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

Characterization of Burkholderia cepacia complex from environment influenced by human waste

The natural environment is a primary source of infections caused by members of Burkholderia cepacia complex (BCC), but the release of human waste may in return enrich the natural environment with clinically relevant BCC. Seven BCC isolates from environment influenced by human liquid or solid waste across Croatia, and one clinical isolate was characterised. B. multivorans recovered from the soil at illegal dumpsite belonged to sequence type (ST)19; B. ambifaria from the agricultural soil fertilized with swine or poultry manure to ST927 or new ST; B. cenocepacia from creek sediment, river water and wound swab to new STs. Antimicrobial susceptibility of isolates ranged from sensitive to multidrug-resistant. A variety of bla_TEM genes was confirmed in isolates. Isolates expressed the virulence factors and survived in river water during 50 days. The BCC present natural environments influenced by the human waste are of clinical relevance and a potential source of sporadic infections.

Klebsiella pneumoniae carbapenemase (KPC) in urinary infection isolates

Recently, emergence of carbapenem-resistance, in particular due to Klebsiella pneumoniae carbapenemase (KPC), was observed among K. pneumoniae causing urinary tract infections in Croatia. The aim of the study was to characterize, antimicrobial susceptibility, carbapenem resistance, virulence traits and plasmid types of the urinary KPC positive isolates of K. pneumoniae. The antimicrobial susceptibility to a wide range of antibiotics was determined by broth microdilution method. The transferability of meropenem resistance was determined by conjugation (broth mating method) employing Escherichia coli J63 strain resistant to sodium azide. Genes encoding broad and extended-spectrum β-lactamases, plasmid-mediated AmpC β-lactamases, group A and B carbapenemases, and carbapenem hydrolyzing oxacillinases (bla_OXA-48like), respectively, were determined by Polymerase chain reaction (PCR). In total 30 KPC-positive K. pneumoniae urinary isolates collected from different regions of Croatia were analysed. The isolates were uniformly resistant to all tested antibiotics except for variable susceptibility to gentamicin, sulphamethoxazole/trimethoprim, and colistin, respectively. Four isolates were resistant to colistin with MICs values ranging from 4 to 16 mg/L. All tested isolates were susceptible to ceftazidime/avibactam. Sixteen isolates transferred meropenem resistance to E. coli recipient strain by conjugation. Other resistance markers were not co-transferred. PCR was positive for bla_KPC and bla_SHV genes in all isolates whereas 13 isolates tested positive also for bla_TEM genes. PCR based replicon typing (PBRT) revealed the presence of FIIs in 13 and FIA plasmid in two strains. The study showed dissemination of KPC-producing K. pneumoniae in urinary isolates, posing a new epidemiological and treatment challenge. Sulphamethoxazole/trimethoprim, colistin, and ceftazidime/avibactam remain so far, as the therapeutic options.

Characterization of the extended-spectrum β-lactamases and determination of the virulence factors of uropathogenic Escherichia coli strains isolated from children

BACKGROUND AND AIM

The aim of the study was to characterize ESBL-producing uropathogenic Escherichia coli (UPEC) strains isolated in children. That included the investigation of virulence factors and the analysis of the types of β-lactamases at the molecular genetic level.

MATERIAL AND METHODS

During the 2-year study period, 77 ESBL-producing E. coli strains were recovered from urine samples of febrile children with significant bacteriuria hospitalized at one Croatian hospital. Susceptibility of isolates to bactericidal serum activity was tested by Shiller and Hatch method, while adhesin expression was determined by agglutination methods. Characterization of ESBLs was performed by PCR with specific primers for ESBLs and by sequencing of bla (ESBL) genes. Genotyping of the E. coli isolates was performed by pulsed-field gel electrophoresis (PFGE).

