Serum bactericidal effect on Pseudomonas aeruginosa isolates from cystic fibrosis patients

Antibody-Dependent Enhancement of Bacterial Disease: Prevalence, Mechanisms, and Treatment

Antibody-dependent enhancement (ADE) of viral disease has been demonstrated for infections caused by flaviviruses and influenza viruses; however, antibodies that enhance bacterial disease are relatively unknown. In recent years, a few studies have directly linked antibodies with exacerbation of bacterial disease. This ADE of bacterial disease has been observed in mouse models and human patients with bacterial infections. This antibody-mediated enhancement of bacterial infection is driven by various mechanisms that are disparate from those found in viral ADE. This review aims to highlight and discuss historic evidence, potential molecular mechanisms, and current therapies for ADE of bacterial infection. Based on specific case studies, we report how plasmapheresis has been successfully used in patients to ameliorate infection-related symptomatology associated with bacterial ADE. A greater understanding and appreciation of bacterial ADE of infection and disease could lead to better management of infections and inform current vaccine development efforts.

Mechanisms of humoral immune response against Pseudomonas aeruginosa biofilm infection in cystic fibrosis

P. aeruginosa chronic lung infection is the major cause of morbidity and mortality in patients with cystic fibrosis (CF), and is characterized by a biofilm mode of growth, increased levels of specific IgG antibodies and immune complex formation. However, despite being designed to combat this infection, such elevated humoral response is not associated with clinical improvement, pointing to a lack of anti-pseudomonas effectiveness. The mode of action of specific antibodies, as well as their structural features, and even the background involving B-cell production, stimulation and differentiation into antibody-producing cells in the CF airways are poorly understood. Thus, the aim of this review is to discuss studies that have addressed the intrinsic features of the humoral immune response and provide new insights regarding its insufficiency in the CF context.

Psl Produced by Mucoid Pseudomonas aeruginosa Contributes to the Establishment of Biofilms and Immune Evasion

Despite years of research and clinical advances, chronic pulmonary infections with mucoid Pseudomonas aeruginosa remain the primary concern for cystic fibrosis patients. Much of the research on these strains has focused on the contributions of the polysaccharide alginate; however, it is becoming evident that the neutral polysaccharide Psl also contributes to biofilm formation and the maintenance of chronic infections. Here, we demonstrate that Psl produced by mucoid strains has significant roles in biofilm structure and evasion of immune effectors. Though mucoid strains produce less Psl than nonmucoid strains, the Psl that is produced is functional, since it mediates adhesion to human airway cells and epithelial cell death. Additionally, Psl protects mucoid bacteria from opsonization and killing by complement components in human serum. Psl production by mucoid strains stimulates a proinflammatory response in the murine lung, leading to reduced colonization. To determine the relevance of these data to clinical infections, we tested Psl production and biofilm formation of a panel of mucoid clinical isolates. We demonstrated three classes of mucoid isolates, those that produce Psl and form robust biofilms, those that did not produce Psl and have a poor biofilm phenotype, and exopolysaccharide (EPS) redundant strains. Collectively, these experimental results demonstrate that Psl contributes to the biofilm formation and immune evasion of many mucoid strains. This is a novel role for Psl in the establishment and maintenance of chronic pulmonary infections by mucoid strains.

Cystic fibrosis patients are engaged in an ongoing battle against chronic lung infections by the bacterium Pseudomonas aeruginosa. One key factor contributing to the maintenance of chronic infections is the conversion to a mucoid phenotype, where the bacteria produce copious amounts of the polysaccharide alginate. Once the bacteria become mucoid, existing treatments are poorly effective. We proposed that mucoid bacteria produce an additional polysaccharide, Psl, which is important for their establishment and maintenance of chronic infections. This work demonstrates that Psl enhances attachment of mucoid bacteria to lung surfaces and leads to inflammation and damage in the lung. Additionally, we find that 50% of mucoid bacteria isolated from patients with chronic infections rely on Psl for the structure of their biofilm communities, suggesting that treatments against Psl should be investigated to enhance the success of current therapies.

