in tight microcolonies attached to sputum components. Several genes, such as algD, oprF and lasR but not fliC, were required for tight microcolony formation. Among the sputum components, amino acids, lecithin, DNA, salt and low iron were required for tight microcolony formation. Amino acids were also shown to be responsible for various other cystic-fibrosis-specific phenotypes of P. aeruginosa, such as diversification of colony morphology, alterations in LPS structure and hyperexpression of OprF. Since the amino acid content of sputum is elevated in severe lung disease, it is suggested that the tight microcolony biofilm is maintained in these conditions and that they contribute to the vicious cycle of disease severity and failure to eradicate the organism. Thus, growth of P. aeruginosa in artificial sputum medium is an appropriate model of chronic lung colonization and may be useful for evaluating therapeutic procedures and studying antibiotic-resistance mechanisms.

Type III secretion phenotypes of Pseudomonas aeruginosa strains change during infection of individuals with cystic fibrosis

Pseudomonas aeruginosa is a frequent cause of respiratory exacerbations in individuals with cystic fibrosis. An important virulence determinant of this pathogen is its type III protein secretion system. In this study, the type III secretion properties of 435 P. aeruginosa respiratory isolates from 56 chronically infected individuals with cystic fibrosis were investigated. Although it had been previously reported that 75 to 90% of P. aeruginosa isolates from patients with hospital-acquired pneumonia secreted type III proteins, only 12% of isolates from cystic fibrosis patients did so, with nearly all of these isolates secreting ExoS and ExoT but not ExoU. Despite the low overall prevalence of type III protein-secreting isolates, at least one secreting isolate was cultured from one-third of cystic fibrosis patients. Interestingly, the fraction of cystic fibrosis patient isolates capable of secreting type III proteins decreased with duration of infection. Although 90% of isolates from the environment, the presumed reservoir for the majority of P. aeruginosa strains that infect patients with cystic fibrosis, secreted type III proteins, only 49% of isolates from newly infected children, 18% of isolates from chronically infected children, and 4% of isolates from chronically infected adults with cystic fibrosis secreted these proteins. Within individual patients, isolates of clonal origin differed in their secretion phenotypes, indicating that as strains persisted in cystic fibrosis patient airways, their type III protein secretion properties changed. Together, these findings indicate that following infection of cystic fibrosis patient airways, P. aeruginosa strains gradually change from a type III protein secretion-positive phenotype to a secretion-negative phenotype.

Oral vaccination of BALB/c mice with Salmonella enterica serovar Typhimurium expressing Pseudomonas aeruginosa O antigen promotes increased survival in an acute fatal pneumonia model

Pseudomonas aeruginosa is a leading cause of nosocomial pneumonia. We compared the efficacies of oral and intraperitoneal (i.p.) vaccinations of BALB/c mice with attenuated Salmonella enterica serovar Typhimurium SL3261 expressing P. aeruginosa serogroup O11 O antigen to protect against P. aeruginosa infection in an acute fatal pneumonia model. Oral and i.p. vaccines elicited O11-specific serum immunoglobulin G (IgG) antibodies, but IgA was observed only after oral immunization. Challenge of orally vaccinated mice with an O11 strain (9882-80) at 6 and 12 times the 50% lethal dose showed increased survival in mice that received the vaccine compared to phosphate-buffered saline (PBS)- and vector-treated controls; no difference in survival was seen with a heterologous strain, 6294 (serogroup O6). In addition, significant protection against 9882-80 was not observed in i.p. vaccinated animals. Bronchoalveolar lavage fluid taken from immunized mice harbored O11-specific IgA and IgG in orally immunized mice but only modest levels of IgG in i.p. vaccinated mice. To correlate protection, opsonophagocytosis assays were performed with pooled sera from orally immunized animals. Efficient killing of five O11 clinical isolates was observed, while no killing was noted with 6294, indicating that the recombinant SL3261 oral vaccine induces an O11-specific reaction. We next determined the ability of orally vaccinated animals to clear bacteria from their lungs. Following P. aeruginosa challenge, the numbers of viable bacteria were significantly fewer in orally vaccinated animals than in PBS- and vector-treated controls. Our results suggest that oral immunization with recombinant SL3261 is efficacious in protection against pneumonia caused by P. aeruginosa.

