By the end of his impressive and accomplished life, the industrialist/aviator/ filmmaker Howard Hughes was undone by a paralyzing fear of germs. He saw them everywhere: microscopic swarms of bacteria, parasites and viruses on every surface, infecting his body with untold horrors. To his credit, Hughes wasn’t completely nuts. A close look at even the healthiest patch of human skin would reveal a rich diversity of microbial life, including some bugs with the potential to do great physical harm.
A microbe is any single-celled organism, whether plant, animal, fungus or bacterium. Viruses are usually considered microbes, even though they aren’t cells themselves, but rather bundles of RNA that invade and hijack healthy cells. Microbes are literally everywhere. Your body is home and host to hundreds of trillions of microbes, inside and out. Your intestinal tract alone holds too trillion bacteria, far outnumbering every tissue, blood and bone cell in your entire body.
Microbes thrive in warm, moist conditions, but are some of the only life forms that can survive in the planet’s most extreme places, like the glaciers of Antarctica or the red-hot plume of an underwater volcano. Scientists divide microbes into four broad categories: bacteria, protozoa, fungi and viruses. If a microbe has the ability to make us sick (pathogenic), like some bacteria and most viruses and protozoa, we call it a germ.
Of those hundreds of trillions of microbes living on or inside your body, a significant percentage of them are germs. The good news is that germs typically exist in small enough quantities that the immune system can neutralize them before they cause disease. Sometimes, however, germ colonies breach our defences and flourish.
The definition of disease is when cells in your body stop functioning properly. One of the many causes of disease is infection, when a germ enters the body (through the digestive, respiratory or circulatory systems), multiplies rapidly and begins to inhibit normal cell function. Some protozoa like the malaria parasite colonise red blood cells and rupture them, leading to severe anaemia, while some bacteria like E coli emit toxins that destroy cells along the intestinal or urinary tracts. Some of the most common symptoms of disease – fever, vomiting, sneezing, coughing and diarrhoea – are not directly caused by the microbes themselves. It’s just your immune system trying to fight off the infection by killing or physically expelling the little beasties.
Of course, not all microbes are bad. Life itself began four billion years ago as a form of bacteria, and it was an ancient type of cyanobacteria that was the first to perform the magic act of photosynthesis, turning sunlight into oxygen. Even today, microbes are the miniature factories that regulate and recycle the essential building blocks of life. When an organism dies, its carbon is salvaged and recycled into the environment by a host of microbes, including bacteria and fungi. Bacteria in the soil ‘fix’ nitrogen from the air and make it available to plants. Phytoplankton, composed of both protozoa and cyanobacteria, transform C02 into solid, reusable carbon compounds. And bacteria in our intestines, notably lactobacillus acidophilus, help us better digest and extract nutrients from food.
Unfortunately, the few seriously nasty microbes give the rest a bad name. Infectious disease caused by microbial infections kills more people worldwide than any other single cause. Just think of the diseases that can trace their roots to a viral, protozoan or bacterial infection: HIV, TB, malaria, pneumonia, sleeping sickness and historical pandemics like the bubonic plague, Spanish flu and smallpox. The discovery of antibiotics (penicillin itself was derived from a fungus) has saved countless lives, but overuse of them has resulted in even more virulent and drug-resistant strains of bacteria, including so-called ‘superbugs’ that spread in hospital settings and target the critically ill and the elderly.
Microbial infections are a rightful cause for concern, but let’s not get all Howard Hughes about it. The best protection is to keep your hands clean with soap and water and to keep your hands away from your face. Get all of your vaccinations and vaccinate your children (a surprising number of adults die from chicken pox every year, usually contracted by their unvaccinated child). Take these simple everyday precautions and your well-evolved immune system should take care of the rest.
Types of germs
Bacteria are some of the smallest and oldest life on Earth. Fossil evidence of these single-cell organisms dates back 3.5 billion years and may represent some of the first life on the planet. Bacteria live everywhere and can thrive in the most extreme cold and heat, but they love the warm comfort of the human body. Only one per cent of known bacteria are harmful to humans, but we know a few of them too well: strep throat, E coli, botulism, the list goes on. Good bacteria help plants and animals extract nutrients from food and soil. Bacteria cells have no walled-off nucleus, just a nucleoid with a single chromosome containing a closed circular strand of DNA.
EXAMPLE: Tooth cavities
This isn’t an old wives’ tale. Strains of bacteria in the mouth, such as lactobacillus acidophilus, feed on sugars and release lactic acid. If you don’t clean your teeth regularly, the acid will eat away at the minerals in the surface, forming an infected hole called a cavity.
Biologists have only identified 100,000 species of fungi out of what could be millions in existence. Most fungi exist as microscopic networks of cells, but their colonies can grow so large that we can see them with the naked eye: on the surface of spoiling food, rotting logs, or as the large fruiting bodies we call mushrooms. Fungal cells grow in elongated tubes called ‘hyphae’ that branch off and interconnect. Humans have learned to use fungi to ferment beverages and foods (yeast) and create life-saving drugs (penicillin), but some fungi can cause rashes (athlete’s foot, jock itch, yeast infections), allergies and chronic lung diseases.
EXAMPLE: Fungal infection
The fungus known as ‘tinea’ thrives in the warm and wet confines of human skin. If left unchecked, colonies will grow rapidly, causing irritation and inflammation of the skin underneath. Tinea pedis is the fungus that loves the space between your toes, causing itching, dryness and cracking.
Protozoa are the world’s smallest animals. Amoebas are the most famous protozoa, shape-shifting blobs that engulf their prey (bacteria, microfungi) and digest them in stomach-like sacks called ‘vacuoles’. Most protozoa are parasites or predators, including the infamous Plasmodium falciparum, which causes malaria.
EXAMPLE: Amoebic dysentery
In the case of amoebic dysentery, a person ingests a mature cyst of the protozoan parasite entamoeba histolytica, usually from food or water contaminated within fecal matter. Once the cyst reaches the intestinal tract, it releases trophozoites, active amoeba that burrow into the intestinal lining, causing violent diarrhoea and sometimes even death.
Viruses are the smallest germs of all. In fact, they aren’t even cells – just molecules of genetic material (DNA or RNA), which are coated in a protective shell of protein. They come in all different shapes (rods, spheres, multi-sided, even little ‘tadpoles’) and, unlike other microbes, are almost always bad for you. Viruses target individual types of cells, attaching to landing sites on the cell surface. The virus then injects molecules of DNA or RNA into the cell, which directs the cell to produce even more virus particles before destroying itself. Diseases spread by viruses range from the common cold to smallpox, hepatitis, polio, ebola and HIV.
EXAMPLE: Chicken pox
Chicken pox is caused by the varicella zoster virus, a highly virulent germ (infection rates are as high as 90 per cent) that first attacks the cells at the back of the nasal passages before spreading through the blood stream to nerve and other tissue. In most healthy children, the body’s immune system fights off the virus, often causing fevers and body aches in addition to the trademark itchy pox. However, the varicella virus can lie dormant in nerve cells, emerging later in life as shingles, chicken pox’s more painful cousin.