Washington, July 9 - Is the explosive growth of obesity worldwide being triggered by an infectious agent? Investigators are closing in on the role of oral bacteria as a potential direct contributor to obesity.

J.M. Goodson and colleagues, who carried out a recent study, measured salivary bacterial populations of overweight women.

Saliva was collected from 313 women with a body mass index (BMI, weight to height ratio) between 27 and 32 and bacterial populations were measured by DNA probe analysis. A BMI above 25 is a sign of being overweight.

Levels in this group were compared with data from a population of 232 healthy individuals from periodontal disease studies.

Analysis of saliva revealed that 98.4 percent of the obese women could be identified by the presence of a single bacterial species (Selenomonas noxia) at levels greater than 1.