Improving antibiotic treatment of bacterial biofilm by hyperbaric oxygen therapy: Not just hot air

Bacteria and fungi show substantial increased recalcitrance when growing as infectious biofilms. Chronic infections caused by biofilm growing microorganisms is considered a major problem of modern medicine. New strategies are needed to improve antibiotic treatment of biofilms. We have improved antibiotic treatment of bacterial biofilms by reviving the dormant bacteria and thereby make them susceptible to antibiotics by means of reoxygenation. Here we review the rationale for associating lack of oxygen with low susceptibility in infectious biofilm, and how hyperbaric oxygen therapy may result in reoxygenation leading to enhanced bactericidal activity of antibiotics. We address issues of feasibility and potential adverse effects regarding patient safety and development of resistance. Finally, we propose means for supplying reoxygenation to antibiotic treatment of infectious biofilm with the potential to benefit large groups of patients.

Antibiotic resistance in Pseudomonas aeruginosa strains with increased mutation frequency due to inactivation of the DNA oxidative repair system

The chronic Pseudomonas aeruginosa infection of the lungs of cystic fibrosis (CF) patients is characterized by the biofilm mode of growth and chronic inflammation dominated by polymorphonuclear leukocytes (PMNs). A high percentage of P. aeruginosa strains show high frequencies of mutations (hypermutators [HP]). P. aeruginosa is exposed to oxygen radicals, both those generated by its own metabolism and especially those released by a large number of PMNs in response to the chronic CF lung infection. Our work therefore focused on the role of the DNA oxidative repair system in the development of HP and antibiotic resistance. We have constructed and characterized mutT, mutY, and mutM mutants in P. aeruginosa strain PAO1. The mutT and mutY mutants showed 28- and 7.5-fold increases in mutation frequencies, respectively, over that for PAO1. These mutators had more oxidative DNA damage (higher levels of 7,8-dihydro-8-oxodeoxyguanosine) than PAO1 after exposure to PMNs, and they developed resistance to antibiotics more frequently. The mechanisms of resistance were increased beta-lactamase production and overexpression of the MexCD-OprJ efflux-pump. Mutations in either the mutT or the mutY gene were found in resistant HP clinical isolates from patients with CF, and complementation with wild-type genes reverted the phenotype. In conclusion, oxidative stress might be involved in the development of resistance to antibiotics. We therefore suggest the possible use of antioxidants for CF patients to prevent the development of antibiotic resistance.

Characterization of paired mucoid/non-mucoid Pseudomonas aeruginosa isolates from Danish cystic fibrosis patients: antibiotic resistance, beta-lactamase activity and RiboPrinting

The purpose of this study was to characterize 42 paired mucoid and non-mucoid Danish cystic fibrosis (CF) Pseudomonas aeruginosa isolates collected in 1997, by RiboPrinting, antibiotic susceptibility and beta-lactamase activity. Eight P. aeruginosa isolates collected before 1991 were included for comparison. Eighteen of the 42 paired mucoid and non-mucoid isolates showed the same ribotype; the remaining 24 belonged to different ribogroups. Mucoid isolates showed higher susceptibility to antibiotics and lower beta-lactamase activity compared with non-mucoid isolates. Significant differences (P < or = 0.01) between mucoid and non-mucoid isolates were found for the meropenem and colistin MICs for the isolates with the same ribotype, and for the MICs of ceftazidime, piperacillin, aztreonam, meropenem, tobramycin, ciprofloxacin and in the basal levels of beta-lactamase for the paired isolates belonging to different ribogroups. A dominant ribotype 73-S2 with hyperinducible beta-lactamase production and significantly higher MICs of piperacillin, meropenem and tobramycin compared with the other major ribotypes (73-S1, 207-S3 and 227-S8) was present among the 84 CF isolates. The isolates collected before 1991 had an antibiotic susceptibility pattern similar to the 1997 isolates. Despite prolonged and intensive antibiotic treatment, susceptible mucoid isolates were isolated from the CF sputum, possibly because these bacteria are protected from the selective pressure of antibiotics by the resistant non-mucoid isolates co-existing in the biofilm in the lungs of CF patients.

Typing of Pseudomonas aeruginosa strains in Norwegian cystic fibrosis patients

OBJECTIVES

Typing of Pseudomonas aeruginosa isolates from Norwegian cystic fibrosis (CF) patients with chronic Pseudomonas lung infection in order to see whether cross-infection might have occurred.

METHODS

Isolates from 60 patients were collected during the years 1994-98, and typed by pulsed field gel electrophoresis.

RESULTS

Seventy-one strains were identified. One large cluster of identical strains included 27 patients, and 13 smaller clusters of 2-4 patients were found (26 patients). Seven patients had a strain not shared by other patients (private strains). Harboring the main cluster strain was significantly associated with participation in summer camps and training courses (P = 0.004, chi-squared test). There were no associations with regular admissions to hospital (intravenous antibiotic courses) or smaller social gatherings of short duration. Small clusters and private strains were not associated with any of the risk factors. All strains were sensitive to colistin. The minimal inhibitory concentrations were generally lower in Norwegian P. aeruginosa strains compared with isolates from Danish patients.

