Antifungal susceptibility of Candida biofilms: unique efficacy of amphotericin B lipid formulations and echinocandins

Novel antiseptic urinary catheters for prevention of urinary tract infections: correlation of in vivo and in vitro test results

Urinary catheters are widely used for hospitalized patients and are often associated with high rates of urinary tract infection. We evaluated in vitro the antiadherence activity of a novel antiseptic Gendine-coated urinary catheter against several multidrug-resistant bacteria. Gendine-coated urinary catheters were compared to silver hydrogel-coated Foley catheters and uncoated catheters. Bacterial biofilm formation was assessed by quantitative culture and scanning electron microscopy. These data were further correlated to an in vivo rabbit model. We challenged 31 rabbits daily for 4 days by inoculating the urethral meatus with 1.0 x 10(9) CFU streptomycin-resistant Escherichia coli per day. In vitro, Gendine-coated urinary catheters reduced the CFU of all organisms tested for biofilm adherence compared with uncoated and silver hydrogel-coated catheters (P < 0.004). Scanning electron microscopy analysis showed that a thick biofilm overlaid the control catheter and the silver hydrogel-coated catheters but not the Gendine-coated urinary catheter. Similar results were found with the rabbit model. Bacteriuria was present in 60% of rabbits with uncoated catheters and 71% of those with silver hydrogel-coated catheters (P < 0.01) but not in those with Gendine-coated urinary catheters. No rabbits with Gendine-coated urinary catheters had invasive bladder infections. Histopathologic assessment revealed no differences in toxicity or staining. Gendine-coated urinary catheters were more efficacious in preventing catheter-associated colonization and urinary tract infections than were silver hydrogel-coated Foley catheters and uncoated catheters.

Micafungin: a review of its use in the prophylaxis and treatment of invasive Candida infections in pediatric patients

Intravenous micafungin (Mycamine; Funguard) is an echinocandin indicated in Japan and the EU for the treatment of pediatric patients (including neonates) with invasive candidiasis and as prophylaxis against Candida infection in pediatric patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). In the EU, micafungin is also indicated in pediatric patients who are expected to have neutropenia for >/=10 days. In Japan, children may also receive micafungin for the treatment of, or as prophylaxis against, invasive Aspergillus infection. Micafungin is not currently approved for use in pediatric patients in the US. Micafungin has very good antifungal activity against a wide range of Candida spp. in vitro. It has a favorable pharmacokinetic profile allowing for once-daily administration, has few drug-drug interactions, and reports of resistance are rare. The results of pediatric substudies indicate that intravenous micafungin is effective in a majority of patients for the treatment of candidemia and other types of invasive candidiasis, and provides effective prophylaxis against invasive fungal infections in pediatric patients undergoing HSCT. The tolerability profile of micafungin in pediatric patients was generally acceptable. In the EU, micafungin is indicated for use when other antifungal medications are not appropriate. Therefore, micafungin provides an alternative to other antifungal agents used in the management of candidemia and invasive candidiasis in pediatric patients, or as prophylaxis against fungal infections in pediatric patients undergoing HSCT.

Architectural analysis, viability assessment and growth kinetics of Candida albicans and Candida glabrata biofilms

The human fungal pathogen Candida is able to form biofilms in almost all the medical devices in current use. Indeed, biofilm formation is a major virulence attribute of microorganisms and account for a majority of human infections. Therefore, understanding processes appertaining to biofilm development is an important prerequisite for devising new strategies to prevent or eradicate biofilm-related infections. In the present study we used an array of both conventional and novel analytical tools to obtain a comprehensive view of Candida biofilm development. Enumeration of colony forming units, colorimetric (XTT) assay, Scanning Electron Microscopy (SEM) and novel Confocal Laser Scanning Microscopy (CLSM) coupled with COMSTAT software analyses were utilised to evaluate growth kinetics; architecture and viability of biofilms of a reference (ATCC) and a clinical strain each of two Candida species, C. albicans and C. glabrata. Biofilm growth kinetics on a polystyrene substrate was evaluated from the initial adhesion step (1.5 h) up to 72 h. These analyses revealed substantial inter- and intra-species differences in temporal organisation of Candida biofilm architecture, spatiality and cellular viability, while reaching maturity within a period of 48 h, on a polystyrene substrate. There were substantial differences in the growth kinetics upon methodology, although general trend seemed to be the same. Detailed architectural analysis provided by COMSTAT software corroborated the SEM and CSLM views. These analyses may provide a strong foundation for down stream molecular work of fungal biofilms.

Clinical practice guidelines for the diagnosis and management of intravascular catheter-related infection: 2009 Update by the Infectious Diseases Society of America

These updated guidelines replace the previous management guidelines published in 2001. The guidelines are intended for use by health care providers who care for patients who either have these infections or may be at risk for them.

Antimicrobial dendrimer active against Escherichia coli biofilms

We have investigated the ability of a previously reported antimicrobial peptide dendrimer (RW)(4D) to inactivate Escherichia coli RP437 in planktonic culture and in biofilms. The results show that the dendrimer inhibits bacterial growth in both planktonic and biofilm states. Live/Dead staining assays reveal that most bacteria in a preformed biofilm lose viability after treatment with this peptide. This result is in marked contrast to most existing reports that antimicrobial peptides are ineffective against mature bacterial biofilms.

