Fluconazole susceptibilities of bloodstream Candida sp. isolates as determined by National Committee for Clinical Laboratory Standards method M27-A and two other methods

Comparison of the in vitro Effect of Chemical and Herbal Mouthwashes on Candida albicans

Background:

During the recent decades research has focused to find scientific evidence for the effects of herbal medicines. Researchers are interested in herbal remedies for medication and aim to substitute herbal material instead of chemical formula with limited side effects for human being.

Objectives:

The aim of the current study was to compare the in vitro effect of herbal and chemical mouthwashes against Candida albicans.

Materials and Methods:

In this research, we used a standard strain of C. albicans, PTCC 5027. The suspension was made by a fresh culture of C. albicans (24 hours) and the optical density (turbidity equating to a McFarland standard of 0.5) was read at 530 nm. The C. albicans suspension was cultured on Sabouraud dextrose agar plate. Next, two wells were filled with mouthwashes and after incubation at 30ºC for 24 hours, the inhibition zone was measured. Minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of mouthwashes were determined. Data were analyzed using the SPSS software, independent T-tests and one-sided variance analysis (ANOVA-one way).

Results:

Based on these findings on agar diffusion with (P = 0.764), MIC and MFC tests (P = 0.879), there were no significant differences between the antifungal effect of herbal and chemical mouthwashes.

Conclusions:

This study showed that, chemical mouthwashes acted better than herbal mouthwashes and among different chemical mouthwashes, Oral B was most effective.

Comparison of Neo-Sensitabs tablet diffusion assay with CLSI broth microdilution M38-A and disk diffusion methods for testing susceptibility of filamentous fungi with amphotericin B, caspofungin, itraconazole, posaconazole, and voriconazole

We compared the Neo-Sensitabs tablet assay to both reference M38-A broth microdilution and disk diffusion methods for testing the susceptibility of 183 filamentous isolates to amphotericin B, caspofungin, itraconazole, posaconazole, and voriconazole. Neo-Sensitabs and disk assay inhibition zone diameters, in millimeters, were obtained on nonsupplemented Mueller-Hinton agar at 16 to 48 h. The reproducibility of zone diameters (i.e., the percentage of replicate zone diameters that were within 2 standard deviations of the means), their correlation with either MICs or minimum effective concentrations (for caspofungin only), and the categorical agreement were similar between tablet and disk assays (93 to 100% [R, >0.70] and 79 to 96%, respectively) with four of the five agents. The exceptions were the results for posaconazole tablets (R, 0.686; disk, 0.757; 84% categorical agreement for tablet and 96% for disk). These data suggest the potential value of the Neo-Sensitabs assay for testing 5-microg caspofungin and 1-microg voriconazole posaconazole tablets against all mold isolates, 8-microg itraconazole and 5-microg tablets against all mold isolates except zygomycetes, and 10-microg amphotericin B tablets against zygomycete isolates only.

Correlation of Neo-Sensitabs tablet diffusion assay results on three different agar media with CLSI broth microdilution M27-A2 and disk diffusion M44-A results for testing susceptibilities of Candida spp. and Cryptococcus neoformans to amphotericin B, caspofungin, fluconazole, itraconazole, and voriconazole

We compared the Neo-Sensitabs tablet assay to both reference M27-A2 broth microdilution and M44-A disk diffusion methods for testing susceptibilities of 110 isolates of Candida spp. and Cryptococcus neoformans to amphotericin B, caspofungin, fluconazole, itraconazole, and voriconazole. Neo-Sensitabs assay inhibition zone diameters in millimeters on three agars (Mueller-Hinton agar supplemented with 2% dextrose and 0.5 microg/ml methylene blue [MGM], Shadomy [SHA], and RPMI 1640 [RPMI, 2% dextrose]) were obtained at 24 to 72 h. The correlation coefficient of Neo-Sensitabs results with MICs was similar to that of the disk method for most of the five agents on MGM (R, 0.80 to 0.89 versus 0.76 to 0.89, respectively). Overall, superior correlation was observed at 24 h for most agents. The exception was amphotericin B (R values of 0.68 and 0.5 for disk and tablet, respectively, at 48 h versus 0.68 and 0.48, respectively, at 24 h). In general, Neo-Sensitabs results were less consistent on SHA and RPMI agars. Although agreement by breakpoint category of Neo-Sensitabs and disk results with CLSI method M27-A2 was also similar on MGM (92.7 to 98.2% versus 95.5 to 100%, respectively), the Neo-Sensitabs method failed to identify two of the six isolates with high amphotericin B MICs. These data suggest the potential value of the Neo-Sensitabs assay for testing at least four of the five agents against yeasts evaluated in the clinical laboratory.

