Elucidating fungal and bacterial polymicrobial interactions during catheter-associated urinary tract infections

SUMMARY: CAUTI is one of the most common healthcare associated infections, accounting for 40% of nosocomial infections worldwide. Recent clinical studies have estimated that during long term catheterization, up to 97% of CAUTIs are polymicrobial. Although studies involving two different pathogens have been done, trying to understand the interactions between three species, especially cross-kingdom, are few and far between. Hence, the proposed studies are intended to narrow the knowledge gap in understanding polymicrobial infections during CAUTI by three of the most prevalent uropathogens, gram negative E. coli, gram positive E. faecalis, and fungal pathogen C. albicans. Our preliminary results showed that E. coli inhibits hyphal morphogenesis as well as decrease microbial burden of C. albicans both in vitro and in vivo. In contrast, our in vivo preliminary data showed that C. albicans colonization in the bladder and on the catheter increases with E. faecalis co-infection, even in the presence of E. coli. To understand these interactions, first, we have identified that C. albicans’ transcriptional regulator, EFG1, is critical for virulence and hyphal formation in urine or during CAUTI. Therefore, we hypothesize that expression of EFG1 and/or its targets is affected by other uropathogens, impacting C. albicans’ growth, filamentation, virulence, and biofilm formation. For this R21 exploratory grant, we are proposing three independent but complementary aims to: 1) investigate E. coli’s antagonistic effect against C. albicans, specifically, on EFG1 expression and downstream genes through RNA-sequencing and validation by RT-PCR in vitro and in vivo. 2) Identify E. coli’s antagonistic factors. Our preliminary data showed that secreted small peptides of E. coli are responsible for inhibition of fungal growth and hyphal morphology. Thus, we will use a mass spectrometry-based proteomic approach to identify small peptides secreted by E. coli that may be responsible for C. albicans’ growth inhibition. 3) Characterize how E. faecalis mitigates the antagonistic effect of E. coli against C. albicans. E. faecalis highly expresses two secreted proteases, SprE and GelE, under urine conditions and during CAUTI. These proteases have been shown to target different host proteins, resulting in the modulation of host response and worsen disease outcome. We will use purified SprE and GelE to examine whether they also target E. coli’s small peptides for degradation, reducing the negative effects against C. albicans. The results from these experiments will help us gain further understanding of the complex cross- kingdom interactions during CAUTIs and eventually lead to better treatment and prevention strategies.