Absence of the cystic fibrosis transmembrane regulator (Cftr) from myeloid-derived cells slows resolution of inflammation and infection

The absence or reduction of CFTR function causes CF and results in a pulmonary milieu characterized by bacterial colonization and unresolved inflammation. The ineffectiveness at controlling infection by species such as Pseudomonas aeruginosa suggests defects in innate immunity. Macrophages, neutrophils, and DCs have all been shown to express CFTR mRNA but at low levels, raising the question of whether CFTR has a functional role in these cells. Bone marrow transplants between CF and non-CF mice suggest that these cells are inherently different; we confirm this observation using conditional inactivation of Cftr in myeloid-derived cells. Mice lacking Cftr in myeloid cells overtly appear indistinguishable from non-CF mice until challenged with bacteria instilled into the lungs and airways, at which point, they display survival and inflammatory profiles intermediate in severity as compared with CF mice. These studies demonstrate that Cftr is involved directly in myeloid cell function and imply that these cells contribute to the pathophysiological phenotype of the CF lung.

Serum susceptibility in clinical isolates of Burkholderia cepacia complex bacteria: development of a growth-based assay for high throughput determination

Burkholderia cepacia complex (BCC) bacteria can cause devastating chronic infections in people with cystic fibrosis. Of particular concern is “cepacia syndrome,” a rapidly progressive and usually fatal decline in health, characterized by a necrotizing bacteremic pneumonia. An important component of defense against bloodstream infections is the bactericidal action of serum. Traditional methods to determine the capacity of bacterial isolates to resist the bactericidal effects of serum are relatively low-throughput viability assays. In this study, we developed a novel growth-based assay for serum susceptibility, which allows for high throughput analysis. We applied this assay to a range of clinical isolates of BCC as well as isolates comprising the BCC experimental strain panel. Our data demonstrate that isolates from all species of BCC examined can possess serum resistant or serum sensitive/intermediate phenotypes. Of particular clinical significance, we also found no direct link between the last saved pulmonary isolate from patients who subsequently developed “cepacia syndrome” and their capacity to resist the inhibitory effects of human serum, suggesting serum resistance cannot be used as a marker of an isolate’s capacity to escape from the lung and cause bacteremia.

Serum sensitivity of Burkholderia (Pseudomonas) cepacia isolates from patients with cystic fibrosis

Bacterial strains which are sensitive to the bactericidal activity of serum are generally considered to be less virulent than serum-resistant strains and are seldom associated with bacteraemia. Burkholderia (Pseudomonas) cepacia is an important pathogen in cystic fibrosis and is associated with rapid fatal pulmonary decline and bacteraemia in 20% of colonised patients. In this study 19 isolates of B. cepacia expressing either rough or smooth LPS were investigated to determine the degree of serum sensitivity. Strains expressing rough-LPS were serum-sensitive: these included a highly transmissible strain of B. cepacia isolated from approximately 50 cystic fibrosis patients attending various U.K. regional centres and associated with cases of bacteraemia.

Heterogeneity, persistence, and distribution of Pseudomonas aeruginosa genotypes in cystic fibrosis patients

A collection of 222 isolates of Pseudomonas aeruginosa was obtained from the respiratory tract of 16 patients with cystic fibrosis over a 4- to 9-month period. Fourteen of these patients were unrelated, while the remaining two were siblings. Isolates were typed by conventional pyocin typing and also by the use of a DNA probe containing 741 bp immediately upstream of the exotoxin A structural gene and the initial 732 bp of the exotoxin A structural gene. By pyocin typing, 69% (11 of 16) of the patients were shown to harbor a single type that persisted in the lung throughout the study. By genotyping (DNA probe typing), all but three patients (13 of 16, 81%) harbored a single persistent genotype in their lungs. Six patients other than the sibling pair (6 of 14, 43%) shared a common genotype in their lungs as judged by DNA probing, and the pyocin type of these isolates was also identical. In four of these six patients, the shared genotype was also the persistent genotype. The sibling pair studied also carried a common genotype in their lungs as indicated by DNA probing, even though the pyocin type of these isolates varied. Results presented suggest that the majority of patients harbor a persistent strain in their lungs and that cross-colonization may occur.