Biofilm formation and effect of caspofungin on biofilm structure of Candida species bloodstream isolates

Candida biofilms are microbial communities, embedded in a polymeric matrix, growing attached to a surface, and are highly recalcitrant to antimicrobial therapy. These biofilms exhibit enhanced resistance against most antifungal agents except echinocandins and lipid formulations of amphotericin B. In this study, biofilm formation by different Candida species, particularly Candida albicans, C. tropicalis, and C. parapsilosis, was evaluated, and the effect of caspofungin (CAS) was assessed using a clinically relevant in vitro model system. CAS displayed in vitro activity against C. albicans and C. tropicalis cells within biofilms. Biofilm formation was evaluated after 48 h of antifungal drug exposure, and the effects of CAS on preformed Candida species biofilms were visualized using scanning electron microscopy (SEM). Several species-specific differences in the cellular morphologies associated with biofilms were observed. Our results confirmed the presence of paradoxical growth (PG) in C. albicans and C. tropicalis biofilms in the presence of high CAS concentrations. These findings were also confirmed by SEM analysis and were associated with the metabolic activity obtained by biofilm susceptibility testing. Importantly, these results suggest that the presence of atypical, enlarged, conical cells could be associated with PG and with tolerant cells in Candida species biofilm populations. The clinical implications of these findings are still unknown.

Liposomal amphotericin B: a review of its use as empirical therapy in febrile neutropenia and in the treatment of invasive fungal infections

Liposomal amphotericin B (AmBisome) is a lipid-associated formulation of the broad-spectrum polyene antifungal agent amphotericin B. It is active against clinically relevant yeasts and moulds, including Candida spp., Aspergillus spp. and filamentous moulds such as Zygomycetes, and is approved for the treatment of invasive fungal infections in many countries worldwide. It was developed to improve the tolerability profile of amphotericin B deoxycholate, which was for many decades considered the gold standard of antifungal treatment, despite being associated with infusion-related events and nephrotoxicity. In well controlled trials, liposomal amphotericin B had similar efficacy to amphotericin B deoxycholate and amphotericin B lipid complex as empirical therapy in adult and paediatric patients with febrile neutropenia. In addition, caspofungin was noninferior to liposomal amphotericin B as empirical therapy in adult patients with febrile neutropenia. For the treatment of confirmed invasive fungal infections, liposomal amphotericin B was more effective than amphotericin B deoxycholate treatment in patients with disseminated histoplasmosis and AIDS, and was noninferior to amphotericin B deoxycholate in patients with acute cryptococcal meningitis and AIDS. In adults, micafungin was shown to be noninferior to liposomal amphotericin B for the treatment of candidaemia and invasive candidiasis. Data from animal studies suggested that higher dosages of liposomal amphotericin B might improve efficacy; however, in the AmBiLoad trial in patients with invasive mould infection, there was no statistical difference in efficacy between the standard dosage of liposomal amphotericin B 3 mg/kg/day and a higher 10 mg/kg/day dosage, although the standard dosage was better tolerated. Despite being associated with fewer infusion-related adverse events and less nephrotoxicity than amphotericin B deoxycholate and amphotericin B lipid complex, liposomal amphotericin B use is still limited to some extent by these adverse events. Both echinocandins were better tolerated than liposomal amphotericin B. The cost of liposomal amphotericin B therapy may also restrict its use, but further pharmacoeconomic studies are required to fully define its cost effectiveness compared with other antifungal agents. Based on comparative data from well controlled trials, extensive clinical experience and its broad spectrum of activity, liposomal amphotericin B remains a first-line option for empirical therapy in patients with febrile neutropenia and in those with disseminated histoplasmosis, and is an option for the treatment of AIDS-associated cryptococcal meningitis, and for invasive Candida spp. or Aspergillus spp. infections. Amphotericin B, a macrocyclic, polyene antifungal agent, is thought to act by binding to ergosterol, the principal sterol in fungal cell membranes and Leishmania cells. This results in a change in membrane permeability, causing metabolic disturbance, leakage of small molecules and, as a consequence, cell death. In vitro and in vivo studies have shown that liposomal amphotericin B remains closely associated with the liposomes in the circulation, thereby reducing the potential for nephrotoxicity and infusion-related toxicity associated with conventional amphotericin B. Amphotericin B shows very good in vitro activity against a broad spectrum of clinically relevant fungal isolates, including most strains of Candida spp. and Aspergillus spp., and other filamentous fungi such as Zygomycetes. Liposomal amphotericin B has proven effective in various animal models of fungal infections, including those for candidiasis, aspergillosis, fusariosis and zygomycosis. Liposomal amphotericin B also shows immunomodulatory effects, although the mechanisms involved are not fully understood, and differ from those of amphotericin B deoxycholate and amphotericin B colloidal dispersion. In adult patients with febrile neutropenia, intravenous liposomal amphotericin B has nonlinear pharmacokinetics, with higher than dose-proportional increases in exposure being consistent with reticuloendothelial saturation and redistribution of amphotericin B in the plasma compartment. Liposomal amphotericin B is rapidly and extensively distributed after single and multiple doses, with steady-state concentrations of amphotericin B attained within 4 days and no clinically relevant accumulation of the drug following multiple doses of 1-7.5 mg/kg/day. In autopsy tissue, the highest concentrations of the drug were found in the liver and spleen, followed by the kidney, lung, myocardium and brain tissue. Elimination of liposomal amphotericin B, like that of amphotericin B deoxycholate, is poorly understood; its route of metabolism is not known and its excretion has not been studied. The terminal elimination half-life is about 7 hours. No dosage adjustment is required based on age or renal impairment. In several randomized, double-blind trials (n = 73-1095) in adult and/or paediatric patients, liposomal amphotericin B was effective as empirical therapy or as treatment for confirmed invasive fungal infections, including invasive candidiasis, candidaemia, invasive mould infection (mainly aspergillosis), histoplasmosis and cryptococcal meningitis. All agents were administered as an intravenous infusion; the typical dosage for liposomal amphotericin B was 3 mg/kg/day. Treatment was generally given for 1-2 weeks. Participants in trials evaluating empirical therapy had neutropenia and a persistent fever despite antibacterial treatment and had received chemotherapy or undergone haematopoietic stem cell transplantation. As empirical therapy in adult and paediatric patients, liposomal amphotericin B appeared to be as effective as amphotericin B deoxycholate (approximately 50% of patients in each group achieved treatment success) or amphotericin B lipid complex (approximately 40% of liposomal amphotericin B recipients experienced treatment success). Of note, in the first trial, results of the statistical test to determine equivalence between treatments were not reported. In the second trial, efficacy was assessed as an 'other' endpoint. In another trial, caspofungin was shown to be noninferior to liposomal amphotericin B, with approximately one-third of patients in each group experiencing treatment success. Liposomal amphotericin B was significantly more effective than amphotericin B deoxycholate for the treatment of moderate to severe disseminated histoplasmosis in patients with AIDS, with 88% and 64% of patients, respectively, having a successful response. Liposomal amphotericin B was noninferior to amphotericin B deoxycholate for the treatment of cryptococcal meningitis in terms of mycological success. Micafungin therapy was shown to be noninferior to liposomal amphotericin B for the treatment of adult patients with candidaemia or invasive candidiasis. In a substudy in paediatric patients, which was not powered to determine noninferiority, liposomal amphotericin B was as effective as micafungin for the treatment of candidaemia or invasive candidiasis. In this patient population, within each trial, 90% of adult patients and approximately three-quarters of paediatric patients in both treatment groups experienced a successful response. In patients with invasive mould infection (mainly aspergillosis), there was no difference in efficacy between a higher dosage of liposomal amphotericin B (10 mg/kg/day) and the standard dosage (3 mg/kg/day), with 46% and 50% of patients experiencing a favourable overall response. In well designed clinical trials, liposomal amphotericin B was generally at least as well tolerated as other lipid-associated formulations of amphotericin B and better tolerated than amphotericin B deoxycholate in adult and paediatric patients. Compared with other amphotericin B formulations, liposomal amphotericin B treatment was associated with a lower incidence of infusion-related adverse events and nephrotoxicity. A higher than recommended dosage of liposomal amphotericin B (10 mg/kg/day) was associated with an increased incidence of nephrotoxicity compared with the standard dosage (3 mg/kg/day), although the incidence of infusion-related reactions did not differ between treatment groups. In general, liposomal amphotericin B treatment was not as well tolerated as echinocandin therapy in well designed clinical trials. As empirical therapy or for the treatment of confirmed invasive fungal infections in adult patients, liposomal amphotericin B recipients experienced more infusion-related events and nephrotoxicity than caspofungin or micafungin recipients. There was no difference in the incidence of these adverse events between the liposomal amphotericin B and micafungin groups in a study in paediatric patients.

