RESPIRATORY TRACT BACTERIOLOGY IN CYSTIC FIBROSIS

Long Persistence of a Streptococcus pneumoniae 23F Clone in a Cystic Fibrosis Patient

Streptococcus pneumoniae is a common resident in the human nasopharynx. However, carriage can result in severe diseases due to a unique repertoire of pathogenicity factors that are rare in closely related commensal streptococci. We investigated a penicillin-resistant S. pneumoniae clone of serotype 23F isolated from a cystic fibrosis patient on multiple occasions over an unusually long period of over 3 years that was present without causing disease. Genome comparisons revealed an apparent nonfunctional pneumococcus-specific gene encoding a hyaluronidase, supporting the view that this enzyme adds to the virulence potential of the bacterium. The 23F clone harbored unique mosaic genes encoding penicillin resistance determinants, the product of horizontal gene transfer involving the commensal S. mitis as donor species. Sequences identical to one such mosaic gene were identified in an S. mitis strain from the same patient, suggesting that in this case S. pneumoniae played the role of donor.

Streptococcus pneumoniae isolates of serotype 23F with intermediate penicillin resistance were recovered on seven occasions over a period of 37 months from a cystic fibrosis patient in Berlin. All isolates expressed the same multilocus sequence type (ST), ST10523. The genome sequences of the first and last isolates, D122 and D141, revealed the absence of two phage-related gene clusters compared to the genome of another ST10523 strain, D219, isolated earlier at a different place in Germany. Genomes of all three strains carried the same novel mosaic penicillin-binding protein (PBP) genes, pbp2x, pbp2b, and pbp1a; these genes were distinct from those of other penicillin-resistant S. pneumoniae strains except for pbp1a of a Romanian S. pneumoniae isolate. All PBPs contained mutations that have been associated with the penicillin resistance phenotype. Most interestingly, a mosaic block identical to an internal pbp2x sequence of ST10523 was present in pbp2x of Streptococcus mitis strain B93-4, which was isolated from the same patient. This suggests interspecies gene transfer from S. pneumoniae to S. mitis within the host. Nearly all genes expressing surface proteins, which represent major virulence factors of S. pneumoniae and are typical for this species, were present in the genome of ST10523. One exception was the hyaluronidase gene hlyA, which contained a 12-nucleotide deletion within the promoter region and an internal stop codon. The lack of a functional hyaluronidase might contribute to the ability to persist in the host for an unusually long period of time.

IMPORTANCEStreptococcus pneumoniae is a common resident in the human nasopharynx. However, carriage can result in severe diseases due to a unique repertoire of pathogenicity factors that are rare in closely related commensal streptococci. We investigated a penicillin-resistant S. pneumoniae clone of serotype 23F isolated from a cystic fibrosis patient on multiple occasions over an unusually long period of over 3 years that was present without causing disease. Genome comparisons revealed an apparent nonfunctional pneumococcus-specific gene encoding a hyaluronidase, supporting the view that this enzyme adds to the virulence potential of the bacterium. The 23F clone harbored unique mosaic genes encoding penicillin resistance determinants, the product of horizontal gene transfer involving the commensal S. mitis as donor species. Sequences identical to one such mosaic gene were identified in an S. mitis strain from the same patient, suggesting that in this case S. pneumoniae played the role of donor.

Cystic fibrosis therapy: a community ecology perspective

Current therapy for cystic fibrosis (CF) focuses on minimizing the microbial community and the host's immune response through the aggressive use of airway clearance techniques, broad-spectrum antibiotics, and treatments that break down the pervasive endobronchial biofilm. Antibiotic selection is typically based on the susceptibility of individual microbial strains to specific antibiotics in vitro. Often this approach cannot accurately predict medical outcomes because of factors both technical and biological. Recent culture-independent assessments of the airway microbial and viral communities demonstrated that the CF airway infection is considerably more complex and dynamic than previously appreciated. Understanding the ecological and evolutionary pressures that shape these communities is critically important for the optimal use of current therapies (in both the choice of therapy and timing of administration) and the development of newer strategies. The climax-attack model (CAM) presented here, grounded in basic ecological principles, postulates the existence of two major functional communities. The attack community consists of transient viral and microbial populations that induce strong innate immune responses. The resultant intense immune response creates microenvironments that facilitate the establishment of a climax community that is slower-growing and inherently resistant to antibiotic therapy. Newer methodologies, including sequence-based metagenomic analysis, can track not only the taxonomic composition but also the metabolic capabilities of these changing viral and microbial communities over time. Collecting this information for CF airways will enable the mathematical modeling of microbial community dynamics during disease progression. The resultant understanding of airway communities and their effects on lung physiology will facilitate the optimization of CF therapies.