Pseudomonas aeruginosa variants isolated from patients with cystic fibrosis are killed by a bactericidal protein from human polymorphonuclear leukocytes

The susceptibility of paired mucoid and nonmucoid variants of Pseudomonas aeruginosa isolated from 13 patients with cystic fibrosis (CF) to killing by a 55,000-Da bactericidal protein (BP55) from human polymorphonuclear leukocytes was studied. Mucoid and nonmucoid variants were equally sensitive to killing by BP55 at both pH 5.6 and pH 7.2. Eleven of the isolates were resistant to the bactericidal activity of 10% normal human serum but were as sensitive as the serum-sensitive isolates to BP55. Similarly, the 15 isolates with lipopolysaccharides (LPS) containing O-polysaccharide side chains (smooth LPS) were as sensitive to BP55 as those isolates with rough LPS.P. aeruginosa isolates from patients in poor clinical condition were more likely to have LPS of the smooth type and to be resistant to killing by 10% human serum than the isolates from patients in good clinical condition. We have concluded that the susceptibility of the P. aeruginosa isolates from patients with CF to killing by BP55 does not correlate with mucoid or nonmucoid variations, with the presence or absence of smooth LPS, or with the sensitivity or resistance to killing by normal human serum.

Cystic fibrosis. Infection and immunity to Pseudomonas

Chronic pulmonary infection with P. aeruginosa in CF may result from: 1. An initial failure of clearance mechanisms (increased adherence) leading to the development of a highly compartmentalized inflammatory reaction; 2. Inhibition of clearing mechanisms for bacteria present in the bronchial lumen; and 3. A largely ineffective, and possibly damaging, hyperactivity of inflammatory cells in the lumen and bronchial wall. The special relationship between the CF host and P. aeruginos, always long-term, and frequently subtle in its complexity, needs further understanding in order to develop new strategies for the treatment of chronic lung infections with this organism.

Serotype and serum sensitivity of Pseudomonas aeruginosa from children with cystic fibrosis: longitudinal studies and typing with monoclonal antibodies

Pseudomonas aeruginosa isolated from the respiratory tract of children with cystic fibrosis from Perth, Sydney or Brisbane, were serotyped with polyclonal antisera using the International Antigenic Serotyping System. Predominant strains were untypable among isolates from Brisbane (86% of 50 strains) and Sydney (60% of 50 strains) but 64% of the 408 isolates from Perth were polyagglutinating. The frequency distributions of typable strains showed differences from those reported in clinics in the northern hemisphere, but it appears that these local differences do not affect the emergence of strains with defective lipopolysaccharide antigens. Isolates from patients studied longitudinally showed correlation between duration of colonization, appearance of untypable or polyagglutinating strains and sensitivity to normal serum. Mucoid colonies were found more commonly from patients colonized for at least 12 months but, overall, there was no significant association between serotype and mucoid colonial morphology. Commercial monoclonal antibodies did not react with polyagglutinating or untypable strains and gave identical results to the polyvalent typing system with strains classified as typable.

Conversion of Pseudomonas aeruginosa to the phenotype characteristic of strains from patients with cystic fibrosis

Isolates of Pseudomonas aeruginosa from cystic fibrosis patients are unusual; they are often susceptible to the bactericidal effect of human serum, have a rough lipopolysaccharide, and produce an exopolysaccharide that is responsible for the characteristic mucoid phenotype. In contrast, strains from the environment and from patients with other diseases usually have smooth lipopolysaccharide, do not produce very much mucoid exopolysaccharide, and are phenotypically nonmucoid. The predominance of mucoid strains of P. aeruginosa in infections of patients with cystic fibrosis has not been explained. In the lower airways, where P. aeruginosa persists in cystic fibrosis, nutrients for bacterial growth may be limited. We investigated whether growth of P. aeruginosa under conditions of suboptimal nutrition causes conversion to the characteristic cystic fibrosis phenotype. Ninety-two strains of P. aeruginosa were maintained for up to 90 days in a minimal medium with acetamide as the sole carbon source. In 56 (52%) of 107 cultures, isolates with rough lipopolysaccharide emerged, and in 20 (19%) of 104 nonmucoid cultures, mucoid isolates were recovered. Strains with rough lipopolysaccharide also were sensitive to the bactericidal effect of normal human serum. Under conditions of suboptimal nutrition in vitro, isolates of P. aeruginosa emerged that produced rough lipopolysaccharide and were mucoid, typical of many isolates from cystic fibrosis patients. This peculiar phenotype may arise as a consequence of nutritional limitation within the cystic fibrosis respiratory tract rather than from features unique to these strains of bacteria.

