Airway Biofilm Disease: Clinical Manifestations and Therapeutic Possibilities Using Macrolides

Macrolides: From Toxins to Therapeutics

Macrolides are a diverse class of hydrophobic compounds characterized by a macrocyclic lactone ring and distinguished by variable side chains/groups. Some of the most well characterized macrolides are toxins produced by marine bacteria, sea sponges, and other species. Many marine macrolide toxins act as biomimetic molecules to natural actin-binding proteins, affecting actin polymerization, while other toxins act on different cytoskeletal components. The disruption of natural cytoskeletal processes affects cell motility and cytokinesis, and can result in cellular death. While many macrolides are toxic in nature, others have been shown to display therapeutic properties. Indeed, some of the most well known antibiotic compounds, including erythromycin, are macrolides. In addition to antibiotic properties, macrolides have been shown to display antiviral, antiparasitic, antifungal, and immunosuppressive actions. Here, we review each functional class of macrolides for their common structures, mechanisms of action, pharmacology, and human cellular targets.

Mechanistic action of weak acid drugs on biofilms

Selective permeability of a biofilm matrix to some drugs has resulted in the development of drug tolerant bacteria. Here we studied the efficacy of a weak organic acid drug, N-acetyl-L-cysteine (NAC), on the eradication of biofilms formed by the mucoid strain of Pseudomonas aeruginosa and investigated the commonality of this drug with that of acetic acid. We showed that NAC and acetic acid at pH < pKa can penetrate the matrix and eventually kill 100% of the bacteria embedded in the biofilm. Once the bacteria are killed, the microcolonies swell in size and passively shed bacteria, suggesting that the bacteria act as crosslinkers within the extracellular matrix. Despite shedding of the bacteria, the remnant matrix remains intact and behaves as a pH-responsive hydrogel. These studies not only have implications for drug design but also offer a route to generate robust soft matter materials.

Pathogenicity of exopolysaccharide-producing Actinomyces oris isolated from an apical abscess lesion

Aim

To demonstrate a capacity for producing exopolysaccharides (EPSs) and an ability to form biofilm on abiotic materials of Actinomyces oris strain K20.

Methodology

The productivity of EPSs and the ability to form biofilm of strain K20 were evaluated by measuring viscosity of spent culture media and by scanning electron microscopy (SEM) and the biofilm assay on microtitre plates, respectively. High-performance liquid chromatography was used to determine the chemical composition of the viscous materials. To examine the role of the viscous materials attributable to the pathogenicity in this organism, the ability of strain K20 to induce abscess formation was compared in mice to that of ATCC 27044.

Results

The viscosity of the spent culture media of K20 was significantly higher than that of ATCC 27044. Strain K20 showed dense meshwork structures around the cells and formed biofilms on microtitre plates, whereas ATCC 27044 did not. Chemical analysis of the viscous materials revealed that they were mainly composed of neutral sugars with mannose constituting 77.5% of the polysaccharides. Strain K20 induced persistent abscesses in mice lasting at least 5 days at a concentration of 10⁸ cells mL⁻¹, whereas abscesses induced by ATCC 27044 healed and disappeared or decreased in size at day 5.

Conclusions

Strain K20 produced EPSs, mainly consisting of mannose, and formed biofilms. This phenotype might play an important role for A. oris to express virulence through the progression of apical periodontitis.

Comparison of the virulence of exopolysaccharide-producing Prevotella intermedia to exopolysaccharide non-producing periodontopathic organisms

BACKGROUND

Evidence in the literature suggests that exopolysaccharides (EPS) produced by bacterial cells are essential for the expression of virulence in these organisms. Secreted EPSs form the framework in which microbial biofilms are built.

METHODS

This study evaluates the role of EPS in Prevotella intermedia for the expression of virulence. This evaluation was accomplished by comparing EPS-producing P. intermedia strains 17 and OD1-16 with non-producing P. intermedia ATCC 25611 and Porphyromonas gingivalis strains ATCC 33277, 381 and W83 for their ability to induce abscess formation in mice and evade phagocytosis.

