Relation between antibody response to Pseudomonas aeruginosa exoproteins and colonization/infection in patients with cystic fibrosis

Phospholipase C: underrated players in microbial infections

During bacterial infections, one or more virulence factors are required to support the survival, growth, and colonization of the pathogen within the host, leading to the symptomatic characteristic of the disease. The outcome of bacterial infections is determined by several factors from both host as well as pathogen origin. Proteins and enzymes involved in cellular signaling are important players in determining the outcome of host-pathogen interactions. phospholipase C (PLCs) participate in cellular signaling and regulation by virtue of their ability to hydrolyze membrane phospholipids into di-acyl-glycerol (DAG) and inositol triphosphate (IP3), which further causes the activation of other signaling pathways involved in various processes, including immune response. A total of 13 PLC isoforms are known so far, differing in their structure, regulation, and tissue-specific distribution. Different PLC isoforms have been implicated in various diseases, including cancer and infectious diseases; however, their roles in infectious diseases are not clearly understood. Many studies have suggested the prominent roles of both host and pathogen-derived PLCs during infections. PLCs have also been shown to contribute towards disease pathogenesis and the onset of disease symptoms. In this review, we have discussed the contribution of PLCs as a determinant of the outcome of host-pathogen interaction and pathogenesis during bacterial infections of human importance.

Targeting the Pseudomonas aeruginosa Virulence Factor Phospholipase C With Engineered Liposomes

Engineered liposomes composed of the naturally occurring lipids sphingomyelin (Sm) and cholesterol (Ch) have been demonstrated to efficiently neutralize toxins secreted by Gram-positive bacteria such as Streptococcus pneumoniae and Staphylococcus aureus. Here, we hypothesized that liposomes are capable of neutralizing cytolytic virulence factors secreted by the Gram-negative pathogen Pseudomonas aeruginosa. We used the highly virulent cystic fibrosis P. aeruginosa Liverpool Epidemic Strain LESB58 and showed that sphingomyelin (Sm) and a combination of sphingomyelin with cholesterol (Ch:Sm; 66 mol/% Ch and 34 mol/% Sm) liposomes reduced lysis of human bronchial and red blood cells upon challenge with the Pseudomonas secretome. Mass spectrometry of liposome-sequestered Pseudomonas proteins identified the virulence-promoting hemolytic phospholipase C (PlcH) as having been neutralized. Pseudomonas aeruginosa supernatants incubated with liposomes demonstrated reduced PlcH activity as assessed by the p-nitrophenylphosphorylcholine (NPPC) assay. Testing the in vivo efficacy of the liposomes in a murine cutaneous abscess model revealed that Sm and Ch:Sm, as single dose treatments, attenuated abscesses by >30%, demonstrating a similar effect to that of a mutant lacking plcH in this infection model. Thus, sphingomyelin-containing liposome therapy offers an interesting approach to treat and reduce virulence of complex infections caused by P. aeruginosa and potentially other Gram-negative pathogens expressing PlcH.

Potential Therapeutic Targets for Combination Antibody Therapy against Pseudomonas aeruginosa Infections

Despite advances in antimicrobial therapy and even the advent of some effective vaccines, Pseudomonas aeruginosa (P. aeruginosa) remains a significant cause of infectious disease, primarily due to antibiotic resistance. Although P. aeruginosa is commonly treatable with readily available therapeutics, these therapies are not always efficacious, particularly for certain classes of patients (e.g., cystic fibrosis (CF)) and for drug-resistant strains. Multi-drug resistant P. aeruginosa infections are listed on both the CDC’s and WHO’s list of serious worldwide threats. This increasing emergence of drug resistance and prevalence of P. aeruginosa highlights the need to identify new therapeutic strategies. Combinations of monoclonal antibodies against different targets and epitopes have demonstrated synergistic efficacy with each other as well as in combination with antimicrobial agents typically used to treat these infections. Such a strategy has reduced the ability of infectious agents to develop resistance. This manuscript details the development of potential therapeutic targets for polyclonal antibody therapies to combat the emergence of multidrug-resistant P. aeruginosa infections. In particular, potential drug targets for combinational immunotherapy against P. aeruginosa are identified to combat current and future drug resistance.

Diagnostic and prognostic significance of systemic alkyl quinolones for P. aeruginosa in cystic fibrosis: A longitudinal study

Background

Pulmonary P. aeruginosa infection is associated with poor outcomes in cystic fibrosis (CF) and early diagnosis is challenging, particularly in those who are unable to expectorate sputum. Specific P. aeruginosa 2-alkyl-4-quinolones are detectable in the sputum, plasma and urine of adults with CF, suggesting that they have potential as biomarkers for P. aeruginosa infection.

Aim

To investigate systemic 2-alkyl-4-quinolones as potential biomarkers for pulmonary P. aeruginosa infection.

Methods

A multicentre observational study of 176 adults and 68 children with CF. Cross-sectionally, comparisons were made between current P. aeruginosa infection using six 2-alkyl-4-quinolones detected in sputum, plasma and urine against hospital microbiological culture results. All participants without P. aeruginosa infection at baseline were followed up for one year to determine if 2-alkyl-4-quinolones were early biomarkers of pulmonary P. aeruginosa infection.

Results

Cross-sectional analysis: the most promising biomarker with the greatest diagnostic accuracy was 2-heptyl-4-hydroxyquinoline (HHQ). In adults, areas under the ROC curves (95% confidence intervals) for HHQ analyses were 0.82 (0.75–0.89) in sputum, 0.76 (0.69–0.82) in plasma and 0.82 (0.77–0.88) in urine. In children, the corresponding values for HHQ analyses were 0.88 (0.77–0.99) in plasma and 0.83 (0.68–0.97) in urine.

Longitudinal analysis: Ten adults and six children had a new positive respiratory culture for P. aeruginosa in follow-up. A positive plasma HHQ test at baseline was significantly associated with a new positive culture for P. aeruginosa in both adults and children in follow-up (odds ratio (OR) = 6.67;-95% CI:-1.48–30.1;-p = 0.01 and OR = 70; 95% CI: 5–956;-p < 0.001 respectively).

Conclusions

AQs measured in sputum, plasma and urine may be used to diagnose current infection with P. aeruginosa in adults and children with CF. These preliminary data show that plasma HHQ may have potential as an early biomarker of pulmonary P. aeruginosa. Further studies are necessary to evaluate if HHQ could be used in clinical practice to aid early diagnosis of P. aeruginosa infection in the future.

Interaction between extracellular lipase LipA and the polysaccharide alginate of Pseudomonas aeruginosa

Background

As an opportunistic human pathogen Pseudomonas aeruginosa is able to cause acute and chronic infections. The biofilm mode of life significantly contributes to the growth and persistence of P. aeruginosa during an infection process and mediates the pathogenicity of the bacterium. Within a biofilm mucoid strains of P. aeruginosa simultaneously produce and secrete several hydrolytic enzymes and the extracellular polysaccharide alginate. The focus of the current study was the interaction between extracellular lipase LipA and alginate, which may be physiologically relevant in biofilms of mucoid P. aeruginosa.

Results

Fluorescence microscopy of mucoid P. aeruginosa biofilms were performed using fluorogenic lipase substrates. It showed a localization of the extracellular enzyme near the cells. A microtiter plate-based binding assay revealed that the polyanion alginate is able to bind LipA. A molecular modeling approach showed that this binding is structurally based on electrostatic interactions between negatively charged residues of alginate and positively charged amino acids of the protein localized opposite of the catalytic centre. Moreover, we showed that the presence of alginate protected the lipase activity by protection from heat inactivation and from degradation by the endogenous, extracellular protease elastase LasB. This effect was influenced by the chemical properties of the alginate molecules and was enhanced by the presence of O-acetyl groups in the alginate chain.

