Selma Tobudic

Antifungal susceptibility of Candida albicans in biofilms

Candida albicans are the most common fungi associated with biofilm‐related infections. Biofilms are defined as microbial communities encased in a matrix of extracellular polymeric substances. The most important feature of biofilm growth is the high resistance to antimicrobial agents that can be up to 1000‐fold greater than that of planktonic cells. This review discusses the factors affecting antifungal resistance as well as activity of mono‐ and combination therapy of different antifungal classes and antifungal activity in vitro and in vivo against C. albicans biofilms.

In vitro activity of antifungal combinations against Candida albicans biofilms.

OBJECTIVES The aim of the present study was to evaluate the in vitro activity and synergism of the combinations of amphotericin B/caspofungin and amphotericin B/posaconazole against Candida albicans, grown either as planktonic cells or in biofilms. METHODS Ten C. albicans bloodstream isolates used in this study were collected from intensive care patients admitted to the Vienna University Hospital between 2006 and 2007. Chequerboard tests were employed to determine the efficacy of the antifungal combinations amphotericin B/caspofungin and amphotericin B/posaconazole against both planktonic cells and biofilms. C. albicans biofilms were prepared using the static microtitre plate model. The activity of antifungal combination therapy was determined by visual reading for planktonic cells and using the XTT assay for biofilms. RESULTS For Candida biofilms the median MIC was 4 mg/L for amphotericin B and caspofungin, and >256 mg/L for posaconazole. The combination amphotericin B/posaconazole yielded synergism [fractional inhibitory concentration index (FICI) <0.26], whereas amphotericin B/caspofungin yielded indifferent interaction only (FICI 0.75-1.25) against all isolates when grown in biofilms. Under planktonic conditions, synergism was demonstrable for the combination amphotericin B/caspofungin against 4 of the 10 isolates, whereas the combination of caspofungin/posaconazole was indifferent against all tested isolates. CONCLUSIONS We showed that MICs for planktonic and biofilm forms of C. albicans were much lower when treated with an antifungal combination than when treated with single agents. The combination of amphotericin B/posaconazole yielded synergism against Candida biofilms, whereas amphotericin B/caspofungin yielded indifferent interaction.

Antifungal activity of amphotericin B, caspofungin and posaconazole on Candida albicans biofilms in intermediate and mature development phases

The aim of this study was to examine the antifungal activity of amphotericin B, caspofungin and posaconazole on Candida albicans biofilms in the intermediate and mature development phases. Candida albicans biofilms, previously grown for either 24, 48 or 72 h in 96‐well microtitre plates, were treated for 48 h with amphotericin B, caspofungin or posaconazole in increasing concentrations according to the respective minimal inhibitory concentration (MIC) determined for planktonic cells (1–128 × MIC). The biofilms were quantified using the mean optical density (OD) determined by XTT assay. Antifungal activities were expressed as percentage of reduction in OD of drug‐treated biofilms compared to untreated biofilms. To test the fungicidal activity of antifungal agents, the unfixed biofilms were scraped off and seeded to Sabouraud agar. Caspofungin and amphotericin B showed higher activity against C. albicans biofilm grown for 24 h and 72 h (≥50% reduction of OD) than biofilms grown for 48 h, whereas posaconazole showed similar, but reduced activity against all phases of C. albicans biofilm (≤50% reduction of OD). Caspofungin at 1–4 × MIC achieved the greatest decrease in the biofilm OD grown for 24, 48 and 72 h, whereas amphotericin B showed dose‐dependent activity. However, all tested antifungals failed to reach fungicidal activity in all biofilm development phases.

Azole-resistant Candida spp. – emerging pathogens?

Invasive fungal infections cause significant morbidity and mortality in immunocompromised patients. Azoles, and fluconazole in particular, are very active against Candida albicans, and are used widely because of their good tolerability. However, the increasing use of azole antifungals for the treatment of mucosal and systemic Candida infections has resulted in the selection and/or emergence of resistant Candida strains. The main mechanisms of azole resistance among Candida species are the development of bypass pathways, alterations in the ERG 11 gene encoding the azole target enzyme, and the up‐regulation of genes encoding efflux pumps. A better understanding of the mechanisms and clinical impact of antifungal resistance is essential to prompt and efficient treatment of patients with invasive mycoses and to improve the outcome of such infections.

