In Vitro Antifungal Activity of Commonly Used Antiseptics and Disinfectants Against Candida auris Isolates

Abstract

Objective

Candida auris (C. auris) has emerged as a multidrug-resistant nosocomial pathogen associated with outbreaks in healthcare settings and high mortality rates. Its ability to persist in the hospital environment highlights the importance of effective disinfection strategies. This study aimed to evaluate the in vitro susceptibility of clinical C. auris isolates to commonly used antiseptics and disinfectants under conditions reflecting routine clinical practice.

Methods

Ten clinical C. auris isolates, along with reference strains of C. krusei (ATCC 6258) and C. parapsilosis (ATCC 22019), were tested. Sodium hypochlorite (5%, 1%, 0.5%), hydrogen peroxide (6%, 3%), povidone-iodine (10%, 5%, 2.5%), a chlorhexidine/n-propanol-containing liquid soap, and an ethanol/isopropyl alcohol-based hand disinfectant were evaluated by a qualitative suspension test at contact times of 1, 2, 5, 10, and 30 minutes. Growth inhibition was assessed after incubation.

Results

Povidone-iodine at all concentrations, chlorhexidine/n-propanol-containing liquid soap, alcohol-based hand disinfectant, and sodium hypochlorite at 5% and 1% achieved complete growth inhibition of all isolates within the first minute. In contrast, 0.5% sodium hypochlorite and hydrogen peroxide showed reduced efficacy at early contact times. Growth was observed in some C. auris isolates after 1 minute of exposure to 6% hydrogen peroxide, and in a larger proportion of isolates after 1-2 minutes of exposure to 3% hydrogen peroxide. Similar variability was observed in reference strains, particularly with hydrogen peroxide.

Conclusions

Commonly used antiseptics and disinfectants are effective against C. auris when applied at appropriate concentrations and contact times. However, reduced efficacy at lower concentrations and with shorter exposure times underscores the importance of proper disinfectant use in preventing environmental persistence and transmission in healthcare settings.

INTRODUCTION

Candida auris (C. auris) has emerged over the past decade as a major global health threat, particularly in healthcare settings. Since its first description in 2009, C. auris has been reported worldwide and is frequently associated with hospital outbreaks and high mortality rates, especially among critically ill patients^{1, 2}. Unlike most other C. species, C. auris demonstrates a remarkable ability to persist in the hospital environment and to colonize patients for prolonged periods, facilitating transmission within healthcare facilities^{2, 3}.

A key feature contributing to the clinical importance of C. auris is its multidrug-resistant profile. Resistance to azoles is common, and reduced susceptibility to amphotericin B and echinocandins has also been reported, significantly limiting available therapeutic options^{4, 5}. In addition to antifungal resistance, C. auris can survive on various surfaces for extended periods and exhibits tolerance to environmental stress conditions, further complicating infection control efforts³.

Environmental cleaning and disinfection are therefore critical components of strategies to prevent the spread of C. auris. However, accumulating evidence suggests that the efficacy of commonly used disinfectants may vary considerably depending on the agent, concentration, formulation, and contact time^{6, 7, 8}. Some studies have demonstrated that while chlorine-based disinfectants and iodine-containing agents are generally effective, other compounds such as certain quaternary ammonium-based products or improperly used agents may show reduced activity against C. auris^{6, 7}.

Moreover, many previous studies have evaluated disinfectant efficacy under standardized laboratory conditions using optimal concentrations and exposure times, which may not fully reflect routine clinical practice^{7, 8}. Data obtained under routine clinical conditions—where dilution errors, shorter contact times, and varying organic loads may occur—remain limited. Additionally, variability among clinical isolates may further influence susceptibility patterns⁸.

In this context, the present study aimed to evaluate the in vitro susceptibility of clinical C. auris isolates obtained from our hospital to a range of commonly used antiseptics and disinfectants at varying concentrations and contact times, thereby reflecting routine infection control practices.

MATERIALS and METHODS

Study Design and Microorganisms

This experimental study used 12 C. isolates. Ten clinical C. auris isolates obtained from various clinical specimens in our laboratory were included. In addition, one C. krusei strain (ATCC 6258) and one C. parapsilosis strain (ATCC 22019) were used as reference strains.

Antiseptics and disinfectants, all routinely used in our hospital, were tested: sodium hypochlorite (5%, 1%, and 0.5%), hydrogen peroxide (6% and 3%), povidone-iodine (10%, 5%, and 2.5%), a liquid soap containing chlorhexidine gluconate (4%) and n-propanol, and a hand disinfectant containing ethanol (60%) and isopropyl alcohol (10%). All disinfectants were prepared according to the manufacturers’ recommendations and used at the indicated concentrations.