Pseudomonas hyperimmune globulin passive immunotherapy for pulmonary exacerbations in cystic fibrosis

We studied the effect of an intravenously administered gamma globulin [Ps-ivIG] enriched fivefold over conventional ivIG for Pseudomonas aeruginosa lipopolysaccharide [PA LPS] antibodies on ten patients with cystic fibrosis [CF] aged 19-32 years during hospitalization for pulmonary deterioration. All were colonized with greater than or equal to 1 PA phenotype resistant to all antibiotics at the time of admission and they received 500 mg/kg Ps-ivIG intravenously as a single dose in addition to conventional treatment, including antibiotics and chest physiotherapy. No adverse effects occurred. Circulating immune complexes and complement levels remained unchanged from baseline. Serum levels of anti-PA LPS IgG, as measured by ELISA for eight PA LPS immunotypes, increased to 244 +/- 65% (mean +/- SE) of baseline levels 1 hour post-infusion (P less than 0.01), remained significantly elevated during a mean hospital stay of 17 days, and returned to near baseline by follow-up 4 weeks after hospital discharge. Plasma half-life and clearance values were similar to those of other subjects receiving conventional ivIG. Sputum PA density declined from 3.0 to 1.2 x 10(8) cfu/mL 1 week post-infusion (P approximately equal to 0.05), and returned to baseline at follow-up. Serum anti-PA opsonic activity increased after infusion (P less than 0.01), but returned to baseline by 72 hours. Clinical scores improved from admission to discharge (P less than 0.005) without decline at follow-up. Forced vital capacity [FVC] and forced expiratory volume in one second [FEV1] increased from admission to discharge (P less than 0.01 and P less than 0.05, respectively) without decline at follow-up. Using autologous historical control data, standard hospital therapy without Ps-ivIG resulted in no improvement in FVC or FEV1, and a subsequent decline in these parameters (P less than 0.05 for each) during a similar follow-up period. This occurred despite the fact that half the patients did not have antibiotic-resistant PA on the control admission. We conclude that Ps-ivIG is a safe adjunctive therapy for pulmonary exacerbations in moderately ill cystic fibrosis patients colonized with resistant PA, and may be associated with both greater and more prolonged improvement in pulmonary function than standard therapy alone.

Characterization of the susceptibility of Pseudomonas aeruginosa to complement-mediated killing: role of antibodies to the rough lipopolysaccharide on serum-sensitive strains

The mechanism of complement-mediated killing of seven serum-sensitive Pseudomonas aeruginosa strains was examined. All seven strains were sensitive to the bactericidal activity of 20% pooled normal human serum (PNHS) containing magnesium EGTA, which blocks the classical complement pathway (CCP), or 20% PNHS preheated to 50 degrees C for 20 min, which inactivates the alternative complement pathway, suggesting that either pathway was effective against these strains. However, for four of these strains, optimal killing required the function of both pathways. Preabsorption of PNHS with serum-sensitive strains dramatically reduced the killing activity of serum for the homologous strains when a concentration of 10% serum was used, implying a role for antibody in the activation of complement via the CCP. Affinity purification of antibodies to the rough lipopolysaccharide (LPS) on strain 144M resulted in a pool of antibodies which could restore all of the bactericidal activity and most of the C3 activation-deposition activity of serum which had been lost by preabsorption with 144M. Confirmation that the LPS was the target for these bactericidal antibodies was provided by demonstrating that exogenously added 144M LPS inhibited the killing activity of PNHS. These anti-144M LPS-specific antibodies were also bactericidal for the six other serum-sensitive strains examined, suggesting that all seven strains shared an antigenic determinant recognized by these anti-144M LPS-specific antibodies. Results from cross-absorption studies imply that there are bactericidal antibodies in PNHS directed to additional bacterial targets. These studies suggest that part of the bactericidal activity of PNHS is due to binding of antibodies to the rough LPS on serum-sensitive strains, initiating activation of the CCP, and that all seven strains examined shared this bactericidal antibody-binding site.

