AAC Accepts, published online ahead of print on 28 April 2008

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Antimicrob. Agents Chemother. doi:10.1128/AAC.00018-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Fitness tradeoffs in bla_TEM evolution

Joanna E. Mroczkowska and Miriam Barlow^*

Institution at which research was done: University of California, Merced

^* To whom correspondence should be addressed. Email: mbarlow{at}ucmerced.edu.

bla_TEM-1 expression results in penicillin resistance whereas expression of many bla_TEM-1 descendents called extended spectrum -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 acids substitutions, R164S and E240K that have occurred repeatedly among ESBL bla_TEM-1 descendents. Using a SNP specific real-time qPCR method we analyzed fitness of strains expressing the 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.

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]