Association of fluconazole area under the concentration-time curve/MIC and dose/MIC ratios with mortality in nonneutropenic patients with candidemia

The present study tested in vitro susceptibility of Candida bloodstream isolates to fluconazole to determine if the ratio of the fluconazole area under the concentration-time curve (AUC) or weight-normalized daily dose (dose(wn)) to MIC correlated with mortality. Fluconazole susceptibility and outcome data were determined for 77 patients with a positive Candida blood culture between 2002 and 2005. The most commonly isolated Candida species were C. albicans (64%), C. glabrata (14%), C. parapsilosis (8%), C. tropicalis (6%), and C. lusitaniae (4%). Only two isolates were classified as fluconazole resistant by the CLSI M27-A2 method. Fluconazole MICs were highest against C. glabrata relative to other Candida species. Overall the crude mortality assessed at hospital discharge was 19.4% (n = 15). Mortality rates by species were as follows: C. albicans, 16.3%; C. glabrata, 36.4%; C. parapsilosis, 0%; C. tropicalis, 0%; C. lusitaniae, 33.3%. A mortality rate of 50% was noted among patients infected with nonsusceptible isolates (MIC > or = 16 microg/ml) compared to 18% for patients infected with susceptible (MIC < or = 8 microg/ml) isolates (P = 0.17). The fluconazole dose(wn)/MIC (24-h) values were significantly higher for the 62 survivors (13.3 +/- 10.5 [mean +/- standard deviation]) compared to the 15 nonsurvivors (7.0 +/- 8.0) (P = 0.03). The fluconazole AUC/MIC (24 h) values also trended higher for survivors (775 +/- 739) compared to nonsurvivors (589 +/- 715) (P = 0.09). These data support the dose-dependent properties of fluconazole. Underdosing fluconazole against less-susceptible Candida isolates has the potential to increase the risk of mortality associated with candidemia.

Sensititre YeastOne caspofungin susceptibility testing of Candida clinical isolates: correlation with results of NCCLS M27-A2 multicenter study

The ability of Sensititre YeastOne to discriminate isolates with reduced caspofungin susceptibility was determined against 36 Candida spp. (6 with a known FKS1 mutation). Results were compared with those of M27-A2. The MIC endpoint was 100% growth inhibition. Overall agreement (+/-2 log2) was 87.16%. Sensititre YeastOne detected strains with reduced caspofungin susceptibility.

Comparison of disk diffusion method and broth microdilution method for antifungal susceptibility testing of dermatophytes

The use of the agar diffusion Neo-Sensitabs method to determine antifungal susceptibility of 59 isolates of dermatophytes, namely Epidermophyton floccosum, Microsporum canis, M. gypseum, Trichophyton mentagrophytes, T. rubrum and T. tonsurans to Clotrimazole (CLZ), Itraconazole (ITZ) and Terbinafine (TBF) is described. Results obtained are compared to the minimum inhibitory concentrations (MIC) determined by an adaptation of the NCCLS-M38-A procedure. Using the diffusion method, all strains showed a broad zone of inhibition at the first available reading time (3 or 7 days). Using the broth microdilution method, the geometric mean MIC (microg/ml) with regard to all isolates was < or = 0.03 for TBF, < or = 0.069 for CLZ and < or = 0.919 for ITZ. In both methods, TBF was the most active antifungal agent against all isolates tested. The two methods evaluated were able to detect the resistance of the quality control strains of Aspergillus fumigatus to ITZ. Even though a reference method for testing dermatophytes still has not been developed, our data suggest that the Neo-Sensitabs diffusion method could provide a simple procedure for the antifungal susceptibility testing of dermatophytes in the routine clinical laboratory.

