Bacteria in dogs mouth

Is a Dog’s Mouth Cleaner Than a Human’s Mouth?

You’ve probably heard the expression “a dog’s mouth is cleaner than a human’s mouth” at least once in your life. Most of us have just accepted this as fact, when we think about it at all, but have you ever wondered if it is actually true?

Here’s a hint: the answer is no.

Apples and Oranges

Comparing a dog’s mouth to a human’s mouth is “like comparing apples and oranges,” according to Colin Harvey, a professor at the University of Pennsylvania’s School of Veterinary Medicine and the executive secretary at the American Veterinary Dental College.

This is because both dog and human mouths are full of microbes. While there is some overlap in the types of bacteria between species, there are also a host of different dental bacteria in your dog’s mouth that you won’t find in yours.

Take the bacterial family known for causing periodontal disease in humans and dogs, Porphyromonas. Researchers discovered that dogs have a type of Porphyromonas called P. gulae, whereas human mouths contain its relative, P. gingivalis. Both bacteria are what most of us would consider “dirty,” and can cause problems for dog and human teeth.

In fact, dogs have more than 600 different types of bacteria in their mouths, which is a similar number to the 615 and counting types of bacteria Harvard researchers have found in human mouths. These bacteria can also be joined by other bacteria that we (humans and dogs) pick up from our environments, adding to the mix.

Can Humans Get Dog Germs?

Perhaps part of the reason the idea that “a dog’s mouth is cleaner than a human’s mouth” came to be so widely believed is that we don’t typically swap diseases with our dogs when we swap saliva. You are not going to get the flu from a dog kiss, but you might get it from kissing a human loved one.

Most of the bacteria in your dog’s mouth are not zoonotic, which means you probably won’t get a disease from a big old doggy kiss. There are exceptions to this. Dogs that are fed a raw diet are at an increased risk of contracting salmonella, which can be spread to humans, and you really don’t want to share kisses with a dog that regularly raids the litter box.

In other words, kissing your dog is less risky than kissing another human, but that does not mean that your dog’s mouth is necessarily cleaner than a human’s — he just has a mostly incompatible set of germs.

Can Dog Saliva Heal Wounds?

While we’re on the subject of dog mouths, there is another folk belief that you’ve probably heard before about dog mouths: dog saliva helps heal wounds.

This gets a little more complicated. Most mammals, humans included, lick their wounds. Historically, ancient cultures even believed that dog saliva had curative powers, and the Greeks and Egyptians both used dog saliva in healing practices and featured dogs in their religious healing rites.

They may have been on to something. The act of licking, alone, offers some benefits to wound healing. The tongue removes dirt and debris from the wound site, which lowers the risk of contamination and infection. Of course, too much licking can lead to self-trauma, as in the case of hot spots, and can actually make things much worse.

But what about the saliva itself?

As it turns out, there are certain proteins in saliva called histatins that can ward off infection, and further research has revealed that there are other beneficial chemical compounds in saliva that can help protect cuts from bacterial infections. As if that wasn’t enough, there is even more evidence that suggests licked wounds heal twice as fast as unlicked wounds.

Dog saliva is not alone in these properties. Human and other mammal saliva show similar wound-healing activity, which might help explain why we instinctively hold a cut to our mouths and kiss “boo-boos.”

Does this mean that you should have your dog lick your wounds, or that you should lick your own wounds?

Maybe not. Not all of the research about saliva was good. Curative properties aside, saliva has its risks. Take the bacterium Pastuerella, for example. This bacterium is harmless in the mouth, but can lead to serious infections if introduced into an open wound, resulting in sickness, amputation, and even death. And there are plenty of other germs we can pick up from our environments in our mouths that we do not want a wound exposed to. Also, excessive licking of a wound can lead to infection and self-mutilation.

In short, while there is some truth to this folk remedy, you are probably better off treating your wounds and your dog’s wounds with more conventional care to avoid any unnecessary risks. If you have more questions about whether or not you should let your dog lick your wounds, contact your doctor or your veterinarian for professional medical advice.

Oral Hygiene

Comparing the cleanliness of human and dog mouths misses a major point: oral hygiene.

Both dogs and humans are equally susceptible to dental disease and benefit from good oral hygiene practices to keep their mouths clean and healthy. Regular brushing and dental cleanings help humans and dogs keep harmful bacteria, like the kind that cause periodontal disease, in check and are an important part of a daily routine.

You can begin brushing your dog’s teeth when he is a puppy. This will make it easier down the road when your dog is older and full of firm ideas about what he does and doesn’t like. Training your dog to enjoy tooth brushing is just as important as getting him used to the process. Talk to your veterinarian about ways to make tooth brushing enjoyable, and be sure to use toothpaste designed for dogs and never human toothpastes, which can contain harmful substances such as xylitol.

