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Antibiotics Block Growth and Kill Pathogens

Antibiotics are drugs, taken orally, intermuscularly, or intravenously, that counter an infection. They include agents such as penicillin, tetracycline, ciprofloxacin, and erythromycin. Common bacterial diseases treated with antibiotics are tuberculosis and gonorrhea. Fungal and protozoan diseases are also treatable, but with agents specific for these organisms. (The biochemistry of fungi and protozoa differs substantially from that of bacterial cells.) Antiviral agents constitute a third set of specialized compounds. In general, little cross-reactivity exists among the categories, that is, agents used for fungi do not cure infections caused by viruses, bacteria, or protozoa. However, the principles underlying action and resistance are the same; consequently, in Antibiotic Resistance we lump all these agents together as antibiotics. Combining all the agents into a single category risks confusion, because the public has been told repeatedly not to use antibiotics for viral diseases. In this instruction, antibiotics are equated to antibacterials, and indeed antibacterials should not be used for viral infections. But the world is changing. We now have many antiviral and antifungal agents that are just as antibiotic as penicillin. The important issue is to identify principles that enable experimental data obtained with one agent to be used for making decisions with another. Such a cross-disciplinary effort is facilitated by having a general term (antibiotic); we use specific terms, such as antibacterial and antiviral, only when we need to distinguish the agents.

In molecular terms, antibiotics are small molecules that interfere with specific life processes of pathogens. Antibiotics generally enter a pathogen, bind to a specific component, and prevent the component from functioning. In cases of lethal antibacterials, treatment leads to formation of toxic reactive oxygen species that contribute to bacterial death. Not all antibiotics kill pathogens. Indeed, many of the older drugs only stop pathogen growth. Nevertheless, they can be quite effective because they give our natural defense systems time to remove the pathogens.

Antibiotics have been called magic bullets and miracle drugs because they quickly cure diseases that might otherwise cause death. When penicillin first became available in the middle of World War II, it gave life to soldiers who were otherwise doomed by infection of minor wounds. Penicillin was so valuable that urine was collected from treated soldiers and processed to recover the drug. Now antibiotics enable many complicated surgeries to be performed without fear of infection. Developments in molecular biology have even enabled pharmaceutical companies to design antibiotics that work against viruses. Among the more striking examples are antibiotics that attack the human immunodeficiency virus (HIV): They reduce the viral load and relieve many symptoms of HIV disease.

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