Combined antifungal resistance and biofilm tolerance: the global threat of Candida auris

The enigmatic yeast Candida auris has emerged over the last decade and rapidly penetrated our consciousness. The global threat from this multidrug-resistant yeast has generated a call to arms from within the medical mycology community. Over the past decade, our understanding of how this yeast has spread globally, its clinical importance, and how it tolerates and resists antifungal agents has expanded. This review highlights the clinical importance of antifungal resistance in C. auris and explores our current understanding of the mechanisms associated with azole, polyene, and echinocandin resistance. We also discuss the impact of phenotypic tolerance, with particular emphasis on biofilm-mediated resistance, and present new pipelines of antifungal drugs that promise new hope in the management of C. auris infection

Evaluating Streptococcus mutans strain dependent characteristics in a polymicrobial biofilm community

Aim: The purpose of this study was to investigate strain dependent differences of the cariogenic biofilm forming Streptococcus mutans within both simple and complex communities. Methods: A mono-species containing representative S. mutans clinical isolates (caries and non-caries), and a multispecies in vitro caries biofilm model containing Lactobacillus casei, Veillonella dispar, Fusobacterium nucleatum and Actinomyces naeslundii, and either of two representative S. mutans clinical isolates (caries and non-caries), was developed as a comparison model. Compositional analysis of total and live bacteria within biofilms, and transcriptional analysis of biofilm associated virulence factors were evaluated by live/dead PCR and quantitative PCR, respectively. Scanning electron microscopy (SEM) was used to analyze the architecture of biofilm. One-way analysis of variance and t-tests were used to investigate significant differences between independent groups of data. Results: Within a mono-species biofilm, different S. mutans strains responded similarly to one another during biofilm formation in different carbohydrate sources, with sucrose showing the highest levels of biofilm biomass and galactose showing the lowest. Within the polymicrobial biofilm system, compositional analysis of the bacteria within the biofilm showed that S. mutans derived from a caries-free patient was preferentially composed of both total and viable L. casei, whereas S. mutans derived from a caries patient was dominated by both total and viable S. mutans (p < 0.001). Normalized gene expression analysis of srtA, gtfB, ftf, spaP, gbpB, and luxS, showed a general upregulation within the S. mutans dominant biofilm. Conclusion: We were able to demonstrate that individual strains derived from different patients exhibited altered biofilm characteristics, which were not obvious within a simple mono-species biofilm model. Influencing the environmental conditions changed the composition and functionality S. mutans within the polymicrobial biofilm. The biofilm model described herein provides a novel and reproducible method of assessing the impact on the biofilm microbiome upon different environmental influences

Fungal biofilm resistance

Fungal biofilm infections have become increasingly recognised as a significant clinical problem. One of the major reasons behind this is the impact that these have upon treatment, as antifungal therapy often fails and surgical intervention is required. This places a large financial burden on health care providers. This paper aims to illustrate the importance of fungal biofilms, particularly Candida albicans, and discusses some of the key fungal biofilm resistance mechanisms that include, extracellular matrix (ECM), efflux pump activity, persisters, cell density, overexpression of drug targets, stress responses, and the general physiology of the cell. The paper demonstrates the multifaceted nature of fungal biofilm resistance, which encompasses some of the newest data and ideas in the field

Prior in vitro exposure to voriconazole confers resistance to amphotericin B in aspergillus fumigatus biofilms

Triazoles are the mainstay of treatment for aspergillosis, although resistance to these antifungal agents may be associated with treatment failure. Refractory infections often necessitate a switch to other antifungal agents, including amphotericin B (AmB), although these infections may not resolve. The aim of this study was to investigate the effect of prior azole exposure on AmB sensitivity in Aspergillus fumigatus biofilms. It was hypothesised that sequential antifungal therapy has the potential to impact adaptive resistance mechanisms. Antifungal sensitivity was determined for each isolate against AmB ± voriconazole (VRZ) exposure by a broth microdilution method and an XTT metabolic assay. To analyse the role of extracellular DNA (eDNA) and Hsp90 activation, sensitivity to AmB ± DNA-digesting enzyme (DNase) or Hsp90 inhibitor [geldanamycin (GDA)] was also tested. Finally, scanning electron microscopy was performed to assess phenotypic changes. The in vitro data revealed that A. fumigatus sensitivity to AmB was decreased when it was tested in combination with VRZ. In addition, a two- to four-fold decreased sensitivity to AmB was recorded against VRZ-exposed germlings compared with controls. It was also shown that depletion of eDNA by DNase treatment enhanced AmB activity against VRZ-exposed cells by eight-fold, which visually could be explained by destabilisation of the biofilm when examined microscopically. Pharmacological inhibition of Hsp90 by GDA significantly improved biofilm susceptibility to AmB by four- to eight-fold. In conclusion, A. fumigatus pre-exposure to VRZ concomitantly induces eDNA release and activates the stress response, which collectively confers AmB resistance in vitro

Candida auris: a decade of understanding of an enigmatic pathogenic yeast

Candida auris is an enigmatic yeast that continues to stimulate interest within the mycology community due its rapid and simultaneous emergence of distinct clades. In the last decade, almost 400 manuscripts have contributed to our understanding of this pathogenic yeast. With dynamic epidemiology, elevated resistance levels and an indication of conserved and unique pathogenic traits, it is unsurprising that it continues to cause clinical concern. This mini-review aims to summarise some of the key attributes of his remarkable pathogenic yeast