Correlation of wbiI genotype, serotype, and isolate source within species of the Burkholderia cepacia complex

Gram-negative bacteria of the Burkholderia cepacia complex (Bcc) are opportunistic pathogens that can infect the lungs of cystic fibrosis (CF) patients and can be transmitted among these patients, causing epidemics in the CF community. Lipopolysaccharide (LPS) is an important virulence factor of many gram-negative bacteria, with the O antigen component of LPS being responsible for serotype specificity. The goal of this work was to develop a genetic method of determining the serotype of Bcc isolates based on the conserved gene wbiI. Homologues of wbiI are found in polysaccharide biosynthesis gene clusters in other bacteria. Primers to a conserved region of the Bcc wbiI gene were able to amplify by PCR a single product in 67 of 80 Bcc isolates tested. Sequencing and restriction enzyme digestion of this wbiI PCR product revealed sufficient DNA polymorphisms to distinguish and group various isolates. In five of nine instances, Bcc isolates of a single serotype had a single wbiI restriction fragment length polymorphism (RFLP) pattern, while isolates of the other four serotypes could have multiple wbiI RFLP types. Species determination of the Bcc isolates revealed no obvious correlation between wbiI RFLP type and species. There was also no apparent correlation between wbiI RFLP type and the ability of a single Bcc isolate to infect an individual with CF. However three of five Bcc outbreaks involved isolates with the same wbiI RFLP type, indicating that wbiI RFLP typing may be a useful tool to help track Bcc outbreaks.

The galU Gene of Pseudomonas aeruginosa is required for corneal infection and efficient systemic spread following pneumonia but not for infection confined to the lung

Acute pneumonias and corneal infections due to Pseudomonas aeruginosa are typically caused by lipopolysaccharide (LPS)-smooth strains. In cystic fibrosis patients, however, LPS-rough strains of P. aeruginosa, which lack O antigen, can survive in the lung and cause chronic infection. It is not clear whether an LPS-rough phenotype affects cytotoxicity related to the type III secretion system (TTSS). We previously reported that interruption of the galU gene in P. aeruginosa results in production of a rough LPS and truncated LPS core. Here we evaluated the role of the galU gene in the pathogenesis of murine lung and eye infections and in cytotoxicity due to the TTSS effector ExoU. We studied galU mutants of strain PAO1, of its cytotoxic variant expressing ExoU from a plasmid, and of the inherently cytotoxic strain PA103. The galU mutants were more serum sensitive than the parental strains but remained cytotoxic in vitro. In a corneal infection model, the galU mutants were significantly attenuated. In an acute pneumonia model, the 50% lethal doses of the galU mutants were higher than those of the corresponding wild-type strains, yet these mutants could cause mortality and severe pneumonia, as judged by histology, even with minimal systemic spread. These findings suggest that the galU gene is required for corneal infection and for efficient systemic spread following lung infection but is not required for infection confined to the lung. Host defenses in the lung appear to be insufficient to control infection with LPS-rough P. aeruginosa when local bacterial levels are high.

Differential post-transcriptional activation of human phagocytes by different Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa is a pulmonary pathogen in individuals with impaired mucociliary clearance such as cystic fibrosis or mechanical ventilation. Non-opsonic phagocytosis of P. aeruginosa can be mediated by either CR3 or CD14 and different strains appear to have a bias towards one or the other receptor. Strain Fc808 is ingested through CD14 whereas P1 (Fc194) uses CR3. In an in vitro culture system, the inflammatory response of macrophages to these two different strains of P. aeruginosa was divergent at the protein level, with higher IL-6 and tumour necrosis factor (TNF)-alpha production generated in response to strain P1 and higher IL-1 beta production in response to strain Fc808. Interaction of macrophages with these two bacterial strains induced distinct gene expression patterns as detected by gene array analysis, with prominence of genes encoding pro-inflammatory cytokines, surface receptors, transcription factors and proteins involved in phagocytosis. However, comparison of gene expression data and cytokine response data with the two bacterial strains indicated that production of IL-1 beta, IL-6 and TNF-alpha was under differential post-transcriptional control. Interestingly, this effect did not correlate with receptor bias but instead was related to the different LPSs of the two strains. The use of specific mitogen-activated protein kinase (MAPK) inhibitors suggested a role for extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) in the differential cytokine production by strains P1 and Fc808. These results indicate that strains of the same species of bacteria may induce differential macrophage phagocytic and inflammatory responses with likely consequence for bacterial clearance and host injury.