Conclusion

We demonstrate that the extracellular lipase LipA from P. aeruginosa interacts with the polysaccharide alginate in the self-produced extracellular biofilm matrix of P. aeruginosa via electrostatic interactions suggesting a role of this interaction for enzyme immobilization and accumulation within biofilms. This represents a physiological advantage for the cells. Especially in the biofilm lifestyle, the enzyme is retained near the cell surface, with the catalytic centre exposed towards the substrate and is protected from denaturation and proteolytic degradation.

Anr and its activation by PlcH activity in Pseudomonas aeruginosa host colonization and virulence

Pseudomonas aeruginosa hemolytic phospholipase C (PlcH) degrades phosphatidylcholine (PC), an abundant lipid in cell membranes and lung surfactant. A ΔplcHR mutant, known to be defective in virulence in animal models, was less able to colonize epithelial cell monolayers and was defective in biofilm formation on plastic when grown in lung surfactant. Microarray analyses found that strains defective in PlcH production had lower levels of Anr-regulated transcripts than the wild type. PC degradation stimulated the Anr regulon in an Anr-dependent manner under conditions where Anr activity was submaximal because of the presence of oxygen. Two PC catabolites, choline and glycine betaine (GB), were sufficient to stimulate Anr activity, and their catabolism was required for Anr activation. The addition of choline or GB to glucose-containing medium did not alter Anr protein levels, growth rates, or respiratory activity, and Anr activation could not be attributed to the osmoprotectant functions of GB. The Δanr mutant was defective in virulence in a mouse pneumonia model. Several lines of evidence indicate that Anr is important for the colonization of biotic and abiotic surfaces in both P. aeruginosa PAO1 and PA14 and that increases in Anr activity resulted in enhanced biofilm formation. Our data suggest that PlcH activity promotes Anr activity in oxic environments and that Anr activity contributes to virulence, even in the acute infection phase, where low oxygen tensions are not expected. This finding highlights the relationships among in vivo bacterial metabolism, the activity of the oxygen-sensitive regulator Anr, and virulence.

Activation of the epithelial sodium channel (ENaC) by the alkaline protease from Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that significantly contributes to the mortality of patients with cystic fibrosis. Chronic infection by Pseudomonas induces sustained immune and inflammatory responses and damage to the airway. The ability of Pseudomonas to resist host defenses is aided, in part, by secreted proteases, which act as virulence factors in multiple modes of infection. Recent studies suggest that misregulation of protease activity in the cystic fibrosis lung may alter fluid secretion and pathogen clearance by proteolytic activation of the epithelial sodium channel (ENaC). To evaluate the possibility that proteolytic activation of ENaC may contribute to the virulence of Pseudomonas, primary human bronchial epithelial cells were exposed to P. aeruginosa and ENaC function was assessed by short circuit current measurements. Apical treatment with a strain known to express high levels of alkaline protease (AP) resulted in an increase in basal ENaC current and a loss of trypsin-inducible ENaC current, consistent with sustained activation of ENaC. To further characterize this AP-induced ENaC activation, AP was purified, and its folding, activity, and ability to activate ENaC were assessed. AP folding was efficient under pH and calcium conditions thought to exist in the airway surface liquid of normal and cystic fibrosis (CF) lungs. Short circuit measurements of ENaC in polarized monolayers indicated that AP activated ENaC in immortalized cell lines as well as post-transplant, primary human bronchial epithelial cells from both CF and non-CF patients. This activation was mapped to the γ-subunit of ENaC. Based on these data, patho-mechanisms associated with AP in the CF lung are proposed wherein secretion of AP leads to decreased airway surface liquid volume and a corresponding decrease in mucocilliary clearance of pulmonary pathogens.

Proteases, cystic fibrosis and the epithelial sodium channel (ENaC)

Proteases perform a diverse array of biological functions. From simple peptide digestion for nutrient absorption to complex signaling cascades, proteases are found in organisms from prokaryotes to humans. In the human airway, proteases are associated with the regulation of the airway surface liquid layer, tissue remodeling, host defense and pathogenic infection and inflammation. A number of proteases are released in the airways under both physiological and pathophysiological states by both the host and invading pathogens. In airway diseases such as cystic fibrosis, proteases have been shown to be associated with increased morbidity and airway disease progression. In this review, we focus on the regulation of proteases and discuss specifically those proteases found in human airways. Attention then shifts to the epithelial sodium channel (ENaC), which is regulated by proteolytic cleavage and that is considered to be an important component of cystic fibrosis disease. Finally, we discuss bacterial proteases, in particular, those of the most prevalent bacterial pathogen found in cystic fibrosis, Pseudomonas aeruginosa.

Rapid and sensitive detection of Pseudomonas aeruginosa in chlorinated water and aerosols targeting gyrB gene using real-time PCR

AIMS

For the rapid detection of Pseudomonas aeruginosa from chlorinated water and aerosols, gyrB gene-based real-time PCR assay was developed and investigated.

METHODS AND RESULTS

Two novel primer sets (pa722F/746MGB/899R and pa722F/746MGB/788R) were designed using the most updated 611 Pseudomonas and 748 other bacterial gyrB genes for achieving high specificity. Their specificity showed 100% accuracy when tested with various strains including clinical isolates from cystic fibrosis patients. The assay was tested with Ps. aeruginosa-containing chlorinated water and aerosols to simulate the waterborne and airborne transmission routes (detection limit 3·3 × 10² CFU per PCR-2·3 × 10³ CFU per PCR). No chlorine interference in real-time PCR was observed at drinking water level (c. 1 mg l⁻¹), but high level of chorine (12 mg l⁻¹) interfered the assay, and thus neutralization was needed. Pseudomonas aeruginosa in aerosol was successfully detected after capturing with gelatin filters with minimum 2 min of sampling time when the initial concentration of 10⁴ CFU ml⁻¹ bacteria existed in the nebulizer.

CONCLUSIONS

A highly specific and rapid assay (2-3 h) was developed by targeting gyrB gene for the detection of Ps. aeruginosa in chlorinated water and aerosols, combined with optimized sample collection methods and sample processing, so the direct DNA extraction from either water or aerosol was possible while achieving the desired sensitivity of the method.

SIGNIFICANCE AND IMPACT OF THE STUDY

  The new assay can provide timely and accurate risk assessment to prevent Ps. aeruginosa exposure from water and aerosol, resulting in reduced disease burden, especially among immune-compromised and susceptible individuals. This approach can be easily utilized as a platform technology for the detection of other types of micro-organisms, especially for those that are transmitted via water and aerosol routes, such as Legionella pneumophila.

Usefulness of serum IgG4 in the diagnosis and follow up of autoimmune pancreatitis: A systematic literature review and meta-analysis

High circulating serum immunoglobulin G4 (IgG4) levels have been proposed as a marker of autoimmune pancreatitis (AIP). The aim of the present study was to review the data existing in the English literature on the usefulness of the IgG4 serum levels in the diagnosis and follow up of patients with AIP. A total of 159 patients with AIP and 1099 controls were described in seven selected papers reporting the usefulness of serum IgG4 in diagnosing AIP. In total, 304 controls had pancreatic cancer, 96 had autoimmune diseases, and the remaining 699 had other conditions. The summary receiver-operating characteristic curve analysis was carried out by means of Meta-DiSc open-access software. Serum IgG4 showed good accuracy in distinguishing between AIP and the overall controls, pancreatic cancer and other autoimmune diseases (area under the curve [+/- SE]: 0.920 +/- 0.073, 0.914 +/- 0.191, and 0.949 +/- 0.024, respectively). The studies analyzed showed significantly heterogeneous specificity values in each of the three analyses performed. The analysis of the four studies comparing AIP and pancreatic cancers also showed significantly heterogeneous values of sensitivities and odds ratios. Regarding the usefulness of IgG4 as a marker of efficacy of steroid treatment, a decrease in the serum concentrations of IgG4 was found in the four available studies. The serum IgG4 subclass is a good marker of AIP, and its determination should be included in the diagnostic workup of this disease. However, the heterogeneity of the studies published until now means that more studies are necessary in order to better evaluate the true accuracy of IgG4 in discriminating AIP versus other autoimmune diseases.