RESULTS

Twenty-seven (35.1 %) and 50 (64.9 %) ESBL-producing UPEC strains were isolated in neonates and infants, respectively. Of 70 strains investigated for the presence of virulence factors, adhesins were detected in 48.6 % strains (8.6 % in the neonate and 40 % in the infants group) giving a statistically significant difference in adhesin expression between the two groups (p < 0.01). Hemolysin was produced by 84.3 %, whereas 70 % of strains were serum-resistant. The bla (TEM) gene was detected in 22 (28 %) and bla (SHV) gene in 57 strains (74 %), whereas bla (CTX-M) gene was detected in only two isolates (2.5%). In ten isolates, bla (TEM) and bla (SHV) were simultaneously detected. Sequencing of bla (SHV) genes revealed that SHV-5 β-lactamase was by far the most prevalent and was found in 51 strains (66 %). The strains were clonally related as demonstrated by PFGE and assigned into ten clusters.

CONCLUSIONS

Infection control measures should be employed and the consumption of expanded-spectrum cephalosporins in the hospital should be restricted.

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

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

Expression, purification, and biochemical characterization of WbpP, a new UDP-GlcNAc C4 epimerase from Pseudomonas aeruginosa serotype O6

B-band lipopolysaccharide is an important virulence factor of the opportunistic pathogen Pseudomonas aeruginosa. WbpP is an enzyme essential for B-band lipopolysaccharide production in serotype O6. Sequence analysis suggests that it is involved in the formation of N-acetylgalacturonic acid. To test this hypothesis, overexpression and biochemical characterization of WbpP were performed. By using spectrophotometric assays and capillary electrophoresis, we show that WbpP is a UDP-GlcNAc C4 epimerase. The K(m) for UDP-GlcNAc and UDP-GalNAc are 197 and 224 micrometer, respectively. At equilibrium, 70% of UDP-GalNAc is converted to UDP-GlcNAc, whereas the yield of the reverse reaction is only 30%. The enzyme can also catalyze the inter-conversion of non-acetylated substrates, although the efficiency of catalysis is significantly lower. Only 15 and 40% of UDP-Glc and UDP-Gal, respectively, are converted at equilibrium. WbpP contains tightly bound NAD(H) and does not require additional cofactors for activity. It exists as a dimer in its native state. This paper is the first report of expression and characterization of a C4 UDP-GlcNAc epimerase at the biochemical level. Moreover, the characterization of the enzymatic function of WbpP will help clarify ambiguous surface carbohydrate biosynthetic pathways in P. aeruginosa and other organisms where homologues of WbpP exist.

Alginate lyase promotes diffusion of aminoglycosides through the extracellular polysaccharide of mucoid Pseudomonas aeruginosa

We demonstrated that a 2% suspension of Pseudomonas aeruginosa alginate completely blocked the diffusion of gentamicin and tobramycin, but not that of carbenicillin, illustrating how alginate production can help protect P. aeruginosa growing within alginate microcolonies in patients with cystic fibrosis (CF) from the effects of aminoglycosides. This aminoglycoside diffusion barrier was degraded with a semipurified preparation of P. aeruginosa alginate lyase, suggesting that this enzyme deserves consideration as an adjunctive agent for CF patients colonized by mucoid strains of P. aeruginosa.

Isolation and characterization of two genes, waaC (rfaC) and waaF (rfaF), involved in Pseudomonas aeruginosa serotype O5 inner-core biosynthesis

