Alaska Science ForumMay 11, 1995
Dog Saliva: the Next Wonder Drug?
by Ned Rozell
This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell, is a science writer at the institute.
In the name of science, Kyle Manger and Joel Cladouhos sat down in front of Kyle's Labrador retriever, Yogi, and started to eat dinner. Almost instantly, gelatinous icicles of drool began dripping from the dog's jowls.
Instead of being grossed out, the two sophomores at Juneau-Douglas High School held a sterile glass tube under the stream and collected Yogi's saliva for use in their science fair experiment, titled "Dog Saliva: The Next Wonder Drug?"
Seven-hundred miles north, in Fairbanks, West Valley High School senior Patryce McKinney was busy reaching inside the mouths of 102 dogs to complete her award-winning science project, titled "Antibiotics and Dog Saliva."
Each of the students, who hadn't heard of one another's projects, became interested in the rumored ability of dog saliva to kill bacteria. Joel said his father works at a health clinic where a nurse said that wounds inflicted by human bites get infected more often than dog bite wounds. Patryce had heard that a wound will heal faster if you let a dog lick it.
They went about their experiments a bit differently. Kyle and Joel, both 15 and students of John Norton's introductory biology course, used sterile cotton swabs to collect samples containing bacteria found at their school. They swabbed a hand, nose, ear, mouth, and a table, and placed their samples in a petri dish on a bed of agar, a seaweed-derived substance that acts as bacteria food.
After the bacteria had flourished a few days, they made a broth of each type. They then simultaneously placed the bacteria broth and dog saliva in new agar dishes, and let them react for two days.
Patryce, 18, a student of Don Peterson's biotechnology class, obtained millions of Escherichia coli, a disease-causing bacteria commonly found in human and dog feces, from a biological supply company. She made an E.-coli broth, from which she grew a "lawn" of the one-celled organisms on a petri dish.
On her saliva quest, Patryce advertised in the West Valley teacher's lounge for volunteer dogs, and she also went to the animal shelter. Including her border collie, Oreo, she sampled 102 dogs. She chose dogs of different breeds and ages so no particular breed trait would skew her results.
Patryce went straight to the source; wearing latex gloves, she touched a tiny circle of sterile filter paper directly to the rear upper gum of the dogs, back by the molars.
Two of a dog's four saliva ducts, the zygomatic and parotid, empty saliva from glands of the same name at the points from where Patryce sampled. She said she wanted "fresh stuff" as opposed to saliva off the tongue.
After gathering three samples from each dog, Patryce placed the saliva-drenched paper on the E. coli lawns, and, as Kyle and Joel did, looked for "rings of inhibition," where the saliva slowed or stopped the growth of bacteria.
Their findings: Kyle and Joel found that dog saliva did inhibit growth, especially on nose mucous bacteria, but they also found many types of bacteria in the dog saliva itself. They concluded perhaps dog saliva is not the next wonder drug.
Patryce found that in 16 percent of her samples, E. coli growth was inhibited by the dog saliva, which to her was significant enough to show that the antibiotic properties of dog saliva merit further study.
"But it wasn't enough for me to start mass production of dog spit and marketing it," she said.
In a 1990 study done at the University of California, Davis, researchers found dog saliva killed E. coli and Streptococcus canis, another harmful bacteria. The scientists concluded that when mother dogs licked their nipples it helped keep puppies free from disease, and that dogs licking their own wounds accomplished the same goal.
I'll never turn my head from my dog's kiss again.