Candida infective endocarditis: report of 15 cases from a prospective multicenter study

Candida species are an uncommon cause of infective endocarditis (IE). Given the rarity of this infection, the epidemiology, prognosis, and optimal therapy of Candida IE are poorly defined. We conducted a prospective, observational study at 18 medical centers in Italy, including all consecutive patients with a definite diagnosis of IE admitted from January 2004 through December 2007.A Candida species was the causative organism in 8 cases of prosthetic valve endocarditis (PVE), 5 cases of native valve endocarditis (NVE), 1 case of pacemaker endocarditis, and 1 case of left ventricular patch infection. Candida species accounted for 1.8% of total cases, and for 3.4% of PVE cases. Most patients (86.6%) had a health care-associated infection. PVE associated with a health care contact occurred after a median of 225 days from valve implantation. Ten patients (66.6%) were treated with caspofungin alone or in combination with other antifungal drugs. The overall mortality rate was 46.6%. Mortality was higher in patients with PVE (5 of 8 cases, 62.5%) than in patients with NVE (2 of 5 patients, 40%). A better outcome was observed in patients treated with a combined medical and surgical therapy.Candida IE should be classified as an emerging infectious disease, usually involving patients with intravascular prosthetic devices, and associated with substantial related morbidity and mortality. Candida PVE usually is a late-onset disease, which becomes clinically evident even several months after an initial episode of transient candidemia.

Efficacy of novel antimicrobial gloves impregnated with antiseptic dyes in preventing the adherence of multidrug-resistant nosocomial pathogens

BACKGROUND

Contaminated gloves are a major source of transmission of bacteria in the hospital and food industry. We investigated the efficacy of gloves impregnated with a combination of antiseptics consisting of brilliant green dye and chlorhexidine (Gardine).

METHODS

Gardine-coated and uncoated 1-cm(2) segments of latex examination and nitrile examination gloves (Spontex, Columbia, TN) were exposed to 1.5 x 10(8) colony-forming units (CFU)/mL methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, multidrug resistant (MDR) Escherichia coli, MDR-Acinetobacter baumannii, or Candida albicans as indicated by our brief exposure method. At least 3 glove segments were tested in each group, and growth was scored as mean CFU/cm(2). Segments were dried for various time periods (30 seconds, 10 minutes, 30 minutes, and 1 hour) and streaked face down on agar plates. Plates were incubated overnight at 37 degrees C, and growth was quantitated.

