Cross-resistance to cefiderocol and ceftazidime–avibactam in KPC β-lactamase mutants and the inoculum effect

Abstract

Objectives: Ceftazidimeeavibactam (CZA) and cefiderocol are recently commercialized molecules active against highly drug-resistant bacteria, including carbapenem-resistant members of the Enterobacteriaceae. Mutants resistant to CZA have been described, notably in Klebsiella pneumoniae carbapenemase (KPC) producers. Considering the structural similarities between ceftazidime and cefiderocol, we hypothesized that resistance to CZA in KPC-producing members of the Enterobacterales may lead to crossresistance to cefiderocol. Methods: CZA-resistant mutants from three clinical isolates of the Enterobacterales carrying either bla KPC-2 or bla KPC-3 were selected in vitro. Mutants with increased MIC to CZA compared to the ancestral allele were cloned in a pBR322 plasmid and expressed in Escherichia coli TOP10. We evaluated the impact of these mutations on cefiderocol MICs and minimal bactericidal concentrations (MBCs), and we assessed the impact of bacterial inoculum size on cefiderocol MICs. Results: We used 37 KPC mutants with increased CZA MICs. Of these, six have been described previously in clinical isolates. Compared to the wild-type alleles, increases in the cefiderocol MICs of 4-to 32-fold were observed for 75.6% of tested mutants (28/37), MICs reaching up to 4 mg/L in E. coli TOP10 for KPC-31 (D179YeH274Y mutations). MBCs and MICs of cefiderocol were similar, confirming the bactericidal activity of this drug. Finally, when using higher inocula (10 7 CFU/mL), a large increase in cefiderocol MIC was observed, and all isolates were categorized as resistant. Conclusion:We observed that most of the CZA-resistant KPC variants have a possible impact on cefiderocol by increasing the cefiderocol MICs. In addition, cefiderocol is greatly impacted by the inoculum effect, suggesting that precautions should be taken when treating infections with a suspected high inoculum.

New Delhi Metallo-Beta-Lactamase Facilitates the Emergence of Cefiderocol Resistance in Enterobacter cloacae

“…The inoculum effect is defined as attenuation of antibacterial activity at higher bacterial densities above those used for susceptibility testing (>5 × 10 5 colony-forming unit [CFU]/mL) ( 19 ). This phenomenon is generally attributed to β-lactam antibiotics, especially cephalosporins, and has been recently described for cefiderocol ( 20 ). Higher bacterial density may increase the tolerant subpopulations and, thus, increase the chances of spontaneous mutations conferring resistance or leading to a more efficient enzymatic degradation of the antibiotic substance.…”

Cefiderocol: An Overview of Its in-vitro and in-vivo Activity and Underlying Resistant Mechanisms

“…Mutations in β-lactamases may also lead to CFDC resistance ( Figure 1 ). A 4- to 32-fold increase of an MIC90 was observed in D179Y-H274Y mutations of KPC-31 compared to the wild-type alleles reported by Hobson et al in 2021 ( 35 ). Shields et al have reported that the deletion of positions 292 and 293, which are located in the R2 loop of AmpC, causes the decreased susceptibility of Enterobacterales ( 38 ).…”

“…An MIC90 value at 16–64 mg/l was observed in a K. pneumoniae infected neutropenic murine thigh model, which was infected with 10 7 CFU/ml bacterial suspension ( 34 ). According to the EUCAST breakpoints, Hobson et al have also reported that high inocula (10 7 CFU/ml) with KPC-producing Enterobacteriaceae will lead the resistance to CFDC compared to usual inocula (10 5 CFU/ml) in 2021 ( 35 ).…”

Place in Therapy of the Newly Available Armamentarium for Multi-Drug-Resistant Gram-Negative Pathogens: Proposal of a Prescription Algorithm

“…In addition, Hobson et al pointed out the risk of cross-resistance with ceftazidime is caused by extension of KPC spectrum through specific mutations (namely KPC-31). Furthermore, they revealed a strong impact of a high-inoculum effect on CFDC MICs, which is even more worrisome [ 65 ]. Tiseo et al described a case of recurrent KPC- Kp bacteremia successfully treated with MVB after in vivo, CZA-induced resistance development to CZA and CFDC [ 44 ].…”