Evaluation of two commercial methods for the susceptibility testing of Candida species: Vitek 2® and Sensititre YeastOne®

Comparative study of antifungal susceptibility testing methods for clinical Candida albicans isolates

PURPOSE

Candida albicans is the second most common cause of candidemia in Malaysia. The Clinical and Laboratory Standards Institute (CLSI) broth microdilution method is the gold standard for determining its minimum inhibitory concentration (MIC); however, it is laborious and time-consuming. This study was conducted to evaluate the usefulness of alternative methods, namely Sensititre YeastOne (SYO), VITEK 2 system, and E-test for determining the MIC of clinical C. albicans isolates.

MATERIALS AND METHODS

The susceptibilities of 95 C. albicans isolates were compared between SYO, VITEK 2 system, and E-test with CLSI broth microdilution method. The categorical agreement (CA), essential agreement (EA), very major errors (VME), major errors (ME) and minor errors (MiE) were calculated.

RESULTS

Our finding showed the CA varied for SYO from 96.8% to 100%, while the EA ranged from 91.6% to 100%. The SYO method showed 1.1% of VME and ME, and up to 3.2% of MiE. Next, the CA and EA ranges for the VITEK 2 system were 97.8%-100% and 23.2%-100%, respectively. In the VITEK 2 technique, 1.1% of VME were found. For the E-test, the CA varied from 83.2% to 100% while the EA ranged from 64.2% to 98.9%. The E-test method showed 1.1% of VME and up to 16.8% of MiE.

CONCLUSIONS

In conclusion, SYO and VITEK 2 (except flucytosine) could be potential alternatives to the CLSI broth microdilution method in determining the MIC of C. albicans.

Diagnosis and Treatment of Invasive Candidiasis

Candida species, belonging to commensal microbial communities in humans, cause opportunistic infections in individuals with impaired immunity. Pathogens encountered in more than 90% cases of invasive candidiasis include C. albicans, C. glabrata, C. krusei, C. tropicalis, and C. parapsilosis. The most frequently diagnosed invasive infection is candidemia. About 50% of candidemia cases result in deep-seated infection due to hematogenous spread. The sensitivity of blood cultures in autopsy-proven invasive candidiasis ranges from 21% to 71%. Non-cultural methods (beta-D-glucan, T2Candida assays), especially beta-D-glucan in combination with procalcitonin, appear promising in the exclusion of invasive candidiasis with high sensitivity (98%) and negative predictive value (95%). There is currently a clear deficiency in approved sensitive and precise diagnostic techniques. Omics technologies seem promising, though require further development and study. Therapeutic options for invasive candidiasis are generally limited to four classes of systemic antifungals (polyenes, antimetabolite 5-fluorocytosine, azoles, echinocandins) with the two latter being highly effective and well-tolerated and hence the most widely used. Principles and methods of treatment are discussed in this review. The emergence of pan-drug-resistant C. auris strains indicates an insufficient choice of available medications. Further surveillance, alongside the development of diagnostic and therapeutic methods, is essential.

Comparison of Six Antifungal Susceptibilities of 11 Candida Species Using the VITEK2 AST-YS08 Card and Broth Microdilution Method

