076 - Candida albicans impacts Group B Streptococcus Virulence

Publication Number: 76.4160

Alexia N. Pearah, USF Health Morsani College of Medicine, Tampa, FL, United States; April Lindon, University of south florida, Tampa, FL, United States; Kristen Dominguez, university of south florida, miami, FL, United States; Nichol John-Lewis Edwards, University of South Florida, Port Richey, FL, United States; Ryan K. Handel, USF Morsani College of Medicine, Tampa, FL, United States; Cinthya N. Zelaya Aparicio, USF Health Morsani College of Medicine, Tampa, FL, United States; Sophie Darch, University of South Florida, Tampa, FL, United States; Tara M. Randis, University of South Florida, Tampa, FL, United States

Background: Group B Streptococcus (GBS) is a leading cause of infant sepsis worldwide. Colonization of the gastrointestinal tract is a critical precursor to late-onset (LO) disease in exposed newborns. Previous data demonstrate that Candida albicans (CA) promotes GBS colonization of host tissues including the bladder and vagina. However, its impact on GBS colonization of intestinal tissues and GBS pathogenesis remains unknown. Our laboratory has a well-established mouse model of LO GBS disease. We adapted this model to study GBS and CA co-colonization in the newborn host and found greater GBS burden in both the small intestine and colon when CA was present.

Objective: The goal of this study was to identify the mechanism responsible for this enhanced GBS colonization as well as to complete fixed tissue staining of the mouse intestines to visualize potential GBS and CA interactions in the gut.

Design/Methods: GBS and CA were co-cultured in Tryptic Soy broth for 4 hours at 37°C and bacterial RNA was extracted and converted to cDNA for real-time PCR analysis using the comparative CT Method (ΔΔCT Method) with recA as the reference gene. Candidate genes hypothesized to contribute to LO GBS pathogenesis were amplified using previously validated primers. Two biological replicates for each condition with 6 technical replicates were analyzed. We collected colonic tissues from mice co-colonized with CA and GBS which were fixed and stained with antibodies directed against CA and GBS for visualization with confocal microscopy and then analyzed with the Imaris software.

Results: We noted a significant upregulation of cylE, hvgA, srr2, fbsB, and spb1 expression (all p< 0.002, unpaired t test) in GBS when co-incubated with CA as compared to GBS monoculture. Confocal imaging of the stained mouse colon revealed co-localization of CA and GBS within colonic tissues.

Conclusion(s): Increased expression of these genes suggests that the presence of CA increases GBS ability to survive and colonize the neonatal gut. Co-localization of CA and GBS in the mouse colon indicates that a physical association between CA and GBS may be important for understanding the CA-mediated effects on GBS pathogenicity. Further exploration of factors driving these transcriptomic changes will be explored using heat-killed CA and/or spent media. Understanding the mechanism of GBS and CA co-colonization of human infants may reveal novel risk factors and therapeutic treatments for late onset GBS disease.

GBS gene expression following incubation with CA
Following incubation with Candida albicans, we observed a significant upregulation of genes important for GBS pathogenesis: cylE (cytotoxin), hvgA (adhesin), Srr2 (adhesin), fbsB (important for invasion), and spb1 (pilus island derivative) (all p< 0.002, unpaired t test).

GBS attaches to CA in the neonatal murine gut.
220.3_C_p2_100x_rendered CA hyphae with GBS .jpegLaser confocal scanning microscopy rendered image of GBS and CA co-infected colon of mouse pups.
[green = CA, FITC; purple = GBS, anti-GBS IgG Alexa Fluor™ 568]