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Your feet are teeming with fungi.

Government researchers have just done the first genetic survey of all the fungi that live on our skin. Their findings?  They’re in your ears, they’re in your nose and, yes, they are in the goop between your toes.

Humans are covered with hundreds of different types of fungus, the team at the National Institutes of Health found. What’s surprising is that one family covers most of our bodies, but our feet are crawling with hundreds of different species of fungi, they report in the journal Nature.

"This is going to make me always wear flip flops in the locker room. When you see how many fungi can live on your feet, you realize … you are sharing your fungi with everyone who is walking around that locker room with you,” says Julie Segre, who led the team at the National Human Genome Research Institute.

They found DNA from fungi in the nostrils and on the ears, the scalp and the hands. But the feet are really covered with fungus -- something that may not surprise anyone who’s suffered through a bout of athlete’s foot.

The team found just one single genus of fungus, called Malassezia, dominates the head and trunk of the body.  They found 11 different species of Malassezia, one of which causes dandruff.

"I was surprised that there was just one type of predominant fungus on your core body," Segre says.

But the feet? They’re fungus heaven.

National Human Genome Research Institute

Bacteria and fungi surround a hair follice, as seen under a fluorescent microscope.Fungi appear blue-green, bacteria appear pink and skin cells and the hair shaft appears yellow.

Segre’s team sampled 10 health volunteers for their study, taking samples from 14 different spots.

Two of the volunteers looked like they may have had fungal infections – marked by scaly heels and thick toenails. Those two had similar-looking fungal communities on their feet, while the other eight had different fungi on theirs.

And the fungi don't just cause disease. "The fungi help to make your feet stinky," Segres says. "The odor is a byproduct of the microorganisms, the bacteria and the fungi."

Besides Malassezia, the researchers found Penicillium -- the mold that penicillin comes from -- Saccharomyces, the yeast used in making bread and beer, and Aspergillus, among others, on the feet of their volunteers. Species that live in between the toes are different from the species found on the heels. In all, there were 80 different genera of fungi on the feet, Segre’s team reports.

Antifungal creams aim to remove pathogenic fungi but Segres said it's futile and undesirable to try to get rid of all the fungi. "Even when you really scrub your skin you are not removing all the bacteria and fungi," she said. Good fungi, just like good bacteria, help keep the skin healthy, she said.

"We have to start thinking about our bodies as ecosystems," Segres said in a telephone interview. "Just as many of the foot powders will cause your feet to be less sweaty, when you put on moisturizer you are fertilizing the fungal microorganism garden."

Why are the feet so hospitable to fungi? "I think it's temperature," Segres said. Feet can be as much as 15 degrees cooler than the rest of the body. "Because your feet can be sometimes hot, sometimes cold, there can be different fungi," she said.

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Researchers trying to figure out if microbes living in your body might be a factor in weight gain say a breath test could show if you’re loaded with greedy germs that pull every last calorie out of food.

Study after study is showing that people are covered in bacteria, fungi and other microorganisms that help digest food, that can keep teeth healthy and even that cause dandruff. And they’re finding that the types of microbes living in the colon and intestines may play a major role in just how much nutrition the body gets out of food.

“Normally, the collection of microorganisms living in the digestive tract is balanced and benefits humans by helping them convert food into energy,” says Dr. Ruchi Mathur, an endocrinologist at at Cedars-Sinai Medical Center in Los Angeles.

Mathur and colleagues were looking at a species of bacteria called Methanobrevibacter smithii – M. smithii for short. As its name indicates, it makes a lot of methane – the odorless gas responsible for burps and other inconvenient emissions.

People who produced the most methane and another gas, hydrogen, in their breath weighed more and had more body fat than people who produced the lowest amounts, they reported in the Journal of Clinical Endocrinology & Metabolism.

“This is the first large-scale human study to connect the dots and show an association between gas production and body weight,” Mathur said in a statement.