The combination of PCR and serology increases the diagnosis of Pseudomonas aeruginosa colonization/infection in cystic fibrosis

BACKGROUND

Early diagnosis of Pseudomonas aeruginosa colonization/infection in patients with cystic fibrosis (CF) using microbiological culturing methods may be difficult. Serology and polymerase chain reaction (PCR) may be useful techniques for early detection of P. aeruginosa in children with CF.

METHODS

A cross-sectional analysis comparing results obtained by three different methods for P. aeruginosa identification was performed in 87 CF patients with a mean age of 9.7 years. Microbiological culturing and PCR targeting the algD GDP mannose dehydrogenase gene of P. aeruginosa were performed in sputum or oropharyngeal swabs samples, and serum antibodies against three P. aeruginosa antigens (elastase, alkaline protease, and exotoxin A) were assessed once.

RESULTS

It was possible to isolate P. aeruginosa by culture in samples from 42 patients (48.2%), while PCR was positive in 53 (60.9%) patients. Serology was positive in 38 patients (43.6%), with a higher positivity for elastase (37.9%), followed by alkaline protease (29.9%) and exotoxin A (19.5%). The difference among the three isolated methods was not statistically significant. The combination of PCR + serology was significantly superior to single methods, to PCR + culture and also to culture + serology.

CONCLUSIONS

PCR identified a higher number of patients with P. aeruginosa than serology and conventional culture, but the difference did not reach statistical significance. Any of the combination methods that included PCR resulted in significantly statistical differences in relation to isolated microbiological or serology methods, but not to the PCR method alone, suggesting that PCR may be the main additive method for P. aeruginosa identification.

Diagnostic value of serological tests against Pseudomonas aeruginosa in a large cystic fibrosis population

BACKGROUND

Serological methods to monitor Pseudomonas aeruginosa colonisation in patients with cystic fibrosis (CF) are advocated but the diagnostic value of a commercially available P aeruginosa antibody test to detect early and chronic P aeruginosa colonisation in a non-research setting has not been assessed.

METHODS

Colonisation with P aeruginosa was estimated by regular culture of sputum or oropharyngeal swabs during three consecutive years in 220 patients with CF aged 0-65 years. Commercially available ELISA tests with three P aeruginosa antigens (elastase, exotoxin A, alkaline protease) were performed at the end of the study period. In a subgroup of 57 patients (aged 4-14 years) serological tests were performed annually.

RESULTS

Using culture as the reference standard, the ELISA tests using the advised cut off values had a sensitivity of 79% and a specificity of 89% for chronic colonisation. Receiver-operator characteristic curves were created to optimise cut off values. Applying these new cut off values resulted in a sensitivity of 96% and a specificity of 79%. All three individual serological tests discriminated well between the absence and presence of chronic P aeruginosa colonisation. The sensitivity of the individual antibody test was 87% for elastase, 79% for exotoxin A, and 76% for alkaline protease. First colonisation was preceded by positive serological results in only five of 13 patients (38%).

CONCLUSION

In patients with CF, serological tests using specific antigens are sensitive for diagnosing chronic P aeruginosa colonisation. However, the failure of serological tests to detect early colonisation in young patients emphasises the need for continued reliance on cultures.

Detection of Pseudomonas aeruginosa in patients with cystic fibrosis

Chronic pulmonary colonisation with Pseudomonas aeruginosa (PA) in patients with CF is associated with a high morbidity and mortality. Adequate treatment of first acquisition of PA might prevent or postpone chronic colonisation. Early detection of PA is therefore of major importance. Currently, cultures of oropharynx or sputum are most commonly practised. However, oropharyngeal culture has limitations both in the positive and negative predictive value for the presence of PA in the lower respiratory tract. Induction of sputum has little benefit in detection of PA. Serology might have additional value in early detection, when bacterial density is too low to be detected by culture. Molecular techniques are not yet widespread used for detection of PA, but have in general a high sensitivity. In this review, we describe the value of different diagnostic techniques for detecting PA.

Early immune response to the components of the type III system of Pseudomonas aeruginosa in children with cystic fibrosis

The lungs of patients with cystic fibrosis (CF) are colonized initially by Pseudomonas aeruginosa, which is associated with progressive lung destruction and increased mortality. The pathogenicity of P. aeruginosa is caused by a number of virulence factors, including exotoxin A (ETA) and the type III cytotoxins (ExoS, ExoT, ExoU, and ExoY). P. aeruginosa contacts the plasma membrane to deliver type III cytotoxins through a channel formed by PopB, PopD, and PcrV; ETA enters mammalian cells via receptor-mediated endocytosis. The Wisconsin CF Neonatal Screening Project is a longitudinal investigation to assess the potential benefits and risks of newborn screening for CF; the project was the source of serum samples used in this study. Past studies evaluated the longitudinal appearance of antibodies to ETA and elastase and P. aeruginosa infections in patients with CF. The current study characterized the longitudinal appearance of antibodies to components of the type III system in children with CF. Western blot analyses showed that serum antibodies to PopB, PcrV, and ExoS were common. Longitudinal enzyme-linked immunosorbent assays determined that the first detection of antibodies to pooled ExoS/PopB occurred at a time similar to those of detection of antibodies to a P. aeruginosa cell lysate and the identification of oropharyngeal cultures positive for P. aeruginosa. This indicates that children with CF are colonized early with P. aeruginosa expressing the type III system, implicating it in early pathogenesis, and implies that surveillance of clinical symptoms, oropharyngeal cultures, and seroconversion to type III antigens may facilitate early detection of P. aeruginosa infections.

Predictors of deterioration of lung function in cystic fibrosis

The severity of lung disease in cystic fibrosis (CF) may be related to the type of mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and to environmental and immunological factors. Since pulmonary disease is the main determinant of morbidity and mortality in CF, it is important to identify factors that can explain and predict this variation. The aim of this longitudinal study of the whole Swedish CF population over age 7 years was to correlate genetic and clinical data with the rate of decline in pulmonary function. The statistical analysis was performed using the mixed model regression method, supplemented with calculation of relative risks for severe lung disease in age cohorts.The severity of pulmonary disease was to some extent predicted by CFTR genotype. Furthermore, the present investigation is the first long-term study showing a significantly more rapid deterioration of lung function in patients with concomitant diabetes mellitus. Besides diabetes mellitus, pancreatic insufficiency and chronic Pseudomonas colonization were found to be negative predictors of pulmonary function. In contrast to several other reports, we found no significant differences in lung function between genders. Patients with pancreatic sufficiency have no or only a slight decline of lung function with age once treatment is started, but an early diagnosis in this group is desirable.

Pseudomonas aeruginosa quorum-sensing systems may control virulence factor expression in the lungs of patients with cystic fibrosis

Individuals with cystic fibrosis (CF) are commonly colonized with Pseudomonas aeruginosa. The chronic infections caused by P. aeruginosa are punctuated by acute exacerbations of the lung disease, which lead to significant morbidity and mortality. As regulators of virulence determinants, P. aeruginosa quorum-sensing systems may be active in the chronic lung infections associated with CF. We have examined the levels of autoinducer molecules and transcript accumulation from the bacterial populations found in the lungs of patients with CF. We detected biologically active levels of N-(3-oxododecanoyl)-L-homoserine (3-oxo-C12-HSL) and N-butyryl-L-homoserine lactone (C4-HSL) in sputum from CF patients. Interestingly, it appears that C4-HSL is less frequently detected than 3-oxo-C12-HSL in the lungs of patients with CF. We also examined the transcription of the autoinducer synthase gene lasI and showed that it is frequently expressed in the lungs of patients with CF. We observed a significant correlation between the expression of lasI and four target genes of the Las quorum-sensing system. Taken together, our results indicate that quorum-sensing systems are active and may control virulence factor expression in the lungs of patients with CF.

