New approaches to optimizing antimicrobial therapy in patients with cystic fibrosis

In vitro antibacterial screening of six proline-based cyclic dipeptides in combination with β-lactam antibiotics against medically important bacteria

The in vitro synergistic antibacterial activity of six proline-based cyclic dipeptides [cyclo(D-Pro-L-Leu), cyclo(L-Pro-L-Met), cyclo(D-Pro-L-Phe), cyclo(L-Pro-L-Phe), cyclo(L-Pro-L-Tyr), and cyclo(L-Pro-D-Tyr)] in combination imipenem and ceftazidime was investigated in the present manuscript. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the cyclic dipeptides were compared with those of the standard antibiotics (imipenem and ceftazidime). The synergistic antibacterial activities of cyclic dipeptides with imipenem or ceftazidime were assessed using the checkerboard and time-kill methods. The results of the present study showed that the combined effect of six cyclic dipeptides with imipenem predominantly recorded synergistic interaction (FIC index <0.5), whereas combination of certain cyclic dipeptides with ceftazidime recorded additive. The time-kill curve showed that the growth of the test bacteria was completely attenuated after 12-24 h of treatment with a 50:50 ratio of proline-based cyclic dipeptides and antibiotics. These synergistic effects have a potential role in delaying the development of resistance as the antibacterial activity is achieved with the very low concentrations of cyclic dipeptides and antibiotics. The cytotoxicity of cyclic dipeptides was tested against VERO cell line (African green monkey kidney cell line), and no cytotoxicity was recorded for cyclic dipeptides up to 100 μg/mL. These findings suggest that combination of cyclic dipeptides and antibiotics might be a good strategy for the individualization of novel templates for the development of new antimicrobial agents or combinations of drugs for antimicrobial chemotherapy. Moreover, these combinations may lead to the development of a new and vital antimicrobial combination against the infections caused by pathogenic bacteria. The in vitro synergistic activity of cyclic dipeptides with antibiotics against medically important bacteria is reported here for the first time.

Synergistic antibacterial and antibiofilm effect between (+)-medioresinol and antibiotics in vitro

In this study, antibacterial effects of (+)-Medioresinol isolated from stem bark of Sambucus williamsii and its synergistic activities in combination with antibiotics such as ampicillin, cefotaxime, and chloramphenicol were tested by antibacterial susceptibility testing and checkerboard assay. (+)-Medioresinol possessed antibacterial effects against antibiotics-susceptible- or antibiotics-resistant strains. Most of combinations between (+)-Medioresinol and each antibiotic showed synergistic interaction (fractional inhibitory concentration index ≤ 0.5) against bacterial strains including antibiotics-resistant Pseudomonas aeruginosa. Furthermore, the antibiofilm effect of (+)-Medioresinol alone or in combination with each antibiotic was investigated. The results indicated that not only (+)-Medioresinol but also its combination with each antibiotic had antibiofilm activities. It concludes that (+)-Medioresinol has potential as a therapeutic agent and adjuvant for treatment of bacterial infection.

In vitro synergistic activity of diketopiperazines alone and in combination with amphotericin B or clotrimazole against Candida albicans

The synergistic anticandidal activity of three diketopiperazines [cyclo-(L-Pro-L-Leu) (1), cyclo-(D-Pro-L-Leu) (2), and cyclo-(D-Pro-L-Tyr) (3)] purified from a Bacillus sp. N strain associated with entomopathogenic nematode Rhabditis (Oscheius) in combination with amphotericin B and clotrimazole was investigated using the macrodilution method. The minimum inhibitory concentration and minimum fungicidal concentration of the diketopiperazines was compared with that of the standard antibiotics. The synergistic anticandidal activities of diketopiperazines with amphotericin B or clotrimazole were assessed using the checkerboard and time-kill methods. The results of the present study showed that the combined effects of diketopiperazines with amphotericin B or clotrimazole predominantly recorded synergistic (<0.5). Time-kill study showed that the growth of the Candida was completely attenuated after 12-24 h of treatment with 50:50 ratios of diketopiperazines and antibiotics. These results suggest that diketopiperazines combined with antibiotics may be microbiologically beneficial and not antagonistic. These findings have potential implications in delaying the development of resistance as the anticandidal effect is achieved with lower concentrations of both drugs (diketopiperazines and antibiotics). The cytotoxicity of diketopiperazines was also tested against two normal human cell lines (L231 lung epithelial and FS normal fibroblast) and no cytotoxicity was recorded for diketopiperazines up to 200 μg/mL. The in vitro synergistic activity of diketopiperazines with antibiotics against Candida albicans is reported here for the first time.