Tolerance of Pseudomonas aeruginosa in in vitro biofilms to high level peracetic acid disinfection

Biofilm has been suggested as a cause of disinfection failures in flexible endoscopes where no lapses in the decontamination procedure can be identified. To test this theory, the activity of peracetic acid (PAA), one of the commonly used disinfectants in the reprocessing of flexible endoscopes, was evaluated against both planktonic and sessile communities of Pseudomonas aeruginosa. To investigate the ability of P. aeruginosa biofilm to survive high level PAA disinfection. The susceptibility of planktonic cells of P. aeruginosa and biofilms 24, 48, 96 and 192 h old to PAA was evaluated by estimating their viability using resazurin viability and plate count methods. The biomass of the P. aeruginosa biofilms was also quantified using crystal violet assay. Planktonic cells of P. aeruginosa were treated with 5 - 30 ppm concentration of PAA in the presence of 3.0 g/L of Bovine serum albumin (BSA) for 5 min. Biofilms of P. aeruginosa were also treated with various PAA concentrations (100 - 3000 ppm) for 5 min. Planktonic cells of P. aeruginosa were eradicated by 20 ppm of PAA, whereas biofilms showed an age dependent tolerance to PAA, and 96 h old biofilm was only eradicated at PAA concentration of 2500 ppm. 96 h old P. aeruginosa biofilm survives 5 min treatment with 2000 ppm of PAA, which is the working concentration used in some endoscope washer disinfectors. This implies that disinfection failure of flexible endoscopes could occur when biofilms are allowed to build up in the lumens of endoscopes

Fungi at the scene of the crime: innocent bystanders or accomplices in oral infections?

Purpose of Review: Over the last decade, microbiome studies have enhanced our knowledge and understanding of the polymicrobial nature of oral infections. Recently, profiling of the fungal microbiome has expanded our conventional understanding of oral ecology, revealing the critical importance of yeasts within this complex microbiome. This review aims to explore our current appreciation of interkingdom interactions in oral disease. Recent Findings: There is a growing evidence base of interactions and pathogenic synergy and antagonism with bacterial species within oral disease. Recent studies have helped to develop our knowledge of how Candida albicans, alongside bacteria such as Porphyromonas gingivalis, Streptococcus mutans, Staphylococcus aureus, Enterococcus faecalis, and Lactobacillus species, influence overall pathogenicity. Summary: Clinical and experimental evidence makes a compelling case for a role for C. albicans in a number of oral infections, though whether its role is an active accomplice or passive bystander remains to be determined

<i>Candida albicans</i> fungaemia following traumatic urethral catheterisation in a paraplegic patient with diabetes mellitus and candiduria treated by caspofungin

A 58-year-old paraplegic male, with long-term indwelling urethral catheter, developed catheter block. The catheter was changed, but blood-stained urine was drained intermittently. A long segment of the catheter was seen lying outside his penis, which indicated that the balloon of Foley catheter had been inflated in urethra. The misplaced catheter was removed and a new catheter was inserted correctly. Gentamicin 160 mg was given intravenously; meropenem 1 gram every eight hours was prescribed; antifungals were not given. Twenty hours later, this patient developed distension of abdomen, tachycardia, and hypotension; he was not arousable. Computed tomography of abdomen revealed inflamed uroepithelium of right renal pelvis and ureter, 4 mm lower ureteric calculus with gas in right ureter proximally, and vesical calculus containing gas in its matrix. Urine and blood culture yielded &lt;i&gt;Candida albicans&lt;/i&gt;. Identical sensitivity pattern of both isolates suggested that the source of the bloodstream infection was most likely urine. Both isolates formed consistently high levels of biofilm formation in vitro as assessed using a biofilm biomass stain, and high levels of resistance to voriconazole were observed. Both amphotericin B and caspofungin showed good activity against the biofilms. HbA1c was 111 mmol/mol. This patient was prescribed human soluble insulin and caspofungin 70 mg followed by 50 mg daily intravenously. He recovered fully from candidemia

New strategic insights into managing fungal biofilms

Fungal infections have dramatically increased in the last decades in parallel with an increase of populations with impaired immunity, resulting from medical conditions such as cancer, transplantation or other chronic diseases. Such opportunistic infections result from a complex relationship between fungi and host, and can range from self-limiting to chronic or life-threatening infections. Modern medicine, characterized by a wide use of biomedical devices, offers new niches for fungi to colonize and form biofilm communities. The capability of fungi to form biofilms is well documented and associated with increased drug tolerance and resistance. In addition, biofilm formation facilitates persistence in the host promoting a persistent inflammatory condition. With a limited availability of antifungals within our arsenal, new therapeutic approaches able to address both host and pathogenic factors that promote fungal disease progression, i.e. chronic inflammation and biofilm-formation, could represent an advantage in the clinical setting. In this paper we discuss the antifungal properties of Myriocin, Fulvic Acid and Acetylcholine in light of their already known anti-inflammatory activity and as candidate dual action therapeutics to treat opportunistic fungal infections

The application of phenotypic microarray analysis to anti-fungal drug development

Candida albicans metabolic activity in the presence and absence of acetylcholine was measured using phenotypic microarray analysis. Acetylcholine inhibited C. albicans biofilm formation by slowing metabolism independent of biofilm forming capabilities. Phenotypic microarray analysis can therefore be used for screening compound libraries for novel anti-fungal drugs and measuring antifungal resistance