Construction and characterization of Pseudomonas aeruginosa algB mutants: role of algB in high-level production of alginate

The algB gene, which is involved in the production of alginate in Pseudomonas aeruginosa, was localized to approximately 2.2 kilobases of DNA from strain FRD by using transposon Tn501 insertion mutagenesis, subcloning, and complementation techniques. The previously reported alg-50(Ts) mutation, which confers the phenotype of temperature-sensitive alginate production, was here designated as an algB allele. A transduction-mediated gene replacement technique was used for site-directed mutagenesis to isolate and characterize algB::Tn501 mutants of P. aeruginosa FRD. Although algB::Tn501 mutants had a nonmucoid phenotype (indicating an alginate deficiency), they still produced about 1 to 5% of wild-type levels of alginate in most growth media and up to 16% in very rich media. The algB::Tn501 mutations had no apparent effect on growth rate or growth requirements. Using another gene replacement technique called excision marker rescue, we constructed a chromosomal algB deletion (delta algB) mutant of P. aeruginosa FRD. The delta algB mutant also produced low levels of alginate as did the algB::Tn501 mutants. The alginate produced by algB::Tn501 mutants resembled wild-type alginate by all criteria studied: molecular weight, acetylation, and proportion of mannuronic and guluronic acids. Thus, the algB gene product is apparently involved in the high-level production of alginate by P. aeruginosa and is not directly involved in the pathway leading to its biosynthesis. Chromosomal mapping of an algB::Tn501 insertion showed linkage to the trp-2 marker on the FRD chromosome as does the algB50(Ts) mutation. The excision marker rescue technique was also used to place the algB::Tn501 marker on the chromosome of characterized strains of P. aeruginosa PAO. The algB::Tn501 mutation mapped near 21 min on the PAO chromosome.

Hospital epidemiology of Pseudomonas aeruginosa from patients with cystic fibrosis

Pseudomonas aeruginosa colonizes the respiratory tract of most older patients with cystic fibrosis. The means by which these bacteria are acquired and the risk for patient-to-patient spread among subjects with cystic fibrosis are poorly understood. We studied the spread of Ps. aeruginosa within a hospital environment. Pseudomonas was rarely recovered from the inanimate environment surrounding patients with cystic fibrosis or from hand or rectal cultures of patients who were colonized in the oropharynx. There was transient cross-colonization with Ps. aeruginosa between patients with cystic fibrosis sharing a hospital room in three of seven pairs studied. In all cases the "new" isolate was recoverable only once and was not found during a 2-year follow-up. Three of four sibling pairs with cystic fibrosis shared the same Ps. aeruginosa serotype(s). The risk of sustained cross-colonization by Ps. aeruginosa between patients with cystic fibrosis appears to be minimal, except under conditions of prolonged close contact.

Interaction of complement with serum-sensitive and serum-resistant strains of Pseudomonas aeruginosa

The interaction of complement with the following two strains of Pseudomonas aeruginosa was examined: 144M, a mucoid, serum-sensitive strain bearing short lipopolysaccharide O chains, and 144M-SR, a mucoid, serum-resistant strain bearing long lipopolysaccharide O chains isolated by repeated passage of 144M in increasing concentrations of pooled normal human serum (PNHS). While significant killing of 144M occurred in 5 to 40% PNHS, no killing of 144M-SR was observed. Both strains activated complement, especially 144M-SR which consumed 88.7, 96.4, and 100% of the available complement 3 (C3), C5, and C9, respectively, in 10% PNHS during a 60-min incubation at 37 degrees C. Although it activated more C3 than did 144M (54.9% consumption), 144M-SR bound only half as much C3 as 144M. Similarly, although 144M-SR activated more C9 than did 144M (50.0% consumption in 60 min), there was considerably less C9 attached to 144M-SR (2,990 molecules of C9 per bacterium) than to 144M (13,700 molecules per bacterium) after 60 min of incubation. Furthermore, only 162 molecules of the C9 bound to 144M-SR remained bound after treatment with 0.1% trypsin, while 5,692 molecules of the C9 bound to 144M remained bound under similar conditions. These results show that the serum resistance of 144M-SR does not represent a failure to activate complement efficiently, but instead reflects failure of the assembled terminal complement complex C5b-9 to insert stably into the outer membrane of this strain.