RESULTS

EPS-producing P. intermedia strains 17 and OD1-16 induced highly noticeable abscess lesions in mice at 107 colony-forming units (CFU). In comparison, P. intermedia ATCC 25611 and P. gingivalis ATCC 33277, 381 and W83, which all lacked the ability to produce viscous materials, required 100-fold more bacteria (109 CFU) in order to induce detectable abscess lesions in mice. Regarding antiphagocytic activity, P. intermedia strains 17 and OD1-16 were rarely internalized by human polymorphonuclear leukocytes, but other strains were readily engulfed and detected in the phagosomes of these phagocytes.

CONCLUSIONS

These results demonstrate that the production of EPS by P. intermedia strains 17 and OD1-16 could contribute to the pathogenicity of this organism by conferring their ability to evade the host's innate defence response.

Influence of adjunct azithromycin on the mortality of experimental Pseudomonas aeruginosa sepsis

The aim of this study was to determine the in vivo influence of azithromycin subinhibitory concentrations on mortality in a peritonitis-sepsis model. One hour after an intraperitoneal injection of Pseudomonas aeruginosa, mice were randomized to receive: ceftazidime, 500 mg/kg SC q4hxtwo doses alone; azithromycin, 20 mg/kg SCxone dose alone; ceftazidime plus azithromycinxone dose; ceftazidime plus azithromycinxtwo doses (1 and 24 h); ceftazidime plus prophylactic azithromycin (three doses at -48, -24, 1 h); or no treatment (control). A significant decrease in the rate of mortality was observed in animals treated with all ceftazidime plus azithromycin groups when compared with those receiving ceftazidime alone. These data indicate a potential role for adjunctive azithromycin therapy in P. aeruginosa infection.

Biofilm-like structures and pathogenicity of Escherichia hermannii YS-11, a clinical isolate from a persistent apical periodontitis lesion

Escherichia hermannii, formerly classified as enteric group 11 of Escherichia coli, is considered to be nonpathogenic. In this report, we described some of the pathogenic properties of a viscous material-producing E. hermannii strain YS-11, which was clinically isolated from a persistent apical periodontitis lesion. YS-11 possessed cell surface-associated meshwork-like structures that are found in some biofilm-forming bacteria and its viscous materials contained mannose-rich exopolysaccharides. To further examine the biological effect of the extracellular viscous materials and the meshwork structures, we constructed a number of mutants using transposon mutagenesis. Strain 455, which has a transposon inserted into wzt, a gene that encodes an ATP-binding cassette transporter, lacked the expression of the cell surface-associated meshwork structures and the ability to produce extracellular materials. Complementation of the disrupted wzt in strain 455 with an intact wzt resulted in the restoration of these phenotypes. We also compared these strains in terms of their ability to induce abscess formation in mice as an indication of their pathogenicity. Strains with meshwork-like structures induced greater abscesses than those induced by strains that lacked such structures. These results suggest that the ability to produce mannose-rich exopolysaccharides and to form meshwork-like structures on E. hermannii might contribute to its pathogenicity.

Anti-neutrophil cytoplasmic autoantibodies against bactericidal/permeability-increasing protein in patients with rheumatoid arthritis and their correlation with bronchial involvement

Anti-neutrophil cytoplasmic autoantibodies against bactericidal/permeability-increasing protein (BPI-ANCA) are known to be present in patients with cystic fibrosis, diffuse panbronchiolitis, and inflammatory bowel disease, especially in relation to chronic Gram-negative bacterial infection. To investigate the possible role of BPI-ANCA in rheumatoid arthritis (RA), we measured the serum titer of BPI-ANCA and examined clinical manifestations, including pulmonary complications, in patients with RA. Seventy-four RA patients were recruited to our study. The titer of BPI-ANCA was measured by enzyme-linked immunosorbent assay (ELISA). Pulmonary complications were evaluated using high-resolution computed tomography (HRCT), which revealed 26 patients with bronchial diseases (BD group), 25 with interstitial pneumonia (IP group), and 23 without any particular lung lesion (normal group). The correlations between the titer of BPI-ANCA and patients' clinical and laboratory findings were then analyzed. The numbers of tender joints, swollen joints, and the Disease Activity Score including 28 joint count were significantly higher in the BD group. The titer of BPI-ANCA was positively correlated with age, erythrocyte sedimentation rate (ESR), and bronchial involvement in all subjects. Stepwise multiple regression analysis of factors affecting the titer of BPI-ANCA selected ESR and bronchial involvement as independent variables. Our results show that BPI-ANCA was positively correlated with chronic inflammatory status in RA patients, and we is believe it is positively linked with bronchial diseases.