In vitro fluconazole susceptibility of 1565 clinical isolates of candida species evaluated by the disk diffusion method performed using NCCLS M44-A guidelines

We determined the in vitro activity of fluconazole against 1565 clinical Candida spp. isolates collected from different specimens of non-AIDS outpatients and inpatients in 3 different regions of Italy. Susceptibility testing was performed by agar disk diffusion using the NCCLS document M44-A guidelines. Candida albicans was the most frequently isolated yeast (68%) followed by C. glabrata (15%), C. tropicalis (5%), C. parapsilosis (5%), and C. krusei (5%). Other yeasts represented 4% of all isolates. Of the 1565 isolates tested, 1449 (92.6%) were susceptible (S) to fluconazole, 43 (2.7%) were susceptible dose-dependent (S-DD) and 73 (4.7%) were resistant (R). Almost all (98.2%) of the C. albicans isolates were classified as S or S-DD. Despite its widespread use, fluconazole displayed good activity against the isolates we tested, and the disk diffusion method was confirmed as a reliable approach to the evaluation of in vitro susceptibility of yeasts to this antimycotic agent.

Ciclopiroxolamine: in vitro antifungal activity against clinical yeast isolates

The in vitro susceptibility of 225 clinical isolates of yeasts to ciclopiroxolamine (CPO) was compared with that of clotrimazole, econazole, ketoconazole, miconazole, tioconazole, fluconazole, itraconazole and nystatin using a standardized agar diffusion method (NeoSensitabs). Two hundred and eight strains of yeasts comprising 16 species of Candida and 22 strains belonging to other yeast genera were tested. One strain (0.4%) was resistant, four strains (1.8%) of intermediate susceptibility and 220 strains (97.3%) susceptible to CPO. More strains were susceptible to CPO than to the other antifungals studied. Susceptibility patterns of antifungal agents were not linked to species. The in vitro antifungal susceptibility profile of CPO was better than topical azole derivatives or fluconazole and itraconazole against a wide variety of clinically important yeasts.

Frequency and clinical significance of bloodstream infections caused by C albicans strains with reduced susceptibility to fluconazole

Reduced susceptibility to fluconazole (RSF) is relatively common in non-albicans Candida isolates and in Candida albicans recovered from HIV-infected patients with relapsing Candida stomatitis or esophagitis. However, little clinical data on bloodstream infections caused by C. albicans with RSF is available. We analyzed 116 episodes of C. albicans fungemia detected over an 11-year period. Four patients (3.4%) had a blood isolate of C. albicans with RSF. Fluconazole MICs were 16 (3 SDD strains) and 128 microg/ml (1 resistant strain), respectively. Three of the patients were HIV (+) and the fourth was a liver transplant recipient. All of them had been previously treated with an azole compound. The liver recipient had breakthrough fungemia while being treated with 400 mg of preemptive fluconazole despite having an MIC of 16 microg/ml. Fluconazole clinical failure was documented in two of the remaining three cases. Only five other patients with C. albicans fungemia caused by fluconazole-resistant strains (>or=64 microg/ml) are described in the literature. Candida albicans fungemia produced by strains with RSF is still uncommon. It should be suspected in patients previously treated with azole agents or with breakthrough fungemia. In our experience, fluconazole remains a safe option for the treatment of most C. albicans fungemias, although surveillance seems advisable.

Susceptibility testing of fluconazole by the NCCLS broth macrodilution method, E-test, and disk diffusion for application in the routine laboratory

Antifungal susceptibility testing may be an important aid in the treatment of patients with life-threatening yeast infections. In order to establish the suitability of different susceptibility test methods for fluconazole with yeasts, the Rosco tablet and the E-test were compared with the gold standard NCCLS broth macrodilution method for 106 yeast strains. These included 102 clinical isolates of Candida spp., including Candida glabrata (n = 30), Candida albicans (n = 20), Candida tropicalis (n = 13), Candida parapsilosis (n = 10), Candida krusei (n = 8), plus Cryptococcus neoformans (n = 3), Saccharomyces cerevisiae (n = 2), and 16 strains belonging to other Candida spp. Four American Type Culture Collection strains of Candida were included as quality controls. The NCCLS method was found to be too complex and labor-intensive for routine testing. The E-test is an accurate alternative, but experience in determining MICs and careful attention to procedural details are critically important. The Rosco tablet showed the best agreement with the NCCLS reference method, especially when newly established breakpoints of R < or = 10 mm and S > or = 21 mm were used.