CONCLUSIONS

Our results indicate that cross-infection with P. aeruginosa between cystic fibrosis patients has occurred.

Pseudomonas aeruginosa and the in vitro and in vivo biofilm mode of growth

The biofilm mode of growth is the survival strategy of environmental bacteria like Pseudomonas aeruginosa. Such P. aeruginosa biofilms also occur in the lungs of chronically infected cystic fibrosis patients, where they protect the bacteria against antibiotics and the immune response. The lung tissue damage is due to immune complex mediated chronic inflammation dominated by polymorphonuclear leukocytes releasing proteases and oxygen radicals.

Rapid development in vitro and in vivo of resistance to ceftazidime in biofilm-growing Pseudomonas aeruginosa due to chromosomal beta-lactamase

The aim of this study was to examine the development of resistance of biofilm-growing P. aeruginosa during treatment with ceftazidime. Biofilms were established in vitro using a modified Robbins device (MRD) and in vivo in the rat model of chronic lung infection. Three P. aeruginosa strains isolated from the lungs of cystic fibrosis (CF) patients (MICceftazidime-basal/induced beta-lactamase activity: PAO 579= 0.8 mg/l-19/550 milliunits, 19676A=50 mg/l-38/957 milliunits, 17107B=100 mg/l-504/947 milliunits) were studied. After 1 or 2 weeks of continuous or intermittent (4 h/day) administration of ceftazidime to biofilms established in MDR, a statistically significant development of resistance to ceftazidime in PAO 579 or 19676A bacterial populations occurred. When ceftazidime was administered 4 h/day (200 mg/l) for 2 weeks, the frequency of resistant 19676A having MIC>25 mg/l was 4.4 10(-1) compared to 6.0-10(-5) in the control biofilm. The same trend was observed after continuous administration of ceftazidime. MICceftazidime of the more resistant variants was increased 500-fold for PAO 579 and 8-fold for 19676A, and the specific basal beta-lactamase activities from 19 to 1,400 units for PAO 579 and from 38 to 10,000 units for 19676A. Chronic P. aeruginosa lung infection was established with alginate-embedded PAO 579, 19676A or 17107B in 146 Lewis rats which were treated with ceftazidime 4 g/kg intraperitoneally twice a day for 1 week. A statistically significant development of resistance was observed for all three strains. The MICceftazidime of the more resistant variants was increased 15-fold for PAO 579, 8-fold for 19676A, and 4-fold for 17107B, and the specific basal 3-lactamase activity from 19 to 100 units for PAO 579, from 38 to 1,300 units for 19676A, and from 500 to 1,300 units for 17107B. It was shown that, during treatment with ceftazidime, biofilm-growing P. aeruginosa had the capacity to develop resistance due to the production of chromosomal beta-lactamase.

Molecular mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from cystic fibrosis patients

Twenty P. aeruginosa isolates were collected from six cystic fibrosis (CF) patients, aged 27 to 33, in 1994 (9 isolates) and 1997 (11 isolates) at the CF Center, Copenhagen, Denmark, and were typed by pulse-field gel electrophoresis (PFGE) or ribotyping. Five of the patients had isolates with the same PFGE or ribotyping patterns in 1997 as in 1994, and ciprofloxacin had a two- to fourfold higher MIC for the isolates collected in 1997 than those from 1994. Genomic DNA was amplified for gyrA, parC, mexR, and nfxB by PCR and sequenced. Eleven isolates had mutations in gyrA, seven isolates had mutations at codon 83 (Thr to Ile), and four isolates had mutations at codon 87 (Asp to Asn or Tyr). Sixteen isolates had mutations in nfxB at codon 82 (Arg to Leu). Increased amounts of OprN were found in six isolates and OprJ in eight isolates as determined by immunoblotting. No isolates had mutations in parC or mexR. Six isolates had mutations in efflux pumps without gyrA mutations. The average number of mutations was higher in isolates from 1997 than in those from 1994. The results also suggested that efflux resistance mechanisms are more common in isolates from CF patients than in strains from urine and wounds from non-CF patients, in which mutations in gyrA and parC dominate (S. Jalal and B. Wretlind, Microb. Drug Resist. 4:257-261, 1998).

Chromosomal beta-lactamase is packaged into membrane vesicles and secreted from Pseudomonas aeruginosa

Membrane vesicles were isolated from one beta-lactam-sensitive and three beta-lactam-resistant Pseudomonas aeruginosa clinical isolates from patients with cystic fibrosis. The presence of the chromosomally encoded beta-lactamase in the membrane vesicles was shown by electron microscopy and enzymatic studies. This is the first report of extracellular secretion of beta-lactamase in P. aeruginosa and it seems that the enzyme is packaged into membrane vesicles.

