New evidence has suggested that oral and gut microflora may have significant impacts on the predisposition, development, and stability of obesity in adults over time—although less is known about this phenomenon in children. Compared with healthy-weight controls, overweight and obese adult patients are now known to harbor specific pathogens, such as Selenomonas noxia (S. noxia), that are capable of digesting normally non-digestible cellulose and fibers that significantly increase caloric extraction from normal dietary intake. To evaluate this phenomenon, clinical saliva samples (N = 122) from subjects with a normal BMI (18–25) and a BMI over 25 (overweight, obese) from an existing biorepository were screened using qPCR. The prevalence of S. noxia in samples from normal-BMI participants were lower (21.4%) than in overweight-BMI (25–29; 46.1%) and obese-BMI (30 and above; 36.8%) samples—a strong, positive correlation that was not significantly affected by age or race and ethnicity. These data strongly suggest that S. noxia may be intricately associated with overweight and obesity among patients, and more research will be needed to determine the positive and negative feedback mechanisms that may be responsible for these observations as well as the interventions needed to remove or reduce the potential effects of this oral pathogen.