Subspecific differentiation of Burkholderia cepacia isolates in cystic fibrosis

Thirty clinical isolates of Burkholderia cepacia from cystic fibrosis (CF) patients in the UK and Denmark were characterised, together with other clinical isolates and laboratory strains of B. cepacia, B. gladioli and B. vietnamiensis. Outer-membrane protein (OMP) profiles were determined, and the organisms were typed genotypically by pulsed-field gel electrophoresis after DNA restriction analyses with Xbal and DraI. This latter method revealed four clusters among the clinical isolates studied; one of these contained isolates of the UK and intercontinental CF epidemic lineage ET12, a cluster which appeared to contain three subtypes. Each of the four clusters appeared less closely related to laboratory strains of B. cepacia than were laboratory strains of B. vietnamiensis, but more closely related to both these species than to B. gladioli. Two types of OMP profile were distinguished among the clinical isolates and strains, and were designated A and B. In type A isolates the major proteins had mol.wts of 39, 27 and 18 kDa. Type B strains additionally contained a group of proteins in the size range 80-90 kDa, although detection of these depended upon the conditions for sample denaturation. In most cases, the OMP type correlated with the genotype, suggesting that examination of OMPs might be of value in the initial characterisation of isolates.

Epidemiology of Pseudomonas aeruginosa in cystic fibrosis and the possible role of contamination by dental equipment

Cystic fibrosis (CF) patients often suffer from Pseudomonas aeruginosa lung infection yet the source of this organism is not known. In order to determine whether CF patients might be contaminated with P. aeruginosa from dental equipment, a total of 103 water samples from 25 dental sessions in Frederiksberg Municipal Oral Health Care Service were examined. Three samples (2.9%) were positive for P. aeruginosa. Three hundred and twenty-seven water samples from 82 dental sessions from various other Municipal Oral Health Services in Denmark, attended by CF patients, were also examined. Eighteen of 327 samples (5.5%) from nine sessions (11%) were positive for P. aeruginosa. In one case, genotypically identical (RFLP, pulsed-field gel electrophoresis) P. aeruginosa strains were found both in water from the dental equipment and in the CF patients sputum. This indicates a small risk for acquiring P. aeruginosa from dental sessions, which is however equal to the yearly 'natural background' incidence (1-2%) of acquisition of P. aeruginosa in our CF centre.

Quantitative analysis of the IgG and IgG subclass immune responses to chromosomal Pseudomonas aeruginosa beta-lactamase in serum from patients with cystic fibrosis by western blotting and laser scanning densitometry

BACKGROUND

Antibodies against chromosomal beta-lactamase of Pseudomonas aeruginosa (a beta ab) are markers of the development of resistance of P aeruginosa to beta-lactam antibiotics in patients with cystic fibrosis and chronic lung infection. The role of these antibodies in patients with chronic lung infection with P aeruginosa was further investigated by correlating the a beta ab IgG subclasses with pulmonary function in patients with cystic fibrosis.

METHODS

Immunoglobulin G (IgG) and IgG subclass a beta ab were investigated by western blotting and quantified by laser scanning densitometry. A longitudinal study on 43 consecutive patients with cystic fibrosis who developed chronic lung infection with P aeruginosa was performed.

RESULTS

IgG subclass a beta ab appeared in all patients with chronic infection with P aeruginosa. Eleven years after the onset of infection all the patients had IgG1, 79% had IgG4, 56% IgG2, and only 16% of the patients had IgG3 a beta ab. The IgG1 and IgG4 a beta ab appeared first, and more than 50% of the patients were IgG1 and IgG4 a beta ab positive within 2-3 years of the onset of infection, but IgG2 positivity only appeared after seven years and IgG3 remained absent from most of the patients. The median a beta ab levels increased during chronic infection: 100-fold for IgG1, 22-fold for IgG2, and 45-fold for IgG4. A 16-fold increase in the IgG3 a beta ab levels was detected in the six patients who developed IgG3 a beta ab. In the first four years of the chronic infection the a beta ab titres were higher in patients with good lung function than in those with poor lung function.

CONCLUSIONS

The association of a weak IgG3 and a strong IgG4 a beta ab response suggests that the contribution of a beta ab antibodies to lung diseases mediated by immune complexes might be less important than other antipseudomonal antibodies. A beneficial neutralising effect of the a beta ab antibodies on the antibiotic destroying enzymes may be an additional factor.

Antibodies against Pseudomonas aeruginosa chromosomal beta-lactamase inpatients with cystic fibrosis are markers of the development of resistance of P. aeruginosa to beta-lactams

Chromosomal beta-lactamase production is considered to be the most important resistance mechanism of Pseudomonas aeruginosa against beta-lactams. Recently we have detected serum and sputum antibodies against P. aeruginosa chromosomal beta-lactamase (a beta ab), using immunoblotting techniques. In this study we have developed an enzyme-linked-immunosorbent assay to measure serum a beta ab response in 124 cystic fibrosis patients in a cross-sectional study and in 54 cystic fibrosis patients in a longitudinal study. The a beta ab response occurred after a median of 3 years following onset of chronic infection and was significantly higher (P < 0.0002) in patients chronically infected with resistant strains than in those from whom resistant strains were occasionally isolated. The a beta ab levels correlated (r = 0.51, P = 0.0001) with the number of beta-lactam courses. A 14 fold increase in a beta ab levels occurred during the 14 year period covered by the longitudinal study. The results of this study show that a beta ab to P. aeruginosa is a specific marker for resistance development of P. aeruginosa to beta-lactams.