Your dog’s mouth might not be cleaner than yours, but keeping your dog’s mouth healthy will make you feel better about those sloppy, wet dog kisses.

Bacteria From Your Pet’s Mouth: How Dangerous Is It?


An elderly lady and her pet Italian greyhound – sounds like the lovely opening to a sweet story doesn’t it? The story, however, is rather dark. According to a recent medical case report, the greyhound was the likely source of an infection resulting in a lengthy hospital stay and potentially fatal sepsis. Thankfully, this particular patient survived, but the story raises some interesting questions about our increasingly close relationship with the domestic dog.

The bug responsible was Capnocytophaga canimorsus, a bacteria commonly found in the mouths of dogs and cats. It’s estimated that up to three quarters of healthy dogs harbour this bacteria in their mouths. These animals suffer no ill effects and, in truth, humans coming into contact with this bacteria rarely suffer any medical consequences.

But, occasionally, problems might arise, especially if you have reduced immune function. With a reported mortality rate of 30%, awareness of susceptibility to Capnocytophaga canimorsus infection is important for groups who might be at particular risk, such as the elderly. The interesting point about this case is that the patient appeared to have acquired the infection via a lick from her dog and not by a bite as is more commonly reported.

Where infection is associated with dog bites, the consequences can be extreme, including gangrene and amputations. The potential for spread of this bacteria from dog licks, which is often perceived as a friendly, bonding gesture by dog owners, might suggest we should re-evaluate how close we get to our dogs’ mouths.

Dog bites have long been associated with illness. Rabies remains responsible for about 60,000 human deaths annually, mostly in developing countries. A range of other disease-causing organisms are also known to be transmitted from dogs to humans. Close relationships with our dogs might enhance the transmission of nasties, either direct from the dog, or from a contaminated environment. For example, Salmonella causes severe gastrointestinal symptoms and can be acquired by exposure to infected faecal matter.

Toxocara canis is a parasite that can cause blindness in humans and infection also comes from close contact with infected dog poo. The horrific sounding visceral larva migrans is a rare complication of Toxocara infection, when the larval parasites migrate haphazardly through the body tissues, leaving a trail of damaged tissue in their wake. Equally, there can be few dog owners who haven’t experienced the minor, short-lived irritation of a flea bite.

On the positive side

So, how healthy is our relationship with our pet dogs? Many reports detail the diverse benefits of dog ownership, from physical activity benefits to their ability to improve and promote social interactions. There are even historical accounts of dogs being encouraged and trained to lick human wounds to encourage healing. The scientific validity of this method might be questionable, but anecdotal reports remain about the potential healing value of canine saliva.

Dogs are increasingly being used as therapy animals in hospitals, hospices and other medical facilities. This is much more about their physical and behavioural attributes than their wound healing ability, however. In these environments it is important that infection control is high, both for the benefit of the patient and the welfare of the visiting dog. With good hygiene, transmission of diseases can be kept to a minimum and, despite this recent report, the value of dogs as companions and therapeutic interventions probably outweighs the risk.

Dogs, how deadly is your human?

Disease spread is a two-way street. Irina Kozorog/

We cannot ignore the fact that we also transmit pathogens to our dogs. Zoonotic diseases are those that can be spread from humans to animals and back again. Studies have demonstrated that dogs can carry multi-drug resistant strains of bacteria, many of which have probably been transmitted to them by humans. We have a responsibility for minimising infection risk – yes from our dogs but also to our dogs.

So, should you worry about your dogs’ deadly saliva? In general no, although these rare stories are often a timely reminder that while we often share our lives, homes and sometimes our beds with our dogs, they can harbour “partners” that might not be such ideal companions for us.

The next time your dog tries to lick your face, instead of worrying about Capnocytophaga canimorsus infection, it might be more prudent to think about what your dog last licked – that might be a scarier consideration.

By Jacqueline Boyd, Lecturer in Animal Science, Nottingham Trent University. This article was originally published on The Conversation. Read the original article.

Dog Saliva: 5 Fast Facts You Should Know

Dog saliva may produce allergies in humans. While many people believe that pet fur is the culprit of allergic reactions to dogs, many of these allergies actually stem from proteins found in dog saliva. According to a study published in the European Journal of Allergy and Clinical Immunology, dog saliva contains at least 12 different allergy-causing protein bands. When dogs lick their fur, the saliva dries, and these proteins become airborne. Researchers who conducted the study concluded that dog saliva has greater potential as an allergen source than dog dander.

