Two clinical isolates of Klebsiella michiganensis from the same patient were genetically compared, revealing differing resistance profiles: one was resistant to piperacillin-tazobactam and intermediate to cefotaxime, while the other was resistant to ceftazidime but susceptible to piperacillin-tazobactam.
* A mutation in the bla gene, resulting in a L169M change in the Ω loop, was identified as a key factor in the resistance differences.
* Cloning experiments in E. coli demonstrated that this mutation allowed for increased resistance to ceftazidime and cefepime but reduced resistance to piperacillin-tazobactam, marking a novel discovery of how