Key Findings

The study identifies three types of inhibitor-resistant (IR) CTX-M mutants with mutations S130G, K234R, and S237G, which confer resistance to beta-lactams plus beta-lactamase inhibitors (BBLIs). The S130G mutation was the most frequent and provided the highest resistance levels to BBLIs, while the K234R and S237G mutations had a smaller effect. The study also shows that the S130G mutation can lead to a decrease in resistance to cephalosporins, demonstrating an antagonistic pleiotropy effect.