A novel rRNA hybridization-based approach to rapid, accurate Candida identification directly from blood culture

Invasive fungal infections are increasingly common and carry high morbidity and mortality, yet fungal diagnostics lag behind bacterial diagnostics in rapidly identifying the causal pathogen. We previously devised a fluorescent hybridization-based assay to identify bacteria within hours directly from blood culture bottles without subculture, called phylogeny-informed rRNA-based strain identification (Phirst-ID). Here, we adapt this approach to unambiguously identify 11 common pathogenic Candida species, including C. auris, with 100% accuracy from laboratory culture (33 of 33 strains in a reference panel, plus 33 of 33 additional isolates tested in a validation panel). In a pilot study on 62 consecutive positive clinical blood cultures from two hospitals that showed yeast on Gram stain, Candida Phirst-ID matched the clinical laboratory result for 58 of 59 specimens represented in the 11-species reference panel, without misclassifying the 3 off-panel species. It also detected mixed Candida species in 2 of these 62 specimens, including the one discordant classification, that were not identified by standard clinical microbiology workflows; in each case the presence of both species was validated by both clinical and experimental data. Finally, in three specimens that grew both bacteria and yeast, we paired our prior bacterial probeset with this new Candida probeset to detect both pathogen types using Phirst-ID. This simple, robust assay can provide accurate Candida identification within hours directly from blood culture bottles, and the conceptual approach holds promise for pan-microbial identification in a single workflow.

LAY SUMMARY

Candida bloodstream infections cause considerable morbidity and mortality, yet slow diagnostics delay recognition, worsening patient outcomes. We develop and validate a novel molecular approach to accurately identify Candida species directly from blood culture one day faster than standard workflows.

738. A Novel Molecular Diagnostic Assay for Identification of Fungal Pathogens

Background

A rapid and accurate diagnostic method for invasive fungal infections remains a critical clinical need. We recently reported a rapid molecular method for bacterial species identification directly from clinical samples that targets highly abundant ribosomal RNA on a multiplexed hybridization platform called NanoString. Here we report an adaptation of this assay that accurately distinguishes common fungal pathogens with limit of detection at a single yeast cell.

Methods

Building on our bacterial approach, we computationally designed specific hybridization probes targeting species-specific variable regions of fungal 18S and 28S rRNA from 12 clinically relevant fungi: Aspergillus fumigatus, Cryptococcus neoformans, and 10 Candida species, including Candida auris. Following mechanical lysis of crude specimens, fungi were detected from laboratory culture or artificial cerebrospinal fluid via multiplexed hybridization on a NanoString (Seattle, WA) instrument which yielded results within 7 hours from sample collection. Assay sensitivity was probed using serial dilutions of lysed C. albicans in culture, and cell-equivalents were confirmed by plating.

Results

Our hybridization probes targeting fungal rRNA specifically recognized all species tested to date: A. fumigatus, C. neoformans, and C. albicans with no cross-reactivity (Fig 1a). Serial dilutions of C. albicans lysate demonstrated a limit of detection around 0.1 cell equivalents without rRNA amplification (Fig 1b), capitalizing on the intrinsic abundance of rRNA in fungal cells.

Figure 1.

Conclusion

We adapted a rapid, ultrasensitive hybridization-based diagnostic assay that has proven successful in bacteria, to fungi. Here we show the accurate detection of Aspergillus, Cryptococcus, and Candida species, including a computational design that will enable the distinction of 10 different Candida species, including C. auris, within hours from clinical specimen collection.

Disclosures

All Authors: No reported disclosures

Association of ghrelin receptor promoter polymorphisms with weight loss following Roux-en-Y gastric bypass surgery

BACKGROUND

Ghrelin plays a role in appetite and has been hypothesized to play a role in the mechanism of Roux-en-Y gastric bypass (RYGB) surgery. Single nucleotide polymorphisms (SNPs) in the promoter region of its receptor gene (growth hormone secretagogue receptor type 1a--GHSR) have also been associated with weight loss outcomes following long-term dietary intervention in adults with impaired glucose tolerance. Our objectives were to evaluate changes in serum ghrelin levels and determine the effect of GHSR promoter polymorphisms on post-RYGB surgery weight loss.

METHODS

Preoperative and 6-month postoperative serum ghrelin levels were measured in 37 patients with extreme obesity undergoing RYGB surgery. Total ghrelin was also measured in liver tissue collected intraoperatively. Association analysis between genotypes for SNPs rs9819506 and rs490683 in the promoter region of the GHSR gene and weight loss outcomes in the 30 months following surgery was performed in over 650 RYGB patients.

RESULTS

Serum ghrelin levels increased after RYGB surgery. Weight loss trajectories were significantly different using an additive model for both ghrelin SNPs, with patients homozygous for the rs490683 CC genotype exhibiting the most weight loss. Weight loss trajectories were also different using a dominant model. The rs490683 risk allele demonstrated decreased promoter activity in vitro.

CONCLUSIONS

The role of increased ghrelin levels in weight loss outcomes following RYGB surgery may be influenced by variation in the GHSR gene.