| Abstrakt: |
blaTEM-1expression results in penicillin resistance, whereas expression of many blaTEM-1descendants, 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-1is still the most abundant blaTEMallele 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-1descendants. 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-1allele have a fitness advantage over those expressing either blaTEM-10or blaTEM-12when exposed to ampicillin. This observation, combined with the fact that penicillins are the most prevalent antimicrobials prescribed worldwide, may explain why blaTEM-1has persisted as the most frequently encountered blaTEMallele in bacterial populations. |