The team tested 792 volunteers, dividing them into four groups – those with “normal” levels of gases in their breath, those who had more methane than average, those who breathed out more hydrogen than average and those who produced extra amounts of both methane and hydrogen.

Those in the last group, exuding the highest concentrations of both hydrogen and methane, also had higher body mass indexes or BMI, the standard measure of height to weight that doctors use to determine obesity. They also had more body fat than the others.

This fits in with other work Mathur’s team has done on the role of this particular bug in obesity, they noted. For one, obese people with more methane detectable in their breath weighed nearly 15 pounds more than other obese people who didn’t produce as much methane.

M. smithii needs hydrogen, and it gets it from other bacteria living in the gut, which produce hydrogen gas as a byproduct of metabolizing food.  The researchers are not entirely sure how a methane-producing bug might make people fatter, but said it’s possible methane gas slows the passage of food through the intestines and colon, allowing more calories to be extracted.

Diet could affect this, and the researchers didn’t ask their volunteers for details about what they ate. “However, given the large sample size, these individual variations may be mitigated between groups,” they wrote.

Researchers are trying to figure out if it’s possible to kill off the guilty germ and help people lose weight. But they know better than to just kill gut bacteria willy-nilly – studies have shown that taking antibiotics can alter the balance of microbes in a bad way, causing stomach upset, allowing deadly infections such as C. difficile to take hold and, perhaps, even allowing a takeover by the obesity-generating germs.

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It’s a stomach-churning video – a young woman turning a silicone buttock implant around and around under her skin and wondering out loud if this could possibly be right.

It’s not, says Dr. Anthony Youn, a Michigan-based plastic surgeon who runs the blog Celebrity Cosmetic Surgery. “It’s pretty shocking,” Youn says.

NBC News was unable to contact the unidentified woman in the video, but Youn said he thinks it’s for real. “When she moves the implant around, it’s shaped like a real buttock implant,” he says.

An increase in the demand for such procedures means surgery-gone-horribly-wrong cases are almost certain to be on the rise, Youn says.

“A lot of people want it but they don’t have the money, so they take it upon themselves to inject substances like silicone,” Youn said in a telephone interview.

“If it’s not performed almost perfectly, you could have major problems.”

“Major problems” can include death. In Feb. 2011, a 20-year-old British woman died in Philadelphia after getting a bargain-basement buttock enhancement procedure in her hotel room. Just weeks before, 36-year-old Whalesca Castillo was arrested for operating without a license and injecting women’s breasts and buttocks with liquid silicone from her home in the Bronx. She was sentenced to a year in prison after pleading guilty this past June.

In July, Oneal Ron Morris of Miami was charged with manslaughter in the death last March of Shatarka Nuby, 31. Morris was already facing charges of practicing health care and without a license and causing serious bodily injury for allegedly injecting at least two women with a toxic mixture of Fix-a-Flat tire sealant, mineral oil and cement in a backroom attempt at buttock enhancement. Nuby died after receiving injections to enlarge her breasts, allegedly from Oneal.

The American Society for Aesthetic Plastic Surgery has a long list of such incidents. “Disturbing reports of patients being injected with everything from liquid silicone to baby oil and other unapproved products are appearing in the press on a regular basis," the group says on its website. "Make sure your clinician is using only FDA-approved products purchased within the United States. If he or she refuses to give you this information, seek another clinician.”

Gluteal enhancement – known colloquially as “butt implants” -- are among the more unusual cosmetic procedures that people ask for but are becoming more common, according to the American Society for Plastic Surgeons.

Its data shows that in 2011, 1,149 people got buttock implants, compared to 806 in 2010. There are no statistics for earlier years. That compares to 4,546 people who got buttock lifts in 2011, and 301,000 who got breast augmentation. The  American Society for Aesthetic Plastic Surgery counted 2,100 buttock augmentation procedures in 2004.

