Comparison of the MUREX C. albicans, Albicans-Sure, and BactiCard Candida test kits with the germ tube test for presumptive identification of Candida albicans

A Membrane-Targeted Photosensitizer Prevents Drug Resistance and Induces Immune Response in Treating Candidiasis

Candida albicans (C. albicans), a ubiquitous polymorphic fungus in humans, causes different types of candidiasis, including oral candidiasis (OC) and vulvovaginal candidiasis (VVC), which are physically and mentally concerning and financially costly. Thus, developing alternative antifungals that prevent drug resistance and induce immunity to eliminate Candida biofilms is crucial. Herein, a novel membrane-targeted aggregation-induced emission (AIE) photosensitizer (PS), TBTCP-QY, is developed for highly efficient photodynamic therapy (PDT) of candidiasis. TBTCP-QY has a high molar absorption coefficient and an excellent ability to generate 1 O2 and •OH, entering the interior of biofilms due to its high permeability. Furthermore, TBTCP-QY can efficiently inhibit biofilm formation by suppressing the expression of genes related to the adhesion (ALS3, EAP1, and HWP1), invasion (SAP1 and SAP2), and drug resistance (MDR1) of C. albicans, which is also advantageous for eliminating potential fungal resistance to treat clinical infectious diseases. TBTCP-QY-mediated PDT efficiently targets OC and VVC in vivo in a mouse model, induces immune response, relieves inflammation, and accelerates the healing of mucosal defects to combat infections caused by clinically isolated fluconazole-resistant strains. Moreover, TBTCP-QY demonstrates excellent biocompatibility, suggesting its potential applications in the clinical treatment of OC and VVC.

Raman Imaging of Pathogenic Candida auris: Visualization of Structural Characteristics and Machine-Learning Identification

Invasive fungal infections caused by yeasts of the genus Candida carry high morbidity and cause systemic infections with high mortality rate in both immunocompetent and immunosuppressed patients. Resistance rates against antifungal drugs vary among Candida species, the most concerning specie being Candida auris, which exhibits resistance to all major classes of available antifungal drugs. The presently available identification methods for Candida species face a severe trade-off between testing speed and accuracy. Here, we propose and validate a machine-learning approach adapted to Raman spectroscopy as a rapid, precise, and labor-efficient method of clinical microbiology for C. auris identification and drug efficacy assessments. This paper demonstrates that the combination of Raman spectroscopy and machine learning analyses can provide an insightful and flexible mycology diagnostic tool, easily applicable on-site in the clinical environment.

The emergence of non-albicans candidemia and evaluation of HiChrome Candida differential agar and VITEK2 YST® platform for differentiation of Candida bloodstream isolates in teaching hospital Kandy, Sri Lanka

Background

Candidemia is an emerging hospital-acquired bloodstream infection (BSI). It is common among severely ill and immunocompromised patients. Even following appropriate therapy in candidemia, recent studies reveal relative high mortality (40%). The global incidence of candidemia shows an incline. In Sri Lanka, candida speciation often difficult where basic facilities are less available. We have compared the risk factors, epidemiology, demography, and performance of HiChrome Candida differential agar (HiCA) characteristics with the VITEK2 YST platform for differentiation of Candida albicans (CA) and non-albicans candida (NAC) from blood culture isolate.

Methods

This is a laboratory-based cross-sectional study. Positive aerobic BACTEC blood cultures having yeast were identified using HiCA and VITEK2® platform. Epidemiology, risk factors, and clinical outcomes were compared between CA and NAC bloodstream isolates.

Results

Out of 120 positive yeast samples, VITEK2® has identified 110 (92%) as Candida sp. From that CA-34 (31%) and NAC-76 (69%) were isolated. Candidemia following NCA in neonates (p = 0.02), infants (p = 0.04) and adults (p = 0.02) in ICU and immunocompromised patients were significantly higher. Compared to CA, NAC bacteremia period prevalence (0.00041%) and incidence (0.23 per 100,000-person-years) was significantly high (p = 0.03). NAC 48 (63%) isolates were resistance to azoles. Exposure to antifungals (odds ratio (OR); p = 0.03), prolonged intensive care stay > 14 days (OR-3.3; p = 0.04), having a central venous line for > 8 days (OR-4.3; p = 0.03) and on immunosuppressive treatment (OR-2.4; p = 0.04) was significantly poses risk for NAC candidemia. Sen day mortality was significant among non-albicans cases (p = 0.03) while 30-day mortality was significant among albicans cases (p = 0.04). Compared to VITEK2®, the HiCA method was 93% sensitive and 93% specific in detecting CA.