Avirulence and altered physiological properties of cystic fibrosis strains of Pseudomonas aeruginosa

Twenty Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis in good and poor clinical condition were typed by the American Scientific (Difco Laboratories, Detroit, Mich.) Typing Scheme. Only five strains were agglutinated with a single typing serum. Ten strains were agglutinated with more than one serum, and five were not agglutinated with any serum, suggesting some type of lipopolysaccharide alteration in the majority of these strains. Of the strains from patients in good clinical condition, 72% demonstrated proteolytic activity, while 60% of the strains from patients in poor clinical condition demonstrated no proteolytic activity. Twenty-three cystic fibrosis strains of P. aeruginosa examined demonstrated reduced bacteremic virulence when compared with a virulent burn strain with a 50% lethal dose (LD50) of 1.5 X 10(1) CFU in an invasive burned mouse model. Ninety-two percent of the strains tested were avirulent at doses of 10(3) to 10(5) CFU. The LD50s were determined for 10 selected strains which exhibited specific important morphological and physiological deficiencies. Five of the strains tested gave LD50s greater than 10(6) CFU. Reduced virulence of these strains was associated with loss of two or more physiological characteristics associated with virulence. The cystic fibrosis strains of P. aeruginosa which morphologically and physiologically resembled the virulent burn strain were the most virulent (LD50s of 10(2) to 10(4). Results suggest that some degree of virulence is associated only with classic strains prevalent in early infections. The data suggest that a selection transition occurs in the lungs of patients with cystic fibrosis that favors P. aeruginosa avirulence. The avirulent state may be caused by alterations in the cell envelope, including associated factors such as motility and chemotaxis and protease production.

Flagella and motility alterations in Pseudomonas aeruginosa strains from patients with cystic fibrosis: relationship to patient clinical condition

Selected physiological parameters of 31 classic and rough Pseudomonas aeruginosa strains from respiratory tract cultures of patients with cystic fibrosis were examined. An association of a patient's clinical condition (good or poor) with strain physiology was made. Rough strains from patients in poor clinical condition demonstrated severe alterations in motility when compared with M-2, a highly motile and chemotactic burn strain. Of the 10 rough strains from patients in poor clinical condition, 70% lacked flagella, as determined by electron microscopy. The remaining few flagellated strains from this group exhibited weak motility both in soft agar and by the capillary assay. Their chemotactic response to three amino acids, when compared with that of strain M-2, was reduced approximately 30 to 90%. Classic strains from patients in poor clinical condition were less chemotactic than those from patients in good clinical condition. A majority of classic and rough strains from patients in good clinical condition were comparable to M-2 in both chemotaxis and motility. Changes in other physiological characteristics indicated by reduced growth rates, or auxotrophy, were seldom observed in the cystic fibrosis strains studied. The data suggest that host-selective pressures, associated primarily with patients with cystic fibrosis that are in poor clinical condition, result in the loss of factors related to invasiveness such as motility and chemotaxis. We propose that these results may reflect that there is a more general alteration in the cell envelope of cystic fibrosis strains.

Role of exoenzyme S in chronic Pseudomonas aeruginosa lung infections

Exoenzyme S is an extracellular ADP-ribosyltransferase enzyme produced by Pseudomonas aeruginosa. Mutants of Pseudomonas aeruginosa deficient in this enzyme have been shown to have reduced virulence in infections of burned mice. The contribution of exoenzyme S to the pathogenesis of chronic lung infections with this organism was evaluated by examining the incidence of exoenzyme S production by Pseudomonas aeruginosa strains isolated from cystic fibrosis patients and comparing an exoenzyme S deficient mutant and its exoenzyme S producing parent in a rat chronic lung infection model. Of 51 isolates examined, 43% produced detectable levels of exoenzyme S. While both the exoenzyme S deficient mutant and its parent strain were equally capable of colonizing and persisting in rat lungs, the exoenzyme S producing parent elicited a greater degree of lung damage. These data suggest that exoenzyme S contributes to the pathogenesis of chronic lung infections.

Polyagglutinability due to loss of O-antigenic determinants in Pseudomonas aeruginosa strains isolated from cystic fibrosis patients

O-polyagglutinable P. aeruginosa are prevalent among chronically infected cystic fibrosis patients. In the present work, one O-group 3, one O-group 9 and one polyagglutinable 0-3/9 strain were analysed by use of both corresponding group specific antisera against the O-antigen and polyspecific antisera against all extractable antigens of the 3 strains. Quantitative immunoelectrophoresis and classical tube-agglutination methods were employed in the analysis. The results showed that the polyagglutinable strain contained 0.1% and the 0-9 strain 1%, respectively, of the O-antigen-containing LPS present in the 0-3 strain. It is discussed whether these differences represent a gradual antigenic adjustment to the defence mechanisms of the chronically infected patients.