Nasal polyps in cystic fibrosis: clinical endoscopic study with nasal lavage fluid analysis

STUDY OBJECTIVES

Nasal polyps frequently appear in patients with cystic fibrosis (CF). The aims of this study were to focus on what problems (symptoms, endoscopic findings, and laboratory correlates) nasal polyps cause the CF patient, and how these correlate to the total health situation of this patient group.

PATIENTS AND STUDY DESIGN

The clinical histories, endoscopic investigations of the nasal cavity, and analyses of nasal lavage fluid of 44 patients with CF complicated with nasal polyposis have been compared with those of 67 CF control subjects. The patients were examined at annual control examinations (with pulmonary tests, working capacity, liver tests, and bacterial and blood tests) from 1995 to 1996 at Stockholm Cystic Fibrosis Center, Huddinge University Hospital. All patients were > 2 years of age. The endoscopic findings were related to the actual pulmonary function, inflammatory blood parameters, colonizing pathogens, antibodies (Staphylococcus aureus and Pseudomonas aeruginosa), and genotype.

RESULTS

The patients with nasal polyps differed with respect to chronic colonization of P aeruginosa in sputum samples and had a higher occurrence of serum antibodies against the same species. The two groups did not differ in pulmonary functions, inflammatory parameters, or genotype. The polyps found were mainly small (within the meatus media) and gave no significant increase in ongoing clinical symptoms such as rhinorrhea, nasal obstruction, or hyposmia. Neither was any significantly marked finding concerning the nose (mucosal swellings, secretion, etc.) made in the polyp patients. The patients with CF scored slightly lower in a smell identification test in comparison with the healthy control group. The nasal lavage fluid was analyzed (in 93 of the 111 patients) for the occurrence of P aeruginosa (by polymerase-chain reaction [PCR]), interleukin [IL]-5, IL-8, and lysozyme. The lysozyme and IL-8 content was equal in the two CF groups but increased in comparison with the healthy control group. P aeruginosa was not detected with PCR in any nasal lavage fluid. No measurable levels of IL-5 in the nasal lavage were found.

CONCLUSIONS

There was a higher frequency of chronic colonization of P aeruginosa in the lower respiratory tract in patients with nasal polyps. Otherwise, nonsevere nasal polyposis was not an indicator of lower respiratory tract morbidity in CF patients.

Potential role of phospholipases in virulence and fungal pathogenesis

Microbial pathogens use a number of genetic strategies to invade the host and cause infection. These common themes are found throughout microbial systems. Secretion of enzymes, such as phospholipase, has been proposed as one of these themes that are used by bacteria, parasites, and pathogenic fungi. The role of extracellular phospholipase as a potential virulence factor in pathogenic fungi, including Candida albicans, Cryptococcus neoformans, and Aspergillus, has gained credence recently. In this review, data implicating phospholipase as a virulence factor in C. albicans, Candida glabrata, C. neoformans, and A. fumigatus are presented. A detailed description of the molecular and biochemical approaches used to more definitively delineate the role of phospholipase in the virulence of C. albicans is also covered. These approaches resulted in cloning of three genes encoding candidal phospholipases (caPLP1, caPLB2, and PLD). By using targeted gene disruption, C. albicans null mutants that failed to secrete phospholipase B, encoded by caPLB1, were constructed. When these isogenic strain pairs were tested in two clinically relevant murine models of candidiasis, deletion of caPLB1 was shown to lead to attenuation of candidal virulence. Importantly, immunogold electron microscopy studies showed that C. albicans secretes this enzyme during the infectious process. These data indicate that phospholipase B is essential for candidal virulence. Although the mechanism(s) through which phospholipase modulates fungal virulence is still under investigations, early data suggest that direct host cell damage and lysis are the main mechanisms contributing to fungal virulence. Since the importance of phospholipases in fungal virulence is already known, the next challenge will be to utilize these lytic enzymes as therapeutic and diagnostic targets.

Potential role of phospholipases in virulence and fungal pathogenesis

Microbial pathogens use a number of genetic strategies to invade the host and cause infection. These common themes are found throughout microbial systems. Secretion of enzymes, such as phospholipase, has been proposed as one of these themes that are used by bacteria, parasites, and pathogenic fungi. The role of extracellular phospholipase as a potential virulence factor in pathogenic fungi, including Candida albicans, Cryptococcus neoformans, and Aspergillus, has gained credence recently. In this review, data implicating phospholipase as a virulence factor in C. albicans, Candida glabrata, C. neoformans, and A. fumigatus are presented. A detailed description of the molecular and biochemical approaches used to more definitively delineate the role of phospholipase in the virulence of C. albicans is also covered. These approaches resulted in cloning of three genes encoding candidal phospholipases (caPLP1, caPLB2, and PLD). By using targeted gene disruption, C. albicans null mutants that failed to secrete phospholipase B, encoded by caPLB1, were constructed. When these isogenic strain pairs were tested in two clinically relevant murine models of candidiasis, deletion of caPLB1 was shown to lead to attenuation of candidal virulence. Importantly, immunogold electron microscopy studies showed that C. albicans secretes this enzyme during the infectious process. These data indicate that phospholipase B is essential for candidal virulence. Although the mechanism(s) through which phospholipase modulates fungal virulence is still under investigations, early data suggest that direct host cell damage and lysis are the main mechanisms contributing to fungal virulence. Since the importance of phospholipases in fungal virulence is already known, the next challenge will be to utilize these lytic enzymes as therapeutic and diagnostic targets.

Pseudomonas aeruginosa hemolytic phospholipase C suppresses neutrophil respiratory burst activity

Pseudomonas aeruginosa is a persistent pathogen in the airways of patients with cystic fibrosis or bronchiectasis from other causes and appears to have evolved strategies to survive the inflammatory response of the host. We hypothesized that the secreted hemolytic phospholipase C (PLC) of P. aeruginosa (PlcHR) would decrease neutrophil respiratory burst activity. We found that while intact wild-type P. aeruginosa cells stimulated moderate respiratory burst activity from human neutrophils, an isogenic mutant pseudomonas (DeltaHR strain) containing a targeted deletion of the plcHR operon induced a much more robust oxidative burst from neutrophils. In contrast, a second pseudomonas mutant (DeltaN) containing a disruption in the gene encoding the nonhemolytic PLC (PlcN) was not different from the wild type in stimulating neutrophil O2.- production. Readdition of purified PlcHR to the DeltaHR strain suppressed neutrophil O2.- production to levels stimulated by wild-type bacteria. Interestingly, purified PlcHR decreased phorbol myristate acetate (PMA)- but not formyl methionyl-leucyl-proline (fMLP)-induced respiratory burst activity, suggesting interference by PlcHR with a protein kinase C (PKC)-specific signaling pathway. Accordingly, the PKC inhibitor bisindolylmaleimide inhibited the oxidative burst induced by either PMA or intact pseudomonas, but not by fMLP, whereas the p38 kinase inhibitor SB-203580 fully inhibited the respiratory burst induced by fMLP or the PlcHR-replete wild-type bacteria, but not PMA or the PlcHR-deficient DeltaHR bacterial mutant. We conclude that expression of PlcHR by P. aeruginosa suppresses bacterium-induced neutrophil respiratory burst by interfering with a PKC-dependent, non-p38 kinase-dependent pathway.