Effects of combined treatment with sansanmycin and macrolides on Pseudomonas aeruginosa and formation of biofilm

OBJECTIVE

To observe the effects of combined treatment with sansanmycin and macrolides on Pseudomonas aeruginosa and formation of biofilm.

METHODS

Micro-dilution method was used to determine the minimal inhibitory concentrations (MICs) of sansanmycin, gentamycin, carbenicillin, polymyxin B, roxithromycin, piperacillin, and tazobactam. PA1 and PA27853 biofilms were observed under optical microscope after staining and under SEM after treatment with sansanmycin at different dosages and combined treatment with sansanmycin and roxithromycin. Viable bacteria in PA1 and PA27853 biofilms were counted after treatment with sansanmycin at different dosages or combined treatment with sansanmycin and roxithromycin.

RESULTS

The MIC of sansanmycin was lower than that of gentamycin and polymyxin B, but was higher than that of carbenicillin. Roxithromycin enhanced the penetration of sansanmycin to PA1 and PA27853 strains through biofilms. PA1 and PA27853 biofilms were gradually cleared with the increased dosages of sansanmycin or with the combined sansanmycin and roxithromycin.

CONCLUSION

Sub-MIC levels of roxithromycin and sansanmycin substantially inhibit the generation of biofilms and proliferation of bacteria. Therefore, combined antibiotics can be used in treatment of intractable bacterial infection.

Multicenter survey on hospital-acquired pneumonia and the clinical efficacy of first-line antibiotics in Japan

OBJECTIVE

The aim of this study was to investigate the pathophysiology of hospital-acquired pneumonia (HAP) and the clinical efficacy of its first-line treatment and to examine the validity of "the Japanese Respiratory Society (JRS) Guidelines for management of HAP".

METHODOLOGY

The observational survey was conducted during the period of June 2002-May 2004 and patients with HAP were prospectively surveyed using the consecutive enrollment method. A total of 1,356 patients from 254 hospitals nationwide were analyzed. Clinical response to first-line antibiotics was evaluated at the end of the medication.

RESULTS

The 30-day mortality rate was 19.8%. Patients were classified into four groups according to the JRS guideline criteria. There were remarkable variances in the number of cases of each group. Mild/moderate pneumonia with no risk factors (group I) accounted for 0.3% of all cases. The mortality rate tended to be higher, as clinical conditions became more serious (group II < III < IV). Alternatively, though categorized in the same group (group III), there was a difference in the mortality rate by the severity of pneumonia (severe cases 32.2% vs. moderate cases 11.0%). First-line medication using carbapenems accounted for 61.7% of total cases. The efficacy rate of guideline-concordant therapy was significantly higher than that of guideline-discordant therapy (54.2% vs. 41.7%).

CONCLUSIONS

This is the first nationwide study on HAP in Japan. The clinical characteristics and prognosis of HAP were elucidated. Review of the current classification of the disease is required and these results provide valuable information for the next revision of the guidelines.

Airway biofilms: implications for pathogenesis and therapy of respiratory tract infections