In Vivo Studies with the Partially Purified Protease (Elastase) from Pseudomonas aeruginosa

An extracellular protease from Pseudomonas aeruginosa exhibiting elastase activity was characterized in vivo after an 80- to 100-fold purification by chemical and chromatographic procedures. The lethality of different samples for white, female mice was determined by intravenous, intranasal, intraperitoneal, and subcutaneous injections. The purified protease exhibited the following 48-hr LD(50) values: intraperitoneally, 9.0 protease units; intranasally, 31.5 protease units; and intranasally, 0.3 protease unit. In the concentrations tested no lethality was observed when the subcutaneous route was employed. Gross and microscopic studies revealed that purified protease was capable of eliciting a variety of tissue responses in mice depending upon its route of administration. Intraperitoneal injections resulted in gastrointestinal tract serosal hemorrhage and necrosis. Intranasal and intravenous injections produced pulmonary hemorrhage, whereas subcutaneous injections resulted in black, necrotic, ulcerating lesions.

Antiphagocytic Effect of Slime from a Mucoid Strain of Pseudomonas aeruginosa

Mucoid strains of Pseudomonas aeruginosa produce a viscid slime when grown on the surface of agar media. These strains are known to colonize persistently the tracheobronchial tree of children with cystic fibrosis. Colonization may result from inhibition of phagocytosis due to slime produced by the organism. Slime separated from one mucoid strain was examined to determine whether it possessed antiphagocytic activity in vitro. Cells of P. aeruginosa, Escherichia coli, and Staphylococcus aureus were rapidly phagocytized by rabbit polymorphonuclear leukocytes when mixtures were rotated for 2 hr at 37 C in the absence of slime. The addition of relatively small amounts of slime to bacteria and leukocytes inhibited phagocytosis as measured by phagocytic killing of the organisms. Inhibition was found to be most complete with P. aeruginosa.

Population structure, antimicrobial resistance, and mutation frequencies of Streptococcus pneumoniae isolates from cystic fibrosis patients

Forty-eight Streptococcus pneumoniae isolates recovered from sputum samples from 26 cystic fibrosis (CF) patients attending our CF unit (1995 to 2003) were studied. Mean yearly incidence of isolation was 5.5%, and all were strains recovered from young patients (< or = 12 years). The isolation was linked to clinical exacerbation in 35% of the cases, but only 27% of these were not accompanied by other CF pathogens. Fifty percent of the patients presented with two to four isolates over the studied period. Pulsed-field gel electrophoresis-SmaI digestion revealed a high heterogeneity (32 pulsotypes among 48 isolates) and the persistence over a 6-month period of a single clone (clone A) in two patients. This clone, presenting a varied multiresistance phenotype, was identified as the Spain23F-1 clone and was also recognized in six other patients, including two out of nine patients from the CF unit of Sant Joan de Deu Hospital, Barcelona, Spain. In our isolates, 16 different serotypes were recognized, the most frequent being 23F (33.3%), 19F (18.8%), 6A (6.2%), and 6B (6.2%). High overall resistance rates were observed: to penicillin, 73%; to cefotaxime, 33%; to erythromycin, 42%; to tetracycline, 58%; to chloramphenicol, 48%; and to trimethoprim-sulfamethoxazole, 67%. Resistance to fluoroquinolones was not detected. Multiresistance was a common feature (60%). The percentage of S. pneumoniae strains with increased frequencies of mutation to rifampin resistance (> or = 7.5 x 10(-8)) was significantly higher (P = 0.02) in CF (60%) than among non-CF (37%) isolates in the same institution (M. I. Morosini et al., Antimicrob. Agents Chemother. 47:1464-1467, 2003). Even though a clear association with acute exacerbations could not be observed, long-term clonal persistence and variability, high frequency of antibiotic resistance, and hypermutability indicate the plasticity for adaptation of S. pneumoniae to the CF lung environment.

Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia

Respiratory infections with Pseudomonas aeruginosa and Burkholderia cepacia play a major role in the pathogenesis of cystic fibrosis (CF). This review summarizes the latest advances in understanding host-pathogen interactions in CF with an emphasis on the role and control of conversion to mucoidy in P. aeruginosa, a phenomenon epitomizing the adaptation of this opportunistic pathogen to the chronic chourse of infection in CF, and on the innate resistance to antibiotics of B. cepacia, person-to-person spread, and sometimes rapidly fatal disease caused by this organism. While understanding the mechanism of conversion to mucoidy in P. aeruginosa has progressed to the point where this phenomenon has evolved into a model system for studying bacterial stress response in microbial pathogenesis, the more recent challenge with B. cepacia, which has emerged as a potent bona fide CF pathogen, is discussed in the context of clinical issues, taxonomy, transmission, and potential modes of pathogenicity.

