Dhall, Atul, Hwang, Geelsu
University of Pennsylvania School of Dental Medicine, Department of Preventive and Restorative Sciences
Candida albicans is a frequently detected fungal pathogen in the oral cavity. It predominantly exists in two morphotypes, yeast cells and hyphae, and forms polymicrobial biofilms with several bacterial species. Specifically, its mutually beneficial interactions with streptococci are known to lead to biofilms with increased microbial carriage, infectivity and antimicrobial resistance. These interactions with different streptococci vary in mechanism. For example, it is known that Streptococcus gordonii uses direct cell-cell interaction to bind avidly to C. albicans hyphae while Streptococcus mutans interacts with C. albicans via extracellular glucans. However, at the single-cell level, the biophysical aspects of such synergistic cross-kingdom interactions that aid biofilm initiation need further investigation.Methods
Here, we measured the binding forces between C. albicans (as yeast cells and hyphae) and S. mutans (or S. gordonii) in the presence and absence of in situ glucans on the fungal surface using single-cell atomic force microscopy (sc-AFM).Results
Our data show that S. gordonii preferred to bind to C. albicans as hyphae rather than yeast cells (~2.5-fold increase). However, the presence of in situ glucans lowered these binding forces in comparison to uncoated C. albicans indicating an obstruction of direct cell-cell interaction. On the other hand, S. mutans displayed similar preference for binding to C. albicans as yeast cells or hyphae. However, the presence of in situ glucans dramatically enhanced the binding forces in comparison to uncoated C. albicans (up to ~6-fold increase).Conclusion
This study provides a novel biophysical aspect to elucidate C. albicans-streptococcal interactions in terms of fungal morphotype and extracellular glucans.