RESULTS

Gardine-coated latex and nitrile gloves showed significant reduction, an average of 6 logs and 5 logs, respectively, within 30 seconds or 10 minutes when tested against MRSA, vancomycin-resistant enterococci, MDR-E coli, MDR-Acientobacter, and C albicans. Complete kill, 8-log reduction, was seen within 30 seconds for MRSA and E coli in both Gardine-coated latex and nitrile gloves.

CONCLUSION

Gloves impregnated with Gardine antiseptic dye were highly efficacious in preventing contamination of nosocomial-resistant pathogens on the outer surface of glove and may be useful in the food industry or clinical setting.

Antifungal combinations against simulated Candida albicans endocardial vegetations

The in vitro effects of flucytosine (5FC), liposomal amphotericin B (L-AmB), and micafungin (Mica) combinations against two Candida albicans strains that simulated 24-hour-old endocardial vegetations were studied. Mica was superior to 5FC or L-AmB, and the 5FC-L-AmB-Mica combination was superior to all other treatments for one strain but no different from the dual combination of L-AmB-Mica for the other strain.

In vitro activity of micafungin against planktonic and sessile Candida albicans isolates

Planktonic and sessile susceptibilities to micafungin were determined for 30 clinical isolates of Candida albicans obtained from blood or other sterile sites. Planktonic and sessile MIC(90)s for micafungin were 0.125 and 1.0 microg/ml, respectively.

Micafungin plus fluconazole in an infected knee with retained hardware due to Candida albicans

OBJECTIVE

To describe the use of micafungin and fluconazole in the management of a fungal prosthetic joint infection caused by Candida albicans.

CASE SUMMARY

A 55-year-old female who had undergone total left knee arthroplasty due to rheumatoid arthritis presented with symptoms of a left knee infection. Intravenous vancomycin 1 g every 12 hours and intravenous ampicillin/sulbactam 1.5 g every 6 hours were initiated. Arthrocentesis produced cloudy synovial fluid with a white blood cell (WBC) count of 5.995 x 10(3)/microL. C-reactive protein (CRP) was 19.8 mg/dL and erythrocyte sediment rate (ESR) was greater than 120 mm/h. Gram stain was negative, but intraoperative cultures grew C. albicans. Four days later the patient's condition worsened and repeat arthrocentesis showed WBC count of 16.8 x 10(3)/microL with budding yeast in the synovial fluid. Antibiotics were stopped and liposomal amphotericin B 5 mg/kg once daily was started but was stopped after a few doses due to renal failure. Intravenous micafungin 100 mg daily was initiated; intravenous fluconazole 400 mg daily was added 2 days later and subsequently changed to oral fluconazole after 2 days of therapy. The patient received combination micafungin/fluconazole therapy for 8 weeks. After approximately 8 weeks of therapy, the CRP level and ESR had decreased from 19.8 to 7.1 mg/dL and greater than 120 to 81 mm/h, respectively. The patient's pain and range of motion in her knee had returned to baseline levels at last follow-up after the total knee arthroplasty. After 8 weeks of combination therapy, micafungin was discontinued but oral fluconazole was continued; approximately 8 weeks later the patient relapsed, requiring removal of the prosthetic knee hardware.

DISCUSSION

Fungal prosthetic joint infections are rare, but definitive data regarding appropriate treatment are lacking. Echinocandins are an attractive treatment option due to their enhanced biofilm penetration. In our patient, treatment with micafungin plus fluconazole for 8 weeks followed by fluconazole monotherapy was associated with an initial good outcome in the treatment of a C. albicans prosthetic knee infection with retained hardware. This was, to our knowledge, the first case using micafungin in a prosthetic joint infection.

CONCLUSIONS

Although micafungin plus fluconazole showed positive results in our patient, more data are needed regarding combination therapy for fungal prosthetic joint infections.

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 x 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 (>or=50% reduction of OD) than biofilms grown for 48 h, whereas posaconazole showed similar, but reduced activity against all phases of C. albicans biofilm (<or=50% reduction of OD). Caspofungin at 1-4 x 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.

Biofilm lifestyle of Candida: a mini review

Candida is the major fungal pathogen of humans causing a variety of afflictions ranging from superficial mucosal diseases to deep seated mycoses. Biofilm formation is a major virulence factor in the pathogenicity of Candida, and Candida biofilms are difficult to eradicate especially because of their very high antifungal resistance. Consequently, research into the pathogenicity of Candida has focused on the prevention and management of biofilm development, their architecture, and antifungal resistance. Although studies have shed some light, molecular mechanisms that govern biofilm formation and pathogenicity still await full clarification. This review outlines the key features of what is currently known of Candida biofilm development, regulation and antifungal resistance and, their proteomics.

Effect of phosphate group addition on the properties of denture base resins

STATEMENT OF PROBLEM

Acrylic resins are prone to microbial adherence, especially by Candida albicans. Surface-charged resins alter the ionic interaction between the denture resin and Candida hyphae, and these resins are being developed as a means to reduce microbial colonization on the denture surface.

PURPOSE

The purpose of this study was to investigate the physical and mechanical properties of phosphate-containing polymethyl methacrylate resins for their suitability as a denture material.

MATERIAL AND METHODS

Using PMMA with cross-linker (Lucitone 199) as a control, 4 experimental groups containing various levels of phosphate with and without cross-linker were generated. The properties examined were impact strength, fracture toughness, wettability (contact angle), and resin bonding ability to denture teeth. Impact strength was tested in the Izod configuration (n=16), and fracture toughness (n=13) was measured using the single-edge notched bend test. Wettability was determined by calculating the contact angle of water on the material surface (n=12), while ISO 1567 was used for bonding ability (n=12). The data were analyzed by 1- and 2-way ANOVA (alpha=.05).