Alginate synthesis by Pseudomonas aeruginosa: a key pathogenic factor in chronic pulmonary infections of cystic fibrosis patients

Pulmonary infection by mucoid, alginate-producing Pseudomonas aeruginosa is the leading cause of mortality among patients suffering from cystic fibrosis. Alginate-producing P. aeruginosa is uniquely associated with the environment of the cystic fibrosis-affected lung, where alginate is believed to increase resistance to both the host immune system and antibiotic therapy. Recent evidence indicates that P. aeruginosa is most resistant to antibiotics when the infecting cells are present as a biofilm, as they appear to be in the lungs of cystic fibrosis patients. Inhibition of the protective alginate barrier with nontoxic compounds targeted against alginate biosynthetic and regulatory proteins may prove useful in eradicating P. aeruginosa from this environment. Our research has dealt with elucidating the biosynthetic pathway and regulatory mechanism(s) responsible for alginate synthesis by P. aeruginosa. This review summarizes reports on the role of alginate in cystic fibrosis-associated pulmonary infections caused by P. aeruginosa and provides details about the biosynthesis and regulation of this exopolysaccharide.

High osmolarity is a signal for enhanced algD transcription in mucoid and nonmucoid Pseudomonas aeruginosa strains

Chronic lung infection with mucoid, alginate-producing strains of Pseudomonas aeruginosa is a major cause of mortality in cystic fibrosis (CF) patients. Transcriptional activation of the P. aeruginosa algD gene, which encodes GDPmannose dehydrogenase, is essential for alginate synthesis. Activation of algD is dependent on the product of the algR gene. Sequence homology between the P. aeruginosa algR gene and the Escherichia coli ompR gene, which regulates the cellular response to changes in osmolarity of the growth medium, together with the abnormally high levels of Na+ and Cl- in respiratory tract fluid in CF patients suggested that high osmolarity in the lung of the CF patient might be a signal contributing to the induction of alginate synthesis (mucoidy) in infecting P. aeruginosa. In both mucoid and nonmucoid P. aeruginosa strains (containing a functional algR gene), transcriptional activation of algD increased as the osmolarity of the culture medium increased. The increased activation of algD at high osmolarity was not in itself sufficient to induce alginate synthesis in nonmucoid strains, however, suggesting that other environmental factors are involved in full activation of the alginate genes. The targets of AlgR and OmpR, the algD promoter and the ompC and ompF promoters, respectively, were found to have appreciable sequence homology in the -60 to -110 regions. In E. coli, OmpR was capable of activating the algD promoter nearly as well as AlgR, but in both cases, activation occurred only under conditions of high osmolarity.

The epidemiology of Pseudomonas cepacia in patients with cystic fibrosis

Pseudomonas cepacia has emerged as an important nosocomial pathogen colonizing and infecting the respiratory tract of patients with cystic fibrosis (CF). Although assessment of outcomes associated with P. cepacia colonization has been difficult, controlled studies have shown that colonized patients experience more adverse outcomes compared with those not colonized. In the United States, an increasing trend in national incidence and prevalence of P. cepacia colonization has been shown, but cases have been unevenly distributed in a few centers. These estimates, however, may be biased by intercenter differences in laboratory methods for detecting P. cepacia in patient sputum. The source and mode of transmission of P. cepacia have not been adequately demonstrated, and may vary from center to center. Until further studies elucidate the epidemiology of P. cepacia in patients with CF, it may be prudent for CF centers to consider the use of selective media to isolate P. cepacia from sputa of patients with CF, to conduct investigations of clusters of P. cepacia-colonized patients, and to consider adopting infection control precautions recommended for control of multiply resistant gram negative organisms.

