The oral microbiome of farmworkers are markedly different than other humans, and pesticide exposure explains why, new research shows.

To measure the impact of pesticides on farmworkers, a team of scientists at the University of Washington collected oral swabs from 65 farmworkers and 52 non-farmworker adults living and working in the Yakima Valley. Samples were taken from participants multiple times during the spring and summer, when pesticides had been recently sprayed and exposure risks were greater, as well as during the winter, when exposure risks were limited.

Adults with concentrations of organophosphate pesticide, Azinphos-methyl, in their blood had a significantly altered oral microbiome.

"[We found] significantly reduced abundances of seven common taxa of oral bacteria, including Streptococcus, one of the most common normal microbiota in the mouth," researcher Ian B. Stanaway said in a news release.

Researchers also found a correlation between pesticide exposure and shifts in the abundance and diversity of several other strains and species of bacteria, including microbes belonging to genera Streptococcus and Halomonas.

Additionally, scientists measured shifts in bacterial diversity related to changing levels of exposure during the seasons.

"The challenge becomes, what does this mean," said researcher Elaine M. Faustman, a toxicologist and professor of environmental sciences. "We don't know, [but] we depend on the micriobiome for many metabolic processes."

The study's findings were detailed in a new paper published this week in the journal Applied and Environmental Microbiology.

Researchers say more work is necessary to tease out the ways pesticide-triggered microbiome changes might affect human health.