Tips for Preventing Periodontal Disease

Dr. Eisner notes that despite the cavity-preventing nature of dog saliva, periodontal disease will still occur without active prevention.

“Saliva coats our teeth,” says Dr. Eisner. “If it’s not brushed off by tooth brushing, it becomes plaque, which further traps the bacteria.” As the condition progresses, the bacteria can cause bone destruction in the tooth-supporting structures of the mouth.

“When a dog or even a person has a mouth that hasn’t been cared for, every time they eat, they get bacteria in the bloodstream,” Eisner says. “It’s a 20-minute transit through the bloodstream, and our immune systems, spleens and livers helps clean the blood. It’s no harm for the very healthy with a good immune system. But young animals and pets with serious medical conditions or autoimmune diseases are more susceptible to circulating bacteria.”

Aside from using dog toothbrushes and dog toothpaste, Dr. Eisner recommends annual dental care for dogs. A puppy should have his first exam at eight weeks of age. Dogs that have periodontal disease may need to visit their vet more frequently to monitor the progress of the condition.

Mythbusters: Dog’s Mouth Cleaner Than Humans
  • Webmaster
  • 14 September, 2015
  • Mythbusting | Wellness |

Man’s best friend has better oral hygiene than man himself, if the old saying is to be believed. But are dog germs and human germs even comparable?

It’s an old saying you’ve likely heard many times before: a dog’s mouth is cleaner than a human’s mouth. Of course, usually you hear it from people who’ve just let their dog lick them all over the face or even … inside their mouths. Where would someone get the idea that a dog has a cleaner mouth than a person? Some say it’s based on dogs licking their own wounds and how they seemingly heal up faster, or how human bites can actually be worse than dog bites. While the legend’s origin may remain a mystery, the facts are not: you really don’t want your dog’s germs getting inside your mouth.

Dog Germs vs Human Germs

Yes, it is a myth, but whether or not a dog’s mouth is cleaner than a human’s mouth can be tricky to prove. Although everyone’s mouth is going to be unique, Fido’s kisser may indeed have fewer germs than yours, as far as numbers go. But the more critical bit of information is the type of germs in a canine’s mouth as opposed to the germs floating around your own. In other words, it’s more a matter of germ quality versus germ quantity. There are human germs and there are dog germs, and they can be two very different things.

Everyone already knows how much bacteria we humans can carry around on our hands. Everything we touch throughout a day – handrails, bathroom door handles, cell phones, TV remotes, etc. – are virtual germ hotbeds. Now compare the cleanliness of the average human’s hands with what is essentially a dog’s hands: its mouth. Your dog is licking, taste testing, gnawing on, or just straight up eating nearly everything in its path throughout his or her life (and anyone who also owns a cat and has a litter box in the house knows what that means). Now just imagine yourself doing the same thing. Not a pretty picture, right?

Dog’s Mouth vs Human Mouth

Oral hygiene also plays a role as well, since a healthy mouth is generally associated with a clean mouth. With that in mind, the better you take care of your (and your dog’s) teeth and gums the healthier both of your mouths will be. But when you take into account what your dog uses its mouth and tongue for throughout a given day, it’s probably best to skip the open mouth kisses and stick with a good ear scratching or belly rub to express your affection, instead.

How Do People Get Infected with Capnocytophaga?

People with these conditions should speak with their doctors about how to safely interact with cats and dogs.

The Capnocytophaga germs that are common in dogs and cats can be spread to people through a bite or after close contact with dogs or cats. Infections are more often linked to dog bites or dog contact.

See the Preventing Dog Bites page for information on how to prevent dog bites and what to do if you are bitten, regardless of your health status.

Other Capnocytophaga germs can also be found in human mouths and can cause illness in some people who have the bacteria in their own mouth. People who have weak immune systems get this type of infection more often than healthy people.

Most reported infections occur in tissues connected to the mouth and throat, including:

  • Periodontal (gum) disease
  • Respiratory tract infections (infections of the mouth, nose, throat, and lungs)
  • Eye infections

In both types of infections—those that spread from animals or from oneself—the bacteria can enter the blood stream, which can lead to infection in various parts of the body. Infection can also cause the following:

  • Septicemia (blood infection)
  • Endocarditis (inflammation of the lining of the heart)
  • Abscesses (collections of pus in the tissue that cause redness and swelling) in various body tissues
  • Inflammation of the eyes, face, lymph nodes, or brain membranes

Most contact with dogs and cats does not lead to a Capnocytophaga infection or any illness, even after a bite. But, you should take precautions if you have contact with animals, especially if you have a condition that puts you at higher risk of infection.

