(Photo Courtesy of The Cell)

Topics discussed on this web page:  
Bacterial Infections, Aerobic Bacteria, Anaerobic Bacteria, 
Gram Positive Bacteria, Gram Negative Bacteria, 
Viral Infections, Fungal Infections.  

It is estimated that there are at least four times as many parasites in nature than there are hosts.  While we humans generally regard ourselves as the top of the food chain, in this section you'll get to know several of types of parasites that look at us as a source of food.  

There are many different infections that can develop in the foot (and body as a whole, for that matter).  They are typically grouped into three major families:  

  • Bacterial Infections

  • Viral Infections

  • Fungal Infections

What's the difference between bacteria, viruses and fungi? 

Bacteria are one-celled creatures.  They exist everywhere, on every square inch of land this earth, and even on top of, and inside of, every one of us.  

How many bacteria does our body harbour?  

According to bacteriologist Theodor Rosebury:  

  • There are estimated to be 200 species of bacteria living on each person, with 80 species of bacteria in the mouth alone.

  • There are an average of 10 million individual bacteria on every square inch of your skin, with the number increasing as much as 1,000 fold in the teeth, mouth and digestive tract.  

  • All the bacteria on your skin could fit into an average-sized pea, but if you include the bacteria in your intestines, the bacteria could fill an area equivalent to a can of soda pop. 

Photo:  Several E.coli bacteria 
(Photo courtesy of The Cell)

While bacteria are normally found all over, including on and in us, this is not bad.  In fact, as we cannot digest all the foods we eat by ourselves, we actually need bacteria to survive.   The problem occurs when bacteria invade areas of the body where they shouldn't be, reproducing at our expense.  This is what is known as an infection.  The bacteria may then spread throughout the body, reproducing and creating more and more individual, one-celled creatures inside the host.  

Your body has several lines of defense against bacterial infection.  The most widely-known defense against bacteria are white blood cells, which is one such line of defense your body possesses to perform this job. 

Image courtesy of

To the left is a view of a human white blood cell trapping invading bacterial cells.  The picture was taken with an electron microscope.


You have likely even seen white blood cells at some point in your life without even knowing it, as much of the material that makes up pus, the whitish, yellowish material that sometimes oozes from a wound, actually consists of white blood cells that have died in the your defense.

What kinds of bacteria infect us?  

There are numerous different bacteria can infect us. The major families of bacteria are:

Gram Positive bacteria: E.g., Staphylococcus, Streptococcus, Clostridium, Corynebacterium.  Being 'gram positive' means that the organisms stains blue when a certain dye is applied.   

Gram Negative bacteria: E.g., Haemophillus, Enterobacter, Neisseria, Proteus, E. Coli, Klebsiella, Citerobacter, Pseudomonas, Morganella, Shigella, and Serratia.  Being 'gram negative' means that the organism stains red when a certain dye is applied.  

Aerobic bacteria: Most of the above are aerobic organisms, meaning they exist in environments with oxygen.  

Anaerobic bacteria:  Anaerobic bacteria exist in environments without oxygen.  Examples of such organisms include Peptostreptococcus (most common), Peptococcus, Clostridium, and Bacteroides.  These infections usually smell putrid.  

Because there are so many types of bacteria, we have to direct treatments to the type of organism infecting each patient.  

Who gets bacterial infections?

Any break in the skin can introduce a bacterial infection.  But diminished circulation decreases your body's ability to mobilize its defense system to fight off an infection, and this is one big reason why bacterial infections are more common in diabetics, smokers, and the elderly.  Diminished immunity, too, increases your odds of getting an infection.  AIDS patients and patients on steroids are two examples of individuals who have a difficult time fighting off bacterial infections because of diminished immunity.

Perhaps the most common bacterial infection of the foot is that associated with an ingrown toenail, a condition often seen with young people.  

Pictured at right is the single most common infective agent with ingrown nails, and indeed most foot infections--staphylococcus aureus.

Image courtesy of

How do you know when you have an infection?

For information on this topic, visit our web page on identifying an infection.

How do you treat infections?  

Most infections are treated through the following:  

  • Antibiotics  Antibiotics such as penicillin are agents designed to kill the infectious organism.  These are the most common way to treat most infections.   

  • Local wound care:  Whenever there is some sort of wound (cut, ulcer, abscess, incision line, etc.), it is important to keep the wound clean, remove any dead tissue, keep the wound properly dressed and protected.  

  • Surgery:  In the case of an aggressive infection not responding to antibiotics and advancing up the foot or through the body (sepsis), in the case of antibiotics not being delivered to the infected area because of large quantities of pus, dead tissue, or in cases of bone infection or joint infection, which often don't respond to antibiotics alone, surgical intervention may be required.   

How do antibiotics work?

Because bacteria have a cell wall that is different from our the cell walls that make up our body and because bacteria have different cellular components inside cell than we have inside ours, we have designed antibiotics to target this difference.  Most antibiotics work by weakening the bacterial cell wall, or disrupting the internal function of the bacteria.  While bacteria are killed with antibiotics, our cells remain unaffected by those antibiotics because antibiotics are built specifically to act on bacteria only. 