Randomized, Single Blind, Controlled Trial to Evaluate the Prime-Boost Strategy for Pneumococcal Vaccination in Renal Transplant Recipients

Renal transplant recipients are at increased risk of developing invasive pneumococcal diseases but may have poor response to the 23-valent pneumococcal polysaccharide vaccine (PPV). It may be possible to enhance immunogenicity by priming with 7-valent pneumococcal conjugate vaccine (7vPnC) and boosting with PPV 1 year later. In a randomized single-blind, controlled study, adult recipients of renal transplants received either 7nPVC or PPV followed by PPV 1 year later. The vaccine response was defined as 2-fold increase in antibody concentration from baseline and an absolute post-vaccination values ≥1 µg/ml. The primary endpoint was vaccine response of the primed group (7vPnC/PPV) compared with single PPV vaccination. Antibody concentrations for 10 serotypes were measured at baseline, 8 weeks after first vaccination, before second vaccination, and 8 weeks after second vaccination. Of 320 screened patients, 80 patients were randomized and 62 completed the study. Revaccination with PPV achieved no significant increase of immune response in the 7vPnC/PPV group compared with the single PPV recipients A response to at least 1 serotype was seen in 77.1% of patients who received 7vPnC and 93.1% of patients who received PPV (P = 0.046). After second vaccination response to at least 1 serotype was seen in 87.5% patients of 7vPnC/PPV group and 87.1% patients of PPV group (non significant p). The median number of serotypes eliciting a response was 3.5 (95% CI 2.5–4.5) in the 7vPnC/PPV group versus 5 (95% CI 3.9–6.1) in the PPV group (non-significant p). Immunogenicity of pneumococcal vaccination was not enhanced by the prime–boost strategy compared with vaccination with PPV alone. Administration of a single dose of PPV should continue to be the standard of care for adult recipients of renal transplants. Trial Registration EudraCT 2007-004590-25.

Daptomycin, Fosfomycin, or Both for Treatment of Methicillin-Resistant Staphylococcus aureus Osteomyelitis in an Experimental Rat Model

ABSTRACT The in vivo activities of daptomycin, fosfomycin, and a combination of both antibiotics against a clinical isolate of methicillin-resistant Staphylococcus aureus (daptomycin MIC, 0.25 μg/ml; fosfomycin MIC, 0.5 μg/ml) were evaluated in a rat model of osteomyelitis. A total of 37 rats with experimental osteomyelitis were treated for 4 weeks with either 60 mg/kg of body weight of daptomycin subcutaneously once daily, 75 mg/kg fosfomycin intraperitoneally once daily, a combination of both drugs, or a saline placebo. After the completion of treatment, animals were euthanized, and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were found to be positive for methicillin-resistant S. aureus in 9 of 9 (100%) animals of the placebo group, in 9 of 9 (100%) animals treated with daptomycin, in 1 of 10 (10%) fosfomycin-treated rats, and in 1 of 9 (22.2%) rats comprising the combination group. Results of bacterial counts in the bone samples were expressed as log10 CFU/g of bone and analyzed by using the Mann-Whitney U test followed by Bonferronis multiple-comparison test. Based on bacterial counts, treatment with daptomycin was significantly superior to placebo, although it remained inferior to treatment with fosfomycin. No synergistic or antagonistic effect was observed for the combination therapy. No development of resistance against daptomycin or fosfomycin was observed after the 4-week treatment period.

Effectiveness and immunogenicity of pneumococcal vaccination in splenectomized and functionally asplenic patients.