The differentiation of bacterial biofilms in the airway environment, the pathogenesis of airway biofilm, and possible therapeutic methods are discussed. Biofilm diseases that characteristically involve the respiratory system include cystic fibrosis (CF), diffuse panbronchiolitis (DPB), and bronchiectasia with Pseudomonas aeruginosa (P. aeruginosa) infection. There is evidence to suggest that almost all strains of P. aeruginosa have the genetic capacity to synthesize alginate, a main matrix of biofilms, when ecological conditions are unfavorable for their survival. The bacteria inside the mature biofilm show increased resistance to both antibacterials and phagocytic cells, express fewer virulence factors because of their stationary state of growth, and are less stimulatory to the mucosa because of the 'sandwich binding'. These factors facilitate both the colonization of bacteria and their extended survival even under unfavorable conditions. Since the biofilm limits colonization to a latent form, the clinical symptoms in this situation are unremarkable. However, the clinical progression of both CF and DPB proceeds in two characteristic directions. The first is an acute exacerbation caused by planktonic bacteria that have germinated from the biofilm. The second is a slow progression of disease that is induced by harmful immune reactions. The harmful reactions are mediated by alginate, which induces antigen antibody reactions around the airways, as well as formation of circulating immune complexes that are deposited on lung tissue. Furthermore, the highest titer of bacterial permeability increasing anti-neutrophil cytoplasmic autoantibodies (BPI-ANCA) is observed in association with highly impaired pulmonary function in patients with CF and DPB, as well as in patients with a lengthy period of colonization with P. aeruginosa. BPI-ANCA subsequently makes chronic airway infection even more intractable. The long-term use of 14- or 15-ring membered macrolides results in a favorable clinical outcome for patients with DPB and in some patients with CF. In the last 10 years, an increasing number of studies have reported secondary actions of macrolides that include effects on both airway and phagocytic cells, as well as an anti-biofilm activity. The 14- or 15-ring membered macrolides inhibit: (i) the alginate production from P. aeruginosa; (ii) the antibody reaction to alginate, which leads to a decrease in the immune complex formation; and (iii) the activation of the autoinducer 3-O-C12-homoserine lactone and subsequent expression of lasI and rhlI in quorum sensing systems in P. aeruginosa. These anti-biofilm actions of macrolides may represent their basic mechanisms of action on airway biofilm disease.

Combined effect of clarithromycin and imipenem/cilastatin against urinary biofilm infection after pyeloplasty

The present report concerns a 38-year-old man, who had been treated with pyeloplasty and lithotomy for the improvement of urinary excretion and resolution of a kidney stone. The patient developed a biofilm infection involving Pseudomonas aeruginosa and Staphylococcus epidermidis, and had been suffering from recurrent acute pyelonephritis for one year. Combination therapy with clarithromycin (CAM) and imipenem/cilastatin (IMP/CS) consisted of administration of CAM at a dose of 400 mg/day for 1 week, followed by 500 mg/day of IMP by intravenous infusion combined with CAM (400 mg/day) for 5 days. This therapy produced an immediate antimicrobial effect and no further signs of pyuria have been seen during one year of follow-up in this patient.

Understanding bacterial biofilms in patients with cystic fibrosis: current and innovative approaches to potential therapies

Chronic P. aeruginosa infection is characterized by production of mucoid alginate and formation of microcolonies (biofilm) as seen in the lungs of cystic fibrosis patients. Oxygen radicals produced by the inflammatory response polymorphonuclear leucocytes induces the alginate production. The biofilm mode of growth is the survival strategy of environmental bacteria and alginate biofilms are also protected against antibiotics and against the immune response in the lungs of the patient. Quorum sensing is important for early and mature biofilm formation and also for the severity of the infection. The new knowledge of the mechanisms involved in biofilm formation opens up new possibilities for therapeutic intervention strategies involving e.g. inhibitors of quorum sensing.

Analysis of intractable factors in chronic airway infections: role of the autoimmunity induced by BPI-ANCA

The role of anti-neutrophil cytoplasmic autoantibodies against bactericidal/permeability-increasing protein (BPI-ANCA) in chronic airway infections was investigated. The serum BPI-ANCA titer was correlated with the severity of clinical symptoms in patients with chronic airway infections (P < 0.01), and the serum BPI-ANCA titer decreased with the improvement of the clinical picture, compared with its deterioration (P < 0.05). The serum BPI-ANCA titer was significantly higher in patients with far-advanced lesions on chest X-rays than in patients with milder lesions (P < 0.01) and in patients with reduced respiratory function (P < 0.05). Also, the serum BPI-ANCA titer was significantly higher in patients with prolonged colonization of gram-negative bacteria than in those without prolonged gram-negative bacterial colonization (P < 0.05). When neutrophils from healthy volunteers were incubated with BPI-ANCA before stimulation with lipopolysaccharide (LPS), neutrophil elastase levels decreased in a dose-dependent manner (P < 0.01). The phagocytic activity of neutrophils was significantly inhibited by BPI-ANCA in a dose-dependent manner (P < 0.01). The above findings suggest that BPI-ANCA, an autoimmune factor, appears during the course of chronic airway infections, and that this autoimmune factor may make chronic airway infections more intractable, by inhibiting the phagocytic activity of neutrophils for gram-negative bacteria.