There are dozens of antibiotics on the market, with each designed to specifically kill certain strains of bacteria.  Antibiotics are most commonly taken orally, but they can be injected or given intravenously (by I.V.).  In the case with bone infections, we can even implant antibiotics surgically, mixed with special implantable materials.

But bacteria reproduce quickly (a good example of evolution occurring before our very eyes).  An antibiotic that works today on a certain species of bacteria, may not work a few years, or even months, from now.  Indeed, new "super bugs", bacteria resistant to any known antibiotics are quite common in the news these days, making it necessary to develop new antibiotics constantly. 

Because this is such a large topic, we have devoted an entire web page to antibiotics you may wish to visit.   

Viruses, in contrast, are built much differently from bacteria.  Viruses consist only of an outer wall, with a small amount of genetic material inside.  When viruses attack, they inject their genetic material into their host, and they shed their outer wall.  The viral genetic material then moves into the nucleus of the host cell, and take over the function of that cell.  It's sort of like a science fiction movie where an alien species takes over the body of its host.  But it may make you feel better to know that viruses attack bacteria, too.

Do antibiotics work on viruses?

No.  Because the only active part of a virus, the genetic material, lives inside our own cells, there is no foreign cell wall or foreign cell function for antibiotics to target.  So far as antibiotics are concerned, cells that have been infected with a virus are indistinguishable from our regular cells. 

That's why we have no real cure yet for conditions like the common cold, AIDS or warts.  They're all caused from viruses, and there aren't nearly so many anti-viral medications as there are anti-bacterial medications (which are known as antibiotics). 

Fungi (plural for fungus) are very different from both bacteria and viruses.  Fungi have some qualities that would make us classify them as plants, and other qualities that would classify them as animals.  So they are sometimes a little difficult for people to understand.

The photo to the left is of a fungal infection 
growing on a Petri dish.  

(Photo courtesy of The Cell)

There are some types of fungal infections that can invade the body, but these are rarely seen in healthy individuals in North America.  But fungus is still commonly seen when it affects the outside of our bodies--the skin and its components.  Athlete's foot (also known as tinea pedis) is a good example of a fungal infection in the skin, and this same fungus can involve the nails (known as tinea unguium or onychomycosis).  

Do antibiotics work on fungi?

No. Fungus and bacteria are too different.  So, in general, antibiotics don't work on fungus, and antifungal medications don't work on bacteria. 

Fungal infections of the skin are usually treated topically--with cream, powder, spray, oils, ointment, soaks--but oral antifungal medications are sometimes used for difficult-to-penetrate areas like the nails, or in difficult-to-resolve fungal infections of the skin.

What happens if you don't treat the infection?

It depends.  The fight between your body and an infection can go one of three ways. 

  • The first possibility is the usual one--your body is able to fight off the infection completely.  Your body fights off infectious organisms constantly, and obviously our bodies have become quite good at this.  Antibiotics, antifungals and other medications are designed to tip the balance in this direction, in our favour.

  • The second possibility, and the least pleasant one, is that the infection can overwhelm our bodies and kill us.  This is most common in the debilitated patient, the elderly and rarely, with very strong infections that have no known treatment.  Infections can and often have killed people, as they continue to do today.  In fact in the age before antibiotics, infections often killed more soldiers fighting in a war, than did the actual fighting.  This was known since at least the age of Genghis Khan, the 12th century Mongol conqueror, who was known to catapult bodies infected with the plague over the fortress walls of cities he was trying to conquer, in order to weaken the opposing forces before attacking--the first known example of biological warfare.

  • The last possibility is that the contest is a tie.  The body fights off the bacteria well enough to stop its advance, but not well to get rid of it completely from the body.  This is called a chronic infection.  While this is not a healthy situation for the patient, some individuals can function quite well for years, even decades, with chronic infections. 

Where do you get chronic infections? 

Chronic infections can set up in a variety of locations--the lungs, the liver, intestines, for example.  But in podiatric medicine, the most common location is in bone or joint.  

Joints that are infected are called septic joints, and they can be difficult to treat.  Intravenous antibiotics may be tried, but usually surgical decompression of the joint and removal of any diseased tissue is indicated.

An infection in bone is called osteomyelitis, and this may be even more difficult to treat.  Again, intravenous antibiotics can work on some types of these infections, but surgery consisting of removing the dead and infected bone, then packing the wound with special implantable antibiotics, is usually indicated.  

If these conditions are not properly treated, the best you can hope for is to fight the infection to a draw, and live with a chronic infection and the disability it brings.  The danger is that the infection may someday breach the body's natural defences, and spread through the bone and even through the body.   

All photos from this web page courtesy of The Cell and Cells Alive.  




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The Achilles Foot Health Centre
S. A. Schumacher, D.P.M., F.A.C.F.A.S., F.A.C.F.A.O.M.  
Dr. S. A. Schumacher, Podiatric Corporation  

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