A woman’s limbs were amputated after her dogs licked her and gave her a bacterial infection. Most dogs carry the same bacteria.

A Capnocytophaga infection can cause flu-like symptoms

Blisters, fever, confusion, vomiting, and muscle and joint pain can appear anywhere from 1 to 14 days after exposure to the bacteria, according to the Center for Disease Control and Prevention.

The infection can escalate to potentially deadly complications like sepsis, a life-threatening inflammation caused by the body fighting off illness. High fever, chills, extreme pain, shortness of breath, high heart rate, dizziness, and clammy, sweaty skin are all signs of sepsisl

If you suspect an infection and your condition rapidly worsens, seek medical help immediately. The infection can also cause necrosis and gangrene, or tissue death, which may require amputation.

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Anything that weakens your immune system can up your risk of Capnocytophaga infection

Elderly people are particularly susceptible to sepsis from Capnocytophaga infections, according to a 2016 case report, because the immune system can decline with age. Older folks may also be more likely to own pets, the report stated.

Other risk factors include illnesses like HIV or cancer, certain types of medication, and even drinking heavily.

Dog bites are most likely to put you at risk of Capnocytophaga infection

Dogs are more likely to transmit the bacteria than cats, though most often through bites. Still, scratches from either animal can spread germs, so you should always wash any animal bites or scratches with soap and water right away — they can carry a lot more than bacteria, including rabies.

Although 50% of Americans are likely to be bitten by a dog at least once in their lifetime, Capnocytophaga is still extremely rare — just 54 human cases were reported from 1972 to 2004, according to one study. About 200 human cases have been reported worldwide since 1976, according to another study from 2011.

The lesson? Keep playing with your pets, just be sure to properly wash your hands (and any slobbered on body parts) afterward.

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Are Dogs’ Tongues Really Cleaner Than Humans’?

by Abby, Grade 8, Iowa, 2011 YNA Winner


Abby and her dog, Lucy

“Abby! Don’t let the dog lick you! Her tongue is full of bacteria!” Ever since we got a dog a few years ago, my mom has always been saying that. I love when my dog runs to greet me when I get home from school and says “hello” by giving me licks. What I hated, though, was feeling guilty and disgusted about having her doggy bacteria all over my face. So I decided to do a test to see how dirty dogs’ tongues really are.


I hypothesized that human tongues would be cleaner than dog tongues. I thought this because humans brush their teeth at least once a day. I hypothesized that dogs’ tongues would be dirty because they were always licking dirty things like garbage.

Background Research

I read about bacteria on a number of different websites, including the University of California’s Museum of Paleontology and Wikipedia. I also read an article from the Journal of the American Academy of Dermatology called “Dog, Cat, and Human Bites: A Review.” Lastly, I read an article from the Journal of Clinical Microbiologycalled “Cultivable Oral Microbiota of Domestic Dogs.”

Dog 2

What I learned from my bacteriology studies is that bacteria were first called “animalcules” by Antonie van Leeuwenhoek when he discovered them in 1676. Bacteria are single-celled organisms without a nucleus. Because they are so small, bacteria can only be observed with a microscope. These organisms are only a few micrometers long (a micrometer is 1/1000th of a millimeter). There are bacteria covering your skin, inside your body and many other places. Only about 1 percent of bacteria are harmful. Most bacteria are neither harmful nor helpful. For example, useful bacteria cover the inside surface of some of your organs, preventing harmful bacteria from infecting your organs. A lot of neutral bacteria are found in your digestive system, to prevent infection. Many bacteria help your immune system. However, some bacteria cause disease; many infectious diseases are spread by the sharing of saliva infected by harmful bacteria.

Some studies have found differences in the types of infections that happen after being bitten by a human or an animal. But this didn’t tell me which bacteria are normally present. Being bitten in the hand by a human will cause infection for a human. Yet only 1 percent of emergency room visits are for infectious bites from dogs. This made me wonder if humans and dogs have significant differences in the type and amount of bacteria in their mouths.

Project Description

How scientists describe the amount of bacteria on a plate.

1. Finding the lab: After deciding that I had a testable hypothesis, I had to find a lab in which to carry out my experiment. I wrote a grant request to the State Hygienic Lab at the University of Iowa explaining what I wanted to do there and what I was trying to find out. My grant was accepted, and I was assigned a mentor to work with me at the facility.

2. Materials:

    • 12 Fisher’s Finest swabs
    • 12 gram-negative agar plates
    • 12 blood agar plates
    • Disposable loops
    • Safety equipment: gloves, goggles, lab coat

3. Variables, Controls and Sample Size: The only variable I was testing was the difference between species. The control was the human saliva. I had five human samples and seven dog samples because of the limited materials the lab offered me.