[Biofilm, foreign bodies and chronic infections]

Most bacteria occur in the environment as sessile cells adhering to a surface, whereas a minority exists as free floating (planktonic) cells. Biofilms consist of microcolonies embedded in a polysaccharide matrix produced by the bacteria. This polysaccharide slime protects the bacteria against hostile environmental factors. Planktonic daughter cells are liberated from the surface of biofilms and may colonize new surfaces and subsequently produce new biofilms. Biofilms are often consortia of several different bacterial species. The normal microflora on the skin or on the mucous membranes in the human body occurs as a biofilm, which is removed by the shedding of old cells and by the excretion of mucus. Subsequently new cells and new mucus are colonized by biofilm forming bacteria without giving rise to any symptoms. When body surfaces with a normally occurring microflora (A) are connected by means of an implanted foreign body with body surfaces or tissue compartments without a microflora (B) e.g. bronchi, gall bladder, peritoneum, veins, then a translocation of the normal microflora from (A) to (B) may easily occur leading to acute infection, formation of new biofilms on the implanted foreign body and induction of inflammation in the environment of this biofilm. Chronic bacterial infections are frequently caused by biofilm producing bacteria and the pathogenesis of the tissue damage is dominated by a persistent immune complex mediated inflammation. Bacteria growing in biofilms cannot be eradicated by antibiotics and biofilms resist the immunological and non-specific defence mechanisms of the body.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies against chromosomal beta-lactamase

A murine monoclonal anti-chromosomal beta-lactamase antibody was developed and an immunoblotting technique was used to study the presence of serum and sputum antibodies against Pseudomonas aeruginosa chromosomal group 1 beta-lactamase in patients with cystic fibrosis (CF). The serum antibody response was studied with serum samples collected in 1992 from 56 CF patients in a cross-sectional study and with serum samples from 18 CF patients in a longitudinal study. Anti-beta-lactamase immunoglobulin G antibodies were present in all of the serum samples from the patients with chronic bronchopulmonary P. aeruginosa infection (CF + P) but in none of the CF patients with no or intermittent P. aeruginosa infection. Anti-beta-lactamase antibodies were present in serum from CF + P patients after six antipseudomonal courses (median) and correlated with infection with a beta-lactam-resistant strain of P. aeruginosa. The sputum antibody response and the beta-lactamase activity in sputum samples from 14 of the CF + P patients were also studied. beta-lactamase antibodies were present in 10 of these samples. P. aeruginosa strains isolated from these samples were partially derepressed, producing group 1 cephalosporinase. We found a wide range of chromosomal beta-lactamase activity in the sputum samples, with no correlation with basal or induced activity of beta-lactamase expression. The presence of anti-beta-lactamase antibodies in endobronchial sputum could be an important factor in the defense against the infection. On the other hand, immune complexes between the beta-lactamase and corresponding antibodies could play a role in the pathogenesis of bronchopulmonary injury in CF by mediating hyperimmune reactions.

Development of antibiotic resistance in Pseudomonas aeruginosa during two decades of antipseudomonal treatment at the Danish CF Center

At the Danish CF Center patients with chronic Pseudomonas aeruginosa lung infection were treated 3-4 times a year (from 1976) with a 2-week intravenous antipseudomonal course which included preferentially an aminoglycoside and a beta-lactam antibiotic. We investigated the development of antibiotic resistance in P. aeruginosa strains isolated from Danish CF patients over a period of 18 years by testing the in vitro efficacy of carbenicillin, piperacillin, ceftazidime, tobramycin and ciprofloxacin against P. aeruginosa strains collected in 1973 (51 strains), 1980 (80 strains), 1985 (58 strains), and 1991 (100 strains). All the strains were screened and assayed semiquantitatively for beta-lactamase activity by use of nitrocefin. We found a significant (p < 0.005) increase in the MIC values of the P. aeruginosa strains against piperacillin and ceftazidime. However, no significant correlation was found between the MIC and the number of antipseudomonal courses of antibiotics. The proportion of resistant in vivo selected P. aeruginosa strains, presumed to be stably derepressed producers of chromosomal beta-lactamase, also increased significantly during the period studied. Our results confirm that the beta-lactamase production is an important mechanism of antibiotic resistance in P. aeruginosa.