Recent studies have provided evidence to implicate involvement of the core oligosaccharide region of Pseudomonas aeruginosa lipopolysaccharide (LPS) in adherence to host tissues. To better understand the role played by LPS in the virulence of this organism, the aim of the present study was to clone and characterize genes involved in core biosynthesis. The inner-core regions of P. aeruginosa and Salmonella enterica serovar Typhimurium are structurally very similar; both contain two main chain residues of heptose linked to lipid A-Kdo2 (Kdo is 3-deoxy-D-manno-octulosonic acid). By electrotransforming a P. aeruginosa PAO1 library into Salmonella waaC and waaF (formerly known as rfaC and rfaF, respectively) mutants, we were able to isolate the homologous heptosyltransferase I and II genes of P. aeruginosa. Two plasmids, pCOREc1 and pCOREc2, which restored smooth LPS production in the waaC mutant, were isolated. Similarly, plasmid pCOREf1 was able to complement the Salmonella waaF mutant. Sequence analysis of the DNA insert of pCOREc2 revealed one open reading frame (ORF) which could code for a protein of 39.8 kDa. The amino acid sequence of the deduced protein exhibited 53% identity with the sequence of the WaaC protein of S. enterica serovar Typhimurium. pCOREf1 contained one ORF capable of encoding a 38.4-kDa protein. The sequence of the predicted protein was 49% identical to the sequence of the Salmonella WaaF protein. Protein expression by the Maxicell system confirmed that a 40-kDa protein was encoded by pCOREc2 and a 38-kDa protein was encoded by pCOREf1. Pulsed-field gel electrophoresis was used to determine the map locations of the cloned waaC and waaF genes, which were found to lie between 0.9 and 6.6 min on the PAO1 chromosome. Using a gene-replacement strategy, we attempted to generate P. aeruginosa waaC and waaF null mutants. Despite multiple attempts to isolate true knockout mutants, all transconjugants were identified as merodiploids.

Prevalence of gca, a gene involved in synthesis of A-band common antigen polysaccharide in Pseudomonas aeruginosa

Two distinct forms of lipopolysaccharide are expressed by Pseudomonas aeruginosa. These forms are known as the A band and the B band. In an attempt to obtain a better understanding of A-band lipopolysaccharide synthesis, a previously isolated A-band gene known as the gca gene (GDP-D-mannose conversion protein for A-band common antigen polysaccharide) was sequenced and analyzed. Previous protein expression data from our laboratory, along with nucleotide sequence analysis from the present study, suggest that the Gca protein is encoded by the open reading frame ORF36.5. Amino acid homology reveals that this protein may be functioning as a dehydratase or as a bifunctional enzyme, facilitating the conversion of GDP-D-mannose to GDP-D-rhamnose. The distribution of this gca gene among the 20 P. aeruginosa O serotypes, clinical isolates, and other Pseudomonas species was also examined. Southern hybridization results revealed that the gca gene is present and conserved on a 1.6-kb KpnI fragment among all 20 O serotypes with the exception of serotype O12. In addition, the gca gene is not universally found among all pseudomonads; however, probe-reactive profiles are similar to that of P. aeruginosa when the gca gene is present. Primers were designed from the gca nucleotide sequence, and PCR amplification of a 700-bp product was found with each of the 20 O serotypes. Because of the conservation of this gene, gca may be useful as a diagnostic tool for detecting the presence of P. aeruginosa as well as other Pseudomonas species.

Characterization of mucoid Pseudomonas aeruginosa strains isolated from technical water systems

The occurrence of mucoid Pseudomonas aeruginosa strains was investigated in water samples and surface material from non-clinical aquatic environments. Ten of 81 environmental isolates displayed a mucoid colony type after incubation at 36 degrees C for 24 h on Pseudomonas Isolation Agar. The mucoid strains obtained exclusively from surfaces of technical water systems were characterized in terms of medium-dependent expression of mucoid colonial phenotype, exoenzyme profile, pigment production and O-antigen type. The mucoid strains secreted substantially higher quantities of carbohydrate and uronic acid-containing material compared to non-mucoid environmental isolates. Major slime components of the mucoid strains were identified as O-acetylated alginates that contained higher proportions of mannuronate than guluronate monomer residues and were composed of blocks of poly-mannuronate and poly-mannuronate/guluronate, whereas blocks of poly-guluronate were absent. The results suggest that surfaces in aquatic environments may represent a natural habitat for mucoid (i.e. alginate-overproducing) strains of Ps. aeruginosa with properties similar to clinical mucoid strains.

