Investigation of the susceptibility of Candida auris and Candida albicans to chemical disinfectants using European Standards EN 13624 and EN 16615

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Summary

Background

Since the first appearance of Candida auris in 2009, this yeast has become a relevant pathogen in the clinical field. C. auris has been detected on various surfaces in health facilities, and is therefore a target for appropriate disinfection procedures. Preventive measures have to be implemented based on disinfectants with proven efficacy against C. auris.

Aim

The chemical tolerance of C. auris was compared with the surrogate test organism Candida albicans as established in the European standards (EN). In this way, conclusions will be drawn as to whether the disinfectants tested according to EN 13624 and EN 16615 are at least equally effective against C. auris.

Methods

The chemical susceptibility of C. auris and C. albicans was investigated using standardized EN test protocols. EN 13624 and EN 16615 were used in this study to examine two commercially available surface disinfectants based on alcohol and quaternary ammonium compounds (QACs), respectively. In addition, the survival rates of the two yeast species were studied on a defined test surface simulating practical conditions.

Findings

In comparison with C. albicans, C. auris was found to be significantly more susceptible to the alcohol- and QAC-based disinfectants used in this study. C. albicans was found to be more tolerant to drying on the test surface in EN 16615, yielding higher recovery rates.

Conclusion

C. albicans is a suitable surrogate test organism when targeting yeasticidal efficacy, which, based on EN 13624 and EN 16615, includes efficacy against the human pathogen C. auris.

Introduction

Just a few years ago, Candida auris did not feature in the debate about disinfection. This yeast was first detected in 2009 in a patient's external auditory canal in Japan [1], although further analysis of Candida strains suggests a previous appearance of C. auris in 1996 in South Korea [2]. Since then, more and more infections with this pathogen have been diagnosed all over the world [3,4]. The exact number of diseases actually caused by C. auris is unknown, as identification with standard biochemical methods is often impossible or can lead to incorrect results [5]. This is due to the close phylogenetic relationships with other Candida spp., such as Candida haemulonii [1].

The pathogenicity of C. auris can be equated with that of Candida albicans, which is the most pathogenic Candida spp. [6]. C. auris infection can lead to diseases of the blood circulation or wound infections [7]. Worst affected are immunocompromised patients [8]. The two largest C. auris outbreaks took place in 2015–2016 in England and 2016–2017 in Spain. More than 50 people were infected [9]. Furthermore, emergence of fluconazole-resistant and even pan-resistant C. auris strains with established resistance to all three commonly used antifungal drugs (i.e. echinocandins, amphotericin B and fluconazole) is a matter of concern [5,10,11].

The exact route of transmission of C. auris remains unknown. Contamination of surrounding areas in healthcare facilities, such as chairs or window sills, has been detected [12], and the yeast has been recovered from plastic and steel surfaces [13]. As such, contaminated surfaces are considered to be a potential cause of the increasing occurrence of C. auris infection [14]. In view of this incidence and behaviour, effective disinfection of surfaces against this pathogen is desirable [15].

In Europe, chemical disinfectants used for surface disinfection have to be registered under the Biocidal Product Regulation [16] and/or evaluated in a conformity assessment based on the European Medical Devices Regulation to ensure safety and performance as claimed on a legal basis [17]. In order to achieve reliable usage recommendations for disinfectants, efficacy claims must be based on the methodological framework EN 14885 developed by the European Committee for Standardization (CEN) [18]. Based on the philosophy of CEN Technical Committee 216 (CEN/TC 216), a sequential test model is used to evaluate the microbicidal efficacy of disinfectants. Thus, for usage recommendations of disinfectants, it is necessary to consider data from quantitative suspension tests with organic soiling (phase 2, step 1 tests) as well as data derived from quantitative carrier tests simulating more practical conditions such as drying of the inoculum (phase 2, step 2 tests) [18]. To claim antimicrobial efficacy of disinfectants more specifically, a defined set of surrogate organisms which allow claims to be made for bactericidal, yeasticidal, fungicidal and virucidal efficacy, etc. is used [18]. C. albicans has been defined as the relevant surrogate test organism for claiming yeasticidal efficacy. Thus, disinfectants claiming yeasticidal efficacy based on the CEN methods are also expected to be effective against C. auris when applying the usage recommendations made for yeasticidal efficacy.

This study aimed to investigate whether the susceptibility of C. auris to disinfectants is equivalent to that of C. albicans, and to help hygienists choose effective preventive measures against C. auris based on CEN efficacy claims. Two commercially available surface disinfectants based on alcohol or quaternary ammonium compounds (QACs), respectively, were used for this evaluation using the EN 13624 and EN 16615 test protocols [19,20].

Section snippets

Test organisms and growth conditions

C. auris (DSM-21092) and C. albicans (DSM-1386) strains from the German Collection of Microorganisms and Cell Cultures were used for the experiments. The cultivation medium for both micro-organisms was malt extract agar as described in EN 13624 and EN 16615 [19,20], with an incubation of 42–48 h at 30°C ± 1°C.

European test method EN 13624

Quantitative suspension tests were performed as described in EN 13624 [19]. Yeasticidal efficacy was studied using two commercially available disinfectants. A ready-to-use alcohol-based

Quantitative suspension tests EN 13624

EN 13624:2013 requires reduction of at least four decimal logarithms (log10) in order for a surface disinfectant to be claimed as yeasticidal. Using C. auris as a test organism, the QAC-based disinfectant fulfilled this requirement with a contact time of 1 min and a concentration of 0.25%. Furthermore, using a contact time of 2 min for C. auris, a 4 log10 reduction was obtained at the lowest tested concentration of the QAC-based disinfectant, which was 0.125%. In contrast, using C. albicans as

Discussion

Cadnum et al. investigated the chemical sensitivity of C. auris, C. albicans and Candida glabrata to conventional disinfectants in a test series according to ASTM E2197-11 which is similar to EN 13697 [22,23]. Using disinfectants based on actives such as sodium hypochlorite, peracetic acid, hydrogen peroxide, ethanol or QACs, they found no evidence that C. auris has a differing susceptibility to disinfectants compared with C. albicans. However, in their study, only quantitative carrier tests

Conflict of interest statement

CKT, UI, LP and KS are employees of Schülke & Mayr GmbH, Norderstedt, Germany.

Funding source

This study was funded by Schülke & Mayr GmbH, Norderstedt, Germany.

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