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Comparison of Vitek 2C antifungal susceptibility testing with broth microdilution testing for Candida species

Sukanya Sudhaharan , Naga Appala Raju Sundarapu, Umabala Pamidimukkala ,
Volume 18, Issue 5 (9-2024)

Abstract

Background: The reference method for antifungal susceptibility testing is broth microdilution according to Clinical and Laboratory Standard Institute (CLSI) guidelines. However, the fully automated system, Vitek 2C system may reduce the workload and observer bias associated with manual broth microdilution. This study aimed to compare the results of YS08 card with the results of the broth microdilution (BMD) method.
Methods: A total of 50 clinical Candida isolates were included in the study. The susceptibility testing was done by Vitek 2C using the YS08 card. Broth microdilution was done according to CLSI guidelines M27M44S-Ed3.
Results: For C. albicans, the categorical agreement was 85.8%, 71.5%, 85.8%, and 100% for fluconazole, voriconazole, caspofungin, and micafungin, respectively. The minor errors (MiE) of 14.2% for fluconazole and caspofungin, 28.5% for voriconazole, were detected in C. albicans. In C. glabrata, the categorical agreement (CA) was 100% for micafungin, voriconazole, but 63.7% for caspofungin. An MiE of 36.3% was detected for caspofungin. C. parapsilosis showed a 100% CA for fluconazole, caspofungin, and micafungin, and 85.8% for voriconazole. There were 14.2% of MiEs for voriconazole. In C. tropicalis, 100 % CA was observed for fluconazole, micafungin, and caspofungin, and 88.9% for voriconazole. Moreover, 11.1% (1/9) of MiEs was observed for voriconazole. In C. auris, there was a 100% CA for caspofungin and micafungin, 77.8% for fluconazole, and 66.7% for amphotericin B. There was a major error of 22.2% for fluconazole and 33.3% for amphotericin B.
Conclusion: The majority of Vitek 2C showed comparable results with the broth microdilution (BMD) method. Only minor errors (MiEs) were observed in the tested Candida species.

Fosfomycin susceptibility of carbapenem-resistant Enterobacterales and methicillin-resistant Staphylococcus aureus bloodstream isolates in a tertiary care hospital, South India

Apurba Sankar Sastry , Shuruthi Kirubakaran , Sarumathi Dhandapani , Ketan Priyadarshi ,
Volume 19, Issue 5 (9-2025)

Abstract

Background: The emergence of multidrug-resistant organisms has limited the choice of therapeutic options to treat infections. The lack of development of new antimicrobials paved the way for considering the reassessment of older antibiotics like fosfomycin. In this context, we assessed the in-vitro effect of fosfomycin against carbapenem-resistant Enterobacterales and methicillin-resistant Staphylococcus aureus (MRSA) bloodstream isolates by agar dilution, disk diffusion, and screen agar.
Methods: In this study, 141 consecutive blood isolates resistant to carbapenem and 62 MRSA blood culture isolates were collected over a period of 8 months. The methods used were fosfomycin agar dilution (0.25 µg/ml to 512 µg/ml), Kirby-Bauer disk diffusion (150 µg of fosfomycin + 50 µg of glucose-6-phosphate), and fosfomycin screen agar (32 µg/ml, 48 µg/ml, and 64 µg/ml). All three methods were interpreted using the European Committee on Antimicrobial Susceptibility Testing guidelines. The agreement between the new method and the reference method was calculated.
Results: Among the tested isolates, 100% of MRSA, followed by Escherichia coli (E. coli) (86.4%), Klebsiella pneumonia (K. pneumonia) (65.2%), and E. cloacae (50%) were susceptible to fosfomycin. The MIC50 and MIC90 of fosfomycin were 0.5 µg/ml and 2 µg/ml for MRSA, 16 µg/ml and 32 µg/ml for K. pneumoniae, 4 µg/ml and 16 µg/ml for E. coli, and 8 µg/ml and 32 µg/ml for E. cloacae, respectively.
Conclusion: Fosfomycin demonstrated a good in-vitro effect on most of the carbapenem-resistant Enterobacterales and MRSA isolates tested.

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