Chromosomal mapping, expression and synthesis of lipopolysaccharide in Pseudomonas aeruginosa: a role for guanosine diphospho (GDP)-D-mannose

Pseudomonas aeruginosa can express two distinct forms of lipopolysaccharide (LPS), called A-band and B-band. As an attempt to understand the molecular biology of the synthesis and regulation of these LPS antigens, a recombinant plasmid, pFV3, containing genes for A-band expression was isolated previously. In the present study, P. aeruginosa strain PAO1 was mutagenized with transposon Tn5-751 and yielded a B-band-deficient mutant, called ge6. This mutant was mated with a PAO1 genomic library, and transconjugants were screened for complementation of B-band using B-band-specific monoclonal antibody MF15-4. Recombinant plasmid pFV100 was subsequently isolated by its ability to complement B-band expression in ge6. SDS-PAGE analysis of LPS from ge6 and ge6(pFV100) revealed that ge6 was deficient in expression of B-band, while ge6(pFV100) had an LPS profile similar to that of the parent strain PAO1. With A-band and B-band genes cloned in separate plasmids, pFV3 and pFV100 respectively, we were able to determine the map location of these LPS genes on the P. aeruginosa PAO1 chromosome using pulsed-field gel electrophoresis. A-band genes mapped at 5.75 to 5.89 Mbp (SpeI fragment SpK; DpnI fragment DpF2), while genes involved with expression of B-band LPS mapped at 1.9 Mbp (SpeI fragments SpC, SpI and SpAI; DpnI fragment DpD) on the 5.9 Mbp chromosome. We also performed initial characterization of a gene involved with synthesis of A-band present on pFV3. We previously reported that recombinant plasmid pFV3 and subcloned plasmid pFV36 complemented A-band synthesis in rd7513, an A- mutant derived from A+ strain AK1401. pFV36 was mutagenized with transposon Tn1000 to reveal a one-kilobase region capable of complementing the expression of A-band in the A- strain rd7513. This region was subcloned as a 1.6 kb KpnI fragment into plasmid vector pAK1900 and the resulting clone named pFV39. Labelling of proteins encoded by pAK1900 and pFV39 in Escherichia coli maxicells revealed a single unique polypeptide of approximately 37 kDa expressed by pFV39. Supernatants from disrupted cells of rd7513(pFV39) and AK1401 converted 14C-labelled-guanosine diphospho (GDP)-D-mannose to GDP-rhamnose, while supernatants from rd7513 did not show synthesis of GDP-rhamnose. The data therefore suggest that conversion of GDP-D-mannose to GDP-rhamnose is required for synthesis of A-band LPS, and that a 37 kDa protein is involved in this conversion.

Molecular cloning of genes involved with expression of A-band lipopolysaccharide, an antigenically conserved form, in Pseudomonas aeruginosa

Most strains of Pseudomonas aeruginosa can express two chemically and immunologically distinct types of lipopolysaccharide (LPS), an antigenically conserved form called A band and the serotype-specific form called B band. To study the molecular controls regulating expression of the A-band LPS antigen, we have cloned the genes involved with A-band LPS expression. Strain AK1401, a phage-resistant mutant of PAO1 which was shown previously to produce only A-band LPS and not the O-antigen-containing B-band LPS, was mutagenized by using ethyl methanesulfonate to generate an A-band-deficient mutant called rd7513. A cosmid clone bank of P. aeruginosa PAO1 whole genomic DNA was constructed in Escherichia coli. The gene bank was mobilized en masse into strain rd7513, and detection of complementation of synthesis of A band was done by screening transconjugants in a colony immunoblot assay with the A-band-specific monoclonal antibody N1F10. One recombinant cosmid, pFV3, complemented synthesis of A-band polysaccharide in rd7513. Silver-stained polyacrylamide gel and Western immunoblot analyses of LPS extracted from the transconjugant rd7513(pFV3) showed that the A band produced had a higher molecular weight than the A band of AK1401. Analysis of the plasmid pFV3 showed that it contained a chromosomal insert of 27 kb. Two subclones of pFV3, namely, pFV35 and pFV36, containing chromosomal inserts of 5.3 and 4.2 kb, respectively, also complemented A-band expression in rd7513. The LPS banding profile of rd7513(pFV35) was similar to that of AK1401, while the LPS profile of rd7513(pFV36) more closely resembled that of rd7513(pFV3). pFV3 complemented A-band expression in five of the six P. aeruginosa O serotypes which lack A band as well as in rough strain AK44 but failed to complement A-band expression in core mutants AK1012 and AK1282, suggesting that pFV3 contains genes for A-band expression and that synthesis of a complete core region in isogenic mutant strains is required for A-band synthesis.