RESULTS

A trend of increased hydrophilicity, as indicated by lower contact angle, was observed with increased concentrations of phosphate. With regard to the other properties, no significant differences were found when compared with the control acrylic resin.

CONCLUSIONS

No adverse physical effect due to the addition of a phosphate-containing monomer was found in the acrylic denture resins. Additional mechanical and physical properties, biocompatibility, and clinical efficacy studies are needed to confirm the in vivo anti-Candida activity of these novel resins.

Effect of tunicamycin on Candida albicans biofilm formation and maintenance

BACKGROUND

Candida albicans is a common opportunistic pathogen of the human body and is the frequent causative agent of candidiasis. Typically, these infections are associated with the formation of biofilms on both host tissues and implanted biomaterials. As a result of the intrinsic resistance of C. albicans biofilms to most antifungal agents, new strategies are needed to combat these infections.

METHODS

Here we have used a 96-well microtitre plate model of C. albicans biofilm formation to study the inhibitory effect of tunicamycin, a nucleoside antibiotic that inhibits N-linked glycosylation affecting cell wall and secreted proteins, on C. albicans biofilm formation. A proteomic approach was used to study the effect of tunicamycin on levels of glycosylation of key secreted mannoproteins in the biofilm matrix.

RESULTS

Our results revealed that physiological concentrations of tunicamycin displayed significant inhibitory effects on biofilm development and maintenance, while not affecting overall cell growth or morphology. However, tunicamycin exerted a minimal effect on fully mature, pre-formed C. albicans biofilms.

CONCLUSIONS

The effect of tunicamycin on the C. albicans biofilm mode of growth demonstrates the importance of N-linked glycosylation in the developmental stages of biofilm formation. In addition, our results indicate that N-linked glycosylation represents an attractive target for the development of alternative strategies for the prevention of biofilm formation by this important pathogenic fungus.

Shear stress modulates the thickness and architecture of Candida albicans biofilms in a phase-dependent manner

Biofilm formation plays an integral role in catheter-associated bloodstream infections caused by Candida albicans. Biofilms formed on catheters placed intravenously are exposed to shear stress caused by blood flow. In this study, we investigated whether shear stress affects the ability of C. albicans to form biofilms. Candida biofilms were formed on catheter discs and exposed to physiological levels of shear stress using a rotating disc system (RDS). Control biofilms were grown under conditions of no flow. Tetrazolium (XTT) assay and dry weight (DW) measurements were used to quantify metabolic activity and biofilm mass respectively. Confocal scanning laser microscopy (CSLM) was used to evaluate architecture and biofilm thickness. After 90 min, cells attached under no-flow exhibited significantly greater XTT activity and DW than those under shear. However, by 24 h, biofilms formed under both conditions had similar XTT activities and DW. Interestingly, thickness of biofilms formed under no-flow was significantly greater after 24 h than of those formed under shear stress, demonstrating that shear exposure results in thinner, but denser biofilms. These studies suggest that biofilm architecture is modulated by shear in a phase-dependent manner.

A simple and reproducible 96-well plate-based method for the formation of fungal biofilms and its application to antifungal susceptibility testing

The incidence of fungal infections has increased significantly over the past decades. Very often these infections are associated with biofilm formation on implanted biomaterials and/or host surfaces. This has important clinical implications, as fungal biofilms display properties that are dramatically different from planktonic (free-living) populations, including increased resistance to antifungal agents. Here we describe a rapid and highly reproducible 96-well microtiter-based method for the formation of fungal biofilms, which is easily adaptable for antifungal susceptibility testing. This model is based on the ability of metabolically active sessile cells to reduce a tetrazolium salt (2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide) to water-soluble orange formazan compounds, the intensity of which can then be determined using a microtiter-plate reader. The entire procedure takes approximately 2 d to complete. This technique simplifies biofilm formation and quantification, making it more reliable and comparable among different laboratories, a necessary step toward the standardization of antifungal susceptibility testing of biofilms.

Variation of cell surface hydrophobicity and biofilm formation among genotypes of Candida albicans and Candida dubliniensis under antifungal treatment

Candida infections are frequently associated with formation of biofilms on artificial medical devices. This work studied variation of cell surface hydrophobicity (CSH) and formation of biofilm in relation to Candida albicans and Candida dubliniensis genotypes and an effect of some conventional antifungal agents on both CSH and biofilm. The 50 isolates of C. albicans and C. dubliniensis were classified into genotypes A, B, C, and D, genotype D being exclusively represented by C. dubliniensis. No significant differences between CSH of genotypes A and B and B and C were observed with respect to cultivation temperature 25 or 37 degrees C. Candida dubliniensis showed increased CSH in comparison with other C. albicans genotypes (p < 0.001) regardless of temperature used. Using XTT reduction assay and dry masses, genotypes B and C showed reduced ability to form biofilm in comparison with genotype A (p < 0.05) and C. dubliniensis (p < 0.001). Fluconazole reduced biofilm in C. albicans genotypes A, B, and C (p < 0.05) but not CSH. The opposite effect was observed in C. dubliniensis. Voriconazole effectively reduced both biofilm formation and CSH in all tested genotypes of C. albicans and C. dubliniensis (p < 0.05).