Alginate biosynthetic enzymes in mucoid and nonmucoid Pseudomonas aeruginosa: overproduction of phosphomannose isomerase, phosphomannomutase, and GDP-mannose pyrophosphorylase by overexpression of the phosphomannose isomerase (pmi) gene

The specific activities of phosphomannose isomerase (PMI), phosphomannomutase (PMM), GDP-mannose pyrophosphorylase (GMP), and GDP-mannose dehydrogenase (GMD) were compared in a mucoid cystic fibrosis isolate of Pseudomonas aeruginosa and in two spontaneous nonmucoid revertants. In both revertants some or all of the alginate biosynthetic enzymes we examined appeared to be repressed, indicating that the loss of the mucoid phenotype may be a result of decreased formation of sugar-nucleotide precursors. The introduction and overexpression of the cloned P. aeruginosa phosphomannose isomerase (pmi) gene in both mucoid and nonmucoid strains led not only to the appearance of PMI levels in cell extracts several times higher than those present in the wild-type mucoid strain, but also in higher PMM and GMP specific activities. In extracts of both strains, however, the specific activity of GMD did not change as a result of pmi overexpression. In contrast, the introduction of the cloned Escherichia coli manA (pmi) gene in P. aeruginosa caused an increase in only PMI and PMM activities, having no effect on the level of GMP. This suggests that an increase in PMI activity alone does not induce high GMP activity in P. aeruginosa. The heterologous overexpression of the P. aeruginosa pmi gene in the E. coli manA mutant CD1 led to the appearance in cell extracts of not only PMI activity but also GMP activity, both of which are normally undetectable in extracts of CD1. We discuss the implications of these results and propose a mechanism by which overexpression of the P. aeruginosa pmi gene can cause an elevation in both PMM and GMP activities.

Gene amplification induces mucoid phenotype in rec-2 Pseudomonas aeruginosa exposed to kanamycin

Gene amplification in the chromosome of rec-2 Pseudomonas aeruginosa PAO2003 upon growth on kanamycin-supplemented media led to a stable mucoid phenotype. The chromosomal region controlling alginate biosynthesis was shown to be amplified four to six times as a direct tandem repeat of at least 16.8 kilobase pairs. This amplification was deduced from Southern DNA-DNA hybridization patterns of the chromosomal DNA digested with restriction endonucleases BglII and EcoRI and probed with a cloned DNA segment complementing the alg-22 mutation. The part of the amplified unit carrying the novel DNA joint was cloned. The EcoRI junction fragment was further subcloned and used to probe chromosomes of parental strain PAO2003 and mucoid variant VD2003M. As predicted, the EcoRI junction fragment hybridized to the two chromosomal fragments required to produce the novel junction. Though the mucoid phenotype caused by gene amplification was stable, nonmucoid revertants were obtained at a low frequency on tetracycline-containing media. Southern hybridization of chromosomal DNA from a nonmucoid revertant revealed a reduction in the copy number of amplified DNA. These results suggest a direct relationship between amplification of this chromosomal segment and the induction of mucoidy.

Toxic activity against alveolar macrophages of products of Pseudomonas aeruginosa isolated from respiratory and non-respiratory sites

The toxic effect of certain products of Pseudomonas aeruginosa on guinea-pig alveolar macrophages has been studied in an attempt to account for the apparent infrequency with which certain strains of this species are associated with respiratory infection. Texts were carried out on strains derived from the respiratory tract, strains from infection at other sites, and strains from the inanimate hospital environment which were believed not to have been responsible for infection ('environmental' strains). Haemolysin, pigments, enzyme-containing fractions, slime and cell-wall fraction all exhibited toxic activity against macrophages in an in vitro system, although for any given strain of Ps. aeruginosa the haemolysin was by far the most potent factor. The activity of this factor against macrophages was directly proportional to its haemolytic activity against human erythrocytes. The haemolysin fractions of environmental strains, which have previously been found to have little activity on erythrocytes, were also less active against macrophages than haemolysin preparations from 'infective' strains. It is therefore postulated that the ability of a strain of Ps. aeruginosa to initiate respiratory infection may be related to the degree of haemolysin production. The activity of other fractions against macrophages is more variable, but they may contribute in different ways to the development of infection once entry into the lung has been achieved.

Murine gastrointestinal tract as a portal of entry in experimental Pseudomonas aeruginosa infections

Peroral administration of viable Pseudomonas aeruginosa into the stomach of mice resulted in an acute systemic infection, with death occurring within 72 h. One strain, ATCC 19660, a non-encapsulated form of P. aeruginosa, had a median lethal dose of 5.3 X 10(6) colony-forming units, whereas two encapsulated strains, ATCC 17933 and 17934, had median lethal dose values of 5.0 x 10(7) and 5.6 x 10(7) colony-forming units, respectively. Each strain required fewer organisms to establish a lethal infection via the stomach than by intravenous or intraperitoneal routes. The non-encapsulated strain, ATCC 19660, did not cause any diarrhea in the infected animals, whereas the two encapsulated strains, although less virulent, caused diarrhea when administered perorally. No signs of necrosis were noted within the gastrointestinal tract; however, hematogenous spread of the organism resulted in a vasculitis associated with the pulmonary vessels and bacterial invasion of the renal tissues. Treatment of animals with antineoplastic drugs 24 h before or simultaneously with peroral challenge resulted in an increased susceptibility to infection.