Abby and her mentor, Gabriella Gerken

4. Getting the samples: On June 20-21, 2010, I went around to five of my neighbors who are dog owners and obtained saliva samples. I had the owners of the dogs test their dogs and themselves with separate swabs. I asked the subjects to not brush their teeth or eat prior to the sampling to make sure the tests weren’t compromised. This assured that the only variable being tested was the difference between dogs’ and humans’ mouths. I used Fishers’ Finest swabs to swab their tongues. I put the swabs in the refrigerator until I went to plate them on June 21, 2010. I made sure to keep the subjects anonymous by labeling them Human 1 to 5 or Dog 1 to 5.

5. Plating the bacteria: On June 21, 2010, I went to the State Hygienic Lab at the University of Iowa to plate the bacteria on agar. I used blood agar plates that show both gram-negative and gram-positive bacteria, and gram-negative agar plates that have gram-positive antibiotics in them so that only gram-negative bacteria can grow.

The gram stain of bacteria is a way to classify bacteria based their cell walls. To do the gram stain, you put a sample of the bacteria on a plate, stain it purple with a chemical, de-stain it with alcohol, and then stain it with a pink chemical. If the bacteria stain purple, they are gram-positive, which means that their cell walls absorbed the purple chemical. If the bacteria are pink, they are gram-negative, which means that their cell walls didn’t take up the purple chemical but did take up the pink. Gram-positive cells are usually found in the mouth or on the skin, and gram-negative cells are usually found in the intestines.

The light pink Petri dishes are the gram-negative plates that have a gram-positive antibody so only the gram-negative bacteria show on the plate.

I first swabbed a fourth of the agar plate, and then I used a loop to spread the bacteria around so that when the bacteria grew, I could get a better idea of their quantity. To plate bacteria, you first streak a fourth of the plate, and then you take some of the bacteria you placed on the plate and rub it along the next side of the plate using an instrument called a loop. Then you disinfect the loop and take some of the bacteria from the first time you used the loop and rub it around on the next quadrant. Finally, you disinfect the loop again and take some of the bacteria from the second time you used the loop and rub it around the rest of the untouched part of the plate (see diagram).

This red Petri dish is an example of a blood agar plate. This means that both gram negative and gram-positive bacteria can grow.

I learned from my mentor the way scientists describe the amount of bacteria on the plates. She taught me that if, after a few days, there were only bacteria cultures in the original place you streaked with the swab, you would say there is a “rare” amount of bacteria on the plate. If there are bacteria cultures on the first side you used the loop on, you would describe the bacteria amount as “few.” If there were bacteria cultures on the part of the plate where you used the loop for the second time, you would describe the bacteria amount as “moderate.” If there are bacteria cultures on the last place you used the loop, you would describe the bacteria amount as “many.”

6. Growing the bacteria: After the cultures were kept in an incubator at 35°C for 24 hours, I observed their growth.

Petri dishes showing human bacteria growth

7. Analyzing the plates: The next day I went back to the lab and analyzed the plates. I described the amount of bacteria using the method described above. I also determined how many bacterial colonies there were by their different shapes, sizes and colors. All observations were recorded in my lab notebook. When I was finished analyzing the plates, they were autoclaved and disposed of by the Hygienic Lab.

Data Table Averaged Data Average Number of Different Bacterial Colonies

The dog Petri dish samples have many different bacteria as can be seen from the different colors and shapes of the bacteria colonies. Most of these plates would be described as having rare or few bacteria colonies because of the position of all the colonies.

The human Petri dish samples mostly have the same brown flat bacteria or white bacteria, unlike the very diverse dog samples. Most of these samples would range from having “few” to “moderate” bacteria levels. These are blood agar plates that allow both gram-negative and gram-positive bacteria to grow.

I recorded the quantity of bacteria on each plate, and I tried to estimate how many different bacterial colonies were on each plate. (I had to estimate because it is nearly impossible to find the exact number.) When I got home, I averaged the data to better understand it. I first found the average quantity of dog and human total bacteria, gram-positive bacteria and gram-negative bacteria. To do this, I assigned a rating scale in which rare = 1, few = 2, moderate = 3, and many = 4. I averaged the results and recorded them in the data table.


I found the average total for human bacteria to be 3, which is a rating of “moderate.” The average total for dog bacteria was 2.7 (between “few” and “moderate”). The average total of gram-negative dog bacteria was 0.9, which is “rare.” The average total of gram-negative human bacteria was 0.2, which would be considered “very rare.” The average total of gram-positive dog bacteria was 1.9, which is close to “few.” The average total of gram-positive bacteria for humans was 2.8, which is almost “moderate.” (These numbers will be interpreted later in my conclusion.)

