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There is a difference between bacteria and viruses, despite most people’s tendency to lump the two together. They are both small and reproduce by the billions, and yes, they can cause illness, but the differences between them are interesting.

Most bacteria are not only harmless, but absolutely essential to life on this planet. Bacteria, some 3000 categorized species in all, do nothing short of sustain life. They make our bread rise, our wine ferment, our lungs breathe, and our plants grow. In fact, only a small percentage are dangerous to humans.

Staphylococcus aureus, better known as staph, lives a benign existence in the nasal passages in 30% of people, but under certain circumstances can cause blood poisoning and infection. Escherichia coli, better known as e.coli, is a regular and normally harmless resident of our digestive tracts. A nasty strain of e.coli causes digestive ailments and sometimes meningitis in infants. Salmonella, the bane of egg and chicken farmers and steak tartare lovers everywhere, is probably the most infamous of bacterial ailments, causing upwards of 300,000 cases of food poisoning in the United States every year. Most bacterial infections happen when millions of cells infest another creature, but some strains are so potent that only a few hundred are needed to cause the onset of illness.

Viruses are another story. Viruses are even smaller than bacteria and, according to some definitions, do not qualify as living organisms at all. This is because they cannot survive outside another being’s cell walls. Viruses are to blame for the world’s scariest and most deadly diseases, like Ebola and Lassa fever. To be sure, the truly mysterious viruses, like the rare form of encephalitis that killed 250 Malaysians in 1999, have played havoc with modern medicine.

On the other hand, human viruses are the cause of most simple colds and coughs, which run their courses through suburbia without much harm, just inconvenience. Colds and coughs are themselves are not susceptible to treatment by antibiotics.

Antibiotics only combat bacterial infections, not viral infections. Because antibiotics are being prescribed to millions of people every year, their effectiveness against bacterial infections is weakening. When someone treats a bacterial infection--like a cold--with an antibiotic, the weaker bacteria die, but the stronger ones survive and reproduce. The result is a strain of bacteria that is resistant to treatment by that drug.

Bacteria are also able to transmit drug resistance between their own species, a bacterial Internet of sorts. This means that a bacterial strain can become resistant to a drug without ever encountering it. The task for scientists is daunting as they rush to develop new drugs to treat old and new bacterial infections.