Conclusion

Compared to CA, candidemia following NAC was high. NAC isolates were having a high percentage of fluconazole and voriconazole resistance. VITEK2 YST® platform provides antifungal susceptibility with minimal inhibitory concentration (MIC). Impact, this would highlight the use of rapid candida identification flat form with MIC to direct appropriate antifungals for candidemia. For that implementation of novel diagnostic facilities like the VITEK2 YST platform at a tertiary care facility is demanding.

Fungal diagnostics: review of commercially available methods

Fungi and yeasts are critical causes of acute infection. As such, the detection and identification of these organisms are crucial in the diagnosis of affected patient populations. There is a vast array of commercial tests currently available for diagnostic purposes. These vary from traditional culture and biochemical methods to advanced multiparameter molecular tests. Recent technological advances have driven the development of rapid tests which are complementing and in some cases replacing the more traditional methods of detection. Irrespective of the method used the ultimate goal is timely detection of the infectious agent allowing appropriate treatment and improved outcome for the patient.

Invasive candidiasis in pediatric intensive care units

Candidemia and disseminated candidiasis are major causes of morbidity and mortality in hospitalized patients especially in the intensive care units (ICU). The incidence of invasive candidasis is on a steady rise because of increasing use of multiple antibiotics and invasive procedures carried out in the ICUs. Worldwide there is a shifting trend from C. albicans towards non albicans species, with an associated increase in mortality and antifungal resistance. In the ICU a predisposed host in one who is on broad spectrum antibiotics, parenteral nutrition, and central venous catheters. There are no pathognomonic signs or symptoms. The clinical clues are: unexplained fever or signs of severe sepsis or septic shock while on antibiotics, multiple, non-tender, nodular erythematous cutaneous lesions. The spectrum of infection with candida species range from superficial candidiasis of the skin and mucosa to more serious life threatening infections. Treatment of candidiasis involves removal of the most likely source of infection and drug therapy to speed up the clearance of infection. Amphotericin B remains the initial drug of first choice in hemodynamically unstable critically ill children in the wake of increasing resistance to azoles. Evaluation of newer antifungal agents and precise role of prophylactic therapy in ICU patients is needed.

Yeast identification--past, present, and future methods

The focus of this review is the evolution of biochemical phenotypic yeast identification methods with emphasis on conventional approaches, rapid screening tests, chromogenic agars, comprehensive commercial methods, and the eventual migration to genotypic methods. As systemic yeast infections can be devastating and resistance is common in certain species, accurate identification to the species level is paramount for successful therapy and appropriate patient care.

Comparison of 12 liquid media for germ tube production ofCandida albicansandC. tropicalis

Infections caused by yeast of the genus Candida are the most common fungal infections, being Candida albicans the most common isolated species among them. The rapid identification of this yeast is mostly based on the production of germ tube in human or animal serum. This study describes the use of 12 different liquid media for germ tube production at 2, 2.5, 3 and 4 h. We examined 193 yeasts, including 157 (81.3%) C. albicans and 36 (18.7%) Candida tropicalis for the production of germ tube. The germ tube production of C. albicans was mostly observed in human serum (98%) followed by rabbit serum (89.8%), brain heart infusion broth (84%) and sheep serum (74.5%) at 2 h. An incubation time exceeding 2 h i.e. 2.5 h or later, C. tropicalis strains were observed to produce germ tubes. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for germ tube production of human serum at 2 h were 98%, 100%, 100% and 92.3% respectively. In all tested sera, an incubation period of more than 2 h improves the sensitivity, but decreases the specificity as well as PPV and NPV of germ tube test (GTT). In conclusion, human serum was observed to be the most appropriate medium to be preferred for GTT, with an incubation period of 2 h.

Comparative evaluation of four commercial tests for presumptive identification of Candida albicans

Four commercially available tests (Albicans ID2, Chromalbicans Agar, CHROMagar Candida, and BactiCard Candida) and the germ tube (GT) test for presumptive identification of Candida albicans were evaluated using clinical isolates of C. albicans (n=89) and of non-albicans yeasts (n=107). Sensitivities and specificities of all tests regarding the identification of C. albicans were greater than 92%, except for Chromalbicans Agar plates (88.7% after 48 h) and their specificity was 86%. Overall, the four commercial systems were easy to use and are good systems for the routine identification of C. albicans.

