Chlorhexidine Effective Against Candida auris Biofilms

A combination of standard infection prevention measures and the use of disinfectant chlorhexidine should be used to combat the potential spread of Candida auris in hospital environments, according to a study published online January 11 in Emerging Infectious Diseases.

The study showed that C auris can form a biofilm that resists many antifungal agents. A biofilm also enables the fungus to use excretions to adhere to other materials, including medical instruments. The C auris biofilm is not as strong as those of some other clinically significant fungi, but has nonetheless contributed to C auris' ability to survive in hospital environments and cause outbreaks and infections.

"Although unable to form biofilms equivalent to C. albicans, C. auris has a noteworthy virulence capacity that merits further exploration," report Leighann Sherry, PhD, from the University of Glasgow in Scotland, and colleagues. "These factors, together with the innate resistance of C. auris to most antifungal agents, may explain why it is an emerging pathogen."

C auris was initially discovered in 2009 in a patient's infected ear canal in Japan, and the first US cases were detected in 2013 in patients with serious preexisting medical conditions. During the last 7 years, it has been linked to bloodstream and wound infections across the world and caused hospital outbreaks throughout Asia, South America, and the United Kingdom, yet its mode of transmission has remained a mystery.

Dr Sherry's team concluded that antifungal stewardship strategies alone will be unlikely to control C auris' spread, but explored what antifungal agents the pathogen might be susceptible to. Chlorhexidine most successfully controls the fungus, they determined.

"Thus, use of this disinfectant can be advocated for topical control of C. auris at standard concentrations used for skin and wound cleansing and disinfection (0.05%–4.0%)," the authors write. "Infection-prevention measures targeting C. auris biofilms in patients, on medical devices (e.g., equipment in contact with patients), and in the hospital environment will be required."

To better understand the fungus' biofilm capabilities, the researchers compared the biofilm mass of four strains of C auris with that of two other fungi, Candida albicans and Candida glabrata. The C auris strains developed 1.5 to 3 times less biofilm mass than C albicans, but 3 to 6 times greater mass than C glabrata, suggesting C auris biofilm has enough strength to adhere to hospital surfaces and instruments.

The researchers then tested seven antifungal agents' effectiveness against C auris: fluconazole, voriconazole, caspofungin, micafungin, liposomal amphotericin B, amphotericin B, and chlorhexidine. The antiseptic chlorhexidine showed the greatest activity, "requiring <0.02% to effectively inhibit planktonic and sessile cells across all strains tested," the authors report.

Amphotericin B also showed effectiveness in killing biofilms with 4 mg/L. However, liposomal amphotericin B was effective at that concentration against planktonic or isolated fungi, but four times that concentration was required to reduce biofilm metabolic viability by 90%.

Although micafungin and caspofungin inhibited some of the fungus, neither worked against biofilms: voriconazole showed little activity against C auris cells, and fluconazole was altogether ineffective.

Emerg Infect Dis. Published online January 11, 2017.

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References
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Chlorhexidine Effective Against Candida auris Biofilms. Medscape. Jan. 1, 2017.

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