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Antibiotic resistance: road of no return
by Bob Hartzler

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November 1997 - The selection of resistant biotypes is a similar process, whether dealing with weeds resistant to herbicides or bacteria resistant to antibiotics. An article in the 24 October, 1997 issue of Science provides new insights into the persistence of resistance within populations.

The article describes findings reported by Bruce Levin, a population geneticist at Emory University in Atlanta at a meeting of the European Society for Evolutionary Biology. Researchers had hoped that bacteria that have become resistant to antibiotics would 'evolve backward', losing there resistance when doctors stopped prescribing the antibiotic. The driving force for backward evolution was thought to be that the resistance mechanism would make the resistant biotype less fit, therefore in the absence of the antibiotic susceptible biotypes would reestablish themselves as the dominant biotype in the population.

The results suggest that resistance in E. coli may be much more persistent than previously thought. The researchers found that 25% of E. coli populations isolated from baby's diapers at a day care center were still resistant to streptomycin, an antibiotic that has been used rarely during the last 30 years. In a second study, E. coli evolving in an antibiotic-free environment for 10 years (20,000 generations) still maintained resistance to the antibiotic.

Resistance will continue to be an issue facing agriculture as long as we are dependent upon pesticides. It is more difficult to study the persistence of herbicide resistance due to the longer life cycle of weeds compared to bacteria; however, research indicates that resistance will remain in weed populations for a significant time period (see related article). This research reinforces that the best way to manage resistance is to adopt management practices that reduce selection pressure, and therefore the likelihood of selecting resistant weed biotypes.

Source: Morell, V. 1997. Antibiotic resistance: Road of no return. Science 278:575-576.

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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Common chemical and trade names are used in this publication. The use of trade names is for clarity by the reader. Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply nonapproval.