Antifungal Susceptibility Testing: A Primer for Clinicians

Fungal Species ◽

Clinical Laboratories ◽

Invasive Infections ◽

Clinical Breakpoints

Abstract Clinicians treating patients with fungal infections may turn to susceptibility testing to obtain information regarding the activity of different antifungals against a specific fungus that has been cultured. These results may then be used to make decisions regarding a patient’s therapy. However, for many fungal species that are capable of causing invasive infections, clinical breakpoints have not been established. Thus, interpretations of susceptible or resistant cannot be provided by clinical laboratories, and this is especially true for many molds capable of causing severe mycoses. The purpose of this review is to provide an overview of susceptibility testing for clinicians, including the methods used to perform these assays, their limitations, how clinical breakpoints are established, and how the results may be put into context in the absence of interpretive criteria. Examples of when susceptibility testing is not warranted are also provided.

Antifungal susceptibility testing of Aspergillus niger on silicon microwells by intensity-based reflectometric interference spectroscopy

10.1101/804385 ◽

2019 ◽

Author(s):

Christopher Heuer ◽

Heidi Leonard ◽

Nadav Nitzan ◽

Ariella Lavy-Alperovitch ◽

Naama Massad-Ivanir ◽

...

Keyword(s):

Aspergillus Niger ◽

Susceptibility Testing ◽

Fungal Infections ◽

Fungal Growth ◽

Reflectometric Interference Spectroscopy

Label Free ◽

Broth Microdilution ◽

Silicon Phase ◽

AbstractThe increasing number of invasive fungal infections among immunocompromised patients and the emergence of antifungal resistant pathogens has resulted in the need for rapid and reliable antifungal susceptibility testing (AFST). Accelerating antifungal susceptibility testing allows for advanced treatment decisions and the reduction in future instances of antifungal resistance. In this work, we demonstrate the application of a silicon phase grating as sensor for the detection of growth of Aspergillus niger (A. niger) by intensity-based reflectometric interference spectroscopy and its use as an antifungal susceptibility test. The silicon gratings provide a solid-liquid interface to capture micron-sized Aspergillus conidia within microwell arrays. Fungal growth is optically tracked and detected by the reduction in the intensity of reflected light from the silicon grating. The growth of A. niger in the presence of various concentrations of the antifungal agents voriconazole and amphotericin B is investigated by intensity-based reflectometric interference spectroscopy and used for the determination of the minimal inhibitory concentrations (MIC), which are compared to standard broth microdilution testing. This assay allows for expedited detection of fungal growth and provides a label-free alternative to standard antifungal susceptibility testing methods, such as broth microdilution and agar diffusion methods.

SUSCEPTIBILITY TEST FOR FUNGI: CLINICAL AND LABORATORIAL CORRELATIONS IN MEDICAL MYCOLOGY

Revista do Instituto de Medicina Tropical de São Paulo ◽

10.1590/s0036-46652015000700011 ◽

2015 ◽

Vol 57 (suppl 19) ◽

pp. 57-64 ◽

Cited By ~ 57

Author(s):

Ana ALASTRUEY-IZQUIERDO ◽

Marcia S.C. MELHEM ◽

Lucas X. BONFIETTI ◽

Juan L. RODRIGUEZ-TUDELA

Keyword(s):

Susceptibility Testing ◽

Fungal Infections ◽

Fungal Species ◽

Medical Mycology ◽

Candida Spp ◽

Disease Epidemiology ◽

Resistant Strains ◽

European Standards

SUMMARYDuring recent decades, antifungal susceptibility testing has become standardized and nowadays has the same role of the antibacterial susceptibility testing in microbiology laboratories. American and European standards have been developed, as well as equivalent commercial systems which are more appropriate for clinical laboratories. The detection of resistant strains by means of these systems has allowed the study and understanding of the molecular basis and the mechanisms of resistance of fungal species to antifungal agents. In addition, many studies on the correlation of in vitro results with the outcome of patients have been performed, reaching the conclusion that infections caused by resistant strains have worse outcome than those caused by susceptible fungal isolates. These studies have allowed the development of interpretative breakpoints for Candida spp. and Aspergillus spp., the most frequent agents of fungal infections in the world. In summary, antifungal susceptibility tests have become essential tools to guide the treatment of fungal diseases, to know the local and global disease epidemiology, and to identify resistance to antifungals.