The average number of gram-positive bacteria in a human’s mouth was 4.2 colonies. Human mouths had more gram-positive bacteria (the type of bacteria usually found in mouths or on skin) than dogs do. Yet human mouths had fewer gram-negative bacteria (this type of bacteria is mostly in intestines) than dogs do? This makes sense, because dogs probably get gram-negative bacteria from sniffing dog waste or dogs’ behinds. Humans probably have more gram-positive bacteria because of the environment in their mouths.

I also averaged the quality of the plates, or how many different kinds of bacteria were found in each plate (see graph). The average total for dogs was 5.6 different bacterial colonies. The average total for humans was 4.1 different kinds of bacterial colonies. The average number of gram-negative bacteria in a dog’s mouth was 2 colonies. The average number of gram-negative bacteria in a human’s mouth was 0.2 colonies. (One person out of five had one colony of gram-negative bacteria.) The average number of gram-positive bacteria in a dog’s mouth was 3.7 colonies. (These numbers will also be interpreted in my conclusion.)

The graph shows that human mouths have more gram-positive bacteria yet fewer gram-negative bacteria than dogs do (as shown in the Average Data table). Dogs have a greater total of bacterial colonies. This might be because dogs gather many different types of gram-negative bacteria from sniffing other dogs’ waste and bottoms. Dogs also pick up bacteria from the things they sniff and lick. Although humans brush their teeth a lot and clean their mouths often, there are still a lot of bacteria in their mouths. This is probably because there are many harmless bacteria in the world that live naturally in the human mouth.


I concluded that dog and human mouth flora are very different. (Flora means the bacteria found in a mouth or anywhere else.) The bacteria found in human mouths are more similar to another human’s oral bacteria than the bacteria found in a dog’s mouth.

I also concluded that dogs’ mouths are cleaner than humans’ in some ways, and dirtier in other ways. Humans have more bacteria in their mouths than dogs do, based on the total number of bacteria. Most of the humans had a “moderate” number of bacteria, and most of the dogs had “few” bacteria. A possible explanation of this might be that dogs pant a lot, and maybe while panting, bacteria falls off their tongues along with their saliva. But dogs had more types of bacteria. The average number of different bacterial colonies in a dog’s mouth was about 5.7. The average number of different bacterial colonies in a human’s mouth was about 4.1. I think this is so because dogs sniff and lick a variety of things, like carpets, floors, chairs, grass, etc., so they pick up bacteria from many places.

Dogs have more gram-negative bacteria in their mouths. I think this is because they often sniff and lick things on the ground. 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. When they do that, they may get some gram-negative bacteria on their nose that used to be in the other dog’s intestine; then later the dog will lick its nose, getting the bacteria in its mouth. Humans have more gram-positive bacteria in their mouths. I think this is so because the human mouth provides an environment that suits gram-positive bacteria.

In conclusion, will I let my dog continue to lick me? The answer to the question is yes! I will feel guiltless about letting my dog lick me because I found out that human and dog oral bacteria are different, so my dog’s oral bacteria present no harm to me.

Further Research

I would like to research what types of gram-negative bacteria are found in dogs’ mouths and where they came from to see if my hypotheses are true. I would also like to see if brushing dogs’ teeth daily would help prevent harmful bacteria from growing in their mouths. Conducting this experiment on a larger scale with more subjects will help to support my conclusion. It is known that data is more reliable when there are more subjects being tested.


I would like to thank my mom for encouraging me to write a grant to work at the State Hygienic Laboratory at the University of Iowa. I would like to thank Gabriella Gerken for being a great mentor, and for teaching me so much about plating bacteria and understanding the gram stain. I would like to thank my dad for helping me to understand more about the world of bacteria.

I am so grateful to have been able to experience working in a university lab at the age of 13. I have learned so much working with the agar plates and bacteria. I will be perfectly happy if I don’t win, because the experience was incredible and very educational, and I am so happy I get to share my discoveries with the world.


“Bacteria.” Wikipedia. 29 November 2009. Retrieved from

Brook, I. “Microbiology and Management of Human and Animal Bite Wound Infections.” Primary Care 1 (30 March 2003): 25-39.

(HealthDay News) — A Wisconsin man had his lower legs and hands amputated after developing a rare blood infection caused by bacteria in dog saliva.