Avidity of anti-P aeruginosa antibodies during chronic infection in patients with cystic fibrosis

BACKGROUND

In order to study the impact on the lung function of patients with cystic fibrosis of the avidity of antipseudomonal antibodies, the avidity of antibodies against the chromosomal beta-lactamase of Pseudomonas aeruginosa (a beta ab) and against the 60-65 kDa heat shock protein of P aeruginosa (anti-GroEL) were measured in serum samples collected longitudinally during chronic infection with P aeruginosa from a group of patients with poor and good lung function.

METHODS

The thiocyanate elution method in which the molarity of potassium thiocyanate required to elute 50% bound antibody under conditions of antigen excess in ELISA was used to measure the relative avidity.

RESULTS

All patients developed increasing levels of a beta ab and anti-GroEL antibodies during the follow up period but no maturation of the avidity of these antibodies was observed. In patients with good lung function the avidity of a beta ab was higher than in patients with poor lung function (p = 0.018). No significant difference in the avidity of the anti-GroEL antibodies was observed between the two groups of patients.

CONCLUSION

In patients with cystic fibrosis a high avidity of a beta ab could contribute to a more efficient inhibition of the beta-lactamase by these antibodies, resulting in the better lung function seen in this group. The immunopathological implication of the failure in avidity maturation of antibodies in chronic infection is discussed.

The clonal antibody response to Pseudomonas aeruginosa heat shock protein is highly diverse in cystic fibrosis patients

The GroEL protein of Pseudomonas aeruginosa belongs to the bacterial 60-65 kDa heat shock protein family. A strong antibody response to GroEL has been found in cystic fibrosis (CF) patients with chronic pulmonary infection caused by P. aeruginosa. Clonotypes of IgG1 and IgG2 antibodies against GroEL were studied in 60 consecutive sera from 18 CF patients with chronic P. aeruginosa infection using isoelectric focusing in combination with affinity immunoblotting. The persistent antigenic stimulation in CF patients with chronic P. aeruginosa infection induced numerous IgG1 and particularly IgG2 antibody clones against GroEL. The appearance of new clones with time reflected the long duration of the chronic infection. A striking addition of new clonotypes during the observation period occurred when a new unrelated bacterium (Burkholderia cepacia) had become established as a cause of the pulmonary infection, or when the P. aeruginosa infection became chronic.

Pseudomonas aeruginosa isolates from patients with cystic fibrosis have different beta-lactamase expression phenotypes but are homogeneous in the ampC-ampR genetic region

Pseudomonas aeruginosa isolates from 1 of 17 cystic fibrosis patients produced secondary beta-lactamase in addition to the ampC beta-lactamase. Isolates were grouped into three beta-lactamase expression phenotypes: (i) beta-lactam sensitive, low basal levels and inducible beta-lactamase production; (ii) beta-lactam resistant, moderate basal levels and hyperinducible beta-lactamase production; (iii) beta-lactam resistant, high basal levels and constitutive beta-lactamase production. Apart from a base substitution in the ampR-ampC intergenic region of an isolate with moderate-basal-level and hyperinducible beta-lactamase production, sensitive and resistant strains were identical in their ampC-ampR genetic regions. Thus, enhanced beta-lactamase expression is due to mutations in regulatory proteins other than AmpR.

The influence of allotypes on the IgG subclass response to chromosomal beta-lactamase of Pseudomonas aeruginosa in cystic fibrosis patients

Sera from 70 adult cystic fibrosis (CF) patients with chronic lung infection with Pseudomonas aeruginosa were typed for seven GM and two KM allotype determinants. IgG class and all four IgG subclasses of antibodies against chromosomal beta-lactamase of Ps. aeruginosa (a beta ab) were measured in all 70 CF patients in a cross-sectional study. The a beta ab IgG subclass response in sera collected during the first 11 years of chronic infection from 20 CF patients (10 patients with G3M*5 G1M*3/G3M*5 G1M*3 genotype and 10 patients with G3M*21 G1M*1/G3M*21 G1M*1 genotype) was analysed in a longitudinal study. Increased levels of IgG2 were associated with the presence of GM 23 allotype. IgG3 a beta ab levels were the lowest for subjects with the GM 1,2,3,17 23 5,21 and GM 1,3,17 21 phenotypes and the highest in subjects with GM 3,23,5 and GM 3,5. No significant differences in IgG1 and IgG4 a beta ab levels were found between the different phenotypes. IgG1 a beta ab levels were higher in patients with KM*3/KM*3 genotype compared with patients with KM*3, *1 genotype. Patients with G3M*5 G1M*3/G3M*5 G1M*3 genotype had in both the cross-sectional and the longitudinal study higher IgG3 a beta ab, lower IgG4 a beta ab levels and poorer lung function than patients with G3M*21 G1M*1/ G3M*21 G1M*1 genotype. An influence of the allotypes on the clinical course of chronic lung infection with Ps. aeruginosa in patients with CF is suggested.

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.

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.