Anti-inflammatory capabilities of macrolides

Macrolide antibiotics play a significant role in clinical practise due not only to their antibacterial activity, but also to their accompanying anti-inflammatory effect that is independent of their antibiotic action. Several studies reported in literature show that macrolides affect several inflammatory processes, such as migration of neutrophils, the oxidative burst in phagocytes and production of pro-inflammatory cytokines, although the precise mechanisms are not clear. They also inhibit eosinophilic inflammation and may be useful in the treatment of patients with steroid-dependent asthma. Macrolides are also effective in diffuse panbronchiolitis, chronic sinusitis and inflammatory skin diseases.

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.

Effect of subminimal inhibitory concentrations of azithromycin on adherence of Pseudomonas aeruginosa to polystyrene

Pseudomonas aeruginosa forms a bacterial biofilm by producing alginate when it adheres to mucosa or various medical devices. In this study, the effect of subminimal inhibitory concentrations (subMICs) of azithromycin (AZM) on the biofilm formation and in vitro adherence to polystyrene of 14 wild-type P. aeruginosa strains was studied. A total of 35 P. aeruginosa isolates from clinical specimens were used. Glycocalyx production was determined by the tube method, and bacterial adherence to the wells of flat bottom polystyrene tissue culture plates was estimated by the spectrophotometric method. Compared to the control, the adherence ability to polystyrene was inhibited by incubation with subMICs of AZM in a dose-dependent manner. These results support the findings of other investigators suggesting that AZM in subinhibitory concentrations may be useful in the prevention or treatment of biofilm-associated infections due to P. aeruginosa.

[Macrolides and Pseudomonas aeruginosa infection]

Several unique effects of subinhibitory concentrations of C14 and C15 macrolides on Pseudomonas aeruginosa infection are described in vitro: P. aeruginosa virulence factors inhibition, bacterial biofilm disruption, P. glycoprotein expression upregulation, anti-inflammatory and immunoregulatory effects. Clinical trials in vivo are warranted to assess the potential usefulness of macrolides for treatment of chronic infections caused by P. aeruginosa.

Influence of macrolides on guanosine diphospho-D-mannose dehydrogenase activity in Pseudomonas biofilm

The formation of biofilm is regarded as a major cause of intractable infectious disease. Our studies were done to elucidate the action of a 14-membered-ring macrolide (erythromycin; EM) and a 16-membered-ring macrolide (midecamycin; MDM) on guanosine diphospho-d-mannose dehydrogenase (GDP-mannose dehydrogenase; GMD), one of the constituents of bacterial biofilm that is known to produce alginate. The mucoid type of Pseudomonas aeruginosa PT-1578 and the non-mucoid type of P. aeruginosa PAO1 were grown with nutrient-rich and nutrient-poor media. Comparative measurements were made of their GMD enzyme activities, with glucose-6-phosphate dehydrogenase (G6PDH), a cell membrane enzyme, used as a control. It was found that the GMD enzyme activity of mucoid type of Pseudomonas bacteria increased when they were grown on nutrient-poor media. Measurements were also made to determine the effects of EM and MDM against GMD and G6PDH enzyme activities. In media with either EM or MDM added, the production of G6PDH was not inhibited, irrespective of the concentration of EM or MDM. However, EM was effective against the production of GMD, showing a concentration-dependent effect. Scanning electron microscopy studies were also carried out to determine the effects of both macrolides on bacterial alginate production. It was found that reduction of alginate content occurred after the addition of EM. When environmental conditions for bacteria deteriorate, GMD enzyme is activated, production of alginate is initiated, and then biofilm is formed. Our results suggest that EM may have an inhibitory effect on the GMD production cycle, hence inhibiting the formation of biofilm. This may explain the differences in the clinical usefulness of 14-membered-and 16-membered-ring macrolides against biofilm disease.