Pseudomonas aeruginosa lasR transcription correlates with the transcription of lasA, lasB, and toxA in chronic lung infections associated with cystic fibrosis

The role of Pseudomonas aeruginosa quorum-sensing systems in the lung infections associated with cystic fibrosis (CF) has not been examined. The purpose of this study was to determine if genes regulated by the LasR-LasI quorum-sensing system were coordinately regulated by the P. aeruginosa populations during the lung infections associated with CF. We also wanted to ascertain if there was a relationship between the expression of lasR, a transcriptional regulator, and some P. aeruginosa virulence factors during these infections. We extracted RNAs from the bacterial populations of 131 sputa taken from 23 CF patients. These RNAs were blotted and hybridized with probes to P. aeruginosa lasA, lasB, and toxA. The hybridization signals from each probe were ranked, and the rankings were analyzed by a Spearman rank correlation to determine if there was an association between the population transcript accumulations for the three genes. The correlations between the transcript accumulation patterns of pairs of the genes suggested that lasA, lasB, and toxA might be coordinately regulated during CF lung infections. To determine if this coordinate regulation might be due to regulation by LasR, we probed RNAs, extracted from 84 sputa, with the lasR, lasA, lasB, toxA, and algD probes. Statistical analysis indicated that lasR transcript accumulation correlated to lasA, lasB, toxA, and algD transcript accumulations. These results indicated that lasR may at least partially regulate or be coordinately regulated with lasA, lasB, toxA, and algD during the lung infections associated with CF. These results also suggested that the LasR-LasI quorum-sensing system may control the expression of at least some virulence factors in the lungs of patients with CF.

Pseudomonas aeruginosa antigens as potential vaccines

Pseudomonas aeruginosa is one of the most important opportunistic bacterial pathogens in humans and animals. This organism is ubiquitous and has high intrinsic resistance to antibiotics due to the low permeability of the outer membrane and the presence of numerous multiple drug efflux pumps. Various cell-associated and secreted antigens of P. aeruginosa have been the subject of vaccine development. Among pseudomonas antigens, the mucoid substance, which is an extracellular slime consisting predominantly of alginate, was found to be heterogenous in terms of size and immunogenicity. High molecular mass alginate components (30-300 kDa) appear to contain conserved epitopes while lower molecular mass alginate components (10-30 kDa) possess conserved epitopes in addition to unique epitopes. Surface-exposed antigens including O-antigens (O-specific polysaccharide of LPS) or H-antigens (flagellar antigens) have been used for serotyping due to their highly immunogenic nature. Chemical structures of repeating units of O-specific polysaccharides have been elucidated and these data allowed the identification of 31 chemotypes of P. aeruginosa. Conserved epitopes among all serotypes of P. aeruginosa are located in the core oligosaccharide and the lipid A region of LPS and immunogens containing these epitopes induce cross-protective immunity in mice against different P. aeruginosa immunotypes. To examine the protective properties of OM proteins, a vaccine containing P. aeruginosa OM proteins of molecular masses ranging from 20 to 100 kDa has been used in pre-clinical and clinical trials. This vaccine was efficacious in animal models against P. aeruginosa challenge and induced high levels of specific antibodies in human volunteers. Plasma from human volunteers containing anti-P. aeruginosa antibodies provided passive protection and helped the recovery of 87% of patients with severe forms of P. aeruginosa infection. Vaccines prepared from P. aeruginosa ribosomes induced protective immunity in mice, but the efficacy of ribosomal vaccines in humans is not yet known. A number of recent studies indicated the potential of some P. aeruginosa antigens that deserve attention as new vaccine candidates. The outer core of LPS was implicated to be a ligand for binding of P. aeruginosa to airway and ocular epithelial cells of animals. However, heterogeneity exists in this outer core region among different serotypes. Epitopes in the inner core are highly conserved and it has been demonstrated to be surface-accessible, and not masked by O-specific polysaccharide. The use of an in vivo selection/expression technology (IVET) by a group of researchers identified a number of P. aeruginosa proteins that are expressed in vivo and essential for virulence. Two of these in vivo-expressed proteins are FptA (ferripyochelin receptor protein) and a homologue of an LPS biosynthetic enzyme. Our laboratory has identified a highly conserved protein, WbpM, and P. aeruginosa with a deficiency in this protein produces only rough LPS and became serum sensitive. Results from these studies have provided the foundation for a variety of vaccine formulations.

Positive correlation of algD transcription to lasB and lasA transcription by populations of Pseudomonas aeruginosa in the lungs of patients with cystic fibrosis

Pseudomonas aeruginosa causes a chronic infection in the lungs of individuals with cystic fibrosis. The P. aeruginosa isolates from these infections, when grown under laboratory conditions, characteristically are mucoid and produce low levels of the more destructive virulence factors, such as exotoxin A and the proteases. We wanted to determine if during the chronic lung infections associated with CF, the expression of alginate was inversely correlated to the expression of exotoxin A, elastase, and the LasA protease. We measured the transcript accumulation of algD, a marker of alginate, toxA, the structural gene for exotoxin A, lasB, the structural gene for elastase, and lasA, the structural gene for LasA protease, from the sputum bacterial populations of 23 patients. In the 131 samples tested, we frequently detected transcripts from the four genes. When a Spearman rank correlation analysis was done on the samples, we found no correlation between algD transcript accumulation and toxA transcript accumulation. This result suggested that toxA was regulated independently of algD. Curiously, we found a positive correlation between algD transcript accumulation and both lasB and lasA transcript accumulation levels. This correlation may not indicate a direct association between algD and either lasA or lasB. More likely, it indicates a common regulatory element in a cascade of regulators or a common environmental cue that triggers transcription.

Bacterial phospholipases and their role in virulence

Virulence of many bacterial pathogens is based, at least in part, on the action of phospholipases. The consequences may be immediate and direct, as in the action of Clostridium perfringens alpha toxin on red cells or platelets, or subtle, as with phosphatidylinositol-specific phospholipases of Listeria monocytogenes and other bacteria.

Cross-reactive antigens shared by Pseudomonas aeruginosa, Helicobacter pylori, Campylobacter jejuni, and Haemophilus influenzae may cause false-positive titers of antibody to H. pylori

Cystic fibrosis (CF) patients suffer from many of the gastrointestinal conditions which occur in non-CF individuals, e.g., dyspepsia and peptic ulceration. These symptoms may be caused by Helicobacter pylori but could also be due to either pancreatic insufficiency or the intensive antibiotic treatment used in CF patients. Since CF patients chronically infected with Pseudomonas aeruginosa produce antibodies against a wide range of antigens, including antigens common to many other bacteria, e.g., GroEL and lipopolysaccharide, we studied, by the Western blot (immunoblot) technique, the specificity of immunoglobulin G antibodies to H. pylori in Danish CF patients chronically infected with P. aeruginosa, CF patients without P. aeruginosa infection but with Haemophilus influenzae infection, patients with dyspeptic ulcers associated with H. pylori, and patients recovering from acute Campylobacter jejuni or Campylobacter coli infection. Sera from CF patients with chronic P. aeruginosa or H. influenzae infection and patients recovering from acute C. jejuni infection cross-reacted with H. pylori antigens. A strong cross-reacting protein antigen at approximately 14 kDa and minor cross-reactive antigens at approximately 27, 30, and 60 kDa (the heat shock protein GroEL is equivalent to the common antigen of P. aeruginosa) could be demonstrated. The results of this study show that high immunoglobulin G antibody titers against H. pylori in CF patients cannot be regarded as indicating present or past H. pylori infection unless their specificity is proven by absorption studies.