We used a Vitek 2 AST-YS08 (YS08) system and the broth microdilution method (BMD) adopted by the Clinical and Laboratory Standards Institute (CLSI) to compare the susceptibility of 184 isolates of 11 Candida species to fluconazole, voriconazole, micafungin, caspofungin, amphotericin B, and flucytosine. In Candida albicans, the categorical agreement (CA) was 79.2%, 91.7%, 95.8%, and 95.8% for fluconazole, voriconazole, micafungin, and caspofungin, respectively. About 12.5% and 4.2% of very major errors were detected for fluconazole and voriconazole, respectively. C. glabrata showed excellent essential agreements (EAs) (>90%) for azoles but different MIC distributions for fluconazole and caspofungin. The CA between BMD fluconazole MICs and YS08 voriconazole MICs by the method-specific clinical breakpoint (CBP) was 90% in C. glabrata. Over 80% of C. glabrata and C. krusei isolates identified as micafungin-susceptible were labeled intermediate or resistant to caspofungin in YS08. In C. parapsilosis, 5.3% of very major errors and 10.5% of minor errors were found, whereas 33.3% of minor errors were observed in C. tropicalis for fluconazole. For C. tropicalis, 13 (61.9%) non-wild type (WT) isolates of fluconazole and 7 (33.3%) non-WTs of voriconazole were classified in YS08 as WT. For C. auris, the EAs were 93.3%, 100%, 82.2%, 97.8%, and 97.8% for fluconazole, voriconazole, micafungin, caspofungin, and amphotericin B, respectively. YS08 showed comparable results to the BMD. However, considering the lower YS08 fluconazole MIC results compared with BMD in Candida species and YS08 caspofungin results in C. glabrata and C. krusei, improvements are needed. IMPORTANCE The new Vitek 2 AST-YS08 (YS08) card has been updated to reflect the recently revised Clinical and Laboratory Standards Institute (CLSI) guideline. In this study, antifungal drug susceptibility tests were performed using the YS08 card and compared with the CLSI broth microdilution (BMD) method. In conclusion, YS08 showed similar results to BMD, including with C. auris. However, about 12.5% and 4.2% of major errors were detected for fluconazole and voriconazole, respectively, in C. albicans. More than 80% of C. glabrata and C. krusei isolates identified as susceptible to micafungin were labeled moderate or resistant to caspofungin in YS08. The categorical agreement between BMD fluconazole MICs and YS08 voriconazole MICs was 90% by the method-specific CBP of voriconazole, 80% by the current epidemiological cutoff value (ECV) (0.25 μg/mL) of voriconazole, and 85% by the previous ECV (0.5 μg/mL) of voriconazole. Further improvements in YS08 for the detection of fluconazole and echinocandin resistance are thus needed.

Identification of candida albicans and nonalbicans candida resistant species in tobacco users and oral squamous cell carcinoma patients: Comparison of HiCrome agar and automated VITEK 2 system

Introduction:

Candida is most common fungal pathogen in the immunocompromised and medically ill patients. Higher prevalence of Candida albicans has been reported in tobacco users and oral squamous cell carcinoma (OSCC) patients which may be due to immunosuppression. Recently, emergence of nonalbicans candida (NAC) species resistant to conventional antifungal treatment has been observed that requires accurate identification of organisms at species level for reduction of progression of suspicious oral lesions toward malignancy.

Aims and Objectives:

To detect and compare the prevalence of C. albicans and NAC species smokeless tobacco chewers, histopathologically confirmed oral squamous cell carcinoma patients and the normal individuals. Effectiveness of automated Vitek 2 system in comparison to HiCrome agar color media in the identification of the candida species was also evaluated.

Methodology:

One hundred and fifty patients (90 males, 60 females) aged between 20 and 76 years were divided into three groups: Group I individuals with habit of chewing Gutka, and betel quid/pan masala with or without tobacco, Group II individuals with clinically and histopathologically confirmed oral squamous cell carcinoma and Group III comprised of controls. Salivary samples were cultured on HiCrome agar color media and results were compared with those of Vitek 2 system in the accurate identification of candida species. Data were statistically analyzed and Chi-square test was used to estimate the effectiveness of color and Vitek method in the identification of candida species in all the three groups. P < 0.05 was considered to be statistically significant.

RESULTS:

HiCrome agar color method identified six candida isolates C. albicans, Candida tropicalis, Candida krusei and Candida glabrata isolates in all the three groups, with 0.00 unidentified organisms (P = 0.00001) whereas VITEK 2 system identified five isolates of candida; C. albicans, Candida famat, Candida ciferri, Candida gulleri, C. tropicalis, unidentified organisms were observed in 26% of subjects. Further confirmation by supplemental tests indicated the presence of two or three organisms of different species/or subspecies with low reactivity biopattern. Higher incidence of opportunistic infections was seen in Group II OSCC patients (P = 0.00001).

