Metabolic interplay between Proteus mirabilis and Enterococcus faecalis facilitates polymicrobial biofilm formation and invasive disease

Polymicrobial biofilms play an important role in the development and pathogenesis of CAUTI. Proteus mirabilis and Enterococcus faecalis are common CAUTI pathogens that persistently co-colonize the catheterized urinary tract and form biofilms with increased biomass and antibiotic resistance. In this study, we uncover the metabolic interplay that drives biofilm enhancement and examine the contribution to CAUTI severity. Through compositional and proteomic biofilm analyses, we determined that the increase in biofilm biomass stems from an increase in the protein fraction of the polymicrobial biofilm matrix. We further observed an enrichment in proteins associated with ornithine and arginine metabolism in polymicrobial biofilms compared to single-species biofilms. We show that L-ornithine secretion by E. faecalis promotes arginine biosynthesis in P. mirabilis, and that disruption of this metabolic interplay abrogates the biofilm enhancement we see in vitro and leads to significant decreases in infection severity and dissemination in a murine CAUTI model.

Preferential catabolism of l- vs d-serine by Proteus mirabilis contributes to pathogenesis and catheter-associated urinary tract infection

Proteus mirabilis is a common cause of urinary tract infection, especially in catheterized individuals. Amino acids are the predominant nutrient for bacteria during growth in urine, and our prior studies identified several amino acid import and catabolism genes as fitness factors for P. mirabilis catheter-associated urinary tract infection (CAUTI), particularly those for d- and l-serine. In this study, we sought to determine the hierarchy of amino acid utilization by P. mirabilis and to examine the relative importance of d- vs l-serine catabolism for critical steps in CAUTI development and progression. Herein, we show that P. mirabilis preferentially catabolizes l-serine during growth in human urine, followed by d-serine, threonine, tyrosine, glutamine, tryptophan, and phenylalanine. Independently disrupting catabolism of either d- or l-serine has minimal impact on in vitro phenotypes while completely disrupting both pathways decreases motility, biofilm formation, and fitness due to perturbation of membrane potential and cell wall biosynthesis. In a mouse model of CAUTI, loss of either serine catabolism system decreased fitness, but disrupting l-serine catabolism caused a greater fitness defect than disrupting d-serine catabolism. We, therefore, conclude that the hierarchical utilization of amino acids may be a critical component of P. mirabilis colonization and pathogenesis within the urinary tract.

Haemophilus influenzae persists in biofilm communities in a smoke-exposed ferret model of COPD

Rationale

Non-typeable Haemophilus influenzae (NTHi) is a common inhabitant of the human nasopharynx and upper airways that can cause opportunistic infections of the airway mucosa including bronchopulmonary infections in patients with chronic obstructive pulmonary disease (COPD). It is clear that opportunistic infections contribute significantly to inflammatory exacerbations of COPD; however, there remains much to be learned regarding specific host and microbial determinants of persistence and/or clearance in this context.

Methods

In this study, we used a recently described ferret model for COPD, in which animals undergo chronic long-term exposure to cigarette smoke, to define host–pathogen interactions during COPD-related NTHi infections.

Results

NTHi bacteria colonised the lungs of smoke-exposed animals to a greater extent than controls, and elicited acute host inflammation and neutrophilic influx and activation, along with a significant increase in airway resistance and a decrease in inspiratory capacity consistent with inflammatory exacerbation; notably, these findings were not observed in air-exposed control animals. NTHi bacteria persisted within multicellular biofilm communities within the airway lumen, as evidenced by immunofluorescent detection of bacterial aggregates encased within a sialylated matrix as is typical of NTHi biofilms and differential bacterial gene expression consistent with the biofilm mode of growth.

Conclusions

Based on these results, we conclude that acute infection with NTHi initiates inflammatory exacerbation of COPD disease. The data also support the widely held hypothesis that NTHi bacteria persist within multicellular biofilm communities in the lungs of patients with COPD.

Infection of smoke-exposed ferrets with COPD results in mucus obstruction and respiratory symptoms as in patients, and the bacteria are in a distinct mode of growth consistent with biofilmshttps://bit.ly/3euXpbQ