Pseudomonas aeruginosa isolates: comparisons of isolates from campers and from sibling pairs with cystic fibrosis

Sputum or deep throat specimen cultures were obtained from 47 cystic fibrosis (CF) patients residing together at an eight-day summer camp. Pre-camp, initial day, final day and post-camp cultures were obtained and Pseudomonas aeruginosa isolates were characterized by morphology, serotype, pigment production, serum sensitivity, antibiotic susceptibility patterns, hemolysis on blood agar, and CO2 growth requirement. Of the 47 patients, four were not chronically colonized with Pseudomonas and did not become colonized at camp. Analysis of the isolates from the other 43 revealed no significant alteration in the Pseudomonas colonization pattern. Cultures obtained from four sibling pairs among the campers and from 20 additional pairs of siblings revealed that siblings in 20/24 pairs had at least one identical serotype in common. Of the criteria used for characterization, serotyping was the most definitive method for strain identification. Serotyping by both the Homma system and the International system did not detect any serotype at a frequency of more than 31%. In this study, the predominant P. aeruginosa strain of the colonized patients did not change, and non-colonized individuals did not become colonized with P. aeruginosa.

Serum sensitivity of a Pseudomonas aeruginosa mucoid strain

The susceptibility of Pseudomonas aeruginosa 144M (a mucoid strain isolated from the sputum of a cystic fibrosis patient) to the bactericidal activity of pooled fresh normal human serum (FHS) was examined. FHS at concentrations of greater than or equal to 2.5% was capable of killing greater than 95% of strain 144M. Strain 144M was killed by FHS in a dose-dependent manner. Although either immunoglobulin M (IgM) or IgG was bactericidal in the presence of complement, IgM was about 10 times as effective as IgG. However, optimal killing activity required both IgM and IgG and complement, activated by the classical pathway. A role for lysozyme in the killing of 144M was demonstrated only when low concentrations of FHS were used. In contrast to 144M, P. aeruginosa strains 144NM and 144M(SR) were totally resistant to FHS at all of the concentrations tested (up to 50%). Neither the FHS susceptibility of 144M nor the FHS resistance of 144NM or 144M(SR) was altered by choice of growth medium, growth phase, or temperature of growth. Results of absorption studies with whole organisms, isolated outer membrane preparations, or lipopolysaccharide (LPS) from each strain suggest that the antigen(s) which binds the bactericidal immunoglobulins is accessible on the surface of 144M but not on the surface of 144NM or 144M(SR), is insensitive to trypsin treatment, and is believed to be LPS. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the three LPS preparations demonstrated that 144M LPS contained primarily lipid-A-core polysaccharide components, whereas the LPS from 144NM and 144M(SR) were heterogeneous, with various degrees of O-side-chain substitution. These results suggest that at least one target for bactericidal antibody on the surface of 144M is contained in the rough LPS of this strain.

Pulmonary cellular response to chronic irritation and chronic Pseudomonas aeruginosa pneumonia in cats

A model of chronic pulmonary infection was used for studying cellular events in a sequential manner. In this model, agarose beads containing Pseudomonas aeruginosa were instilled endotracheally into cats. Nine cats were inoculated with agarose beads containing P. aeruginosa, and four others were inoculated with sterile beads. With a fiberoptic bronchoscope, bronchial washings were obtained biweekly for up to 30 weeks. The quantitative pulmonary inflammatory cell response and alveolar macrophage morphology of the animals exposed to P. aeruginosa were compared with those for the animals exposed to a chronic irritant (agarose beads). Bronchial washings of all animals before inoculation showed that 70 to 90% of the cells were macrophages. After inoculation with P. aeruginosa, a persistent inflammatory response was observed (60 to 70% granulocytes). In the sterile-bead-inoculated group, the response was less prominent (30 to 40% granulocytes). As early as 2 weeks after inoculation, alveolar macrophages from infected animals were larger and had cytoplasmic features that differed from those of controls. Electron microscope examination showed prominent surface alterations in alveolar macrophages from the infected cats. These alterations persisted from 2 to 12 weeks after infection. In animals inoculated with sterile beads, alveolar macrophages exhibited less extensive surface changes that had resolved by week 8. Histologically, chronic bronchiolitis and pneumonia were more severe in the infected animals than in controls. This model of chronic inflammation and macrophage stimulation, which is similar to the chronic pneumonia of cystic fibrosis, may be a useful approach to answer questions on the role of macrophage activation in chronic lung disease.

