<br /> As you might think, bacterial infections are caused by bacteria, and viral infections are caused by viruses. Perhaps the most important distinction between bacteria and viruses is that antibiotic drugs usually kill bacteria, but they aren't effective against viruses.<br />Bacteria<br />Bacteria are single-celled microorganisms that thrive in many different types of environments. Some varieties live in extremes of cold or heat. Others make their home in people's intestines, where they help digest food. Most bacteria cause no harm to people, but there are exceptions.<br />Infections caused by bacteria include:<br /> • Strep throat<br /> • Tuberculosis<br /> • Urinary tract infections<br />Inappropriate use of antibiotics has helped create bacterial diseases that are resistant to treatment with different types of antibiotic medications.<br />Viruses<br />Viruses are even smaller than bacteria and require living hosts — such as people, plants or animals — to multiply. Otherwise, they can't survive. When a virus enters your body, it invades some of your cells and takes over the cell machinery, redirecting it to produce the virus.<br />Diseases caused by viruses include:<br /> • Chickenpox<br /> • AIDS<br /> • Common colds<br />In some cases, it may be difficult to determine whether a bacterium or a virus is causing your symptoms. Many ailments — such as pneumonia, meningitis and diarrhea — can be caused by either bacteria or viruses<br />Diagnosis of Bacterial and Viral Infections<br />You should consult your doctor if you think you have a bacterial or viral infection. Exceptions include the common cold, which is usually not life-threatening.<br />In some cases, it's difficult to determine whether an illness is viral or bacterial because many ailments -- including pneumonia (https://www.webmd.com/lung/tc/pneumonia-topic-overview), meningitis (https://www.webmd.com/brain/understanding-meningitis-basics), and diarrhea (https://www.webmd.com/digestive-disorders/digestive-diseases-diarrhea) -- can be caused by either. But your doctor may be able to determine the cause by listening to your medical history and doing a physical exam (https://www.webmd.com/a-to-z-guides/annual-physical-examinations).<br />If necessary, they also can order a blood (https://www.webmd.com/heart/anatomy-picture-of-blood) or urine test to help confirm a diagnosis, or a "culture test" of tissue to identify bacteria or viruses. Occasionally, a biopsy (https://www.webmd.com/cancer/what-is-a-biopsy) of affected tissue may be required.<br />Treatment of Bacterial and Viral Infections<br />The discovery of antibiotics (https://www.webmd.com/cold-and-flu/rm-quiz-antibiotics-myths-facts) for bacterial infections is considered one of the most important breakthroughs in medical history. Unfortunately, bacteria are very adaptable, and the overuse of antibiotics (https://www.webmd.com/cold-and-flu/video/josephson-antibiotics) has made many of them resistant to antibiotics. This has created serious problems, especially in hospital settings.<br />Antibiotics are not effective against viruses, and many leading organizations now recommend against using antibiotics unless there is clear evidence of a bacterial infection<br />