Activity and synergistic antimicrobial activity between diketopiperazines against bacteria in vitro

The aim of the present study was to determine the synergistic effects of diketopiperazines [cyclo-(L-Pro-L-Leu) (1), cyclo-(D-Pro-L-Leu) (2), and cyclo-(D-Pro-L-Tyr) (3)] purified from a Bacillus sp. N strain associated with entomopathogenic nematode Rhabditis (Oscheius) sp. on the growth of bacteria. The minimum inhibitory concentration and minimum bactericidal concentration of the diketopiperazines was compared with that of the standard antibiotics. The synergistic antibacterial activities of the combination of diketopiperazines against pathogenic bacteria were assessed using the checkerboard assay and time-kill methods. The results of the present study showed that the combination effects of diketopiperazines were predominately synergistic (FIC index <0.5). Furthermore, time-kill study showed that the growth of the tested bacteria was completely attenuated with 4-12 h of treatment with 50:50 ratios of diketopiperazines. These results suggest that the combination of diketopiperazines may be microbiologically beneficial. The three diketopiperazines are nontoxic to normal human cell line (L231 lung epithelial) up to 200 m μg/ml. The in vitro synergistic activity of cyclo-(L-Pro-L-Leu), cyclo-(D-Pro-L-Leu), and cyclo-(D-Pro-L-Tyr) against bacteria is reported here for the first time. These findings have potential implications in delaying the development of resistance as the antibacterial effect is achieved with lower concentrations of both drugs (diketopiperazines).

Diffuse Panbronchiolitis

Diffuse panbronchiolitis (DPB) is characterized by chronic sinobronchial infection and diffuse bilateral micronodular pulmonary lesions consisting of inflammatory cells. Studies on disease etiology point to a genetic predisposition unique to Asians. Early therapy for DPB was largely symptomatic. The advent of macrolide antibiotics, including erythromycin, roxithromycin and clarithromycin, has strikingly changed disease prognosis. Low-dose, long-term macrolide therapy for DPB originated from detailed observations of response to therapy in a single patient. The bactericidal activity of macrolides, particularly erythromycin, is not a significant factor for their clinical efficacy in DPB. Firstly, irrespective of bacterial clearance, clinical improvement is observed in patients treated with erythromycin. Secondly, even in cases with bacterial superinfection with Pseudomonas aeruginosa resistant to macrolides, treatment has proved effective. Thirdly, the recommended dosage of macrolides produces peak levels in tissue that are below the minimum inhibitory concentrations for major pathogenic bacteria that colonize the airway. In the last two decades, the possible mechanism underlying the effectiveness of macrolide therapy has been extensively studied. The proposed mechanism of action includes inhibition of excessive mucus and water secretion from the airway epithelium, inhibition of neutrophil accumulation in the large airway, inhibition of lymphocyte and macrophage accumulation around the small airway, and modulation of bacterial virulence. The great success of macrolide therapy in diffuse panbronchiolitis may extend its application to the treatment of other chronic inflammatory disorders. If the anti-inflammatory activity of macrolides is independent of their bactericidal effect, new anti-inflammatory macrolides without antimicrobial activity should be developed to minimize emergence of macrolide-resistant micro-organisms.

Management of the patient with cystic fibrosis in oral and maxillofacial surgery

Cystic fibrosis (CF) is now an adult disease. Approximately 30,000 children and adults are affected by this disease. CF, an autosomal recessive disease, is considered to be the most lethal inherited trait among Caucasians. The median age for the CF patient has significantly increased over the past 60 years. Today's oral and maxillofacial surgery practice is likely to include patients with CF with varying surgical needs. This article will review diagnosis, pathophysiology, and systemic complications of CF, and discuss relevant information for management of the CF patient for the oral and maxillofacial surgeon. Recommendations will be made for preoperative, perioperative, and postoperative care of these patients.