Biochemical characterization of WbpA, a UDP-N-acetyl-D-glucosamine 6-dehydrogenase involved in O-antigen biosynthesis in Pseudomonas aeruginosa PAO1

WbpA (PA3159) is an enzyme involved in the biosynthesis of unusual di-N-acetyl-d-mannosaminuronic acid-derived sugar nucleotides found in the O antigen of Pseudomonas aeruginosa PAO1 (serotype O5). The wbpA gene that encodes this enzyme was cloned into pET-28a, overexpressed as a histidine-tagged fusion protein, and purified by nickel chelation chromatography. Capillary electrophoresis was used to examine substrate conversion by WbpA, and the data revealed that WbpA is a UDP-N-acetyl-D-glucosamine 6-dehydrogenase (EC 1.1.1.136), which uses NAD(+) as a coenzyme. The enzyme reaction product was purified by HPLC and analyzed using NMR spectroscopy. Our results showed unequivocally that the product of the WbpA reaction is UDP-N-acetyl-d-glucosaminuronic acid. WbpA requires either NH(4)(+) or K(+) for activity and the accompanying anions exert secondary effects on activity consistent with their ranking in the Hofmeister series. Kinetic analysis showed positive cooperativity with respect to UDP-N-acetyl-d-glucosamine binding with a K(0.5) of 94 microM, a k(cat) of 86 min(-1), and a Hill coefficient of 1.8. In addition, WbpA has a K(0.5) for NAD(+) of 220 microM, a k(cat) of 86 min(-1), and a Hill coefficient of 1.1. The oligomerization state of WbpA was analyzed by gel filtration, dynamic light scattering, and analytical ultracentrifugation, with all three techniques indicating that WbpA exists as a trimer in solution. However, tertiary structure predictions suggested a tetramer, which was supported by data from transmission electron microscopy. The electron micrograph of negatively stained WbpA samples revealed structures with 4-fold symmetry.

Early intervention and prevention of lung disease in cystic fibrosis: a European consensus

In patients with cystic fibrosis (CF), early intervention and prevention of lung disease is of paramount importance. Principles to achieve this aim include early diagnosis of CF, regular monitoring of the clinical status, various hygienic measures to prevent infection and cross-infection, early use of antibiotic courses in patients with recurrent or continuous bacterial colonisation and appropriate use of chest physiotherapy.

Alterations in the formation of lipopolysaccharide and membrane vesicles on the surface of Pseudomonas aeruginosa PAO1 under oxygen stress conditions

It has been postulated that phenotypic variation in the relative expression of two chemically distinct types of lipopolysaccharide (LPS), a serotype-specific LPS (B-band) and a common antigen LPS (A-band) in Pseudomonas aeruginosa is an important mechanism enabling this opportunistic pathogen to alter its surface characteristics to mediate adhesion and to survive under extreme conditions. To further investigate this, the relative expression levels of the two distinct types of LPS in P. aeruginosa PAO1 were investigated with cells grown in a chemostat at different dissolved oxygen tensions (pO(2)). The A-band LPS was constitutively expressed as pO(2) was increased from nearly zero to 350 % of air saturation. In contrast, the B-band LPS showed a remarkable increase with increased pO(2). Almost no B-band LPS was found in cells grown at a pO(2) of less than 3 % of air saturation. Electron microscopic examination of cells revealed increased formation of membrane vesicles (MVs) on the surface of P. aeruginosa PAO1 under oxygen stress conditions. The toxicity of the supernatant of P. aeruginosa cultures to the growth of a hybridoma cell line significantly increased in samples taken from oxygen-stressed steady-state cultures. Furthermore, studies of adhesion in a continuous-flow biofilm culture revealed an increased adhesiveness for hydrophilic surfaces in P. aeruginosa PAO1 grown at a higher pO(2). The oxygen-dependent alterations of cell-surface components and properties observed in this work provide a possible explanation for the emergence of P. aeruginosa lacking the B-band LPS in chronically infected cystic fibrosis patients. The results are also useful for understanding the processes involved in the formation of MVs in P. aeruginosa.

Pathophysiology and management of pulmonary infections in cystic fibrosis

This comprehensive State of the Art review summarizes the current published knowledge base regarding the pathophysiology and microbiology of pulmonary disease in cystic fibrosis (CF). The molecular basis of CF lung disease including the impact of defective cystic fibrosis transmembrane regulator (CFTR) protein function on airway physiology, mucociliary clearance, and establishment of Pseudomonas aeruginosa infection is described. An extensive review of the microbiology of CF lung disease with particular reference to infection with P. aeruginosa is provided. Other pathogens commonly associated with CF lung disease including Staphylococcal aureus, Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and atypical mycobacteria are also described. Clinical presentation and assessment of CF lung disease including diagnostic microbiology and other measures of pulmonary health are reviewed. Current recommendations for management of CF lung disease are provided. An extensive review of antipseudomonal therapies in the settings of treatment for early P. aeruginosa infection, maintenance for patients with chronic P. aeruginosa infection, and treatment of exacerbation in pulmonary symptoms, as well as antibiotic therapies for other CF respiratory pathogens, are included. In addition, the article discusses infection control policies, therapies to optimize airway clearance and reduce inflammation, and potential future therapies.