The data presented here support the hypothesis that the cariogenic organism S. mutans
exhibits greatly reduced colonization in the presence of a preexisting saliva-derived biofilms containing no or a minimal amount of S. mutans
. These findings provided evidence for the protective effect of a “normal” oral biofilm in concurrence with the proposed `window of infection' identified based on previous clinical studies [Caufield et al., 1993
According to this report, S. mutans colonization mainly occurs between the second to the third year of life. Study participants who were infected during this crucial time period acquired persistent S. mutans colonization, while uninfected individuals remained S. mutans-free until the eruption of secondary dentition provided new colonization opportunities. It is likely that these uninfected individuals formed a protective biofilm community void of S. mutans, similar to the ones we observe in the in vitro saliva-derived biofilm model system, which significantly reduced the ability of S. mutans to become part of the biofilm community when added later on.
Though the mechanism behind the ability of biofilms to exclude S. mutans
remains to be elucidated, recent studies by Kreth et al
. [Kreth et al., 2005
; Kreth et al., 2008
] demonstrated that the sequence of inoculation determines whether cariogenic S. mutans
or the health-associated S. sanguinis
[Corby et al., 2005
; Corby et al., 2007
;] compete or co-exist with one another. Both species can persist in a biofilm when inoculated at the same time, but given the chance to establish a biofilm first, either species can preclude colonization of the other. In the context of this study, it is possible that the presence of certain species (such as S. sanguinis
) in the established biofilms could mediate the protective effects against exposure to S. mutans
. Interestingly, this protective effect was observed even in the presence of 1% sucrose in the growth medium which, according to the “Ecological Plaque Hypothesis” [Marsh, 2003
], is likely to give the acid-tolerant S. mutans
a competitive advantage through its ability to produce lactic acid from sucrose fermentation. Furthermore, the microbial homeostasis within oral biofilms is suggested to shift when oral environmental changes, such as the ingestion of fermentable sugars, create low pH environments where acid tolerant/generating organisms thrive and promote demineralization. Given consistent sucrose intake, these changes can compound and result in an oral biofilm comprised of predominantly cariogenic pathogens such as S. mutans
. Our results suggest that established S. mutans
-free biofilms, both naturally occurring or through STAMP treatment, are able to reduce the competitive advantage of S. mutans
even in the presence of high sugar content, thus preventing the shift in the biofilm composition toward cariogenesis.
In addition to demonstrating that prior establishment of an S. mutans-free biofilm provides considerable protection against subsequent infection with this oral pathogen, we were able to significantly reduce S. mutans in the inocula with short 5 min exposure, a duration short enough for the application of most oral care products. More importantly, this reduction in S. mutans load achieved via STAMP treatment resulted in biofilms with considerable protective effects against further S. mutans colonization. Taken together, these results suggest that STAMP technology is a potentially useful method for removing S. mutans from saliva, thus establishing an oral flora that can help prevent or reduce further infection of S. mutans.
STAMP technology is by no means limited to modulating oral biofilms. It could potentially extend to other simple or complex microbial communities where a dynamic shift in microbial diversity is required to promote a healthy state for the host. Studies have shown that chronic conditions such as Crohn's disease and ulcerative colitis are associated with shifts in the homeostasis of the flora, and it is reasonable to speculate that inter-species interaction plays a role in determining the disease or non-disease state of the complex community within the gut as well. STAMP technology could be used to remove species that have high occurrence rates in patients suffering these diseases, such as Bacteroides vulgatus
[Mangin et al., 2004
], thus helping to reestablish a balanced flora where the specific niche of B. vulgatus
is filled by other, more benign species. Further studies are underway to examine these potential applications.