Fitness tradeoffs in bla_TEM evolution

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

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

	Abstract

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.