Potential of macrolide antibiotics to inhibit protein synthesis of Pseudomonas aeruginosa: suppression of virulence factors and stress response

Recently we have reported that sub-minimum inhibitory concentrations (MICs) of macrolide antibiotics, such as erythromycin, clarithromycin, and azithromycin, induce loss of viability of Pseudomonas aeruginosa with longer incubation periods. In the present study we examined the effects of sub-MICs of macrolide antibiotics on protein synthesis and the expression of heat shock proteins (Gro-EL) in P. aeruginosa and the association of these factors with the viability of P. aeruginosa. In seven strains of P. aeruginosa clinical isolates, inhibition of protein synthesis was generally observed in bacteria grown on agar with sub-MIC azithromycin (8 microg/ml) at 24 h, and this was followed by loss of viability after an additional 24-h incubation. The inhibition of protein synthesis was shown in bacteria treated with sub-MICs of erythromycin and clarithromycin, but not with sub-MICs of other antibiotics examined (josamycin, tobramycin, ofloxacin, clindamycin, and ceftazidime) even at relatively high sub-MICs. In the heat shock condition (45 degrees C), strong expression of the heat shock protein Gro-EL was induced in bacteria grown on antibiotic-free medium, whereas there was a delay of such a response in bacteria exposed to 4 microg/ml of azithromycin. Reflecting these results, an abrupt reduction of viability in azithromycin-treated bacteria was observed within 3 h in the heat shock condition. Western blot analysis, using specific antibody for Gro-EL, demonstrated that erythromycin, clarithromycin, and azithromycin, at concentrations of 0.5-2 microg/ml, inhibited the expression of lower-molecular weight Gro-EL bands in the constitutive state. These results indicated that macrolides, at concentrations far below the MICs, suppressed protein synthesis in P. aeruginosa, an effect which may be associated with the inhibition of P. aeruginosa virulence and its loss of viability with longer incubation. Moreover, it is likely that the macrolides may sensitize bacteria to stresses, as these antibiotics induced alterations in a major stress protein, Gro-EL, in constitutive and inducible states.

Antimicrobial resistance in Burkholderia pseudomallei

Four strains of Burkholderia pseudomallei were used to determine the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves with 13 single antimicrobial agents: ceftazidime, piperacillin, imipenem, amoxicillin/clavulanic acid, doxycycline, cotrimoxazole, kanamycin, rifampicin, ciprofloxacin, trovafloxacin, clarithromycin, azithromycin and meropenem. The time-kill studies were also performed with 33 pairs of combinations of the above antimicrobial agents: 15 combinations which would be expected to be used for acute therapy and 18 combinations for maintenance therapy. The results show that the single and combination antimicrobial agents with bactericidal effects against the four strains of B. pseudomallei which should be used for clinical trials in acute melioidosis are: imipenem, meropenem, and imipenem + azithromycin. The combination antimicrobial agents which should be further studied for the ability to eliminate biofilm and intracellular killing effect are ciprofloxacin + clarithromycin, ciprofloxacin + azithromycin, and imipenem + azithromycin.

Beneficial effect of adjunctive azithromycin in treatment of mucoid Pseudomonas aeruginosa pneumonia in the murine model

While a time-kill methodology noted no appreciable improvement in bactericidal activity with the addition of azithromycin (AZM) to a ceftazidime (CAZ) regimen, data from the murine pneumonia model showed that the addition of AZM significantly improved survival compared to treatment with CAZ alone. These data suggest that AZM might be a useful adjunctive therapy in the management of pneumonia resulting from mucoid isolates of Pseudomonas aeruginosa.

Adjuvant effect of a 14-member macrolide antibiotic on DNA vaccine

Macrolide antibiotics have unique immunomodulatory actions apart from their antimicrobial properties. We examined the effect of erythromycin (EM), a 14-member macrolide, on the immune response to a DNA vaccine that induces a T-helper-1 (Th1)-biased immune response through a Th1-promoting adjuvant effect of unmethylated CpG motifs within plasmid DNA. EM enhanced Th1 responses in plasmid DNA-immunized mice as measured by antigen-specific IgG2a antibody production, interferon-gamma production by antigen-specific CD4(+) T cells, and cytotoxic T lymphocyte responses. EM augmented the accessory cell activity of unmethylated CpG DNA-stimulated antigen-presenting cells (APCs), suggesting that EM enhances Th1 responses to a DNA vaccine, possibly through augmentation of accessory cell activity of APCs stimulated with CpG motifs within plasmid DNA.