[Will we still have antibiotics tomorrow?]

Since the discovery of antibiotics, it has been generally believed that these antimicrobials are capable of curing almost all bacterial infections. More recently, the appearance of increasing resistance to antibiotics and the emergence of multiresistant microorganisms have given rise to growing concern among physicians, and that concern has now started to filter through to society in general. The problem is further aggravated by a situation that not many people are currently aware of, that is, the limited prospects for future development of new antibiotics in the short to medium term. Appropriate use of available antibiotics based on a thorough understanding of their in vivo activity and the emergence of new forms of administration, such as inhalers, may help to alleviate the problem.

Novel strategies of aerosolic pharmacotherapy

The pulmonary administration of drugs plays a crucial role in the management of various respiratory and systemic diseases. While the cellular properties of airway epithelial cells offer a great potential to deliver drugs into the lungs or the circulation, only little is known about the exact transport pathways. Recently, the high-affinity proton-coupled drug and peptide transporter PEPT2 was identified in the human respiratory tract. The expression of transporter mRNA and protein was localized to the airway epithelium and alveolar type II pneumocytes. In addition, transport studies revealed transporter-mediated uptake of substrates into epithelial cells indicating that the transporter is the molecular basis for the transport of peptides and peptidomimetic drugs in pulmonary epithelial cells. Since genotype analysis revealed no significant differences amongst different transporter genotypes concerning expression and function, the transporter displays an interesting novel target for pulmonary delivery of drugs.

Development of a rapid colorimetric time-kill assay for determining the in vitro activity of ceftazidime and tobramycin in combination against Pseudomonas aeruginosa

It is standard clinical practice to use a combination of two or more antimicrobial agents to treat an infection caused by Pseudomonas aeruginosa. The antibiotic combinations are usually selected empirically with methods to determine the antimicrobial effect of the combination such as the time-kill assay rarely used as they are time-consuming and labour intensive to perform. Here, we report a modified time-kill assay, based on the reduction of the tetrazolium salt, 2,3-bis[2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT), that allows simple, inexpensive and more rapid determination of the in vitro activity of antibiotic combinations against P. aeruginosa. The assay was used to determine the in vitro activity of ceftazidime and tobramycin in combination against P. aeruginosa isolates from cystic fibrosis patients and the results obtained compared with those from conventional viable count time-kill assays. There was good agreement in interpretation of results obtained by the XTT and conventional viable count assays, with similar growth curves apparent and the most effective concentration combinations determined by both methods identical for all isolates tested. The XTT assay clearly indicated whether an antibiotic combination had a synergistic, indifferent or antagonistic effect and could, therefore, provide a useful method for rapidly determining the activity of a large number of antibiotic combinations against clinical isolates.

Adults with cystic fibrosis: meeting the challenge!

The number of adults with cystic fibrosis (CF) is increasing. They are striving for independence and a fulfilling life with focus on career, relationships, education and finances at a time when lung function is likely to be declining and complications of this multi-system disease are increasing. Maintaining the quality and improving the duration of life are continuing challenges for the -clinician and the patient. Increased hope and greater expectations have been provided by a number of recent clinical advances and active research into novel treatments, including gene therapy. There has been increased recognition of the necessity for early diagnosis, adequate monitoring and effective intervention for complications such as diabetes and osteoporosis. Research into multi-resistant bacteria and clonal strains of Pseudomonas aeruginosa is ongoing and attention has focused on infection control policies. Although more high-level evidence is required on many issues confronting people with CF, a considerable effort has been made over the last decade to provide a more evidence-based approach to therapy with a number of large controlled clinical trials. For the adult with CF, there are also more decisions to be made. There is focus on reproductive health, with most couples enjoying the real possibility of having children. For those with advanced disease, the option for lung transplantation is well established. Maintenance of quality care will require adequate planning, effective transition programmes from paediatric to adult care, specialized training for doctors, nurses and allied health professionals and the allocation of sufficient resources to accommodate the inevitable increase in patient numbers.

Inhaled Tobramycin (TOBI??)