When so many people are trying to lose weight, why the pursuit of a larger derriere? “It really started with J-Lo,” says Youn. Singer Jennifer Lopez is known for her curves – especially her shapely bottom. “Part of it is cultural, I think,” added Youn. “We have a popular culture that puts an emphasis on the size of the buttocks.”

He points to Kate Middleton’s younger sister Pippa, whose profile in a tight dress grabbed attention at Middleton’s 2011 wedding to Britain’s Prince William -- but the phenomenon goes back even farther, to Sir Mix-a-Lot’s 1992 hit “Baby Got Back,” which starts with the line “I like big butts”.

For people who want such enhancements, it’s important to go to a professional with a lot of experience, Youn says. Board certified plastic surgeons are members of the American Society for Plastic Surgeons or the American Society for Aesthetic Plastic Surgery, or both. “And you want to make sure they do a lot of these every year. It’s not for the novice doctor,” Youn advises.

Youn says he won’t do buttock implants, but will inject fat to enhance various body areas. A lot can go wrong, he said.

“One reason it is fraught with complications is the area where you put the implant, we consider it a dirty area,” Youn said. “Implants, if they get any type of bacteria on them, can get infected very easily.”

And that can cause a complication no one wants. “When implants get infected they can literally extrude. The body can open the incision and try to push it back out,” he said.

Second, the gluteus maximus is the largest muscle in the body, and needs big blood vessels to supply it. If silicone gets into the blood, it can cause embolisms, which are painful and potentially deadly if they end up in the heart or brain.

The operation itself isn’t fun. “It is a painful operation because you have to sit on that area,” Youn said. “You have to literally avoid sitting on your bottom for weeks afterward.”

Or something might happen like the YouTube video shows.  

“If the pocket that the implant was put in is too big, then the implant will move around like that,” Youn says. “I have seen it with breast implants. You can literally flip the implant around in your breast.”

Buttock implants are shaped with one rounded side and one flat side, Youn said, “You want to put it in the buttocks like a hand in a glove where it really doesn’t move.”

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AP

A clump of Staphylococcus epidermidis bacteria (green) in the extracellular matrix, which connects cells and tissue, taken with a scanning electron microscope. At right, the bacterium Enterococcus faecalis, which lives in the human gut, is just one type of microbe that live on your skin, up your nose, in your gut; enough bacteria, fungi and other microbes that collected together could weigh a few pounds. (AP Photo/National Institute of Allergy and Infectious Diseases (NIAID, Agriculture Department)

Could antibiotics make you fat?

Two studies this week suggest that using antibiotics may save people’s lives, but could also change their metabolisms. Put together, the studies suggest that taking antibiotics might alter digestion to help people absorb calories from food they normally would be unable to digest.

Every human carries pounds of microorganisms that we couldn’t live without. They break down food and extract nutrients like Vitamin K for us. Antibiotics will kill some of these beneficial organisms, which is why so many doctors now tell patients to eat yogurt after taking a course of the drugs, to replace some of the good guys.

“There is emerging evidence suggesting the importance of the microbes in our intestines and their role in absorbing food,” said Dr. Leonardo Trasande of New York University, who led one of the studies.

The two studies look at different sides of the coin, and help answer two questions -- whether antibiotics really do affect how we absorb nutrients, and how they might do so. Together, they support the idea that the drugs kill off some populations of bacteria and allow microbes to flourish that are very good at getting calories out of hard-to-digest plant foods.

Trasande’s team looked at the medical records of more than 11,000 newborns in Britain, who were carefully followed after they were born in the 1990s. The babies who got antibiotics before they were 6 months old were 22 percent more likely to be overweight by the time they were 3 years old, the team reported in the International Journal of Obesity. If they got antibiotics later in childhood, there wasn’t a strong effect – something that could suggest the antibiotics changed the balance of the microbes as they were just setting up shop in the infants. Babies are born with sterile digestive tracts, and they acquire bacteria, yeast and other microorganisms mostly from their mothers. The germs are collectively called “flora” by scientists.

