Background: For years, Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae have represented a serious health problem in hospitals worldwide. Since its approval in 2015, ceftazidime-avibactam (CAZ-AVI) had been successfully used for treating complicated KPC-K. pneumoniae infections, until increasing reports of resistance began to emerge. Methods: Phenotypic tests and molecular analysis were performed in four multidrug-resistant K. pneumoniae isolates, collected from two patients following treatment with CAZ-AVI. Results: In this study, we report two cases of emergence of CAZ-AVI resistance in KPC-3-producing K. pneumoniae isolates, collected from two patients following treatment with CAZ-AVI. Molecular analysis highlighted the D179Y mutation in the bla KPC-3 gene, whose role in the loss of hydrolytic activity (resulting in decreased carpabenem minimum inhibitory concentrations and negative phenotypic tests) of the enzyme has already been shown. Conclusion: Most surveillance schemes aimed at detecting carbapenem-resistant Enterobacteriaceae (CRE) rely on confirmatory phenotypic tests for detecting carbapenemase production. As reports of these treatment-induced, altered CRE phenotypes are increasing, the initial susceptibility testing should be followed by a combination of phenotypic and molecular methods, to make sure that no potential carbapenemase-producing bacteria are missed.
Keywords: Klebsiella pneumoniae; carbapenem-resistance; ceftazidime-avibactam.