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.

Microbiology of airway disease in patients with cystic fibrosis

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.

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.

Complement activation and C3 binding by serum-sensitive and serum-resistant strains of Pseudomonas aeruginosa

The relationship among complement consumption, C3 deposition, and C3 fragmentation pattern was compared for serum-sensitive (Sers) and serum-resistant (Serr) strains of Pseudomonas aeruginosa. The Sers strains, which were mucoid strains derived from patients with cystic fibrosis, had lipopolysaccharide deficient in O-antigen side chains. These organisms generally activated much less complement per organism than their Serr counterparts, characterized by the presence of lipopolysaccharide with long lipopolysaccharide O side chains. Surprisingly, however, although the Serr strains consumed more total hemolytic complement, less C3 was deposited onto the surface of these strains than onto that of the Sers strains. Maximal C3 binding required the participation of both the classical and alternative complement pathways, although classical complement pathway involvement was more important for Serr strains. Finally, while more than half of the C3 deposited on most Sers strains was in the form of C3b, most of the C3 on the Serr strains was in the form of iC3b, indicating a more rapid and extensive conversion of C3b to iC3b on the surface of these strains. Limited complement activation by Sers mucoid strains of P. aeruginosa may confer a selective survival advantage to these organisms in colonizing the airways of patients with cystic fibrosis.

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.

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.

[Infections of the respiratory tract with Pseudomonas aeruginosa in cystic fibrosis]

The main cause of death in cystic fibrosis (CF) patients is progressive pulmonary insufficiency frequently associated with chronic infections of the respiratory tract by Pseudomonas aeruginosa. Bacteria of this species synthesize numerous extracellular products contributing to its pathogenicity. An alginate-like exopolysaccharide is characteristic for mucoid mutants predominating among P. aeruginosa isolates from CF patients. It interferes with immune defense mechanisms of the host and probably protects the bacteria against certain antibiotics. Furthermore, it is involved in the formation of bacterial microcolonies that resist mucociliary clearance, opsonisation, and phagocytosis. Exotoxin A and elastase are regarded as the most important among various extracellular enzymes involved in pulmonary injury in CF patients. Exotoxin A inhibits eukaryotic protein synthesis leading to necrosis; elastase, together with other Pseudomonas-proteases, induces hemorrhagic lesions and necrosis and seems to inactivate immunoglobulins and complement factors. Phospholipase C and glycolipid represent two hemolysins of P. aeruginosa that may contribute to cytopathogenic effects in infected lungs. No primary defect in the immunological defense mechanisms of CF patients has been described so far. Antibodies against various P. aeruginosa antigens including those mentioned above have been demonstrated, but a complete elimination of the bacteria from infected lungs has not been observed. Therapy of pulmonary P. aeruginosa infections in CF patients usually includes combinations of antibiotics of the beta-lactam and aminoglycoside type. Difficulties arise from an unusually high intrinsic resistance of P. aeruginosa as well as from poor penetration of many antibiotics into the sputum of CF patients. Therefore, future efforts to manage the Pseudomonas problem in CF will probably concentrate on prophylactic therapy, e.g. childhood vaccination of CF patients in order to prevent bacterial colonization of the respiratory tract.

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.

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.