Molecular Characterization of KPC-2 and CMY AmpC Beta Lactamases in Ceftazidime-Avibactam Resistant Klebsiella pneumoniae in a Tertiary Care Hospital.

Introduction Multidrug-resistant (MDR) Klebsiella pneumoniae poses significant treatment challenges, particularly in intensive care settings. Ceftazidime-avibactam (CZA) has emerged as a key option against extended-spectrum beta-lactamase (ESBL) and K. pneumoniae carbapenemase (KPC) producing strains; however, increasing resistance, frequently attributed to CMY AmpC β-lactamases and porin loss, threatens its efficacy. Despite clinical use in Pakistan, local molecular data on resistance mechanisms remain limited. This study assessed antimicrobial resistance patterns, determined CZA minimum inhibitory concentrations (MICs), and screened for bla KPC-2 and bla CMY genes in resistant K. pneumoniae isolates from a tertiary care center. Materials & methods This cross-sectional study included 200 non-duplicate clinical specimens collected from various departments of the National Hospital and Medical Centre, Lahore. From these, 120 K. pneumoniae isolates were recovered, which were subsequently identified and analyzed using standard microbiological methods and confirmed 2023 guidelines of the Clinical and Laboratory Standards Institute (CLSI) with the VITEK 2 Compact system (bioMérieux SA, Marcy-l'Étoile, France). Antimicrobial susceptibility testing, including CZA MIC determination, was conducted. Polymerase chain reaction was performed on CZA non-susceptible isolates for the detection of blaKPC-2 and blaCMY genes, with sequencing confirmation of positive amplicons. Data on specimen distribution and MIC profiles were analyzed using IBM SPSS Statistics for Windows, version 20 (IBM Corp., Armonk, New York, United States), GraphPad Prism version 9 (Dotmatics, Boston, Massachusetts, United States), and Microsoft Excel (Microsoft Corporation, Redmond, Washington, United States). Results From 200 clinical specimens, 120 non-duplicate K. pneumoniae isolates were recovered, mainly from urine (26.7%), blood (21.7%), and respiratory samples. Samples were from intensive care unit (ICU) patients (41.7%), followed by the high-dependency unit (HDU) (28.3%) and critical care unit (CCU) (11.7%). Antimicrobial susceptibility testing revealed extensive multidrug resistance, with resistance rates ranging from 93.3% to 99.2% against β-lactams, cephalosporins, carbapenems, and fluoroquinolones. CZA resistance was identified in 30.8% (n = 37) of isolates, while tigecycline (9.2%) and fosfomycin (7.5%) showed the highest susceptibility. CZA MIC analysis classified 63.3% as susceptible and 30.8% as resistant, with resistant isolates exhibiting a significantly elevated mean MIC (91.46 ± 24.36 µg/mL; p < 0.05). Among the 44 CZA non-susceptible isolates, blaCMY was detected in 36.4% (n = 16), whereas blaKPC-2 was not detected in any case. Isolates positive for bla CMY  AmpCF were resistant to CZA, with a statistically significant association (p < 0.05) between the presence of the gene and resistance. Sanger sequencing confirmed 99.3% similarity with bla CMY-2. Conclusion CMY AmpC β-lactamase emerged as the predominant mechanism of CZA resistance in K. pneumoniae, highlighting the need for routine AmpC screening, prudent use of alternatives such as cefiderocol, tigecycline, or fosfomycin, and sustained genomic surveillance to guide therapy and infection control.