Phagocytosis of mucoid and nonmucoid strains of Pseudomonas aeruginosa

In order to evaluate the role of mucoid coating of clinical isolates of Pseudomonas aeruginosa as a virulence factor, opsonophagocytosis of mucoid and nonmucoid strains of P. aeruginosa were studied by three different methods: uptake of [3H]adenine-labeled bacteria, oxygen consumption, and chemiluminescence production by phagocytosing polymorphonuclear leukocytes. All three methods showed a strong correlation with regard to phagocytosis of the bacterial isolates. As a group, the mucoid strains of P. aeruginosa demonstrated significantly reduced phagocytic uptake by leukocytes when compared to nonmucoid strains, although occasionally mucoid strains did exhibit normal uptake. In vitro growth of mucoid strains under nonstationary conditions was associated with reduced mucoid coating and with a corresponding increase in susceptibility to leukocyte phagocytosis. Although the overall bactericidal activity of human polymorphonuclear leukocytes for mucoid strains was diminished, this appears to be a function of reduced ingestion since the rate of intracellular killing was similar for mucoid and nonmucoid strains. The enhanced susceptibility of mucoid strains to spontaneous bactericidal activity of pooled human serum was confirmed. Mucoid-producing strains produced less protease in vitro; however, the role of this phenomenon in influencing phagocytosis is unknown.

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

Twenty-six Pseudomonas aeruginosa strains from patients with cystic fibrosis were typed by the Fisher immunotyping scheme. Only 6 strains were agglutinated by a single typing serum, whereas 15 strains were agglutinated with more than one serum and 5 were not agglutinated by any serum. Neither the polyagglutinable nor the nonagglutinable strains were typable by hemagglutination inhibition or immunodiffusion, suggesting that these polyagglutinable strains did not express multiple serotype antigens, but were instead being agglutinated by antibody to nonserotype determinants. Four typable isolates were resistant to pooled normal human serum, whereas the 12 polyagglutinable and nonagglutinable isolates studied were very sensitive to normal human serum. The outer membranes of 16 strains were isolated and characterized. The data suggested, in general, strong conservation of outer membrane protein patterns. Lipopolysaccharides (LPS) were purified by a new technique which allowed isolation of both rough and smooth LPS in high yields. Three of four typable, serum-resistant strains examined had amounts of smooth, O-antigen-containing LPS equivalent to our laboratory wild type, P. aeruginosa PAO1 strain H103. In contrast, 10 of 12 polyagglutinable or nonagglutinable, serum-sensitive strains had very little or no smooth, O-antigen-containing LPS, and the other two contained less smooth LPS than our wild-type strain H103. In agreement with this data, five independent, rough, LPS O-antigen-deficient mutants of strain H103 were nontypable and serum sensitive. We suggest that the LPS defects described here represent a significant new property of many P. aeruginosa strains associated with cystic fibrosis.

The serum sensitivity, colonial morphology, serogroup specificity, and outer membrane protein of Pseudomonas aeruginosa strains isolated from several clinical sites

Ninety-three strains of Pseudomonas aeruginosa, isolated from 68 patients hospitalized with respiratory tract infections, burns, urinary tract infections, and other illnesses, were examined for: 1) sensitivity to the bactericidal activity of fresh normal human serum (FHS); 2) colonial morphology; 3) serogroup designation; and 4) outer membrane protein (OMP) profile. The purpose of this study was to determine if there was any relationship between any of these microbial characteristics and the propensity of this microorganism to infect a specific clinical site or tissue. The results of this study can be summarized as follows: 1) slime-producing strains were generally more serum-sensitive than non-slime producers, although serum sensitivity was not related to slime production per se; 2) CF strains were much more serum-sensitive than non-CF strains; 3) the clinical isolation site appeared to be the predominant determinant of a strain's sensitivity to FHS; 4) the ability of P. aeruginosa to colonize/infect a specific clinical site or resist the bactericidal activity of FHS was generally unrelated to serogroup specificity; and 5) whereas the OMP profile of a particular strain does not appear to correlate with its response to the bactericidal effect of FHS, it does appear to be related to its clinical isolation site.