The patient – Greg Manteufel – first developed flu-like symptoms such as fever and vomiting. By the next morning, his temperature had soared and he was delirious. After his wife rushed him to the hospital, she noticed his body was covered in bruises, as if he’d been beaten with a baseball bat, the Washington Post reported. Within a week, Manteufel’s legs were amputated from the knees down. Then doctors had to remove his hands.

Doctors diagnosed Manteufel with a rare blood infection caused by Capnocytophaga canimorsus, which is commonly found in the saliva of most healthy dogs and is usually not harmful to humans, the Post reported. But in Manteufel’s case, the bacteria got into his bloodstream, triggering sepsis. The bruises on his body were actually blood spots caused by the sepsis.

Manteufel was given antibiotics to fight the infection, but clots blocked blood flow to his extremities, resulting in tissue and muscle death and the need to amputate his legs and hands in order to save his life, the Post reported. He had further surgery to remove dead tissue and muscle from his leg amputations, and, this week, he will have two more surgeries to remove dead tissue. He may also require nose reconstruction surgery due to necrosis.

Washington Post Article
More Information

Nov. 25, 2019 — Pet owners should seek immediate medical care if they develop unusual flu-like symptoms, doctors say after a case study about a 63-year-old man in Germany who died of a rare infection contracted when he was licked by his dog.

The infection was caused by capnocytophaga canimorsus bacteria, which is commonly found in the mouths of dogs and cats, but rarely transmitted to humans, CNN reported.

The case study was published in the Journal of Case Reports in Internal Medicine.

In May, doctors amputated an Ohio woman’s legs and hands after she contracted a capnocytophaga canimorsus infection, likely caused when her puppy licked an open cut, CNN reported.

Last year, a Wisconsin’s man nose and limbs were amputated after he contracted the same type of infection.

Capnocytophaga canimorsus is “completely normal flora of a dog’s mouth and usually doesn’t cause any sort of significant disease. However, in the wrong place, at the wrong time, in the wrong patient … it can lead to severe infections — but very, very rarely,” Dr. Stephen Cole, lecturer in veterinary microbiology, University of Pennsylvania School of Veterinary Medicine, told CNN.

The deadly reason why you shouldn’t let dogs lick your face

Affectionate dog owners are at risk of catching a potentially deadly disease.

While the man’s best friend are great at cheering their owners up when they’re down, they may be responsible for threatening the life of their keeper.

An expert completely dismissed the myth that a dog’s mouth is much cleaner than a human’s.

Dog expert Marty Becker said: “All you have to do is look, watch, smell and you’ll realise that is not true.

“They raid the garbage can. You know, we give each other a peck on the cheek when we say hello, they give each other a peck on the rear end.”

The friendly animals who love to lick faces can and do carry a long list of bacteria which can severely impact human health.

John Oxford, professor of virology and bacteriology at the Queen Mary University in London, explained how the beautiful creatures get bacteria in the first place.

He said: “It is not just what is carried in saliva.

“Dogs spend half their life with their noses in nasty corners or hovering over dog droppings so their muzzles are full of bacteria, viruses and germs of all sorts.”

The strong bacteria have the power to cause a range of dangerous diseases, some deadly.

Capnocytophaga Canimorsus is a bacteria that lives in a dog’s saliva.

It has the power to cause fatal infections including sepsis, which can ultimately lead to organ failure and even death.

Initial symptoms of this infection are similar to those of other illnesses. But carriers will fall ill much more quickly than those with a commonplace equivalent.

Symptoms of Capnocytophaga Canimorsus include fever, chills, sweats and a lack of energy.

Ringworm is said to be one of the easiest infections dog’s can pass on.

According to reports, owners who take their dogs to places where several animals are close together, such as kennels or shelters, make their pets more susceptible to catching the bacteria.

But if a dog is carrying the infection it will be fairly visible as symptoms including dandruff, hair loss and darkened patches will show on a dog’s skin and hair.

Our furry friends can also carry the potentially fatal MRSA disease, but it will not have any effect on them.

Children are at a greater risk of catching these infections from a dog’s lick.

Should You Allow a Dog to Give You Kisses?

Big, wet sloppy dog kisses are one of the best things about owning a dog — at least, according to some people. For others, their reaction to dog licking is more of a shriek of disgust. Whether you enjoy playing kissy-face with your dog or not, it’s best to understand if you should be allowing these dog kisses or not.

Why Dogs Lick

Licking is a behavior that dogs learn from birth, says Animal Planet. As soon as puppies are born, their mother licks them in order to clean them and stimulate breathing, and the pups learn to lick their mother in return. This licking instinct never goes away. The process of licking releases endorphins that provide a sense of pleasure and help to relieve stress, which is why some dogs resort to obsessive licking behaviors when they get anxious. In dog packs, licking also serves as a sign of submission to more dominant members of the pack. When it comes to dogs licking humans, however, it’s generally a sign of affection, although sometimes your dog might lick you simply because you taste good.