“They play key roles in immune functions, among other things,” Trasande told NBC News. “Antibiotics disrupt the development of the healthy flora in our gut. The earlier the exposure occurs, the more disruptions occur,” Trasande says. “It seems the first few days and months are important. It is difficult to reconstitute that in later life.”

The other piece of the puzzle is whether it’s the antibiotics or something else that is doing this. Dr. Martin Blaser of New York University has been studying the effects of antibiotics on the body for years. A second team he heads has been studying what happens if you feed antibiotics to animals.

They wanted to replicate what farmers have known for decades -- that giving low doses of antibiotics to farm animals make them fatter. Many experts had thought the drugs were keeping the animals from getting infections and making them healthier, but Blaser suspected something else was going on.

When his team gave mice low doses of antibiotics long-term, the mice got fatter even though they weren’t eating any more than other mice. This, they report this week’s issue of the journal Nature, suggests the antibiotics somehow make the mice absorb more calories from their food.

“We have other work that is in process that continues to confirm and extend this,” Blaser said. “That work shows that giving antibiotics early in life, similar to what farmers do in their farm animals, is changing metabolism in mice and making them bigger and fatter.”

The gastrointestinal tract is also the center of hormone production, the researchers said. It’s possible altering the organisms in the intestines – called the microbiome -- could help people better absorb nutrients and calories from “indigestible” foods such as cellulose.

The second NYU team gave the mice varying combinations of the antibiotics penicillin, vancomycin and chlortetracycline. Mice that got the antibiotics piled on more fat than other mice, even though the fatter mice did not eat more. Also, their poop had fewer calories – suggesting they were absorbing more and eliminating less.

Other mouse studies being done by Blaser’s team show that giving antibiotics to mice every once in a while -- akin to giving antibiotics to a child to treat ear infections -- also alter the gut bacteria.

So does that explain why people are getting fatter? Does every dose of antibiotics kill off some bacteria, allowing the energy-efficient species to move in and squeeze every calorie out of an apple peel or bowl of high-fiber cereal?  

“That’s at least one of the mechanisms,” says Blaser. But he notes that studies in people suggest it’s doses very early in life that matter most, just as various colonies of bacteria are getting established in the colon and intestines. And there’s an effect on the immune system, too. Other studies show that changing the balance of bacteria effects immune cells known as T-cells – something that may someday help explain links between diet and diseases such as inflammatory bowel diseases and perhaps even colon cancer.

In other words, it is too soon to say whether a 5-day prescription of Zithromax for strep throat could make you fat.

“A lot of things are interconnected,” Blaser says. “Obesity is multifactorial. I am not saying antibiotic effects on the microbiome are everything but our work suggests it is contributory. Whether it’s 10 percent or 70 percent, we don’t know yet.”

Another big missing piece of the puzzle: Which species of bacteria are the most important? People have trillions of bacteria in and on their bodies. Microbes outnumber human cells by a factor of at least 10 to one and scientists believe at least 10,000 different species live in and on us. Healthy colonies of microbes not only process vitamins, but maintain pH balance on the skin, prevent tooth decay and even protect against infections. So which ones are killed by the antibiotics, and which do we want more of? No one knows yet.

“We are just beginning to scratch the surface,” said Dr. Ilseung Cho, who worked on the study in mice.

While it is important not to use antibiotics when they are not needed, the researchers stress that they do save lives. “I wouldn’t rush to come off any antibiotics right now,” Cho cautioned.

It’s also not clear if food like yogurt, called probiotics, help much. “There is a concept called prebiotics,” Cho said. “It is essentially introducing nutrients into your digestive tract that would select for particular bacteria. Then you might be able to alter the bacteria.”

Prebiotics are found in plain old food such as soybeans, jicama and raw oats, all of which are rich in compounds such as inulin, which people cannot digest, but which certain bacteria love.

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