Candida parapsilosis, an emerging fungal pathogen

SUMMARY

Candida parapsilosis is an emerging major human pathogen that has dramatically increased in significance and prevalence over the past 2 decades, such that C. parapsilosis is now one of the leading causes of invasive candidal disease. Individuals at the highest risk for severe infection include neonates and patients in intensive care units. C. parapsilosis infections are especially associated with hyperalimentation solutions, prosthetic devices, and indwelling catheters, as well as the nosocomial spread of disease through the hands of health care workers. Factors involved in disease pathogenesis include the secretion of hydrolytic enzymes, adhesion to prosthetics, and biofilm formation. New molecular genetic tools are providing additional and much-needed information regarding C. parapsilosis virulence. The emerging information will provide a deeper understanding of C. parapsilosis pathogenesis and facilitate the development of new therapeutic approaches for treating C. parapsilosis infections.

Aspergillus fumigatus forms biofilms with reduced antifungal drug susceptibility on bronchial epithelial cells

Aspergillus fumigatus is a leading cause of death in immunocompromised patients and a frequent colonizer of the respiratory tracts of asthma and cystic fibrosis (CF) patients. Biofilms enable bacteria and yeasts to persist in infections and can contribute to antimicrobial resistance. We investigated the ability of A. fumigatus to form biofilms on polystyrene (PS) and human bronchial epithelial (HBE) and CF bronchial epithelial (CFBE) cells. We developed a novel in vitro coculture model of A. fumigatus biofilm formation on HBE and CFBE cells. Biofilm formation was documented by dry weight, scanning electron microscopy (SEM), and confocal scanning laser microscopy (CSLM). The in vitro antifungal activities of seven antifungal drugs were tested by comparing planktonic and sessile A. fumigatus strains. A. fumigatus formed an extracellular matrix on PS and HBE and CFBE cells as evidenced by increased dry weight, SEM, and CSLM. These biofilms exhibited decreased antifungal drug susceptibility and were adherent to the epithelial cells, with fungi remaining viable throughout 3 days. These observations might have implications for treatment of A. fumigatus colonization in chronic lung diseases and for its potential impact on airway inflammation, damage, and infection.

[Activity of anidulafungin against Candida biofilms]

Currently, no standardized method to study the in vitro activity of antifungal agents on biofilms is available, thus, the comparison among different authors is difficult. The studies discussed in this review use the XTT reduction to measure the activity of antifungals on biofilms of 24 h of maturation. To date, biofilm anidulafungin MICs of 47 isolates of Candida spp. (25 Candida albicans, 16 Candida tropicalis, 5 Candida dubliniensis and 1 Candida parapsilosis) have been published. The geometric mean MIC of anidulafungin on biofilms of Candida spp. is of 1.18 microg/ml. Against isolates of species with great capacity of biofilm formation, the geometric mean MIC is 0.325 (C. albicans), 2 (C. parapsilosis) and 0.5 microg/ml (C. dubliniensis). No echinocandin has activity on C. tropicalis biofilms. In addition, anidulafungin can be used for lock therapy of catheters since it is the echinocandin with the least in vitro paradoxical effect.

Cell density and cell aging as factors modulating antifungal resistance of Candida albicans biofilms

Biofilm formation is a major virulence attribute of Candida pathogenicity which contributes to higher antifungal resistance. We investigated the roles of cell density and cellular aging on the relative antifungal susceptibility of planktonic, biofilm, and biofilm-derived planktonic modes of Candida. A reference and a wild-type strain of Candida albicans were used to evaluate the MICs of caspofungin (CAS), amphotericin B (AMB), nystatin (NYT), ketoconazole (KTC), and flucytosine (5FC). Standard, NCCLS, and European Committee on Antibiotic Susceptibility Testing methods were used for planktonic MIC determination. Candida biofilms were then developed on polystyrene wells, and MICs were determined with a standard 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide assay. Subsequently, antifungal susceptibility testing was performed for greater inoculum concentrations and 24- and 48-h-old cultures of planktonic Candida. Furthermore, Candida biofilm-derived planktonic cells (BDPC) were also subjected to antifungal susceptibility testing. The MICs for both C. albicans strains in the planktonic mode were low, although on increasing the inoculum concentration (up to 1 x 10(8) cells/ml), a variable MIC was noted. On the contrary, for Candida biofilms, the MICs of antifungals were 15- to >1,000-fold higher. Interestingly, the MICs for BDPC were lower and were similar to those for planktonic-mode cells, particularly those of CAS and AMB. Our data indicate that higher antifungal resistance of Candida biofilms is an intrinsic feature possibly related to the biofilm architecture rather than cellular density or cellular aging.

Vascular catheter-associated infections: a microbiological and therapeutic update

The increasing incidence of central venous catheter (CVC)-related infections can be ascribed to the wider indications to central venous catheterization, to the higher attention to this issue paid by clinicians and microbiologists, and to the patient population referred to hospitals, increasingly characterized by different degrees of immunosuppression and often in critical clinical conditions. This phenomenon implies a higher health care burden and higher related costs, as well as a significant attributable mortality, that varies however according to the pathogen involved. The microorganisms most frequently involved in CVC-related infections are coagulase-negative staphylococci, Staphylococcus aureus, aerobic Gram-negative bacilli, and Candida albicans. In the management of suspected or proven central venous catheter-related infections, several issues need to be addressed: the need to remove the device or the possibility of salvage, the immediate start of calculated antibiotic therapy or the possibility of waiting for results of microbiological diagnostics and proceeding to etiologically-guided therapy. The preferred conservative method is the "Antibiotic-Lock technique" (ALT), based on the endoluminal application of antibacterials at extremely high concentrations in situ for a period of time long enough to ensure bactericidal activity. On the other hand, immediate catheter removal and initiation of appropriate calculated therapy immediately after an adequate diagnostic work-up are strongly recommended in a clinical setting of severe sepsis or septic shock.

