Young Naturalist Award Winner Investigates How Dirty Dogs’ Mouths Really Are main content.

Young Naturalist Award Winner Investigates How Dirty Dogs’ Mouths Really Are

by AMNH on

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Abby dressed in a striped shirt with her small terrier dog, Lucy, on a couch.
Abby, pictured here with her dog, Lucy, received a research grant to compare the bacteria in humans’ and dogs’ mouths. Photo courtesy of Abby.

Thirteen-year-old Abby and her mother always disagreed on one point: should Abby let their dog lick her when she returned from school? “Abby! Don’t let the dog lick you,” her mother would scold. “Her tongue is full of bacteria!”

Determined to learn the truth about the level of bacteria in her dog’s mouth, Abby applied for a research grant at the State Hygienic Lab at the University of Iowa. When the lab accepted her proposal and paired her with researcher Gabriella Gerken, Abby began collecting dog and human saliva samples for her investigation. Her findings, detailed in the essay Are Dogs’ Tongues Really Cleaner Than Humans’?, received a 2011 Young Naturalist Award.

Using cheek swabs, Abby collected saliva from her neighbors and their dogs. She then set to work testing the samples for gram-negative bacteria, which are usually found in intestines, and gram-positive bacteria, typically found in mouths or on the skin. By plating the bacteria in Petri dishes and staining them with purple and pink chemicals, Abby was able to compare the various amounts and types of germs in her subjects’ mouths.

The results? There was no clear-cut dirtiest mouth. Overall, dogs had fewer bacteria in their mouths than humans did, but dogs had a greater diversity of bacteria types. Abby also found that her human samples contained more gram-positive bacteria than the canine samples, and that dogs had more gram-negative germs. “I think this is because [dogs] often sniff and lick things on the ground,” Abby reasoned in her essay. “Since gram-negative bacteria are usually only found in the intestines, maybe dogs get the bacteria in their mouths because they sniff other dogs’ bottoms.”

Based on her findings, Abby has decided to keep accepting her dog’s kisses. But she does plan on testing whether brushing dogs’ teeth can make their mouths cleaner.

The Young Naturalist Awards is a nationwide, science-based research contest for students in grades 7 through 12 presented by the Museum. To learn more and to submit your own project, visit The deadline for the 2012 contest is March 9, 2012.

The Young Naturalist Awards are proudly supported by Alcoa Foundation.