Research and analysis

Development of experimental approaches for determining concentrations of antifungals that select for resistance: summary

Published 24 October 2024

Applies to England

1. Chief Scientist’s Group report summary

This project looked at methods for the determination of the lowest concentration of antifungals that can lead to a selective advantage for resistant organisms.

When natural microbial communities are exposed to antimicrobial substances any strain that can resist the harmful effects can come to dominate the population by simply growing and reproducing faster than its neighbours. Hence, exposure to antimicrobials in the environment can result in selection for resistance in the microbial community. The concentration of a substance at which selection for resistance may occur has been studied in antibiotics, but there is limited work on antifungals.

1.1 Background

Antifungals are used widely including as medicines, personal care products and as pesticides in agriculture. There are then numerous pathways by which antifungals can reach the environment and subsequently act on the fungi that are naturally present in soils and waters potentially driving the development of antifungal resistance. The resulting resistant fungi may then subsequently infect people, animals or crops. An understanding of the concentrations of antifungals that can influence development of resistance is therefore important. To date, methods have been developed to estimate the concentrations that may select for antibiotic resistance in bacteria, but these have yet to be applied to antifungals and fungi.

1.2 Approach

The project looked at how to develop laboratory methods to determine the concentrations of antifungals that would drive selection for resistance in fungal populations. This built on previous research, which outlined potential modification of methods developed to study bacteria. The project focused on fungi (yeast) from the genus Candida, some of which are human pathogens and can be transmitted from the environment. The approach involved the development of a competition assay where known resistant and sensitive strains can be tested against each other to compare their relative fitness.

1.3 Findings and outlook

Optimal growth media, suitable fungal strains, and informed concentration ranges for competition assays were identified. The project was able to conduct a fully replicated competition assay, meaning that the concentrations that can drive development of resistance may now be determined for a range of antifungal substances.

In addition, the project found evidence for resistance to agricultural antifungals in yeast strains that were isolated from clinical infections. Though not explored further here, this suggests that resistance in some fungal infections in people may have arisen due to the use of antifungals in agriculture. Further research in this area is warranted to understand the wider sources of resistant infections in humans.

1.4 Publication details

This summary relates to information from project SC220003/R, reported in detail in the following output:
Report: SC220003/R

• Title: Development of experimental approaches for determining concentrations of antifungals that select for resistance
• Project manager: Dr Wiebke Schmidt, Chief Scientist’s Group
• Research contractor: Aimee K. Murray, University of Exeter

This work was carried out as part of the Environment Agency Chief Scientist’s Group research into AMR in the environment and has been funded by the PATH-SAFE programme which has been funded by HM Treasury through the Shared Outcomes Fund.

Enquiries: research@environment-agency.gov.uk.

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