Present status of the detection of antifungal resistance: the perspective from both sides of the ocean

The NCCLS reference methodology for antifungal susceptibility testing is a new milestone of the evolution of medical mycology. The use of this methodology however, is not problem-free. At present, major limitations are a trailing phenomenon with azoles, unreliable detection of resistance to amphotericin B, poor growth of some organisms and unpractical procedures for the clinical laboratory. Herein a overview of NCCLS guidelines for yeasts and filamentous fungi is presented. Likewise, a review of studies conducted trying to overcome the limitations of reference procedures is also included. Several alternative approaches are reviewed as alternative media, inoculum size and incubation time. Modifications of reading procedure and endpoint determination are also evaluated. Agar diffusion methods and other methods for susceptibility testing are cited. Finally, we discuss the data on correlation of the in vitro results with the in vivo activity.

Antifungal susceptibility testing: practical aspects and current challenges

Development of standardized antifungal susceptibility testing methods has been the focus of intensive research for the last 15 years. Reference methods for yeasts (NCCLS M27-A) and molds (M38-P) are now available. The development of these methods provides researchers not only with standardized methods for testing but also with an understanding of the variables that affect interlaboratory reproducibility. With this knowledge, we have now moved into the phase of (i) demonstrating the clinical value (or lack thereof) of standardized methods, (ii) developing modifications to these reference methods that address specific problems, and (iii) developing reliable commercial test kits. Clinically relevant testing is now available for selected fungi and drugs: Candida spp. against fluconazole, itraconazole, flucytosine, and (perhaps) amphotericin B; Cryptococcus neoformans against (perhaps) fluconazole and amphotericin B; and Aspergillus spp. against (perhaps) itraconazole. Expanding the range of useful testing procedures is the current focus of research in this area.

Comparison of Etest and a tablet diffusion test with the NCCLS broth microdilution method for fluconazole and amphotericin B susceptibility testing of Candida isolates

Three methods were compared for the susceptibility testing of yeast isolates to fluconazole and amphotericin B: two fagar diffusion methods (Etest and a tablet diffusion test) and the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution method. Given as MIC(50)s (range), fluconazole endpoints were: for the 24 h broth microdilution test, 0.25 mg/L (0.06-32 mg/L); for the Etest, 0.38 mg/L (0.064-24 mg/L); and for the NCCLS broth microdilution test, 2 mg/L (0.06->or=64 mg/L). With breakpoints of <3 mg/L for susceptible and >16 mg/L for resistant, the Etest and the 24 h microdilution test classified the isolates in agreement with the classification obtained by the NCCLS method. Results obtained by Etest were in closer NCCLS method than those obtained with the tablet test. Amphotericin B endpoints were lower for the 24 h microdilution and Etests than MICs obtained by the NCCLS broth microdilution method. Reproducibility was high for all tests; however, disadvantages of both diffusion tests were microcolonies in the inhibition zone and dependence on stringent standardization of inoculum.

Influence of glucose supplementation and inoculum size on growth kinetics and antifungal susceptibility testing of Candida spp