Antifungal susceptibility testing in Australasian clinical laboratories: we must improve our performance

Pathology ◽

10.1016/j.pathol.2018.01.001 ◽

2018 ◽

Vol 50 (3) ◽

pp. 257-260 ◽

Cited By ~ 2

Author(s):

Sarah E. Kidd ◽

Catriona L. Halliday ◽

Arthur J. Morris ◽

Sharon C-A. Chen

Keyword(s):

Susceptibility Testing ◽

Clinical Laboratories

Antifungal susceptibility testing of candida – Methods and issues in current practice

International Journal of Research in Pharmaceutical Sciences ◽

10.26452/ijrps.v10i3.1372 ◽

2019 ◽

Vol 10 (3) ◽

pp. 1778-1784

Author(s):

Lakshmi Krishnasamy ◽

Priya Santharam ◽

Chitralekha Saikumar

Keyword(s):

Current Practice ◽

Antifungal Agents ◽

Susceptibility Testing ◽

Fungal Infections ◽

Antifungal Drugs ◽

Testing Methods ◽

Antifungal Drug Resistance ◽

Resistant Strains

Despite the availability of many antifungal drugs in clinical practice, the occurrence of antifungal drug resistance is on the rise. Since the antifungal susceptibility testing (AFST) is not done routinely in many of the microbiology laboratories, it is very difficult to determine which antifungal agent is very effective for a particular infection. There is a real need for precise, reproducible and extrapolative antifungal susceptibility testing methods to aid the therapeutic management. The practice of empirical treatment for fungal infections further promotes the emergence of resistant strains. The AFST practice would essentially help the clinicians in appropriate decision making. Although conventional AFST methods are somewhat cumbersome, many novel AFST methods are currently available in many laboratory settings which would provide a quicker result many times. In essence, the application of AFST along with identification of the fungus up to species level would definitely be very helpful in selecting the primary antifungal agents for treatment especially in difficult to manage and invasive fungal infections. This review will throw light on the various AFST methods available and their issues in the current practice.

Candida species distribution and antifungal susceptibility testing according to European Committee on Antimicrobial Susceptibility Testing and new vs. old Clinical and Laboratory Standards Institute clinical breakpoints: a 6-year prospective candidaemia survey from the fungal infection network of Switzerland

Clinical Microbiology and Infection ◽

10.1111/1469-0691.12440 ◽

2014 ◽

Vol 20 (7) ◽

pp. 698-705 ◽

Cited By ~ 67

Author(s):

C. Orasch ◽

O. Marchetti ◽

J. Garbino ◽

J. Schrenzel ◽

S. Zimmerli ◽

...

Keyword(s):

Fungal Infection ◽

Species Distribution ◽

Antimicrobial Susceptibility ◽

Candida Species ◽

Susceptibility Testing ◽

Antimicrobial Susceptibility Testing ◽

European Committee ◽

Clinical Breakpoints

Updated EUCAST Clinical Breakpoints against Aspergillus, Implications for the Clinical Microbiology Laboratory

Journal of Fungi ◽

10.3390/jof6040343 ◽

2020 ◽

Vol 6 (4) ◽

pp. 343

Author(s):

Jesús Guinea

Keyword(s):

Amphotericin B ◽

Susceptibility Testing ◽

Common Species ◽

Clinical Microbiology Laboratory ◽

Closely Related Species ◽

Exposure Category ◽

Clinical Breakpoints ◽

Definition Of

Azole resistance poses a problem for the management of patients with invasive aspergillosis. Former species are in fact groups of closely related species (or complexes); cryptic species frequently show high antifungal resistance. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) Definitive Document (E.Def) 9.3.2 includes guidelines for antifungal susceptibility testing on Aspergillus spp. and clinical breakpoints for amphotericin B, itraconazole, voriconazole, posaconazole, and isavuconazole against A. flavus, A. fumigatus, A. nidulans, A. niger, and A. terreus. New clinical breakpoints were released in February 2020 and one of the most relevant modifications was the definition of the new “susceptible, increased exposure” (formerly “intermediate”) category. Another relevant change was the adoption of the concept of area of technical uncertainty (ATU) that refers to problematic areas which involve uncertainty of susceptibility categorisation (e.g., when minimum inhibitory concentrations (MICs) for susceptible and resistant organisms overlap). To accommodate both the new “susceptible, increased exposure” category and the concept of ATU, MICs of azoles and amphotericin B that fall in the former “intermediate” category have been automatically categorized as either R (amphotericin B) or ATU (triazoles). Finally, EUCAST-AFST (Antifungal Susceptibility Testing) decided to adopt new breakpoints for less common species provided that the epidemiological cut-off value (ECOFF) is below or comparable to the breakpoint for the type species (A. fumigatus).