The role of bacterial proteases in the pathogenesis of cystic fibrosis

Among the roles of mediators damaging the respiratory epithelium in patients with cystic fibrosis (CF) during the course of chronic, purulent bronchitis, that of neutrophil proteases is well established. The role of bacterial proteases is less well known. Among all pathogens colonizing the airways in CF, Pseudomonas aeruginosa is quantitatively the dominant pathogen; Staphylococcus aureus and Haemophilus influenzae are present in lower numbers. Anaerobic bacteria may be detected in numbers exceeding those of Staphylococcus aureus and Haemophilus influenzae. Among all enzymes secreted by these bacterial strains, Pseudomonas elastase and alkaline protease were shown to be secreted in vivo over prolonged periods in the airways. These enzymes, mainly elastase, have proteolytic activity on many proteins involved in host defense mechanisms, often the same as those hydrolyzed by neutrophil proteases. Pseudomonas elastase has damaging effects on the respiratory epithelium; it has recently also been shown to augment the permeability of the respiratory epithelium cultured in vitro by proteolytic attack of tight junctions. The potential role of proteases and other enzymes secreted by anaerobic bacteria has not been studied in this disease. In conclusion, bacterial proteases secreted in vivo may play a role in the pathogenesis of the airway disease in CF; their relative importance to the role of host proteases is, however, often difficult to determine.

Association between transcript levels of the Pseudomonas aeruginosa regA, regB, and toxA genes in sputa of cystic fibrosis patients

In this study, we examined the regulation of exotoxin A (ETA) production by Pseudomonas aeruginosa during chronic lung infections of cystic fibrosis (CF) patients. We used a recently developed technique termed population transcript accumulation in hybridization studies with RNA extracted from sputa. With this technique, we demonstrated that the structural gene for ETA, toxA, as well as two genes encoding positive regulators of ETA synthesis, regA and regB, were expressed in the lungs of CF patients infected with P. aeruginosa. These genes were always expressed together, never alone or in pairs, suggesting coincident expression and a possible regulatory role for regA and regB in this environment. Fluctuations in the levels of the three gene products were observed among samples, consistent with a regulatory phenomenon. The level of regB RNA detected never exceeded that of regA, although the ratio of regA RNA to regB RNA detected did change between samples. These observations are in agreement with in vitro observations which have shown that regB is located 3' to regA in an operon which is expressed from two independently regulated promoters located upstream of regA. The presence of high levels of toxA, regA, and regB RNAs in some sputum samples prompted us to look for hyperproducing-toxin strains in the sputa of CF patients. In vitro, one such strain, 4384, had a transcript accumulation pattern for toxA, regA, and regB similar to that of a laboratory hyperproducer of ETA, strain PA103. These observations suggest that regA and regB are involved in the regulation of ETA production in strains of P. aeruginosa infecting the lungs of CF patients and that some of these strains may regulate ETA production in a manner similar to that of the hyperproducing-ETA strain PA103.

High doses of aminoglycosides did not produce liver toxicity in patients with cystic fibrosis

Liver disease is common in patients with cystic fibrosis, but the pathogenesis is poorly understood. The chronic colonization of bacteria in the lower airways leads to repeated treatments with antibiotics, especially aminoglycosides in high dosages. To investigate the possible role of aminoglycoside treatment in the natural history of liver disease in cystic fibrosis, five patients were studied for 3 years. Four of the patients received repeated courses of antibiotics, in two of the patients at the time of the liver biopsies. One patient did not receive any aminoglycosides. Light and electron microscopical morphometry was done on liver biopsy specimens. The contents of fat and lysosomes were quantified and expressed as volume density of liver cell volume (%). The amount of fat calculated in this way (13-35%) was highest in one patient who had not received any aminoglycosides. The two patients being treated with aminoglycosides at the time of the biopsy showed small amounts of fat in their liver cells (0.2-1.5%); similar values were noted in some patients who had not been treated for years. The lysosomes did not show the specific changes previously reported to occur in the kidney, nor did the morphometrical quantitation reveal any abnormalities which could be related to the administration of aminoglycosides. The present study did not find liver toxicity related to aminoglycosides in repeated high therapeutic dosages given to patients with cystic fibrosis.

Immunoglobulin G antibodies to Pseudomonas aeruginosa lipopolysaccharides and exotoxin A in patients with cystic fibrosis or bacteremia

IgG antibodies to nine Pseudomonas aeruginosa lipopolysaccharides (LPS) and exotoxin A in sera from 11 patients with bacteremia and 51 patients with cystic fibrosis (CF) were analyzed. The methods used were enzyme immunoassay (EIA) and immunoblotting. Nine of the 11 bacteremic patients were infected with strains expressing an LPS serotype identical to one of the test antigens. In sera from six of these nine patients, antibody homologous to the serotype of the infecting strain was observed. An antibody response to heterologous Pseudomonas aeruginosa LPS antigens was observed in nine patients. Eight of the bacteremic patients mounted an antibody response to exotoxin A. Thirty-five CF patients chronically colonized with Pseudomonas aeruginosa possessed significantly higher levels of antibody to all of the test antigens than 16 patients with intermittent or no colonization (p < 0.001). For exotoxin A and serotype 3 the sensitivity was 91% and 94%, and the specificity 94% and 88% respectively. When the results for exotoxin A and serotype 3 were combined, the sensitivity was 91% while the specificity was 81%. The pronounced antibody response to heterologous LPS antigens, as measured by the EIA and immunoblot, suggests expression of a common antigen determinant. A simplified serological assay utilizing exotoxin A and serotype 3 as test antigens may be useful for detecting Pseudomonas aeruginosa infections in patients with CF and chronic colonization and in bacteremic patients from whom cultures are not available.

Bacterial phospholipases C

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.

Population transcript accumulation of Pseudomonas aeruginosa exotoxin A and elastase in sputa from patients with cystic fibrosis

The in vivo regulation of Pseudomonas aeruginosa virulence factors during the chronic lung infections associated with cystic fibrosis is poorly understood. We have developed an approach for the analysis of transcript accumulation of individual virulence factors from the P. aeruginosa populations found in the sputa of patients with cystic fibrosis. This method has been named population transcript accumulation, since we examine the transcript accumulation patterns in RNA extracted from the total bacterial population found in the sputum samples. DNA probes specific for P. aeruginosa elastase (lasB) and exotoxin A (toxA) were used to examine the population transcript accumulation of 21 sputum samples taken from 10 patients. We detected three patterns of population transcript accumulation: lasB and toxA, lasB alone, and neither lasB nor toxA. We also measured the relative levels of elastase and exotoxin A transcript accumulation in 19 of these samples. In the six samples containing both toxA and lasB transcripts, we found that the levels of lasB transcripts were consistently higher than those of toxA. Differences in the stability of the two mRNA species could not completely account for the higher level of lasB population transcript accumulation, since we showed that the mRNA half-life of lasB (11 min) was similar to that of toxA (10 min). Finally, we showed that elastase transcripts could be detected in some samples which contained only mucoid isolates. This finding suggests that both mucoid and nonmucoid populations may be transcribing lasB in the lungs of patients with cystic fibrosis.

Osmoprotectants and phosphate regulate expression of phospholipase C in Pseudomonas aeruginosa

Phospholipase C has been increasingly recognized as a significant virulence determinant in the pathogenesis of Gram-negative and Gram-positive infections. Pseudomonas aeruginosa carries two, non-tandem genes encoding phospholipase C (PLC) activity. One PLC (PLC-H) haemolyses human and sheep erythrocytes while the other is not haemolytic for these kinds of red blood cells. It was previously determined that the synthesis of both PLCs is regulated by inorganic phosphate (Pi), but little else was known regarding the regulation of these potentially important virulence determinants of P. aeruginosa. In this report, data are presented demonstrating that both PLC genes are regulated at the transcriptional level by Pi and by a P. aeruginosa homologue of the positive regulator of genes in the Pi regulon of Escherichia coli, i.e. PhoB. In addition to Pi, it is also shown in this report that the synthesis of both PLC-H and PLC-N is induced by compounds which are not only derived from the substrate product of both enzymes, i.e. phosphorylcholine, but are also known osmoprotectants in eukaryotic and prokaryotic cells. The osmoprotective derivatives of phosphorylcholine which induce the synthesis of PLC in P. aeruginosa include choline, glycine betaine, and dimethylglycine, but not sarcosine (monomethylglycine) or glycine. By constructing mutants which are deficient in the production of each separate PLC and in the production of PhoB it was determined that induction of PLC-H by the osmoprotective compounds is independent of Pi concentration and PhoB, while induction of PLC-N by these compounds requires Pi-deficient conditions and PhoB.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo and in vitro toxicity of phospholipase C from Pseudomonas aeruginosa

Pseudomonas aeruginosa produces phospholipase C (PLC), a heat-labile hemolysin. Histopathological analysis of PLC-treated mice revealed that the primary target organs involved in PLC-induced toxicity were the liver and kidney. Mice treated i.v. with PLC demonstrated significant tubular epithelial necrosis of the kidney with hematuria, while when given i.p. they exhibited hepatonecrosis with cellular infiltration. Splenomegaly was also a consistent finding. Results from in vitro studies indicate that PLC is toxic for mouse peritoneal cells and human leukocytes.