Reduced biocide susceptibility in Candida albicans biofilms

Candida biofilm formation is common during infection and environmental growth. We tested the impacts of three biocides (ethanol [EtOH], H(2)O(2), and sodium dodecyl sulfate) on Candida albicans, C. parapsilosis, and C. glabrata biofilms. Higher concentrations of the biocides were required for efficacy against biofilms than for efficacy against planktonic controls. A combination study with two biocides (EtOH and H(2)O(2)) and fluconazole demonstrated that the combination had enhanced efficacy.

Micafungin for the prophylaxis and treatment of Candida infections

Invasive fungal infection is a significant cause of morbidity and mortality worldwide. The incidence of these infections is steadily increasing. In addition, strains resistant to many commonly used antifungal agents are becoming more prevalent. Many new antifungals have become commercially available in recent years, which have vastly improved the ability to treat these infections effectively. Micafungin is one of three commercially available echinocandins available for use in the USA. This class of agents possess a unique mechanism of action that helps to reduce toxicity while maintaining potent antifungal activity. Micafungin is currently approved for the treatment of esophageal candidiasis in adults and is the only in its class approved for the prophylaxis of Candida infection in patients who have undergone hematopoietic stem cell transplantation. It was also recently approved in the USA for the treatment of candidemia and other forms of invasive candiaisis (acute disseminated candiaisis, Candida peritonitis and abscess). In general, micafungin is well tolerated and has favorable safety and drug-interaction profiles.

Activities and ultrastructural effects of antifungal combinations against simulated Candida endocardial vegetations

In vitro pharmacodynamic model (PDM) simulation of serum antifungal concentrations may predict the value of combination antifungal regimens against Candida sp. endocarditis. We investigated the effects of combinations of flucytosine (5FC), micafungin (Mica), and voriconazole (Vor) against Candida-infected human platelet-fibrin clots, used as simulated endocardial vegetations (SEVs). Single clinical bloodstream isolates of Candida albicans, Candida glabrata, Candida parapsilosis, and Candida tropicalis were used. All four isolates were susceptible to 5FC, while C. glabrata was resistant to Vor and C. tropicalis had a paradoxical resistance phenotype to Mica. The SEVs were prepared with an initial inoculum of 1 x 10(6) CFU/g of SEV and added to a PDM, which utilized yeast nitrogen broth-2% glucose and incubation at 35 degrees C and simulated antifungal pharmacokinetic profiles. Fungal densities in the SEVs were determined in quadruplicate over 72 h. Scanning electron microscopy (SEM) was used to evaluate treatment and control SEVs. Vor was the least active single agent against all Candida spp. except for C. parapsilosis, where it was comparable to Mica. In contrast, 5FC was the most active against all Candida spp. except for C. tropicalis, where it was comparable to Mica. The combination of 5FC plus Vor was superior to either agent alone against C. parapsilosis. The combination of Vor plus Mica was inferior to the use of Mica alone against C. tropicalis. The triple combination of 5FC plus Vor plus Mica was no better than single or dual agents against any of the Candida spp. The ultrastructural features of infected SEVs were unique for each Candida sp., with C. parapsilosis in particular manifesting friable biofilm clusters. In general, 5FC and Mica were superior in their rates and extents of fungal burden reduction compared to Vor against Candida-infected SEVs. Evaluation of 5FC and Mica in animal models of Candida endocarditis is warranted.

[In vitro activity of amphotericin B and anidulafungin against Candida spp. biofilms]

Invasive infections caused by Candida spp. are increasing worldwide and are becoming an important cause of morbidity and mortality in immunocompromised patients. A large number of manifestations of candidiasis are associated with the formation of biofilms on inert or biological surfaces. Candida spp. biofilms are recalcitrant to treatment with conventional antifungal therapies. The aim of this study was dual 1) to determine the prevalence of biofilm producers among clinical isolates from catheter (16 C. albicans ) and blood culture (2 C. albicans and 30 C. tropicalis), and 2) to determine the activity of amphotericin B and anidulafungin against C. albicans and C. tropicalis biofilms of 24 and 48 hours of maturation. Biofilms were developed using a 96-well microtitre plate model and production and activity of antifungal agents against biofilms were determined by the tetrazolium (XTT) reduction assay. Of catheter and blood isolates, 62.5 and 56.25%, respectively, produced biofilms. By species, 68.42% of C. albicans and 53.33% of C. tropicalis were biofilm producers. C. albicans biofilms showed more resistance to amphotericin B and anidulafungin than their planktonic counterparts. Complete killing of biofilms was never achieved, even at the highest concentrations of the drugs tested. Anidulafungin displayed more activity than amphotericin B against C. albicans biofilms of 24 hours of maturation (GM MIC 0.354 vs. 0.686 microg/ml), but against C. tropicalis biofilms amphotericin B was more active (GM MIC 11.285 vs. 0.476 microg/ml). In contrast, against biofilms with 48 hours maturation, amphotericin B was more active against both species.