Specifically formulated for nebulisation using the PARI LC PLUS reusable nebuliser, tobramycin solution for inhalation (TSI) [TOBI] provides a high dose of tobramycin (an aminoglycoside antibacterial with good activity against Pseudomonas aeruginosa) to the lungs of patients with cystic fibrosis, while maintaining low serum concentrations of the drug, thus reducing the risk of systemic toxicity. Intermittent (28-day on/28-day off) treatment with TSI 300 mg twice daily significantly (p < 0.001) improved lung function and sputum P. aeruginosa density compared with placebo (randomised double-blind trials), and was significantly (p = 0.008) more effective than colistin for improvement in forced expiratory volume in 1 second (small nonblind trial) in patients aged > or =6 years with cystic fibrosis and chronic P. aeruginosa infection. Improvements in lung function were most marked in adolescent patients (aged 13-17 years) in placebo-controlled trials. Improvements were maintained for up to 96 weeks in patients in an open-label extension study. Fewer TSI than placebo recipients required parenteral antipseudomonal agents or hospitalisation. In addition, TSI 300 mg twice daily for 28 days reduced P. aeruginosa density in the lower airways of patients aged <6 years with early colonisation and cystic fibrosis, although TSI is not currently indicated in this patient group. A decrease in tobramycin susceptibility of P. aeruginosa isolates and an increase in fungal organisms (Candida albicans and Aspergillus species) during prolonged intermittent treatment with TSI 300 mg twice daily was not associated with adverse clinical outcome. There was no evidence of selection for the most resistant isolates. TSI is generally well tolerated, with no renal toxicity or hearing loss in clinical trials, although transient mild or moderate tinnitus occurred more frequently in TSI than placebo recipients. Bronchospasm after administration of TSI was transient and occurred with a similar incidence to that with placebo; TSI is preservative free and specifically formulated for the lung in terms of osmolality and pH. In conclusion, TSI provides an effective means of delivering tobramycin to the lungs of patients with cystic fibrosis with chronic P. aeruginosa infection, improving lung function and sputum P. aeruginosa density in these patients without the nephrotoxicity or ototoxicity of parenteral aminoglycosides. Further data on the potential for and clinical significance of increased tobramycin resistance and fungal colonisation during TSI treatment would be beneficial, as would longer-term data. In the meantime, TSI represents a valuable option for suppressive antipseudomonal therapy in patients with cystic fibrosis.

The rationale for aerosolized antibiotics

In order for an antimicrobial agent to be effective, it must fulfill two requirements. First, the agent must reach the site of infection and remain in the vicinity for an adequate length of time. Second, it must bind to a target site and remain bound for a length of time sufficient to disrupt the life cycle of the cell. Once these requirements are met, the drug is able to exert its antimicrobial activity against the cell. In an effort to better understand and predict the killing activity of antibiotics, we have attempted to develop parameters that describe the accumulation and diffusion of drug to and from body sites (pharmacokinetics) and quantify how much of a compound is needed at the site of infection to yield the desired effect (minimum inhibitory concentration). Furthermore, integration of these parameters allows us to evaluate host, drug, and microbial factors and formulate criteria to assess and predict drug activity in patients (pharmacodynamics). Knowledge and application of pharmacodynamic principles can assist clinicians in optimizing antimicrobial therapy by allowing them to maximize the antimicrobial activity of an agent while minimizing patient exposure and thus reducing the likelihood of toxicity.

Perspectives on gene therapy for cystic fibrosis airway disease

Since the discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene nearly 12 years ago, cystic fibrosis (CF) has become one of the most intensively investigated monogenetic disorders considered approachable by gene therapy. This has resulted in over 20 clinical trials currently under way, concluded or awaiting approval. Despite the initial promise of gene therapy for CF, and the demonstration of successful gene transfer to the nose and airways of individuals, it has not so far been as effective as initially projected. Here we discuss the rationale behind CF gene therapy and dissect the vast array of literature representing the work that ultimately brought about the current phase I/II clinical trials. In the context of human trials, we review the limitations of current vector systems for CF gene therapy. We come to the conclusion that at present none of the application methods and vector systems are able to achieve the level and persistence of CFTR gene expression in the affected epithelia of CF patients that is required for therapeutic success. We also outline the challenges that must be overcome and describe some of the novel approaches to be taken in order to attain the curative therapy that was originally envisaged for this disease.