Growth kinetics in Candida spp.: Differences between species and potential impact on antifungal susceptibility testing as described by the EUCAST

Efficient Recovery of Candida auris and Five Other Medically Important Candida Species from Blood Cultures Containing Clinically Relevant Concentrations of Antifungal Agents

Candida auris and other Candida species (C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, and C. krusei) are important causes of bloodstream infection. Early or prolonged treatment with antifungal agents is often required. The inhibitory effect of antifungal agents in the patients' bloodstream may compromise the sensitivity of blood culture (BC) to diagnose and/or monitor patients with candidemia. Using a clinical BC simulation model, we compared antimicrobial drug-neutralizing BC media in BacT/Alert FA PLUS (FAP) or Bactec Plus Aerobic/F (PAF) bottles with non-neutralizing BC media in Bactec Mycosis IC/F (MICF) bottles to allow Candida growth in the presence of 100%, 50%, or 25% peak serum level (PSL) antifungal concentrations. In total, 117 organism/antifungal combinations were studied, and Candida growth was detected after incubating bottles into BacT/Alert VIRTUO or Bactec FX BC systems. Compared to control (without antifungal) bottles, both FAP and PAF bottles with 100% PSL antifungal concentrations allowed 100% recovery for C. auris, C. glabrata, and C. parapsilosis, whereas recovery was below 100% for C. albicans, C. krusei, and C. tropicalis. MICF bottles were less efficient at 100%, 50%, or 25% PSL antifungal concentrations, for all Candida species, except for C. auris. While azoles and amphotericin B did not hinder Candida growth in FAP or PAF bottles, echinocandins allowed C. auris, C. glabrata, and C. parapsilosis to grow in FAP, PAF, or MICF bottles. Overall, the maximum time to detection was 4.6 days. Taken together, our findings emphasize the reliability of BCs in patients undergoing antifungal treatment for candidemia. IMPORTANCE While echinocandins remain the preferred antifungal therapy for candidemia, bloodstream infections caused by C. auris, C. glabrata, or, at a lesser extent, C. parapsilosis may be difficult to treat with these antifungal agents. This is in view of the high propensity of the above-mentioned species to develop antifungal resistance or tolerance during treatment. Azoles and amphotericin B are possible alternatives. Thus, optimizing the recovery of Candida from BCs is important to exclude the likelihood of negative BCs for Candida species, owing to the inhibitory effect of antifungal agents present in the blood sample with which BCs are inoculated. Consistently, our results about the recovery of medically important Candida species (including C. auris) from simulated BCs in BacT/Alert FAP, Bactec PAF, or Bactec MICF bottles containing clinically relevant antifungal concentrations add support to this research topic, as well as to the use of BCs for monitoring the clinical and therapeutic course of candidemia.

Clinical utility of time to positivity of blood cultures in cases of fungaemia: A prospective study

PURPOSE

Fungaemia due to yeast is a major cause of morbidity and mortality in critically ill patients. Although, automated blood cultures have improved the time to diagnosis, very few studies have systematically evaluated the utility of blood culture time to positivity (TTP) of fungaemia in the clinical scenario. In this study, we evaluated the TTP for different yeast species to determine its clinical utility.

MATERIAL AND METHODS

A prospective study including 244 consecutive patients admitted to the adult (n ​= ​76) and paediatric (n ​= ​168) intensive care units (ICUs) was conducted between December 2017 through March 2019. The clinical and demographic characteristics, BACTEC blood culture results and TTP for yeast positive blood cultures were recorded for analysis.

RESULTS

A total of 244 patients with 357 episodes of candidaemia were enrolled during the study period. The TTP (mean ​± ​SD) for all yeast species was 26.8 ​± ​23.6 ​h while it was significantly longer in paediatric than adult patients (30.5 ± 24.7 vs. 25.2 ​± ​22.9 ​h; p ​= ​<0.0001). Wickerhamomyces anomalus and Cyberlindnera jadinii (previously C. utilis) were exclusively isolated from paediatric population where W. anomalus demonstrated significantly longer TTP than C. jadinii. Among adult cases, C. albicans exhibited significantly longer TTP than C. tropicalis. In paediatric cases, >80% of C. tropicalis and C. utilis flagged positive in blood culture before 24 ​h while majority (65.9%) of W. anomalus isolates flagged positive later than 24 ​h. Similarly in adult samples, 63% of C. tropicalis isolates beeped positive before 24 ​h.

CONCLUSION

TTP for yeast may provide insight regarding the responsible yeast species before final identification among critical patients with candidaemia. Larger studies are warranted for evaluating clinical utility of TTP considering other complex factors like yeast burden, generation time, virulence and host factors, which may affect TTP.

(MeOPhSe)2, a synthetic organic selenium compound, inhibits virulence factors of Candida krusei: Adherence to cervical epithelial cells and biofilm formation

BACKGROUND

Systemic candidiasis is produced by Candida albicans or non-albicans Candida species, opportunistic fungi that produce both superficial and invasive infections. Despite the availability of a wide range of antifungal agents for the treatment of candidiasis, failure of therapy is observed frequently, which opens new avenues in the field of alternative therapeutic strategies.

METHODS

The effects of p,p'-methoxyl-diphenyl diselenide [(MeOPhSe)₂], a synthetic organic selenium (organochalcogen) compound, were investigated on virulence factors of C. krusei and compared with its antifungal effects on the virulence factors related to adhesion to cervical epithelial cell surfaces with C. albicans.

RESULTS

(MeOPhSe)₂, a compound non-toxic in epithelial (HeLa) and fibroblastic (Vero) cells, inhibited the growth in a dose-dependent manner and changed the kinetics parameters of C. krusei and, most importantly, extending the duration of lag phase of growth, inhibiting biofilm formation, and changing the structure of biofilm. Also, (MeOPhSe)₂ reduced C. albicans and C. krusei adherence to cervical epithelial cells, an important factor for the early stage of the Candida-host interaction. The reduction was 37.24 ± 2.7 % in C. krusei (p = 0.00153) and 32.84 ± 3.2 % in C. albicans (p = 0.0072) at 20 µM (MeOPhSe)₂, and the effect is in a concentration-dependent manner. Surprisingly, the antifungal potential on adhesion was similar between both species, indicating the potential of (MeOPhSe)₂ as a promising antifungal drug against different Candida infections.

CONCLUSION

Overall, we demonstrated the potential of (MeOPhSe)₂ as an effective antifungal drug against the virulence factors of Candida species.

Diphenyl diselenide suppresses key virulence factors of Candida krusei, a neglected fungal pathogen

Candida krusei is a candidiasis etiological agent of relevance in the clinical setting because of its intrinsic resistance to fluconazole. Also, it has opened up new paths in the area of alternative therapeutic techniques. This project demonstrated the effects of diphenyl diselenide (PhSe)₂ and p-cloro diphenyl diselenide (pCl-PhSe)₂, two organochalcogen compounds, on relevant virulence factors for the early stage of the C. krusei host interaction and infection process. Both compounds inhibited adherence of C. krusei to both polystyrene surfaces and cervical epithelial cells and biofilm formation; the structure of the biofilm was also changed in a dose-dependent manner. In addition, both compounds inhibited C. krusei growth, but (PhSe)₂ significantly increased the time duration of the lag phase and delayed the start of the exponential phase in growth kinetics. (PhSe)₂ has more potential antifungal activity than (pCl-PhSe)₂ in inhibiting the adherence to epithelial cells, biofilm formation, and growth of C. krusei.