Is Dog Licking Safe?

While it was once believed that dogs’ mouths were cleaner than those of humans and that dog saliva had healing properties, this myth has been thoroughly debunked. Considering that dogs are prone to nibbling on poop and licking their own unmentionables, it probably comes as no surprise that in reality, a dog’s mouth is a pool of germs. However, while dog saliva can carry such dangerous bacteria as Salmonella and E. coli, as well as parasites like Giardia and Cryptosporidium, these illnesses generally aren’t carried in quantities large enough to pose a danger to most humans, and there is very little evidence that doggie kisses are a means of transmission.

When Dog Kisses Aren’t Safe

Despite the low risk of the average person contracting an illness from dog licking, there are some people for whom the risk is too high to take a chance. Under no circumstances should your dog be allowed to lick anyone who falls into any of these categories, says Vetstreet:

  • Babies
  • Pregnant women
  • The elderly
  • Anyone with pimples or open sores or scratches on their face
  • Anyone with a compromised immune system, including someone undergoing chemotherapy, AIDS patients, diabetics, and anyone recovering from an illness

Lowering the Risk

You can lower the risk of contracting illnesses from dog kisses by simply being a responsible pet parent. Regular health checks that include fecal examinations, deworming and treatments to control fleas, ticks and other parasites can go a long way toward reducing the chances that your dog can pass an infection on to you. Properly disposing of your dog’s deposits and thoroughly washing your hands afterward can also reduce the risk of spreading disease. Additionally, it’s important that your pup’s food should be cooked thoroughly — never give him anything raw that might be a source of bacterial infection, such as raw meat or a pig’s ear to chew on. Choose a dog food that is balanced and formulated for your dog’s health first and foremost. You should also brush your dog’s teeth regularly to maintain his oral health, and kill bacteria that might be looming in his mouth.

Putting a Stop to Dog Licking

While it might be safe to allow your pooch to lick you on the face and mouth, if you’d prefer not to take the chance, the best thing to do is nip the behavior in the bud by teaching your dog not to lick your face. Pet trainer Victoria Stillwell, speaking to Animal Planet, suggests that the best way to do so is to get up and walk away from your dog when he starts to lick, ignoring the behavior completely. Doing so will deprive your dog of any reward he receives from licking, and eventually he’ll stop trying altogether.

If you love swapping kisses with your dog, it’s probably safe to keep doing so, as long as your immune system is up to par. But if the thought of your dog licking you on the mouth sends you running for the antibacterial soap, there exists enough of a risk to justify your aversion. Ultimately, allowing your dog to lick your face comes down to the state of your health and your level of risk tolerance. Either way, there are plenty of other ways to share affection with your dog, so don’t feel bad if licking isn’t one of them.

Contributor Bio

Jean Marie Bauhaus

Jean Marie Bauhaus is a pet parent, pet blogger and novelist from Tulsa, Oklahoma, where she usually writes under the supervision of a lapful of furbabies.

John Oxford, a professor of virology at Queen Mary University of London and an expert in microbiology, said he would never let a dog lick his face, The Hippocratic Post reported.

“It is not just what is carried in saliva,” he said. “Dogs spend half of their life with their noses in nasty corners or hovering over dog droppings so their muzzles are full of bacteria, viruses and germs of all sorts.”

What other illnesses can be transmitted?

Other infections, such as hookworms and roundworms, can be transmitted in a practice called coprophagia, in which animals ingest one another’s stool or by licking each others’ anuses, Dr. Nandi said in an email.

Dr. Joe Kinnarney, the immediate past president of the American Veterinary Medical Association, said in an interview that one study calculated that a puppy could have as many as 20 million to 30 million roundworm eggs in its intestinal tract in one week. He said a client’s child at his practice in Greensboro, N.C., nearly lost an eye from a roundworm infection.

It is conceivable that a dog with fecal material in its mouth could transmit an intestinal parasite to a human through licking, but that is rare, Dr. Sarah Proctor, a clinical assistant professor and the director of the veterinary technology program at the University of New Hampshire, said in an email.

More commonly, a parasite can be contracted by ingesting contaminated soil — via a home garden, for example — where pets have left their droppings.

President Obama even touched on the subject in an interview with Wired magazine that was published in August:

“I still don’t let Sunny and Bo lick me, because when I walk them on the side lawn, some of the things I see them picking up and chewing on, I don’t want that, man,” Mr. Obama said, laughing.