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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 bla_TEM Evolution

University of California, Merced, Merced, California

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

bla_TEM-1 expression results in penicillin resistance, whereas expression of many bla_TEM-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, bla_TEM-1 is still the most abundant bla_TEM 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 bla_TEM-1 descendants. Using a single-nucleotide polymorphism-specific real-time quantitative PCR method, we analyzed the fitness of strains expressing bla_TEM-1, bla_TEM-10, and bla_TEM-12. Our results show that bacteria expressing the ancestral bla_TEM-1 allele have a fitness advantage over those expressing either bla_TEM-10 or bla_TEM-12 when exposed to ampicillin. This observation, combined with the fact that penicillins are the most prevalent antimicrobials prescribed worldwide, may explain why bla_TEM-1 has persisted as the most frequently encountered bla_TEM allele in bacterial populations.

Published ahead of print on 28 April 2008.

This article has been cited by other articles:

• Mroczkowska, J. E., Barlow, M. (2008). Recombination and Selection Can Remove blaTEM Alleles from Bacterial Populations. Antimicrob. Agents Chemother. 52: 3408-3410 [Abstract] [Full Text]