In the following series of in vitro studies, we aimed to investigate the interactions between probiotic lactobacilli and opportunistic oral pathogen species under various conditions. Our study hypothesis was that probiotics integrate into oral biofilms, interact with species in the biofilms, and thus alter their pathogenic potential, which further reduces the risk for some common infectious oral diseases. Investigations on probiotic properties in the presence of oral pathogens in vitro could facilitate and expand our understanding of inherent modes of probiotic activity. First, we evaluated the inhibitory activity of six commercial probiotic lactobacilli against Candida albicans and non-albicans Candida with an agar-overlay method. The inhibitory activity of probiotic lactobacilli against C. albicans was strain-dependent and varied according to pH and carbohydrate source. Lactobacillus rhamnosus GG (LGG) and C. albicans were the species we selected for the sub-studies that followed, because LGG showed the strongest inhibitory activity, and C. albicans was the most susceptible yeast. Second, we assessed the potential risk for lactobacilli on dental hard tissues by investigating the pH of the spent culture medium of lactobacilli in planktonic cultures and in single-species biofilms, as well as when co-cultured with other microbes. In five-species biofilms (5SP) in the presence of LGG, LGG was able to grow well with lactose or sucrose as its only carbohydrate source. LGG did not significantly reduce the pH when cultivated with the other five species of oral pathogens in biofilms, nor did the carbohydrate source affect the pH values. Third, we investigated the growth of (opportunistic) oral pathogens in the presence or absence of LGG in dual- and multi-species biofilms under five carbohydrate conditions. Probiotic LGG promoted the growth of Streptococcus mutans and of S. sanguinis compared to their growth without LGG; LGG suppressed, however, the growth of C. albicans; and C. albicans and S. mutans significantly promoted the growth of LGG. LGG showed no impact on the growth of the pathogens in group 5SP+LGG (including all of the pathogens tested), but LGG was able to reduce the growth ratio of S. sanguinis in four-species biofilms+LGG (including all of the tested pathogens except S. mutans). Further evaluated was also the susceptibility of biofilm species to commercial mouthwashes. LGG neither enhanced nor weakened the mouthwash antimicrobial effects on the pathogens. Their recovery after mouthwash rinsing was not influenced by the residual LGG. In conclusion, LGG could inhibit the growth of C. albicans; however, C. albicans promoted the growth of LGG. Differing from the traditional understanding, LGG growing with multi-species biofilms could survive and grow well under conditions in which lactose or sucrose was the only carbohydrate source. Probiotic LGG and pathogenic streptococci could benefit each other when co-cultured in dual-species biofilms, but this phenomenon did not occur in multi-species biofilms. The probiotics showed no influence on the antimicrobial effect of mouthwashes.
|Place of Publication||Helsinki|
|Publication status||Published - 2020|
|MoE publication type||G5 Doctoral dissertation (article)|
Bibliographical noteM1 - 70 s. + liitteet
Fields of Science
- 313 Dentistry