The aim of the present study was to evaluate the effectiveness and immunogenicity of pneumococcal vaccination in 145 splenectomized and 2 functionally asplenic patients receiving the 23-valent pneumococcal polysaccharide vaccine and/or the 7-valent pneumococcal conjugate vaccine (PCV7) during the period 1996-2009. Progression of underlying malignant disease was the main cause of death in 68% of the 53 deceased patients, followed by septic shock in 13.2%. Twelve of 94 living patients developed post-vaccine complications: pneumonia in 9 patients, otitis media in 2, pneumococcal sepsis in 4. Compared with a non-splenectomized non-vaccinated control group (n=34), splenectomized patients vaccinated in the previous five years (n=15) had significantly higher GMCs (P<0.05) against serotypes 4, 6B, 9V, 14, 18C, 19F and 23F. Our data demonstrated strong serological responses in splenectomized patients within the first 5 years after pneumococcal vaccination by PCV7. Nevertheless, post-vaccine pneumococcal sepsis was still diagnosed in 3.3% of splenectomized survivors.

Pandemic influenza A H1N1 vaccine in recipients of solid organ transplants: immunogenicity and tolerability outcomes after vero cell derived, non-adjuvanted, whole-virion vaccination.

During the 2009/10 pandemic of influenza A (H1N1), the American Society of Transplantation and other health organizations recommended that immunocompromised patients should be vaccinated as the key preventive measure. Since there are no data available for the immunogenicity of the unadjuvanted pandemic influenza vaccine in immunocompromised patients - as opposed to the adjuvanted preparation - the objective of this study was to evaluate the immunogenicity of an adjuvant-free H1N1 vaccine in recipients of solid organ transplants. Patients were recruited at the Vienna General Hospital, Austria. The vaccination schedule consisted of 2 doses of a whole-virion, vero cell derived, inactivated, non-adjuvanted influenza A/California/07/2009 (H1N1) vaccine given with an interval of 3 weeks. A hemagglutination inhibition (HI) assay on blood samples obtained prior to the first and after each vaccination was used for serologic analysis. The primary immunologic endpoint was the seroconversion rate, defined as the proportion of subjects with an individual 4-fold increase in HI titer of at least 1:40. In addition, virus-specific IgG antibodies to the pandemic H1N1 strain were measured using a commercially available ELISA. Twenty-five organ transplant patients (16 males, 9 females) aged 25-79 years were vaccinated and provided blood samples for serologic analysis. The time elapsed since transplantation was 10 months to 25 years (mean: 9 years; 95% CI 6-13 years). The vaccine was well tolerated and no local adverse events were noticed. After two vaccinations 37% of the patients demonstrated seroconversion in the HI assay as defined above and 70% had virus-specific IgG antibodies. Among the HI vaccine responders were 6 of 14 heart transplant recipients and 1 of 4 liver transplant recipients. The number and type of immunosuppressive agents did not significantly differ in their effect on the immune response. Our results show that the novel vero cell derived and adjuvant-free pandemic A/California/07/2009 (H1N1) influenza vaccine induced limited but measurable immune responses in adult recipients of solid organ transplants.

In Vivo Activity of a Novel Polymeric Guanidine in Experimental Skin Infection with Methicillin-Resistant Staphylococcus aureus

ABSTRACT The in vivo efficacy of the novel polymeric guanidine AKACID Plus was evaluated in a guinea pig model of experimental skin infection with methicillin-resistant Staphylococcus aureus (MRSA). Topical application of AKACID Plus at concentrations of ≥0.5% was as effective as mupirocin 2% cream in the treatment of superficial skin infection with MRSA.

Efficacy of Fosfomycin in Experimental Osteomyelitis Due to Methicillin-Resistant Staphylococcus aureus

ABSTRACT The activity of fosfomycin was evaluated in an experimental methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis model. Eighteen rats were treated for 4 weeks with 150 mg of fosfomycin/kg of body weight intraperitoneally once daily or with saline placebo. After treatment, animals were euthanized and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were positive for methicillin-resistant S. aureus in all 9 (100%) untreated controls and in 2 of 9 (22.2%) fosfomycin-treated rats. Thus, fosfomycin treatment was significantly more efficacious than placebo. No development of resistance was observed after the 4-week treatment period.