Conclusion:

The results suggested that there is shift toward NAC species, with higher species diversity in OSCC patients followed by gutka, betel quid/pan masala with or without tobacco users. Conventional agar media culture methods of species identification should be used in conjunction with automated Vitek 2 method for better control of candida-associated oral cancer.

Antibacterial and Antifungal Activity of Propyl-Propane-Thiosulfinate and Propyl-Propane-Thiosulfonate, Two Organosulfur Compounds from Allium cepa: In Vitro Antimicrobial Effect via the Gas Phase

Propyl-propane thiosulfinate (PTS) and propyl-propane thiosulfonate (PTSO) are two volatile compounds derived from Allium cepa with a widely documented antimicrobial activity. The aim of this study was to evaluate their anti-candidiasis activity and the ability of its gaseous phase to inhibit bacterial and yeast growth in vitro. The minimum inhibitory concentration of various antifungal products (including PTS and PTSO) was determined versus 203 clinical isolates of Candida spp. through broth microdilution assay. Additionally, the antimicrobial activity through aerial diffusion of PTS and PTSO was evaluated over the growth of a collection of bacteria and yeasts cultivated in agar plates. All yeasts were susceptible to the antifungals tested, except C. glabrata and C. krusei, that showed azole resistance. PTSO (MIC₅₀ and MIC₉₀ ranged from 4 to 16 mg/L and 8 to 32 mg/L, respectively) was significantly more active against yeasts than PTS (MIC₅₀ and MIC₉₀ ranged from 16 to 64 mg/L and 32 to 64 mg/L). Values were higher than those obtained for antifungal drugs. Gaseous phases of PTS and PTSO generated growth inhibition zones whose diameters were directly related to the substances concentration and inversely related to the microbial inoculum. The quantification of PTS and PTSO levels reached in the growth media through aerial diffusion displayed a concentration gradient from the central zone to the periphery. Only P. aeruginosa ATCC 27853 showed resistance, while yeasts (C. albicans ATCC 200955 and C. krusei ATCC 6258) presented the higher susceptibility to both compounds. These results suggest that PTS and PTSO display antibacterial and anti-candidiasis activity in vitro through aerial diffusion, having potential use in human therapy.

Comparison of the Sensititre YeastOne antifungal method with the CLSI M27-A3 reference method to determine the activity of antifungal agents against clinical isolates of Candidaspp

Background and aim

Infections caused by Candida species are significantly increasing today, and invasive Candida infections are generally associated with high mortality. Early diagnosis and identification of Candida spp. is important for the determination of antifungal agents that will be used for treatment. The aim of the present study was to provide a better regimen for Candida infections in the future.

Materials and methods

TheSensititre YeastOne (SYO) method was compared with The Clinical Laboratory Standards Institute (CLSI) reference broth microdilution (BMD) testing method. Endpoints of minimal inhibitory concentrations (MICs) were determined for both methods.

Results

By using both methods, MIC values of micafungin, caspofungin, voriconazole, and fluconazole were lower than amphotericin B. The values obtained with the SYO method were in high categorical agreement for ecinocandins and amphotericin B. The results of voriconazole and fluconazole were in low categorical agreement. The categorical agreement between the SYO and the BMD results at 24 h was 82.1% for VORI and 98.4% for AMB. Values obtained with SYO method for all antifungal agents were in high essential agreement with the data of the CLSI reference BMD method. The essential agreement between the SYO and the BMD results at 24 h was 94.0% for MFG and 99.0% for AMB.

Conclusions

The SYO method was ready-to use, so it appeared to be easier and more efficient for Candida isolates.