Differential modulatory effects of clarithromycin on the production of cytokines by a tumor

In vitro treatment with clarithromycin inhibited the expression of the matrix metalloproteinase-9, transforming growth factor beta, and tumor necrosis factor alpha genes in 13762NF rat mammary adenocarcinoma cells. Transient enhancement, rather than inhibition, was observed for the interleukin-6 gene, and no significant change was observed for the tissue inhibitor of metalloproteinase-2 gene. Such an effect was not observed for cefotiam or gentamicin.

Inhibitory action of clarithromycin on glycocalyx produced by MRSA

We determined whether clarithromycin (CAM) had the ability to eliminate glycocalyx and biofilm produced by methicillin-resistant Staphylococcus aureus (MRSA) using an in-vitro experimental system (consisting of a bladder model and a kidney model) simulating complicated urinary tract infection (UTI). We also examined whether a combination of CAM and vancomycin (VCM) was effective for eliminating the MRSA biofilm. VCM (urinary concentration simulating drip infusion of 500 mg twice a day for 5 days; minimum inhibitory concentration (MIC) 0.5 &mgr;g/ml) eliminated MRSA from the bladder model medium at 48 h, but reproliferation occurred immediately after withdrawal of the agent. No disappearance of MRSA biofilm was noted, and this appeared to be the cause of the bacterial regrowth. CAM (urinary concentration simulating oral administration of 200 mg twice a day for 5 days; MIC, 128 &mgr;g/ml) allowed microbial recovery to the initial level within 48 h, but led to the disappearance of the glycocalyx-forming biofilm. A combination of VCM and CAM caused microbial elimination from the bladder model medium at 46 h with no regrowth after withdrawal of the antimicrobial agents. Scanning electron microscopy confirmed that the MRSA biofilm disappeared completely and no microbial adhesion was noted. These results suggest that CAM has an inhibitory action on glycocalyx and biofilm of MRSA, and that the combined use of VCM and CAM may be efficacious for the treatment of MRSA UTI

Therapeutic effect of clarithromycin on a transplanted tumor in rats

The therapeutic antitumor effect of clarithromycin (CAM) was examined with the 13762NF mammary adenocarcinoma and F-344 rat system. When CAM treatment at a dosage of 2 mg/kg of body weight orally for 21 days was commenced after inoculation of the tumor, no significant decrease in death rate was observed, although the loss in body weight was less than that in the untreated group. When tumor-bearing (TB) rats were treated with CAM in combination with carboplatin or cyclophosphamide, a significant decrease in the death rate was obtained, although neither treatment alone proved to be effective. A beneficial effect was also observed when CAM treatment was combined with surgical treatment. CAM showed no direct cytotoxicity to this tumor in vitro according to the MTT (3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Spleen cells obtained from TB rats receiving CAM treatment showed a stronger tumor-neutralizing activity than those from rats which had not received CAM treatment (Winn assay). Enhanced induction of cytotoxic cells to allogeneic tumor was also observed in rats immunized with allogeneic tumor cells together with CAM treatment (51Cr release assay). The 13762NF tumor produces transforming growth factor-beta (TGF-beta), tumor necrosis factor alpha, and matrix metalloproteinase-9, and treatment of tumor cells with CAM in vitro for 24 h significantly inhibited the expression of the genes coding for these proteins (reverse transcription-PCR). Levels of expression of the TGF-beta and interleukin-6 genes of spleen cells obtained from CAM-treated TB rats were both significantly lower than those of spleen cells from CAM-untreated TB rats. This study suggests that CAM has biological response modifier activities resulting in a beneficial therapeutic antitumor effect and might be useful for the treatment of human cancers.

Antibacterial agents--phagocytes: new concepts for old in immunomodulation

The possibility that antibacterial agents, primarily directed against microorganisms, also modify host functions is widely recognized. While a knowledge of these non-antimicrobial effects of antibiotics, sometimes considered as 'side-effects', is necessary to prevent antibiotic-associated toxicity, the development of drugs derived from antibacterial agents for use in non-infectious diseases (e.g. motilins and antidiabetic drugs) is a new field of therapeutic research. Interactions between antibacterial drugs and the immune system may contribute to therapeutic efficacy in infectious diseases [1,2]. The immune system itself is a complex pyramid of redundant cellular factors/humoral effectors/mediators, whose fine regulation is just beginning to be unraveled. Phagocytes, ubiquitous and multifaceted cells are key components of cellular immunity, being involved both in immediate defences against non-self targets (pathogens, tumour cells, exogenous molecules, etc.) and in the regulation and triggering of specific immune responses. They are thus, prime targets of immune response modifiers. This review reconsiders the widely explored problem of interactions between antibacterial agents and phagocytes, focusing on future prospects in both infectious and non-infectious diseases.

