Mutation of in Pseudomonas aeruginosa Increases β-Lactam Resistance through Upregulating Pyocyanin Production.

Metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa is increasingly reported worldwide and usually causes infections with high mortality rates. Aztreonam/avibactam is a β-lactam/β-lactamase inhibitor (BLBLI) combination that is under clinical trials. The advantage of aztreonam/avibactam over the currently used BLBLIs lies in its effectiveness against MBL-producing pathogens, making it one of the few drugs that can be used to treat infections caused by MBL-producing P. aeruginosa. However, the molecular mechanisms underlying aztreonam/avibactam resistance development remain unexplored. Here, in this study, we performed an evolution assay by using a previously identified MBL-producing P. aeruginosa clinical isolate, NKPa-71, and found mutations in a novel gene, , in the aztreonam/avibactam-resistant mutants. By mutation of in the reference strain PA14, we verified the role of in the resistance to aztreonam/avibactam and β-lactams. Transcriptomic analyses revealed upregulation of pyocyanin biosynthesis genes among the most overexpressed in the mutant. We further demonstrated that pyocyanin overproduction in the mutant increased the bacterial resistance to β-lactams by reducing drug influx. These data revealed a novel mechanism that might lead to the development of resistance to aztreonam/avibactam and β-lactams.