Are Bacteria Winning the Arms Race?

By now, the alarm bell has sounded loud and clear about the danger posed by bacterial resistance to the inventory of currently useful antibiotics. Although limiting the usage--and overusage--of such drugs may seem like a viable remedy, such a strategy alone may not be sufficient. NIGMS grantee Dr. Bruce Levin of Emory University has reached this grim conclusion based on mathematical modeling studies of antibiotic resistance patterns. The results of these studies, in his words, point to a "dreary" prognosis in which "natural selection appears to be winning the arms race with technology."

Dr. Levin's modeling results have been borne out by laboratory findings. A case in point is a recent study in which Dr. Levin and his group analyzed the bacteria present in infant diapers from a day care center. Nearly one-quarter of the diapers contained strains of the bacterium E. coli that were resistant to the antibiotic streptomycin--a drug that has not been widely prescribed for the last 30 years. The likely explanation for such persistent resistance, he says, is the propensity for different types of bacteria to indiscriminately "share" resistance elements--small, circular bits of DNA that arm a given bacterium against antibiotic drugs--among themselves. Such sharing maintains virtual reservoirs of antibacterial resistance just waiting to happen.

Another of Dr. Levin's group's worrisome conclusions is that while the bacteria's acquisition of resistance coincides with the loss of other useful traits, this appears to be of little detriment to the microbes. Their computer modeling efforts reveal that so-called "fitness"--the ability of the bacteria to thrive and reproduce--seems to be startlingly unaffected by the presence of antibiotics. Nevertheless, Dr. Levin avows, while reducing antibiotic usage may not reverse humans' position in this arms race with evolution, such a strategy is still necessary. "We need to buy time to develop alternative treatments, and more prudent use of antibiotics will certainly slow the pace at which resistance evolves," he says.

REFERENCE

Stewart FM, Antia R, Levin BR, Lipsitch M, Mittler J. The population genetics of antibiotic resistance II: analytical theory for sustained populations of bacteria in a community of hosts. Theoretical Population Biology 1998;53:152-65.

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