Determination of the Role of Glucose and pH in the Production of Biofilms, Phospholipase and Protease in Candida auris

Abstract

First isolated in 2009 from the ear canal of a Japanese patient, Candida auris has become a growing concern. It has been found to have a similar profile of virulence to Candida albicans. It forms biofilms and produces phospholipase and protease activity. The virulence of C. auris varies according to the strain, with aggregating strains showing less virulence than non-aggregating strains, though reports find it to be less virulent overall than C. albicans. Alarmingly, however, it has shown greater resistance to multiple drugs from all three classes of antifungals and routine cleaning protocols. Most at risk of invasive and systemic infections are severely immunocompromised patients in intensive care settings particularly those with a urinary catheter in situ. Due to impaired immunity and associated comorbidities, patients with diabetes mellitus are considered a high-risk group. The study investigated whether synthetic urine mimicking the high glucose and low pH conditions found in diabetic urine would increase the production of biofilms, protease and phospholipase of an aggregating (NCPF 8977) and non-aggregating strain (NCPF 8971) of C. auris. C. auris was found to grow well in the synthetic urine media in its planktonic form where the culture medium is shaken to preventing biofilm formation, and the growth increased in line with glucose concentration and varied in respect to pH with pH 5.6 showing less growth than pH 5.2 or pH 6.3. The study found that there was no significant change in biofilm formation at any of the tested pH levels and glucose concentrations. However, variation in phospholipase and protease activity was seen when the conditions were altered, and this appeared to be in a strain dependent manner. Other studies have shown that C. auris produces protease and phospholipase in a strain dependent manner, though this study has shown that this can vary with respect to glucose and pH.