Qualitative Suspension Test

The antifungal activity of the selected agents was evaluated using a qualitative suspension test method, which is a widely accepted screening approach for assessing disinfectant efficacy under controlled laboratory conditions^{9, 10, 11}. Standardized yeast suspensions adjusted to approximately 0.5 McFarland standard (≈1-5×10⁶ CFU/mL) were exposed to each disinfectant for contact times of 1, 2, 5, 10, and 30 minutes. Following the designated exposure period, the activity of the disinfectants was neutralized using 3% Tween 80, which has been widely used as a neutralizing agent in disinfectant efficacy studies to terminate residual disinfectant activity prior to microbiological evaluation^{9, 10}. For control purposes, fungal suspensions without disinfectant exposure were included.

Culture and Evaluation

After neutralization, samples were inoculated onto 5% sheep blood agar plates and incubated aerobically at 37 °C for 24-48 hours. Following incubation, colony counts on the inoculated plates were recorded for descriptive purposes and interpreted qualitatively as the presence or absence of growth; no log-reduction calculation was performed. The absence of visible growth at a given concentration and contact time was interpreted as indicating effective antifungal activity of the tested disinfectant.

Statistical Analysis

Since this study was based on qualitative observations, no comparative statistical analysis was performed. Results were evaluated descriptively based on the presence or absence of fungal growth at different disinfectant concentrations and contact times. Data organization and documentation were performed using the Statistical Package for the Social Sciences for Windows, version 21.0 (Armonk, NY: IBM Corp., USA).

The study was approved by the Non-Interventional Health Research Ethics Committee of İstanbul Medeniyet University (approval number: 2026/04-28, date: 29.04.2026).

RESULTS

Povidone-iodine (at all tested concentrations), the liquid soap containing chlorhexidine/n-propanol, the antiseptic containing ethanol and isopropyl alcohol, and sodium hypochlorite (at concentrations of 5% and 1%) inhibited the growth of all tested strains within the first minute of exposure. At concentrations of 0.5% sodium hypochlorite and 6% hydrogen peroxide, growth was observed within the first minute in two of the ten C. auris isolates. Among the ten C. auris isolates included in the study, growth was observed in three isolates after 1 minute of exposure to 3% hydrogen peroxide and in four isolates after both 1-minute and 2-minute exposures. For the C. parapsilosis reference strain, growth persisted after 1, 2, 5, and 10 minutes of exposure to 6% hydrogen peroxide, and no growth was detected at 30 minutes. At 3%, growth was observed at all contact times. For the C. krusei isolate, growth was observed within the first minute of exposure to both 3% and 6% hydrogen peroxide (Table 1).

Table 1. In vitro antifungal activity of selected antiseptics and disinfectants against C. auris and reference C. strains at different concentrations and contact times*.

-	Sodium hypochlorite  (5%)					Sodium hypochlorite  (1%)					Sodium hypochlorite (0.5%)					Hydrogen peroxide  (6%)					Hydrogen peroxide  (3%)
Strain/duration (minutes)	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’
C. auris strain-1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2	0	0	0	0	37	3	0	0	0
C. auris strain-2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	16	0	0	0	0
C. auris strain-3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	18	2	0	0	0
C. auris strain-5	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-6	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-7	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	28	6	0	0	0
C. auris strain-8	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0
C. auris strain-9	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	2	0	0	0	0
C. auris strain-10	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	25	3	0	0	0
C. parapsilosis (ATCC 22019)	0	0	0	0	0	0	0	0	0	0	2	2	0	0	0	8	5	2	1	0	12	7	5	5	1
C. krusei (ATCC 6258)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	3	0	0	0	0
-	Povidone-iodine (10%)					Povidone-iodine (5%)					Povidone-iodine (2.5%)					Chlorhexidine/n-propanol (4%)					Ethanol and isopropyl alcohol
Strain/duration (minutes)	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’	1’	2’	5’	10’	30’
C. auris strain-1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-5	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-6	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-7	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-8	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-9	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. auris strain-10	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. parapsilosis (ATCC 22019)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
C. krusei (ATCC 6258)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0

DISCUSSION

C. auris has emerged as a major nosocomial pathogen due to its multidrug resistance, ability to persist in the healthcare environment, and propensity to cause outbreaks, particularly in intensive care settings^{2, 4}. In this context, effective environmental disinfection plays a critical role in limiting transmission. The present study evaluated the in vitro activity of commonly used antiseptics and disinfectants against clinical isolates of C. auris under conditions that reflect routine hospital practice.