Comparison of the Sensititre YeastOne colorimetric antifungal panel with CLSI microdilution for antifungal susceptibility testing of the echinocandins against Candida spp., using new clinical breakpoints and epidemiological cutoff values

Diagnostic Microbiology and Infectious Disease ◽

10.1016/j.diagmicrobio.2012.05.008 ◽

2012 ◽

Vol 73 (4) ◽

pp. 365-368 ◽

Cited By ~ 40

Author(s):

M.A. Pfaller ◽

V. Chaturvedi ◽

D.J. Diekema ◽

M.A. Ghannoum ◽

N.M. Holliday ◽

...

Keyword(s):

Susceptibility Testing ◽

Candida Spp ◽

Cutoff Values ◽

Clinical Breakpoints

Can We Improve Antifungal Susceptibility Testing?

Frontiers in Cellular and Infection Microbiology ◽

10.3389/fcimb.2021.720609 ◽

2021 ◽

Vol 11 ◽

Author(s):

Charlotte Durand ◽

Danièle Maubon ◽

Muriel Cornet ◽

Yan Wang ◽

Delphine Aldebert ◽

...

Keyword(s):

Growth Inhibition ◽

Susceptibility Testing ◽

Fungal Infections ◽

Imaging Techniques ◽

Low Cost ◽

Turnaround Time ◽

Antifungal Stewardship ◽

Minimal Inhibitory Concentrations

Systemic antifungal agents are increasingly used for prevention or treatment of invasive fungal infections, whose prognosis remains poor. At the same time, emergence of resistant or even multi-resistant strains is of concern as the antifungal arsenal is limited. Antifungal susceptibility testing (AFST) is therefore of key importance for patient management and antifungal stewardship. Current AFST methods, including reference and commercial types, are based on growth inhibition in the presence of an antifungal, in liquid or solid media. They usually enable Minimal Inhibitory Concentrations (MIC) to be determined with direct clinical application. However, they are limited by a high turnaround time (TAT). Several innovative methods are currently under development to improve AFST. Techniques based on MALDI-TOF are promising with short TAT, but still need extensive clinical validation. Flow cytometry and computed imaging techniques detecting cellular responses to antifungal stress other than growth inhibition are also of interest. Finally, molecular detection of mutations associated with antifungal resistance is an intriguing alternative to standard AFST, already used in routine microbiology labs for detection of azole resistance in Aspergillus and even directly from samples. It is still restricted to known mutations. The development of Next Generation Sequencing (NGS) and whole-genome approaches may overcome this limitation in the near future. While promising approaches are under development, they are not perfect and the ideal AFST technique (user-friendly, reproducible, low-cost, fast and accurate) still needs to be set up routinely in clinical laboratories.

Antifungal susceptibility testing and resistance

10.1093/med/9780198755388.003.0047 ◽

2017 ◽

Author(s):

Elizabeth M. Johnson

Keyword(s):

Antifungal Agents ◽

Susceptibility Testing ◽

Clinical Laboratory ◽

Invasive Disease ◽

Fungal Species ◽

Limiting Factors ◽

Antifungal Drug Resistance

The availability of choice of systemically active antifungal agents and the proliferation in the number of fungal species implicated in invasive disease have meant that clinicians are increasingly looking for guidance from clinical laboratory results to help select the most appropriate agent. There are now well-established and predictable patterns of innate in vitro resistance to one or more antifungal agents associated with many yeast and mould species. This chapter provides definitions for the most frequently used terminology and outlines some of the issues surrounding antifungal susceptibility testing with yeast and mould isolates. Reference methods published by the Clinical Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) are discussed. Both innate and emergent antifungal drug resistance are increasingly recognized as limiting factors in the selection of antifungal agents, and the epidemiology and mechanisms of resistance are described for each of the major classes of antifungal agent.