Polyacrylamide gel electrophoresis analysis of lipopolysaccharide from Pseudomonas aeruginosa growing planktonically and as biofilm

Lipopolysaccharide (LPS, endotoxin) was extracted from biofilm and planktonically grown monoagglutinable (1118) and polyagglutinable (258 and 15703) strains of Pseudomonas aeruginosa isolated from cystic fibrosis patients with chronic pulmonary infections. Analysis by polyacrylamide gel electrophoresis (PAGE) followed by immune-detection of LPS fractions showed an S-form appearance of strain 1118 and 258 with three distinct clusters of high molecular weight bands, whereas 15703 appeared semi-rough. LPS of semi-rough cells grown planktonically and as biofilm showed a very similar PAGE pattern; however, the core/lipid A R-LPS fraction was more prominent in biofilm-LPS than in planktonic-LPS extracted from the S-form bacteria (1118 and 258). The apparent change in LPS sub-unit components of the bacteria when grown as biofilm may reflect changes in the outer membrane structure that contribute to the altered physico-chemical properties of biofilm bacteria in foreign-device associated infections and chronic P. aeruginosa lung infection in cystic fibrosis patients.

High-level beta-lactamase activity in sputum samples from cystic fibrosis patients during antipseudomonal treatment

The in vivo activity and source of beta-lactamase in sputum samples from 43 patients with cystic fibrosis (CF) during a 2-week antipseudomonal treatment were studied. A colorimetric method, based on the conversion of nitrocefin, was used for quantitation of the sputum beta-lactamase activity. beta-Lactamases in sputum were characterized by isoelectric focusing and inhibition profile and were compared with the beta-lactamases extracted from Pseudomonas aeruginosa isolated from the paired sputum samples. We found that the beta-lactamase activity increased to high levels in sputum from patients with CF during the course of piperacillin, ceftazidime, cefsulodin, or imipenem therapy. Aztreonam therapy lead to opposite results because the beta-lactamase activity decreased and aztreonam was able to mask beta-lactamase activity by acting as an inhibitor. All sputum beta-lactamases displayed characteristics indicative of a class I enzyme, identical to the beta-lactamases extracted from P. aeruginosa. The presence of beta-lactamase at such levels could lead to in vivo inactivation of beta-lactam antibiotics. This study supports the hypothesis that beta-lactamase production is an important in vivo resistance mechanism in P. aeruginosa-infected patients with CF.

Induction of beta-lactamase production in Pseudomonas aeruginosa biofilm

Imipenem induced high levels of beta-lactamase production in Pseudomonas aeruginosa biofilms. Piperacillin also induced beta-lactamase production in these biofilms but to a lesser degree. The combination of beta-lactamase production with other protective properties of the biofilm mode of growth could be a major reason for the persistence of this sessile bacterium in chronic infections.

Rapid emergence of resistance in Pseudomonas aeruginosa in cystic fibrosis patients due to in-vivo selection of stable partially derepressed beta-lactamase producing strains

The development of significant mechanisms of resistance to beta-lactam antibiotics in Pseudomonas aeruginosa in cystic fibrosis (CF) patients have been studied in ten CF patients during a two week course of anti-pseudomonal beta-lactam antibiotic therapy. Sputum samples were collected on days 1, 7 and 15. Entire homogenized sputum samples were examined directly for the number of bacteria resistant to different levels of antibiotics. This allowed the detection of pre-existing resistant subpopulations of bacteria as well as following the changes in beta-lactam antibiotic susceptibility during treatment. P. aeruginosa isolates were characterized by means of sero-grouping, phage- and pyocin-typing. Outer membrane proteins of paired sensitive and resistant strains were characterized. Sonicated extracts of cells were assayed for basal and induced beta-lactamase activity. Beta-lactamase activity was further characterized by isoelectric focusing and inhibition profiles. Our observations were in accordance with the hypothesis that the sensitive inducible population was overrun by the pre-existing resistant subpopulation, during treatment. The resistant in-vivo selected P. aeruginosa population exhibited stable partially derepression but the beta-lactamase inhibitor tazobactam restored beta-lactam antibiotic activity.

Investigation of the criteria for assessing the outcome of treatment in acromegaly

The outcome of treatment in acromegaly is usually assessed by measuring plasma concentrations of growth hormone (GH)--either basal spontaneous levels or during hyperglycaemia. There is no consensus on how cure should be defined. Many studies have considered basal plasma growth hormone concentrations below 20 mU/l (10 ng/ml) as proof of cure, although some recent studies have applied lower values. At present a limit of 10 mU/l (5 ng/ml) seems to be accepted as evidence of cure. We have studied 28 acromegalic patients after transsphenoidal adenomectomy. Plasma GH concentrations (basal and during hyperglycaemia) as well as plasma somatomedin C (SMC) concentrations were measured and compared to the clinical symptoms. There was a close correlation between plasma GH and SMC concentrations (except when plasma GH levels were low) and between the clinical assessment and SMC concentrations. Very low plasma GH levels (less than 1 mU/l or 0.5 ng/ml) were associated with normal SMC values and clinical cure, high GH levels (greater than 10 mU/l or 5 ng/ml) with elevated SMC levels and persisting acromegaly. Moderately elevated plasma GH concentrations (1.9-9.6 mU/l) did not allow any conclusions on the outcome of treatment as assessed from SMC determinations and clinical evaluation. It is concluded that the usual criteria for cure in acromegaly may not be sufficiently strict.