Antibiotics are a uniquely potent defence against bacteria, but they have one fatal weakness: if used to excess, their power fails. This is now happening because of doctors who over-prescribe antibiotics and farmers who regularly add them to animal feed. The overuse of such antibiotics as penicillin and tetracycline has dramatically reduced their effectiveness. Hospital sewage systems discharge substantial quantities of antibiotics into the environment. Bacteria exposed to antibiotics in sewage sludge, or water, have an opportunity to develop resistance

Some doctors prescribe 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. 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

Diseases that are re-emerging in 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; American 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

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 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

In 1993, about 8% of the enterococci encountered in American hospitals were 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

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

1. 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

2. Up to 50% of the antibiotics prescribed could be eliminated through more appropriate prescribing practices. Curbing antibiotic prescriptions for respiratory infections such as sinusitis, bronchitis and other, non-specific infections can reduce the prevalence of antibiotic-resistant bacteria