Significance of amplified fragment length polymorphism in identification and epidemiological examination of Candida species colonization in children undergoing allogeneic stem cell transplantation

Candida albicans and non-C. albicans Candida species are increasingly being isolated from patients in high-risk categories, most notably, those who have undergone stem cell transplantation (SCT). Identification of the presence of non-C. albicans Candida species early in the course of the transplant procedure is important, as these species exhibit different sensitivities to the available antifungal treatments and cause mortality at rates that vary from those for C. albicans. Amplified fragment length polymorphism (AFLP) analysis has been shown to be a reliable method of reproducibly identifying medically important Candida species. We investigated the use of serial AFLP analysis of 54 routine surveillance cultures for the identification and epidemiological examination of Candida sp. colonization in five consecutive children undergoing allogeneic SCT. One child became colonized with a C. albicans strain and remained colonized with this strain during the whole admission period. Another child had persistent colonization with a C. albicans strain with striking variations in its AFLP patterns over time, which was considered indicative of microevolution. Candida dubliniensis, Candida lusitaniae, and Saccharomyces cerevisiae were identified in the three remaining patients, with two children being simultaneously and transiently colonized with different species. These findings show that colonization with yeasts during transplantation is a complex and dynamic interaction between the host and the organism(s). In our study three strains from eight separate time points were incorrectly identified as C. albicans by a rapid enzyme test. AFLP analysis of surveillance cultures allowed more accurate and informative epidemiological evaluations of pathogenic yeasts in children during transplantation.

Performance of BacticardTM Candida compared with the germ tube test for the presumptive identification of Candida albicans

Bacticard Candida was compared with the germ tube test for the rapid, presumptive identification of Candida albicans. This test kit detects the enzymatic activities l-proline aminopeptidase and beta-galactosaminidase in yeast colonies grown on culture media. Candida albicans produces both enzymes whereas other yeasts produce only one or neither of the enzymes. We evaluated 536 isolates including eight genera and 33 species of medically important yeasts, including 228 C. albicans and 36 C. dubliniensis. Both tests did not discriminate between C. albicans and C. dubliniensis isolates. The sensitivity and specificity for the Bacticard Candida test were 97.8 and 96.5%, respectively. Bacticard Candida and germ tube tests detected 246 (93.2%), and 256 (97%) C. albicans plus C. dubliniensis isolates. There were eight false-positive results with BactiCard Candida kit and four false-positive results with the germ tube test. Positive and negative predictive values for Bacticard Candida enzymatic test were 95.3 and 98.4%, respectively, while 97.4 and 98.1% for the germ tube test, its specificity being 98.1% and efficiency 97% (97.7% for germ tube). We have observed slightly lower values of sensitivity and specificity than those reported by others using the BactiCard test kit. Bacticard Candida provides a rapid and accurate alternative to the germ tube test for the presumptive identification of C. albicans.

Comparison of Albicans ID2 agar plate with the germ tube for presumptive identification of Candida albicans

Albicans ID2 (bioMérieux, France) is a commercially available chromogenic medium that allows rapid and specific macroscopic identification of Candida albicans and facilitates the differentiation of species in mixed cultures. We compared it with the standard method for the identification of yeast species, the germ tube test (GT). This study involved 423 clinical isolates, including 163 C. albicans and 260 non-albicans yeasts. Sensitivity of Albicans ID2 agar plates regarding the identification of C. albicans were 98.2% after 48 h of incubation and specificity of 96.6%. This method using rapid enzymatic method shows the same similar sensitivity than the GT test The false negative rate (1.8%) for the GT test is consistent with that previously reported. None tests discriminated between C. albicans and C. dubliniensis isolates.

