Effects of tigecycline and daptomycin on murine gut colonization by Candida albicans

Machine-Learning-Based Virtual Screening to Repurpose Drugs for Treatment of Candida albicans Infection

BACKGROUND

Approximately 30% of Candida genus isolates are resistant to all currently available antifungal drugs and it is highly important to develop new treatments. Additionally, many current drugs are toxic and cause unwanted side effects. 1,3-beta-glucan synthase is an essential enzyme that builds the cell walls of Candida.

OBJECTIVES

Targeting CaFKS1, a subunit of the synthase, could be used to fight Candida.

METHODS

In the present study, a machine-learning model based on chemical descriptors was trained to recognize drugs that inhibit CaFKS1. The model attained 96.72% accuracy for classifying between active and inactive drug compounds. Descriptors for FDA-approved and other drugs were calculated and the model was used to predict the potential activity of these drugs against CaFKS1.

RESULTS

Several drugs, including goserelin and icatibant, were detected as active with high confidence. Many of the drugs, interestingly, were gonadotrophin-releasing hormone (GnRH) antagonists or agonists. A literature search found that five of the predicted drugs inhibit Candida experimentally.

CONCLUSIONS

This study yields promising drugs to be repurposed to combat Candida albicans infection. Future steps include testing the drugs on fungal cells in vitro.

An adjunctive therapy administered with an antibiotic prevents enrichment of antibiotic-resistant clones of a colonizing opportunistic pathogen

A key challenge in antibiotic stewardship is figuring out how to use antibiotics therapeutically without promoting the evolution of antibiotic resistance. Here, we demonstrate proof of concept for an adjunctive therapy that allows intravenous antibiotic treatment without driving the evolution and onward transmission of resistance. We repurposed the FDA-approved bile acid sequestrant cholestyramine, which we show binds the antibiotic daptomycin, as an 'anti-antibiotic' to disable systemically-administered daptomycin reaching the gut. We hypothesized that adjunctive cholestyramine could enable therapeutic daptomycin treatment in the bloodstream, while preventing transmissible resistance emergence in opportunistic pathogens colonizing the gastrointestinal tract. We tested this idea in a mouse model of Enterococcus faecium gastrointestinal tract colonization. In mice treated with daptomycin, adjunctive cholestyramine therapy reduced the fecal shedding of daptomycin-resistant E. faecium by up to 80-fold. These results provide proof of concept for an approach that could reduce the spread of antibiotic resistance for important hospital pathogens.

Risk factors and predictors of mortality of candidaemia among critically ill patients: role of antifungal prophylaxis in its development and in selection of non-albicans species

PURPOSE

The aim of the present study is to identify risk factors for development and predictors of mortality of candidaemia among critically ill patients.

METHODS

A 1:7 case-control study was conducted during a 4-year period (2012-2015) in a Greek Intensive Care Unit (ICU). Candidaemia was confirmed by positive blood cultures. All yeasts were identified using API 20C AUX System or Vitek 2 Advanced Expert System. Epidemiologic data were collected from the ICU computerized database and patients' chart reviews.

RESULTS

Fifty-three patients developed candidaemia with non-albicans species being the predominant ones (33 patients, 62.3%). Multivariate analysis found that prior emergency surgery, malignancy, hospitalization during summer months, prior septic shock by KPC-producing Klebsiella pneumoniae and number of antibiotics administered were independently associated with candidaemia, while, prior administration of azole was a protective factor. Non-albicans candidaemia was associated with number of antibiotics administered and prior administration of echinocandin. Mortality of 14 days was 28.3% (15 patients) and was associated with SOFA score upon infection onset and septic shock, while, appropriate empirical antifungal treatment was associated with better survival.

CONCLUSIONS

Prophylactic azole administration prevents development of candidaemia, while, echinocandin administration predisposes to non-albicans candidaemia. Empirical administration of an appropriate antifungal agent is associated with better survival.

Disruption of the intestinal mucosal barrier in Candida albicans infections

Candida albicans is a common microorganism in the intestine. However, invasive C. albicans infection has emerged as a life-threatening disease in recent years. The mortality rate of invasive candidiasis is high in critically ill hosts. C. albicans can switch from the yeast to the hyphal morphology, and take advantage of the impaired intestinal mucosal barrier and insufficient immunity of the host to facilitate its colonization and penetration. Despite the availability of potent new antifungal drugs in recent years, the treatment of severe candidiasis, especially candidaemia, has not been substantially improved. In this review, the virulence factors of C. albicans, as well as the antagonistic role of the intestinal mucosal barrier will be discussed to illuminate the mechanisms of C. albicans enterogenic infections.

Candida albicans isolates from the gut of critically ill patients respond to phosphate limitation by expressing filaments and a lethal phenotype

Candida albicans is an opportunistic pathogen that proliferates in the intestinal tract of critically ill patients where it continues to be a major cause of infectious-related mortality. The precise cues that shift intestinal C. albicans from its ubiquitous indolent colonizing yeast form to an invasive and lethal filamentous form remain unknown. We have previously shown that severe phosphate depletion develops in the intestinal tract during extreme physiologic stress and plays a major role in shifting intestinal Pseudomonas aeruginosa to express a lethal phenotype via conserved phosphosensory-phosphoregulatory systems. Here we studied whether phosphate dependent virulence expression could be similarly demonstrated for C. albicans. C. albicans isolates from the stool of critically ill patients and laboratory prototype strains (SC5314, BWP17, SN152) were evaluated for morphotype transformation and lethality against C. elegans and mice during exposure to phosphate limitation. Isolates ICU1 and ICU12 were able to filament and kill C. elegans in a phosphate dependent manner. In a mouse model of intestinal phosphate depletion (30% hepatectomy), direct intestinal inoculation of C. albicans caused mortality that was prevented by oral phosphate supplementation. Prototype strains displayed limited responses to phosphate limitation; however, the pho4Δ mutant displayed extensive filamentation during low phosphate conditions compared to its isogenic parent strain SN152, suggesting that mutation in the transcriptional factor Pho4p may sensitize C. albicans to phosphate limitation. Extensive filamentation was also observed in strain ICU12 suggesting that this strain is also sensitized to phosphate limitation. Analysis of the sequence of PHO4 in strain ICU12, its transcriptional response to phosphate limitation, and phosphatase assays confirmed that ICU12 demonstrates a profound response to phosphate limitation. The emergence of strains of C. albicans with marked responsiveness to phosphate limitation may represent a fitness adaptation to the complex and nutrient scarce environment typical of the gut of a critically ill patient.