Metabolite Cross-Feeding Enhances Virulence in a Model Polymicrobial Infection

Microbes within polymicrobial infections often display synergistic interactions resulting in enhanced pathogenesis; however, the molecular mechanisms governing these interactions are not well understood. Development of model systems that allow detailed mechanistic studies of polymicrobial synergy is a critical step towards a comprehensive understanding of these infections in vivo. In this study, we used a model polymicrobial infection including the opportunistic pathogen Aggregatibacter actinomycetemcomitans and the commensal Streptococcus gordonii to examine the importance of metabolite cross-feeding for establishing co-culture infections. Our results reveal that co-culture with S. gordonii enhances the pathogenesis of A. actinomycetemcomitans in a murine abscess model of infection. Interestingly, the ability of A. actinomycetemcomitans to utilize L-lactate as an energy source is essential for these co-culture benefits. Surprisingly, inactivation of L-lactate catabolism had no impact on mono-culture growth in vitro and in vivo suggesting that A. actinomycetemcomitans L-lactate catabolism is only critical for establishing co-culture infections. These results demonstrate that metabolite cross-feeding is critical for A. actinomycetemcomitans to persist in a polymicrobial infection with S. gordonii supporting the idea that the metabolic properties of commensal bacteria alter the course of pathogenesis in polymicrobial communities

In vitro

The purpose of this study was to investigate the antibacterial activity of various adhesive materials against five different oral streptococci. The antibacterial activity of the adhesive systems was evaluated using agar diffusion tests. In each section of each plate, 6-mm-diameter wells were created with sterilized glass cylinders. Ten microlitres of self-etch adhesives and control materials were applied into the shallow holes. After incubation at 37 °C for 24 h, the growth inhibition zones were measured in millimetres. Statistical analyses were performed by using two-way analysis of variance and the Tukey's multiple range test (p < 0.05). A statistically significant difference was found between inhibition zones of oral streptococci cultivated with different adhesive systems (p < 0.01). Clearfil Protect Bond exhibited larger inhibition zones than the other materials that were used against the oral streptococci. The antibacterial effects observed for the different tested adhesive systems may be related to 12-methacryloyloxy dodecyl-pyridinium bromide and the acidic nature of the materials