Serum antibody response to Pseudomonas aeruginosa antigens during corneal infection

Previous studies in our laboratory have indicated that naturally resistant, inbred DBA/2J mice mount a greater serum antibody response to Pseudomonas aeruginosa 19660 than susceptible C57BL/6J mice. However, the specificity of the antibody produced was not known. The present study examines the specificity and kinetics of the humoral response of these mouse strains to potential virulence factors produced by the organism during both a primary and a secondary corneal infection administered 4 weeks after the primary infection. Serum antibody levels specific for lipopolysaccharide (LPS), exotoxin A, phospholipase C (PLC), alkaline protease, elastase, and flagella were measured by enzyme-linked immunosorbent assay. Little or no antibody to either alkaline protease or elastase was detected during either primary or secondary infection. Immunoglobulin G (IgG) antibodies specific to exotoxin A, PLC, and flagella were detected 2 weeks after primary infection, and a rapid response to these antigens was measured 1 week after secondary infection. During primary infection, detectable LPS-specific antibody was only IgM, while IgG appeared only after secondary infection. The kinetics of the humoral response in susceptible C57BL/6J mice were similar to those in resistant DBA/2J mice, although the magnitude of the response varied according to the antigen tested. These results indicate that LPS, exotoxin A, PLC, and flagella are present or produced in amounts that are immunogenic during corneal infection by P. aeruginosa 19660 in the mouse strains tested.

Longitudinal studies of virulence factors of Pseudomonas aeruginosa in cystic fibrosis

Among 111 strains of Pseudomonas aeruginosa from 49 children with cystic fibrosis, duration of colonization correlated with bacterial phenotype. We confirmed that P. aeruginosa from chronically colonized patients tended to be less motile, produce lower levels of protease and elastase, to be more sensitive to normal serum and to be polyagglutinating or untypable with standard antisera. We also showed that phospholipase and heat-stable hemolysin, concerned in metabolism of inorganic phosphate, and exotoxin A, were lower in these isolates. In longitudinal studies there was a decrease in virulence properties when isolates from the same patient were compared. No reversion from altered phenotype to 'wild-type' characteristics was found.

Characterization of antibody response to Pseudomonas aeruginosa in patients with wound infections

ELISA was used to measure the amount and avidity of IgG antibodies to exotoxin A (ExA) and 7 Fisher's immunotypes of lipopolysaccharide (LPS) in the sera of 13 patients with mild or moderate Pseudomonas aeruginosa infections. Changes in the specificity of tested sera during the course of infection were demonstrated. A statistically significant increase was seen in the amount and avidity of the antibodies to ExA in a majority of the sera, and an increase was seen in amount of antibodies to LPS immunotype 4 in the sera of patients with moderate infections.

Antistaphylococcal antibodies in cystic fibrosis

Chronic colonization with Staphylococcus aureus is found in 40-50% of the sputum producing patients with cystic fibrosis treated at Stockholm's Cystic Fibrosis Center, Huddinge University Hospital. 30-40% of these patients had increased ELISA IgG antibody titres against teichoic acid and against alpha-toxin. About half of the number of patients showed increased antibody titres to either antigen during infection. Increased antibody titres against staphylococcal antigens were only found in less than or equal to 10% of patients not chronically colonized with S. aureus (no different from the normal population). The serum titres of antistaphylococcal antibodies were significantly higher in the chronically colonized patients (p less than 0.001). Patients who were also chronically harbouring Pseudomonas aeruginosa had the highest titres of both antibodies. The titres increased with clinical signs of infection and were normalized by antimicrobial chemotherapy. To conclude, the use of ELISA IgG antibodies may prove suitable for routine evaluation of the need for, and control of the efficacy of antistaphylococcal chemotherapy in cystic fibrosis.

Characterization of phospholipase C from Pseudomonas aeruginosa as a potent inflammatory agent

Phospholipase C (PLC) from Pseudomonas aeruginosa induced a marked inflammatory response when injected intraperitoneally in C3H/HeJ mice. This inflammation was characterized by the accumulation of inflammatory cells and plasma protein and the release of arachidonic acid metabolites (6-trans-12-epi-leukotriene B4 [LTB4], 6-trans-LTB4, LTB4, 5-HETE (5-hydroxyeicosatetraenoic acid), LTC4, LTD4, LTE4, prostaglandin E2 [PGE2], PGF2-alpha, and thromboxane B2 [TxB2]) in the peritoneal cavity of the mice. Heat-inactivated PLC did not evoke any of these effects, suggesting that enzyme activity is necessary for PLC-induced inflammation. When human granulocytes were incubated with PLC in vitro, 6-trans-12-epi-LTB4, 6-trans-LTB4, LTB4, 5-HETE, and PGE2 were generated. Mouse peritoneal cells stimulated with PLC released 6-trans-LTB4, LTB4, PGE2, PGF2-alpha, and TxB2. Both human granulocytes and mouse peritoneal cells stimulated with PLC generated significantly increased levels of arachidonic acid metabolites as compared with cells incubated with heat-inactivated PLC. Leukotriene production by both populations of cells was inhibited when the cells were preincubated with nordihydroguaiaretic acid and subsequently stimulated with PLC. Similarly, both cell types released significantly lower amounts of cyclooxygenase pathway products when they were preincubated with indomethacin and subsequently stimulated with PLC.

Pseudomonas aeruginosa flagellar antibodies in patients with cystic fibrosis

An enzyme-linked immunosorbent assay specific for flagellum type (a or b) of Pseudomonas aeruginosa was used to detect serum immunoglobulin antibodies in 98 random outpatients and 14 colonized cystic fibrosis patients. Antibodies were detected to both types of flagella in addition to M-2 lipopolysaccharide. Titers to both flagellar antigens (FlAg) were 10 to 100 times higher in cystic fibrosis patients than in random outpatients of a comparable age group. Mean antibody titers against b-type FlAg were 454 for outpatients (ages newborn to 21 years), whereas the mean titer for cystic fibrosis patients (ages 6 to 21 years) was 51,520. Titers against a-type FlAg were generally lower, with mean outpatient titers of 68 and mean cystic fibrosis patient titers of 34,323. Differences were also seen in antibody titer against M-2 lipopolysaccharide, but these differences did not correspond to M-2 FlAg titers. In 98 random outpatients (ages newborn to 86 years), FlAg titers generally increased with age. To demonstrate further specificity of the enzyme-linked immunosorbent assay for flagellum antibody, Western blots were performed with selected high-titer cystic fibrosis patient sera. Sera that had a high titer (greater than 25,600) for b- or a-type FlAg showed a corresponding reactive band. These results demonstrate that flagellum antibodies are produced in humans in response to P. aeruginosa infection.