Direct evidence for antipseudomonal activity of macrolides: exposure-dependent bactericidal activity and inhibition of protein synthesis by erythromycin, clarithromycin, and azithromycin

Several previous investigators have reported that long-term administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infections, even though the clinically achievable concentrations of these medications are far below their MICs. In the present study, we examined how sub-MICs of macrolide antibiotics affect the viability of and protein synthesis in several strains of P. aeruginosa. We report that 48 h, but not 12 or 24 h, of growth on agar containing a clinically achievable concentration of azithromycin (0.5 microgram/ml, 1/128 the MIC) significantly reduces the viability of strain PAO-1. Similar effects were seen with erythromycin and clarithromycin at 2 micrograms/ml (1/128 and 1/64 the respective MICs), whereas josamycin, oleandomycin, ceftazidime, tobramycin, minocycline, and ofloxacin had no effect on viability, even following 48 h of incubation with concentrations representing relatively high fractions of their MICs. The bactericidal activity of azithromycin seen following 48 h of incubation was not limited to strain PAO-1 but was also seen against 13 of 14 clinical isolates, including both mucoid and nonmucoid strains. Although viability was not decreased prior to 48 h, we found that 4 micrograms of azithromycin per ml inhibits protein synthesis after as little as 12 h and that protein synthesis continues to decrease in a time-dependent manner. We likewise found that P. aeruginosa accumulates azithromycin intracellulary over the period from 12 to 36 h. These results suggested that sub-MICs of certain macrolides are bactericidal to P. aeruginosa when the bacteria are exposed to these antibiotics for longer periods. Exposure-dependent intracellular accumulation of the antibiotic and inhibition of protein synthesis may partially account for the antipseudomonal activity of macrolides over relatively prolonged incubation periods.

Influence of subinhibitory concentrations of ceftazidime, ciprofloxacin and azithromycin on the morphology and adherence of P-fimbriated escherichia coli

The influence of subinhibitory concentrations (1/2, 1/4, 1/8, 1/16 and 1/32 x MIC) of ceftazidime, ciprofloxacin and azithromycin on the morphology and adherence of 29 wild-type P-fimbriated strains of Escherichia coli was studied. Bacterial adherence to the Buffalo green monkey (BGM) cell line was tested before and after treatment with antibiotics and detected by means of an immunofluorescence staining. Significant dose dependent reduction of bacterial adherence was observed, which correlated with the alterations in bacterial cell morphology. After exposure of strains to sub-MICs of antibiotics, normal shapes, spherical forms and filaments were noted. The greatest filamentation and the greatest loss of adherence ability occurred at 1/2 x MIC of ceftazidime. Treatment with sub-MICs of ciprofloxacin resulted in shorter filaments, while filamentation did not occur after bacterial exposure to sub-MICs of azithromycin. Azithromycin was least damaging to the adherence ability of E. coli and at a concentration of 1/2 x MIC caused globoid cell formation.

Biofilm disease: its clinical manifestation and therapeutic possibilities of macrolides

In the investigation of the disease manifestation of DPB from the viewpoint of biofilm disease, the important factors are an excess antigen-antibody reaction in which alginate acts as the antigen and the resulting formation of immune complex. The effects of 14- and 15-membered macrolides are inhibition of immunoreaction induced by alginate and their inhibitory effect on alginate production serving as an antigen at the GMD level. Further, the specificity of macrolides on these actions was also evidenced from the standpoint of structural activity. In my opinion, based on the similarity in pathogenic process between patients with infected cystic fibrosis and patients with Pseudomonas biofilm disease, long-term administration of 14- or 15-membered ring macrolides can be tried in patients with infected cystic fibrosis.