Discrimination between Candida albicans and other pathogenic species of the genus Candida by their differential sensitivities to toxins of a panel of killer yeasts

The differential sensitivities to toxins produced by a short panel of four killer yeasts allowed discrimination between 91 strains of the yeast Candida albicans and 223 non-C. albicans Candida strains. One hundred percent of C. albicans isolates exhibited negative results to the toxin panel, while 100% of non-C. albicans cultures gave well-defined and reproducible positive results to at least one of the four killer toxins. Among C. albicans strains only 96 and 87% gave germ tube (GT)- and chlamydospore-positive results, respectively. In addition a few GT-false-positive strains were detected among non-C. albicans isolates. Susceptibility to the toxin panel is apparently expressed more consistently than either GT or chlamydospore production and may constitute a promising basis for a new simple and easy-to-use procedure for routine discrimination between the species C. albicans and other species of the genus Candida.

Yeast identification in the clinical microbiology laboratory: phenotypical methods

Emerging yeast pathogens are favoured by increasing numbers of immunocompromised patients and by certain current medical practices. These yeasts differ in their antifungal drug susceptibilities, and rapid species identification is imperative. A large variety of methods have been developed with the aim of facilitating rapid, accurate yeast identification. Significant recent commercial introductions have included species-specific direct enzymatic colour tests, differential chromogenic isolation plates, direct immunological tests, and enhanced manual and automated biochemical and enzymatic panels. Chromogenic isolation media demonstrate better detection rates of yeasts in mixed cultures than traditional media, and allow the direct identification of Candida albicans by means of colony colour. Comparative evaluation of rapid methods for C. albicans identification, including the germ tube test, shows that chromogenic media may be economically advantageous. Accurate tests for single species include the Bichrolatex Albicans and Krusei Color tests, both immunologically based, as well as the Remel Rapid Trehalose Assimilation Broth for C. glabrata. Among broad-spectrum tests, the RapID Yeast Plus system gives same-day identification of clinical yeasts, but performance depends on inoculum density and geographic isolate source. The API 20 C AUX system is considered a reference method, but newer systems such as Auxacolor and Fungichrom are as accurate and are more convenient. Among automated systems, the ID 32 C strip, the Vitek Yeast Biochemical Card and the Vitek 2 ID-YST system correctly identify >93% of common yeasts, but the ID-YST is the most accurate with uncommon yeasts, including C. dubliniensis. Spectroscopic methods such as Fourier transformed-infrared spectroscopy offer potential advantages for the future. Overall, the advantages of rapid yeast identification methods include relative simplicity and low cost. For all rapid methods, meticulous, standardized multicenter comparisons are needed before tests are fully accepted.

Comparison of three commercial systems for the identification of germ-tube negative yeast species isolated from clinical specimens

Three commercial systems were evaluated for their ability to identify 171 germ-tube negative yeasts isolated from clinical specimens. The Yeast Biochemical Card and Analytical Profile Index 20 AUX identified 97% of 171 strains tested. The Biolog system had poor clinical utility: only 48% of strains were identified. For Yeast Biochemical Card and Analytical Profile Index 20 AUX, 9% and 6%, respectively, required repeat testing and both systems required supplemental tests for 28% of the strains. These observations indicate that considerable expertise and a battery of reagents in addition to the basic systems are required for accurate identification of germ-tube negative yeasts.

Comparison of the rapid yeast plus panel with the API20C yeast system for identification of clinically significant isolates of Candida species

The RapID Yeast Plus system (Innovative Diagnostic Systems, Norcross, Ga.) is a qualitative micromethod employing conventional tests and single-substrate chromogenic tests and having a 4-h incubation period. This system was compared with the API20C (bioMerieux Vitek, Hazelwood, Mo.) system, a 24- to 72-h carbohydrate assimilation method. One hundred thirty-three clinical yeast isolates, including 57 of Candida albicans, 26 of Candida tropicalis, 23 of Candida glabrata, and 27 of other yeasts, were tested by both methods. When discrepancies occurred, isolates were further tested by the Automated Yeast Biochemical Card (bioMerieux Vitek). Germ tube production and microscopic morphology were used as needed to definitively identify yeast isolates. The RapID Yeast Plus system correctly identified 125 yeast isolates, with an overall accuracy of 94% (125 of 133). Excellent correlation was found in the recognition of the three yeasts most commonly isolated from human sources. The test was 99% (105 of 106 isolates) accurate with C. albicans, C. tropicalis, and C. glabrata. The RapID Yeast Plus system compares favorably with the API20C system and provides a simple, accurate alternative to conventional assimilation methods for the rapid identification of the most commonly encountered isolates of Candida species.