Increased antibiotic use and misuse has generated an increasing number of resistant pathogenic strains, presenting a significant public health problem. Alexander Fleming was one of the first to voice concern about antibiotics and stress that misuse of the drugs could lead to resistance. In his 1945 Nobel Prize lecture, Fleming ended with a cautionary remark saying; but I would like to sound one note of warning it is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them, and the same thing has occasionally happened in the body. His warnings came at the same time as infections with antibiotic resistant bacteria strains were beginning to increase. One hospital reported that the percentage of penicillin-resistant Staphylococcus aureus infections had increased from 14% in 1946 to 59% by 1950.

The ideal dosage and duration of antibiotic treatment will kill all susceptible bacteria and provide minimal opportunity for resistance to occur. When a bacterial infection is treated with antibiotics, any bacteria that have become resistant will survive, particularly if the treatment dose is too low or the duration too short. Antibiotics used for a variety of purposes outside of medicine have also contributed to the increase of resistant strains. The continual exposure of bacteria to low doses of antibiotics added to hand soaps, cleaning products, laundry detergent, and feed for livestock, selects for the survival of antibiotic-resistant bacteria.

Antibiotic resistance is especially dangerous with infectious diseases that are pervasive and easily spread. Diseases like tuberculosis, malaria, and childhood ear infections have become very difficult to treat. Tuberculosis cases in the US were nearly eliminated with the 1940 discovery of isoniazid, but are on the rise again, due to the emergence of resistant strains that can only be treated with less effective drugs. Nearly 2 million patients each year contract bacterial infections during a hospital stay. Staphylococcus aureus is commonly found in hospitals and infects patients with weakened immune systems causing blood poisoning and pneumonia. Strains have been isolated that are resistant to methicillin, oxacillin, penicillin, amoxicillin, and even vancomycin, an antibiotic used when other options fail. The prevalence of antibiotics and antibacterial cleaners in hospitals means that more than 70% of hospital acquired infections in the US are resistant to at least one antibiotic.