Updating of in vitro antifungal susceptibility tests

Fungal diseases, including those caused by (multi)drug-resistant fungi, still represent a global public health concern. Information on the susceptibility of these microorganisms to antifungal agents must be quickly produced to help clinicians initiate appropriate antifungal therapies. Unfortunately, antifungal susceptibility tests are not as developed or widely implemented as antibacterial tests, being similar in design, accuracy and reproducibility, but also laborious and slow. In this article, we review the methods of in vitro susceptibility testing, both reference (CLSI and EUCAST), commercial and new methods based on proteomics (MALDI-TOF MS) and in the detection of resistance genes by nucleic acid amplification techniques. In addi-tion, we discuss the newly established clinical breakpoints, as well as the epidemiological cut-off points, which constitute a new category that can help in the early identification of isolates that have acquired resistance mechanisms. We also discuss the advantages and limitations of each of the methods studied. Therefore, we can conclude that, although there has been much progress in studies of in vitro susceptibility testing to antifungals, there are still limitations in its application in the daily routine of microbiology labo-ratories, although it seems that the future is promising with the new technologies based on proteomics and nucleic acid amplification. Supplement information: This article is part of a supplement entitled «SEIMC External Quality Control Programme. Year 2016», which is sponsored by Roche, Vircell Microbiologists, Abbott Molecular and Francisco Soria Melguizo, S.A. © 2019 Elsevier España, S.L.U. and Sociedad Española de Enfermedades Infecciosasy Microbiología Clínica. All rights reserved.

The association between fluconazole dose and MIC with mortality and persistence in candidemia

To evaluate the association between fluconazole exposure parameters and clinical outcomes in patients with candidemia. We retrospectively included all adults with candidemia in a single center from January 2009 to December 2017, treated initially with fluconazole for fluconazole-susceptible candidemia. We assessed the association between fluconazole exposure parameters and 30-day mortality or 14-day clinical failure, a composite of mortality at day 14 or persistent candidemia ≥ 72 h, in all patients and in patients with C. glabrata candidemia. During the study period, 158 patients fulfilled the inclusion criteria. Main species were C. albicans 66 (41.8%), C. glabrata 35 (22.2%), and C. parapsilosis 31 (19.6%). Sixty patients (38%) died within 30 days. Sixty-one patients (38.6%) experienced 14-day failure. In 30-day survivors, the median AUC₂₄/MIC was 2279 [398, 5989] versus 1764 [238, 6714] h in non-survivors, p = 0.75. Median fluconazole MIC was 0.75 [0.25, 4] and 1 [0.22, 5.50] mg/L, p = 0.54, respectively. Similar non-significant differences were found for other fluconazole exposure parameters and in the 14-day clinical failure analysis. For C. glabrata, a higher AUC₂₄/MIC was observed among 30-day survivors with a median of 230 [77, 539] compared to 96 [75, 164] h in non-survivors, p = 0.008, in parallel with a trend for lower MIC values (median 7 [1, 2] versus 16 [8, 24] mg/L, p = 0.06, respectively). Currently used fluconazole dosing has no association with clinical outcome in Candida with low MIC values. For Candida species with high MICs, attention to dosing is needed.

Impact of high MIC of fluconazole on outcomes of Candida glabrata bloodstream infection: a retrospective multicenter cohort study

To evaluate the impacts of fluconazole minimum inhibitory concentration (MIC) according to primary antifungal agents on Candida glabrata bloodstream infection (BSI), a multicenter retrospective cohort study was conducted in Korea, concerning the time period from January 2010 to February 2016. A total of 197 adult patients with C. glabrata BSI were included in the study, and neutropenia (P = 0.026), APACHE II score (P = 0.004), and fluconazole resistance (HR 3.960, 95% CI 1.395-11.246, P = 0.010) were associated with 30-day mortality in multivariate analysis. In subgroup analysis, fluconazole MIC = 32 μg/mL in the azole-treated group (HR 6.691, 95% CI 1.569-28.542, P = 0.010) and fluconazole MIC ≥ 64 μg/mL in the non-azole-treated group (HR 3.337, 95% CI 1.183-9.411, P = 0.023) showed the highest hazard ratio (HR) for 30-day mortality. Increased fluconazole MIC was associated with poor outcome both in azole- and non-azole-treated patients with C. glabrata BSI.