A reporter virus particle seroneutralization assay for tick-borne encephalitis virus overcomes ELISA limitations.

Tick-borne encephalitis (TBE) virus is the most prevalent tick-transmitted orthoflavivirus in Europe. Due to the nonspecific nature of its symptoms, TBE is primarily diagnosed by ELISA-based detection of specific antibodies in the patient serum. However, cross-reactivity between orthoflaviviruses complicates the diagnosis. Specificity issues may be mitigated by serum neutralization assays (SNT), although the handling of clinically relevant orthoflaviviruses requires biosafety level (BSL) 3 conditions and they have highly divergent viral kinetics and cell tropisms. In the present study, we established a reporter virus particle (RVP)-based SNT in which the infectivity is measured by luminescence and that can be performed under BSL-2 conditions. The RVP-based SNT for TBEV exhibited a highly significant correlation with the traditional virus-based SNT (R2 = 0.8637, p < 0.0001). The RVP-based assay demonstrated a sensitivity of 92.3% (95% CI: 79.7%-97.4%) and specificity of 100% (95% CI: 81.6%-100%). We also tested the cross-reactivity of serum samples in RVP-based assays against other orthoflaviviruses (yellow fever virus, dengue virus type 2, Zika virus, West Nile virus and Japanese encephalitis virus). Interestingly, all serum samples which had tested TBEV-positive by ELISA but negative by RVP-based SNT were reactive for antibodies against other orthoflaviviruses. Thus, the RVP-based seroneutralization assay provides an added value in clinical diagnostics as well as in epidemiological studies.

Upc2-mediated mechanisms of azole resistance in Candida auris.

Candida auris is an emerging yeast pathogen of major concern because of its ability to cause hospital outbreaks of invasive candidiasis and to develop resistance to antifungal drugs. A majority of C. auris isolates are resistant to fluconazole, an azole drug used for the treatment of invasive candidiasis. Mechanisms of azole resistance are multiple, including mutations in the target gene ERG11 and activation of the transcription factors Tac1b and Mrr1, which control the drug transporters Cdr1 and Mdr1, respectively. We investigated the role of the transcription factor Upc2, which is known to regulate the ergosterol biosynthesis pathway and azole resistance in other Candida spp. Genetic deletion and hyperactivation of Upc2 by epitope tagging in C. auris resulted in drastic increases and decreases in susceptibility to azoles, respectively. This effect was conserved in strains with genetic hyperactivation of Tac1b or Mrr1. Reverse transcription PCR analyses showed that Upc2 regulates ERG11 expression and also activates the Mrr1/Mdr1 pathway. We showed that upregulation of MDR1 by Upc2 could occur independently from Mrr1. The impact of UPC2 deletion on MDR1 expression and azole susceptibility in a hyperactive Mrr1 background was stronger than that of MRR1 deletion in a hyperactive Upc2 background. While Upc2 hyperactivation resulted in a significant increase in the expression of TAC1b, CDR1 expression remained unchanged. Taken together, our results showed that Upc2 is crucial for azole resistance in C. auris, via regulation of the ergosterol biosynthesis pathway and activation of the Mrr1/Mdr1 pathway. Notably, Upc2 is a very potent and direct activator of Mdr1.IMPORTANCECandida auris is a yeast of major medical importance causing nosocomial outbreaks of invasive candidiasis. Its ability to develop resistance to antifungal drugs, in particular to azoles (e.g., fluconazole), is concerning. Understanding the mechanisms of azole resistance in C. auris is important and may help in identifying novel antifungal targets. This study shows the key role of the transcription factor Upc2 in azole resistance of C. auris and shows that this effect is mediated via different pathways, including the regulation of ergosterol biosynthesis and also the direct upregulation of the drug transporter Mdr1.