In our study, povidone-iodine, chlorhexidine/n-propanol-containing liquid soap, and alcohol-based hand disinfectant demonstrated rapid and complete antifungal activity against all tested isolates within the first minute of exposure. These findings are consistent with previous reports indicating that alcohol-based formulations and iodine-containing antiseptics are highly effective against C. auris when used at appropriate concentrations^{7, 8}. Moore et al.⁷ reported that iodine-based antiseptics and certain alcohol-based formulations exhibit rapid fungicidal activity against C. auris, supporting their use in infection control practices.

Sodium hypochlorite at concentrations of 5% and 1% also showed immediate and complete inhibition of all isolates, whereas reduced efficacy was observed at a concentration of 0.5%. This finding is in agreement with earlier studies demonstrating that chlorine-based disinfectants are among the most effective agents against C. auris, but their efficacy is strongly dependent on concentration^{6, 8}. Rutala et al.⁶ showed that higher concentrations of sodium hypochlorite are required to achieve consistent activity against C. auris, emphasizing the importance of correct dilution in clinical settings.

In contrast, hydrogen peroxide demonstrated variable and concentration-dependent activity in our study. At a 3% concentration, a substantial proportion of isolates exhibited growth at early contact times; even at 6%, incomplete inhibition was observed in some isolates. These findings are consistent with previous studies suggesting that hydrogen peroxide may be less reliable against C. auris, particularly when used at lower concentrations or shorter exposure times^{8, 12}. The observed variability may be related to differences in isolate susceptibility or methodological factors, which raises concerns regarding the use of hydrogen peroxide as the sole disinfectant in routine practice. From a clinical perspective, these findings suggest that the effectiveness of hydrogen peroxide may be compromised when recommended concentrations or contact times are not strictly maintained. In busy healthcare environments, shortened exposure times or inappropriate dilution may reduce antifungal activity and potentially contribute to the persistence of C. species on environmental surfaces.

Similar variability was observed in the reference strains. The C.parapsilosis isolate demonstrated limited susceptibility to hydrogen peroxide and required prolonged exposure for complete inhibition, while the C. krusei isolate showed growth at early contact times, even at higher concentrations. These findings highlight that reduced susceptibility to certain disinfectants may not be unique to C. auris and may vary across C. species.

An important strength of this study is that disinfectants were tested at concentrations and contact times reflecting routine hospital use, rather than idealized laboratory conditions.

Previous studies have often evaluated disinfectant efficacy under optimal conditions, which may not accurately represent routine clinical practice⁸. Our findings underscore that suboptimal concentrations or insufficient contact times can significantly reduce antifungal efficacy, potentially contributing to environmental persistence and transmission of C. auris.

The findings of this study should be interpreted in light of the qualitative suspension test design, which reflects controlled laboratory conditions but may not fully capture real-life factors such as surface interaction and organic load^{9, 10}.

Study Limitations

This study has several limitations. First, the number of C. auris isolates was limited, and they were derived from a single center; these factors may restrict generalizability. Second, antifungal activity was assessed using a qualitative suspension test without quantitative measures, such as log reduction, thereby limiting precise evaluation of fungicidal efficacy. Third, only planktonic forms were tested, whereas biofilm-associated cells may exhibit increased tolerance to disinfectants. In addition, factors such as organic load, surface type, and environmental conditions were not evaluated. Finally, variations in commercial formulations may influence antifungal activity. Despite these limitations, the study provides clinically relevant data under conditions reflecting routine clinical practice.

CONCLUSION

The present study demonstrates that commonly used antiseptics and disinfectants are generally effective against C. auris isolates when applied at appropriate concentrations and contact times. Povidone-iodine, alcohol-based formulations, and higher concentrations of sodium hypochlorite exhibited rapid and consistent antifungal activity, whereas reduced efficacy was observed with lower concentrations of sodium hypochlorite and hydrogen peroxide, particularly at shorter exposure times. These findings highlight that not only the choice of disinfectant but also its proper dilution and adequate contact time are critical determinants of efficacy against C. auris. Ensuring adherence to manufacturer recommendations is therefore essential to prevent environmental persistence and potential transmission in healthcare settings. Further studies incorporating quantitative methods, larger numbers of isolates, and biofilm models are needed to better define optimal disinfection strategies against this emerging pathogen.

Ethics

Ethics Committee Approval: The study was approved by the Non-Interventional Health Research Ethics Committee of İstanbul Medeniyet University (approval number: 2026/04-28, date: 29.04.2026).

Informed Consent: Not applicable.