Interactions of Pseudomonas aeruginosa with immunoglobulins and complement in sputum

The interactions of Pseudomonas aeruginosa with humoral factors in the sputum of patients with cystic fibrosis were investigated by using an indirect immunofluorescent technique. Fluorescein-conjugated, monovalent antiserum specific to heavy chains of human immunoglobulin A (IgA), IgG, or IgM and to complement C3 were used. All strains of P. aeruginosa recovered from the sputum specimens of patients with cystic fibrosis were found to be coated with antibodies of IgA, IgG, and IgM classes and with C3. The specificity of the antibody coating was determined. The fluorescence was most intense with IgA and was followed in intensity by IgG, IgM, and C3. No difference was noted between rough and mucoid strains of P. aeruginosa. When the subcultured P. aeruginosa was incubated with the sputum eluates, a similar pattern of fluorescence was demonstrated, indicating that these humoral factors are present in the sputum and that the coating process can take place in the lower respiratory tract of the patients. By single radial immunodiffusion, significant quantities of the humoral factors in the sputum eluates were detected. These findings suggest that P. aeruginosa is opsonized in sputum of patients with cystic fibrosis.

Production and characterization of the slime polysaccharide of Pseudomonas aeruginosa

The slime polysaccharides produced by Pseudomonas aeruginosa isolated from a variety of human infections were investigated. Slime production in culture seemed optimal when adequate amounts of carbohydrate were present and under conditions of either high osmotic pressure or inadequate protein supply. The polysaccharides produced by the organisms were similar to each other, to the slime of Azotobacter vinelandii, and to seaweed alginic acids. They were composed of beta-1,4-linked d-mannuronic acid residues and variable amounts of its 5-epimer l-guluronic acid. All bacterial polymers contained o-acetyl groups which are absent in the alginates. The polysaccharides differed considerably in the ratio of mannuronic to guluronic acid content and in the number of o-acetyl groups. The particular composition of the slime was not found to be characteristic for the disease process from which the mucoid variants of P. aeruginosa were obtained.

In vivo studies with collagenase from Pseudomonas aeruginosa

An extracellular protease from Pseudomonas aeruginosa having collagenase activity was assayed in vivo. The lethality of the enzyme for white female mice was determined by use of intravenous, intraperitoneal, intranasal, and subcutaneous routes, respectively. The collagenase exhibited the following 72-hr mean lethal dose values: intranasally, 55 collagenase units; intraperitoneally, 148 collagenase units; and intravenously, 288 collagenase units. In the concentrations tested, no lethality was obtained when the subcutaneous route was employed. Gross and microscopic studies revealed that the collagenase was capable of eliciting a variety of tissue responses in mice depending upon its route of administration. Intranasal instillation resulted in confluent pulmonary hemorrhage, whereas intraperitoneal injections resulted in severe abdominal hemorrhage with foci on the intestinal serosa. Intravenous injections elicited abdominal hemorrhage and petechial hemorrhage with focal necrosis of the lungs, whereas subcutaneous injections resulted in necrotic, ulcerating lesions.

Opsonic defect in patients with cystic fibrosis of the pancreas

Cystic fibrosis of the pancreas is one of the most common inborn errors of metabolism. The high incidence of morbidity and mortality in these patients is primarily due to severe and frequent pulmonary infection. To date, no immune deficiency has been found in cystic fibrosis patients. Their sera contain normal quantities of immunoglobulins and hemolytic complement. In an assay of phagocytosis by alveolar macrophage, six out of nine sera from cystic fibrosis patients failed to support normal phagocytosis of Pseudomonas aeruginosa. This deficiency could be corrected by increasing the concentration of serum used in the assay. By contrast, their sera supported normal phagocytosis of Pseudomonas by blood polymorphonuclear leukocytes and continued to support normal phagocytosis when serum dilutions were used. Two patients with severe isolated deficiences of serum immunoglobulin A were found to have a similar defect in the alveolar macrophage assay, but normal phagocytosis by polymorphonuclear leukocytes. It is postulated that cystic fibrosis patients may have a quantitative and (or) functional defect of IgA antibodies, specific for Pseudomonas, and possibly of importance in the pathogenesis of their pulmonary disease.