The influences of inoculum size and glucose supplementation on the growth kinetics of 60 Candida spp. clinical isolates (Candida albicans, Candida tropicalis, Candida parapsilosis, Candida glabrata, Candida krusei, and Candida lusitaniae [10 isolates each]) are assessed. The combined influence of growth and reading method (visual or spectrophotometric) on the determination of the MICs of amphotericin B, flucytosine, fluconazole, itraconazole, ketoconazole, and voriconazole is also analyzed, and the MICs are compared with those determined by the National Committee for Clinical Laboratory Standards standard microdilution method (NCCLS document M27-A). Glucose supplementation and inoculum size had a significant influence on the growth cycles of these yeasts, and a statistically significant denser growth (optical density at 540 nm) was seen for both incubation periods, 24 and 48 h (P < 0.01). A longer exponential phase and shorter lag phase were also observed. The A540 values at 24 h of incubation with medium containing glucose and an inoculum of 10(5) CFU/ml were >0.4 U for all species, with the exception of that for C. parapsilosis (A540 = 0.26 +/- 0.025). The MICs at 24 h determined by testing with 2% glucose and an inoculum of 10(5) CFU/ml showed the strongest agreement (96.83%) with MICs determined by the reference method. MICs were not falsely elevated, and good correlation indexes were obtained. The reproducibility of results with this medium-inoculum combination was high (intraclass correlation coefficient, 0.955). The best agreement and reproducibility of results for spectrophotometric readings were achieved with endpoints of 50% growth inhibition for flucytosine and azoles and 95% for amphotericin B. Supplementation of test media with glucose and an inoculum size of 10(5) CFU/ml yielded a reproducible technique that shows elevated agreement with the reference procedures and a shorter incubation period for obtaining reliable MIC determinations. The spectrophotometric method offers an advantage over the visual method by providing a more objective and automated MIC determination.

Commercial systems for fluconazole susceptibility testing of yeasts: comparison with the broth microdilution method

Fluconazole susceptibility was tested in 100 clinical yeast isolates (65 Candida albicans, 13 C. glabrata, 8 C. tropicalis, 7 C. parapsilosis, 3 Saccharomyces cerevisiae, 1 each of C. krusei, C. lusitaniae, Cryptococcus neoformans, Rhodotorula glutinis) and two control strains (Candida krusei ATCC 6258, C. parapsilosis ATCC 22019) using broth microdilution (reference method), disk diffusion, Etest strips, Sensititre YeastOne, Candifast, Integral System Yeasts. Using M27-A breakpoints, isolates were classified as susceptible (81%), susceptible-dose dependent or Resistant with broth dilution. Rates of concordance with the reference method were good for Sensititre YeastOne, Etest and disc-diffusion (81.2%-94.7%) but very low for the Candifast (3.1%) and Integral System (16.6%), which classified most susceptible isolates as resistant. Lack of standardisation (inoculum, medium composition) and non-objective interpretation schemes may be the cause of their poor performance. Sensititre YeastOne, Etest and disc-diffusion are potentially useful for fluconazole antifungal susceptibility testing of yeasts in clinical laboratories.

Detection of fluconazole-resistant Candida strains by a disc diffusion screening test

A commercial disc diffusion test has been evaluated as a screening method for the detection of Candida species with decreased susceptibility to fluconazole. A total of 1,407 Candida strains of different species were tested, and the results were compared with the MIC results. The recently published National Committee for Clinical Laboratory Standards breakpoint criteria have been used. Isolates were classified as susceptible if the MIC for the isolates was </=8 microg/ml, susceptible-dose dependent (S-DD) if the MIC was 16 to 32 microg/ml, and resistant if the MIC was >/=64 microg/ml. All 77 resistant strains and 121 of 122 S-DD strains had fluconazole zone diameters of </=21 mm, and most of the strains (91%) had zone diameters of </=15 mm. It was not possible to distinguish between resistant and S-DD strains by the disc test. Among a total of 1,208 strains found to be susceptible by the microdilution method, 49 (4. 1%) yielded fluconazole zone sizes of </=21 mm and would have been misclassified as resistant or S-DD strains on the basis of the disc test. For the majority (86%) of these 49 strains the fluconazole MIC was 8 microg/ml. The fluconazole disc test is recommended as a simple and reliable screening test for the detection of Candida strains with decreased susceptibility to fluconazole. Fluconazole MICs should be determined for strains found to be resistant by the disc test. The reason for confirmatory testing is twofold: to determine if isolates are resistant or S-DD, since the disc test does not make this distinction, and to identify fluconazole-susceptible strains that are found to be falsely resistant by the fluconazole disc test.