Antilipopolysaccharide antibodies and differential diagnosis of chronic Pseudomonas aeruginosa lung infection in cystic fibrosis

Chronic lung infection in cystic fibrosis is characteristically associated with polyagglutinable, serum-sensitive, mucoid strains of Pseudomonas aeruginosa. Enzyme-linked immunosorbent assay (ELISA) methods for standard-free quantitation of immunoglobulin G (IgG) and IgM antibodies to P. aeruginosa lipopolysaccharides (LPSs) have been developed. We now report the development of assays for quantitation of monomer and dimer total IgA and IgA anti-LPS antibodies. Use of these methods in diagnosis of early chronic P. aeruginosa lung infection was assessed. IgG and IgA anti-LPS levels increased significantly at the onset of chronic infection and continued to increase to very high levels in the later stages of infection. IgM anti-LPS levels also rose at the onset of chronic infection but did not increase further. The function of true- and false-positive rates was illustrated by using various concentrations of IgG, IgA, and IgM anti-LPS for discrimination of patients. Values that gave optimum separations were used for statistical evaluation of the diagnostic sensitivities and specificities of anti-LPS antibody concentrations. The results obtained in these assays were compared with a diagnosis, based on the number of precipitins in crossed immunoelectrophoresis, of serum samples from cystic fibrosis patients. In 64 paired serum samples taken before and immediately after the onset of chronic infection, as defined by crossed immunoelectrophoresis precipitins, the predictive values of a positive ELISA were 86% for IgG and 89% for IgA. The predictive values for a negative ELISA were 98% for IgG and 97% for IgA. Results of the IgM anti-LPS ELISA had a lower predictive value. Immunoblotting and absorption studies showed that IgG anti-LPS antibodies were directed specifically against LPS of P. aeuruginosa. ELISAs were developed to determine the specific IgG sublclasses involved. The increase in IgG anti-LPS involved all four subclasses. Highest anti-LPS titers were seen with IgG1 and IgG4, but the largest relative increases were seen with IgG2 and IgG3.

Amount, avidity, and specificity of antibodies to Pseudomonas aeruginosa in normal human sera

Seventy-two normal human sera from healthy blood donors were tested by an enzyme-linked immunosorbent assay in order to determine the amounts and avidities of immunoglobulins M and G antibodies to lipopolysaccharides of seven Fisher's immunotypes of Pseudomonas aeruginosa and to exotoxin A. The patterns of specificity for seven immunotypes in all individual sera were determined. These data show a predominance of antibodies directed to Fisher's immunotypes 7 and 4 in the human population tested and may reflect frequency of occurrence of immunotypes outside the hospital environment.

Longitudinal study of antibody response to lipopolysaccharides during chronic Pseudomonas aeruginosa lung infection in cystic fibrosis

Antibodies to Pseudomonas aeruginosa from 10 cystic fibrosis patients with chronic P. aeruginosa lung infections were quantitatively and qualitatively analyzed. The development of specific antibodies in patient serum was evaluated in a longitudinal study (1972 to 1987). The concentrations and specificities of immunoglobulin G (IgG) and IgM antibodies to purified lipopolysaccharides (LPS) from clinical isolates of P. aeruginosa and to a variety of other gram-negative bacteria were studied by immunoblotting and enzyme-linked immunosorbent assay techniques. Results were compared with the number of immunoprecipitates to P. aeruginosa whole-cell extracts detected by crossed immunoelectrophoresis. IgG, but not IgM, anti-Pseudomonas LPS concentrations increased significantly at the onset of chronic infection and continued to increase during the course of the infection. There was a good positive correlation between the concentration of IgG anti-Pseudomonas LPS antibodies and the number of crossed-immunoelectrophoresis precipitins. The increases in IgG anti-LPS antibody concentrations were much higher to Pseudomonas LPS than to other LPSs. Binding studies demonstrated an increase in binding of IgG anti-Pseudomonas LPS during infection, whereas the binding of other anti-LPS antibodies decreased. Immunoblotting studies confirmed that antibodies reacted strongly with Pseudomonas LPS and weakly with Escherichia coli core-lipid A. The specificity of the reaction with Pseudomonas LPS increased with the duration of infection. It is concluded that anti-LPS response in cystic fibrosis patients during chronic P. aeruginosa infection demonstrates a marked increase in IgG anti-Pseudomonas LPS antibody concentration, specificity, and affinity. The anti-LPS enzyme-linked immunosorbent assay is proposed as a routine test to diagnose and to follow the course of chronic P. aeruginosa lung infection in patients with cystic fibrosis.

Immunologic aspects of cystic fibrosis

Bacterial infections determine life expectancy in the hereditary disease cystic fibrosis (CF). The dominant pathogens are Staphylococcus aureus and Pseudomonas aeruginosa, which persist in the patient's respiratory tract. Current explanations of the chronicity of the infections in the apparently immunocompetent host are based on defective opsonophagocytosis. This may be caused by (1) bacterial exopolysaccharide production, leading to cryptic infection types; (2) cleavage of immunoglobulin, complement, and surface receptors on immunocompetent cells by host proteases; and (3) a change from opsonic to nonopsonic antibody isotypes. Continuous antigenic stimulation of the immune system leads to local immune complex formation and a high chronic hypersensitivity reaction as well as to temporary immune unresponsiveness. Progressive tissue damage caused by lysosomal enzymes and oxygen radicals from polymorphonuclear leukocytes is thought to be ultimately responsible for respiratory failure and death in CF. Besides antibiotic treatment, anti-inflammatory therapy is therefore currently considered beneficial.

Phosphorylcholine stimulates capsule formation of phosphate-limited mucoid Pseudomonas aeruginosa

Production of both alginic acid and lipopolysaccharide by a mucoid strain of Pseudomonas aeruginosa, SRM-3, was studied in a chemostat system during growth under nutrient-limiting conditions chosen to reflect the chronic growth conditions in the lungs of cystic fibrosis patients. Since mucoid strains have been shown to elaborate extracellular proteases and phospholipase C, nitrogen and phosphate limitation were selected for analysis. A modified alginate-promoting medium containing either 1 mM glutamate or 0.05 mM K2HPO4 as limiting nutrient and doubling times of 1.6 to 15.7 h were used. Under nitrogen limitation, strain SRM-3 produced 1.4 mg of uronic acid per mg (dry weight) of cells at all doubling times studied. However, phosphate limitation resulted in the synthesis of only 0.4 mg of uronic acid per mg (dry weight) of cells. The role of phosphate in alginic acid polysaccharide production was further investigated by using phosphorylcholine, a product of phospholipase C activity on phosphatidylcholine, the major lung surfactant. No only were mucoid cells capable of utilizing phosphorylcholine for growth, but a highly specific interaction occurred among phosphorylcholine, alginate, and whole cells, resulting in greatly enhanced culture viscosity. Electron micrographs showed the gradual formation of a capsule during growth on phosphorylcholine, indicating that the mucoid strain has the ability to utilize surfactant not only as a nutrient source but also for constructing a capsule with greatly enhanced adhesive properties.

Significance of immunologic factors in cystic fibrosis

We specifically investigated the significance of antibodies directed against pure preparations of lipopolysaccharide antigens and also against elastase of Pseudomonas aeruginosa. Antibodies were detected by an indirect enzyme-linked immunosorbent assay technique both in serum (IgG) and in sputum (sIgA). Patients with cystic fibrosis (CF) chronically infected with Ps. aeruginosa had significantly higher antibody titers both in serum and sputum than CF patients or non-CF persons not colonized with Ps. aeruginosa. There were differences in the antibody spectrum between the colonized CF group and the two non-colonized control group. The sensitivity was highest for homologous O-specific IgG in serum (91.9%), followed by homologous O-specific sIgA in sputum (79.4%) and sIgA anti-elastase in sputum (66.2%). O-specific IgG antibodies in serum indicate a previous contact with various O-antigens of Ps. aeruginosa rather than reflect the present condition of the patient. In the evaluation of the current status sIgA O-specific antibodies in sputum are an appropriate indicator, with titers increasing during acute exacerbations and decreasing to normal values subsequently.