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A Bedford County driver cleans her bus after a student died from an antibiotic-resistant staph infection last year. |
PROVIDENCE, R.I.--The public has been alerted about outbreaks of infection caused by MRSA (pronounced "mersa"), an abbreviation for methicillin-resistant Staphylococcus aureus, nicknamed "Superbug." Numerous incidents of infection and several deaths have been reported recently, prompting school officials to close their schools to allow cleaning personnel armed with mops and buckets of disinfectant to march in to sanitize buses, classrooms, cafeterias, and gymnasiums.
Person-to-person exposure is the usual mode of transmission through contact with infected skin lesions, nasal discharges, and contaminated hands or by contact with recently contaminated objects as, for example, towels and gym mats. MRSA is not an infection, but refers to a property of "staph," namely, its resistance to the antibiotic methicillin. The Staphylcococcal species is part of the normal flora of the skin and, for the most part, is not a disease producer.
About half the population carries the potential disease-producing
S. aureus
on their skin, hair, and in their throat, and about 25 percent harbor this organism in their nose; occasionally, it causes serious infection.S. aureus
causes disease ranging from pimples and localized skin infections to life-threatening infection when it invades the blood and colonizes the internal organs; it produces a variety of toxins that lead to serious damage. This is what recently caused the death of a 17-year-old boy in Virginia. Treatment was unsuccessful because the staph were resistant to methicillin. Other deaths have occurred following a similar scenario.According to the Centers for Disease Control and Prevention, MRSA accounted for 94,360 life-threatening infections and close to 19,000 deaths in 2005. MRSA kills more Americans each year than does AIDS. The distribution of these cases as cited in an Oct. 17 Journal of the American Medical Association report is cause for alarm.
About 85 percent of the cases were associated with hospitals and other health facilities, as would be expected. Disturbingly, most of the rest of the cases (14 percent) were in people with no known exposure in a hospital setting, indicating that MRSA is no longer confined to health-care facilities, but has escaped.
So schools, prisons, and other environments harboring large populations in close contact are being scrubbed down and methicillin, an antibiotic, is being used to treat people with the infection.
But since Alexander Fleming's serendipitous discovery of penicillin in 1929, bacteria have become "smart" and acquired mechanisms of antibiotic resistance. Fleming warned of this on Dec. 11, 1945, in his acceptance speech on being awarded the Nobel Prize in Medicine: "The time may come when penicillin can be bought by anyone in the shops. Then there is a danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant. "
Moral: If you use penicillin or other antibiotics, use enough.
How does antibiotic resistance come about? It is an outcome of the Darwinian process of natural selection, popularly known as "survival of the fittest." In bacterial populations, as in all populations, variation exists; in bacteria, variation is the result of spontaneous mutations or the passage of DNA from one cell to another. The antibiotic is not the direct causative of change, but the selective agent killing susceptible cells and thereby allowing resistant cells to flourish.
Essentially, antibiotic resistance is the consequence of misuse of antibiotics. Discontinuation of an antibiotic during therapy is a major contributory factor. In the first few doses, antibiotics kill those bacteria that are most susceptible, leaving the more resistant ones to flourish and possibly become invasive; these (hardier) survivors can be transferred to another host.
There are measures that can be implemented to minimize antibiotic resistance that have been described in numerous articles. They include frequent hand-washing (a good prevention against influenza), taking the full dose of an antibiotic as prescribed, a continued search for new antibiotics and other modes of treatment, and surveillance in health and other community-associated facilities.
| Robert Krasner is a professor of biology at Providence College in Rhode Island. This column appeared in the Providence Journal. |
