Antibiotics are a uniquely potent defence against bacteria, but they have one fatal weakness: if used to excess, their power fails. Doctors and veterinarians are prescribing antibiotics against nonbacterial organisms, notably viruses that cause the common cold, for which the drugs are not effective. In the Third World, antibiotics are a cure-all, and are mostly available without prescription. The greatest volume of antibiotics are administered through feed to domestic animals. They then make their way into human food and resistant bacteria into the human food chain. Hospital and household sewage adds substantial quantities of antibiotics into the environment. Bacteria exposed to antibiotics in sewage sludge, or water, have an opportunity to develop resistance. Repeated exposure of bacteria to drugs can result in the development of resistant strains. These resistant bacteria can then spread throughout the population. Thus, treatment for some diseases is now more difficult and expensive.
Resistance to antibiotics is carried by a small circle of DNA called a plasmid, which is separate form the rest of the genes in the bacterium and can move freely to another bacterium.
The overuse of antibiotics, such as penicillin and tetracycline, has dramatically reduced their effectiveness. For example, one type of penicillin, 100% effective in the 1940s against the common Staphylococcus aureus bacterium (MRSA), is now only 10% effective. When an antibiotic is no longer effective, others must be developed to deal with the new resistant forms of the disease. This increases costs and the new drugs may have harsher side effects. The new drug needed to successfully treat Staphylococcus aureus bacterium is 10 times as expensive as the original penicillin. Reduced effectiveness of these drugs costs lives, especially in developing countries.
About 8% of the enterococci encountered in American hospitals (1993) are resistant to vancomycin, 20 times the rate of 4 years previously. This makes enterococcus very dangerous, as it is usually resistant to virtually all antibiotics if it resists vancomycin. Consequently, 19,000 patients a year have untreatable infections.
Diseases that are re-emerging due to antibiotic-resistant strains include penicillin-resistant gonorrhoea, vancomycin-resistant enterococcus, E. coli 0157 food poisoning, antibiotic-resistant influenza, multiply drug-resistant tuberculosis, Lyme disease, and dengue haemorrhagic fever. There are probably many more such drug-resistant diseases; experts say that deaths and contagious outbreaks are not being diagnosed correctly or reported due to underfunded regional medical services. In 1993, an epidemic of yellow fever in Kenya was given full rein as a consequence of a regional laboratory's failure to diagnose the cause of the outbreak correctly.
Up to 75% of antibiotic prescriptions each year in the USA are for acute respiratory infections, mostly caused by viruses. Streptococcus bacteria cause about 10% of sore throat cases in adults; sinusitis is sometimes caused by bacteria. Antibiotic treatment of colds, bronchitis and other upper-respiratory infections is almost always inappropriate.
Bacteria have evolved invulnerability to wonder drugs that once tamed them, resurrecting the possibility of untreatable plagues. Successor drugs are still over the horizon. If the effectiveness of antibiotics is to be saved, physicians and the public must end misuse and frivolous overuse.
Research on bacteria from the frozen corpses of 19th Century arctic explorers has proven that substances other than antibiotics can make bacterial strains become resistant to antibiotics. It is suggested that such resistance may be induced by the body's reaction to heavy metals and that environmental pollution could contribute significantly to the development of this resistance.