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Antimicrobial Agents and Chemotherapy, July 2008, p. 2340-2345, Vol. 52, No. 7
0066-4804/08/$08.00+0     doi:10.1128/AAC.00018-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Fitness Trade-Offs in blaTEM Evolution{triangledown}

Joanna E. Mroczkowska and Miriam Barlow*

University of California, Merced, Merced, California

Received 5 January 2008/ Returned for modification 18 March 2008/ Accepted 22 April 2008

blaTEM-1 expression results in penicillin resistance, whereas expression of many blaTEM-1 descendants, called extended-spectrum β-lactamases (ESBLs), results simultaneously in resistance to penicillins and extended-spectrum cephalosporins. Despite the expanded resistance phenotypes conferred by many ESBLs, blaTEM-1 is still the most abundant blaTEM allele in many microbial populations. This study examines the fitness effects of the two amino acid substitutions, R164S and E240K, that have occurred repeatedly among ESBL blaTEM-1 descendants. Using a single-nucleotide polymorphism-specific real-time quantitative PCR method, we analyzed the fitness of strains expressing blaTEM-1, blaTEM-10, and blaTEM-12. Our results show that bacteria expressing the ancestral blaTEM-1 allele have a fitness advantage over those expressing either blaTEM-10 or blaTEM-12 when exposed to ampicillin. This observation, combined with the fact that penicillins are the most prevalent antimicrobials prescribed worldwide, may explain why blaTEM-1 has persisted as the most frequently encountered blaTEM allele in bacterial populations.

* Corresponding author. Mailing address: 5200 North Lake Road, Merced, CA 95343. Phone: (209) 228-4174. Fax: (209) 228-4060. E-mail: mbarlow{at}ucmerced.edu

{triangledown} Published ahead of print on 28 April 2008.

Antimicrobial Agents and Chemotherapy, July 2008, p. 2340-2345, Vol. 52, No. 7
0066-4804/08/$08.00+0     doi:10.1128/AAC.00018-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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