Antimicrobial resistance: resistance to antifungal agents: mechanisms and clinical impact

Despite advances in preventive, diagnostic, and therapeutic interventions, invasive fungal infections cause significant morbidity and mortality in immunocompromised patients. The burden of antifungal resistance in such high-risk patients is becoming a major concern. A better understanding of the mechanisms and clinical impact of antifungal resistance is essential to the prompt and efficient treatment of patients with invasive mycoses and to improving the outcome of such infections. Although recent guidelines have attempted to standardize antifungal susceptibility testing, limitations still exist as a result of the incomplete correlation between in vitro susceptibility and clinical response to treatment. Four major mechanisms of resistance to azoles have been identified, all of which rely on altered gene expression. Mechanisms responsible for polyene and echinocandin resistance are less well understood. In addition to discussing the molecular mechanisms of antifungal resistance, this article elaborates on the concept of clinical resistance, which is critical to the understanding of treatment failure in patients with invasive fungal infections.

Microplate Alamar blue assay for susceptibility testing of Candida albicans biofilms

Although biofilm-based fungal infections are an important cause of morbidity and mortality in patients, there is no standardized method for the in vitro evaluation of the drug susceptibility of biofilms. We investigated a high-throughput method for determining the susceptibility of Candida albicans biofilms that uses the oxidation reduction indicator Alamar blue (AB). Biofilms from the tested Candida albicans strains were markedly resistant to amphotericin B (AMB), nystatin (NYT), fluconazole (FLC) and 5-fluorouracil (5FC), but susceptible to Conflikt disinfectant. The latter was used in comparative studies of AB reduction with two other methods for assessing in vitro drug susceptibility i.e., 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction and enumeration of viable colony counts (CFU/ml). AB results correlated well with XTT (r=0.88-0.93) and CFU/ml (r=0.93-0.99) for all four C. albicans test strains. This simple, reproducible method for determining in vitro drug susceptibility should facilitate discovery of antifungals active against Candida biofilms.

[In vitro antifungal activity of voriconazole: New data after the first years of clinical experience]

Voriconazole has been developed to meet the increasing need for new and useful antifungal agents for the treatment of invasive mycoses. This review describes the spectrum of voriconazole antifungal activity based on data from in vitro studies published during the last three years. This survey demonstrates that voriconazole has a broad antifungal spectrum against the most common fungal pathogens being its action fungistatic for Candida and fungicidal for Aspergillus and other filamentous fungi. Overall, more than 95% of all Candida isolates tested are susceptible to voriconazole and less than 3% are resistant. Similar or even better activity rates have been described for Aspergillus, Cryptococcus and most of yeasts and moulds of medical importance. We also discuss the limitations related to the azole cross-resistance observed in some Candida glabrata isolates, the poor activity of voriconazole against Scedosporium prolificans, its activity against fungal biofilms and the great potential usefulness of combination of voriconazole with other antifungal drugs.

Fusarium and Candida albicans biofilms on soft contact lenses: model development, influence of lens type, and susceptibility to lens care solutions

Fungal keratitis is commonly caused by Fusarium species and less commonly by Candida species. Recent outbreaks of Fusarium keratitis were associated with contact lens wear and with ReNu with MoistureLoc contact lens care solution, and biofilm formation on contact lens/lens cases was proposed to play a role in this outbreak. However, no in vitro model for contact lens-associated fungal biofilm has been developed. In this study, we developed and characterized in vitro models of biofilm formation on various soft contact lenses using three species of Fusarium and Candida albicans. The contact lenses tested were etafilcon A, galyfilcon A, lotrafilcon A, balafilcon A, alphafilcon A, and polymacon. Our results showed that clinical isolates of Fusarium and C. albicans formed biofilms on all types of lenses tested and that the biofilm architecture varied with the lens type. Moreover, differences in hyphal content and architecture were found between the biofilms formed by these fungi. We also found that two recently isolated keratitis-associated fusaria formed robust biofilms, while the reference ATCC 36031 strain (recommended by the International Organization for Standardization guidelines for testing of disinfectants) failed to form biofilm. Furthermore, using the developed in vitro biofilm model, we showed that phylogenetically diverse planktonic fusaria and Candida were susceptible to MoistureLoc and MultiPlus. However, Fusarium biofilms exhibited reduced susceptibility against these solutions in a species- and time-dependent manner. This in vitro model should provide a better understanding of the biology and pathogenesis of lens-related fungal keratitis.

Infection of intravascular prostheses: how to treat other than surgery

Long-term antimicrobial therapy may be effective in some patients with intravascular prosthesis infection. However, this approach does not represent an alternative to surgery when this is feasible, but is merely the best opportunity for patients too ill to tolerate a re-intervention. Prosthetic valve endocarditis may be treated with antibiotic therapy alone in selected patients who are haemodynamically stable with non-staphylococcal infections and no para-valvular complications. In contrast, infections of pacemaker leads or other implantable cardiac devices require complete hardware removal, as infection recurrence always occurs, even after a seemingly effective initial treatment. Attempts to treat conservatively infections of abdominal aortic grafts can be successful in a few cases, provided the patient is stable, the pathogen has been identified, and antibiotic susceptibility has been demonstrated. Treatment requires at least 4-6 weeks and may be followed by a sequential oral regimen once the acute phase of the infection has subsided. The correct duration of this treatment is often unknown and relapses are common after treatment withdrawal. The availability of novel antibacterial and antifungal agents - showing fast microbicidal activity that includes biofilm micro-organisms - such as daptomycin and caspofungin, or having a wide antimicrobial spectrum, such as tigecycline, may increase the probability of long-standing suppression or even eradication of the infection in these particular subsets of inoperable patients. However, so far, very little experience is available on the efficacy and tolerability of these drugs in intravascular prosthesis infections. Controlled studies are lacking and difficult to plan. Well-designed prospective studies may help to establish guidelines and reach a multidisciplinary consensus on the optimal therapeutic approach, and are therefore awaited.