Unexpected Challenges in Treating Multidrug-Resistant Gram-Negative Bacteria: Resistance to Ceftazidime-Avibactam in Archived Isolates of Pseudomonas aeruginosa

Abstract

e Pseudomonas aeruginosa is a notoriously difficult-to-treat pathogen that is a common cause of severe nosocomial infections. Investigating a collection of ␤-lactam-resistant P. aeruginosa clinical isolates from a decade ago, we uncovered resistance to ceftazidimeavibactam, a novel ␤-lactam/␤-lactamase inhibitor combination. The isolates were systematically analyzed through a variety of genetic, biochemical, genomic, and microbiological methods to understand how resistance manifests to a unique drug combination that is not yet clinically released. We discovered that avibactam was able to inactivate different AmpC ␤-lactamase enzymes and that bla PDC regulatory elements and penicillin-binding protein differences did not contribute in a major way to resistance. By using carefully selected combinations of antimicrobial agents, we deduced that the greatest barrier to ceftazidime-avibactam is membrane permeability and drug efflux. To overcome the constellation of resistance determinants, we show that a combination of antimicrobial agents (ceftazidime/avibactam/fosfomycin) targeting multiple cell wall synthetic pathways can restore susceptibility. In P. aeruginosa, efflux, as a general mechanism of resistance, may pose the greatest challenge to future antibiotic development. Our unexpected findings create concern that even the development of antimicrobial agents targeted for the treatment of multidrugresistant bacteria may encounter clinically important resistance. Antibiotic therapy in the future must consider these factors.

Assessment of the In Vitro Activity of Ceftazidime-Avibactam against Multidrug-Resistant Klebsiella spp. Collected in the INFORM Global Surveillance Study, 2012 to 2014

“…In addition, a small number of isolates with ceftazidimeavibactam MIC values of Ͼ8 g/ml that appeared to lack the transferable metallo-␤-lactamases screened as part of this study were identified, indicating the existence of yet undetermined antimicrobial resistance mechanisms against ceftazidime-avibactam. These mechanisms might include modifications of ␤-lactamase or penicillin-binding protein (PBP) sequences or changes in drug efflux levels (28)(29)(30)(31). Recently, a KPC-3-producing MDR K. pneumoniae isolate with a ceftazidime-avibactam MIC value of 32 g/ml was reported by others (32).…”

Evaluation of the 900 MHz Radiofrequency Radiation Effects on the Antimicrobial Susceptibility and Growth Rate of Klebsiella pneumoniae

“…Bacterial resistance to one or more antibiotics occurs by various mechanisms (24)(25)(26). In this way, EMFs as an environmental agent could influence cellular responses such as antimicrobial susceptibility through different pathways (4,20,22,23,27).…”

In Vivo Emergence of Resistance to Novel Cephalosporin–β-Lactamase Inhibitor Combinations through the Duplication of Amino Acid D149 from OXA-2 β-Lactamase (OXA-539) in Sequence Type 235 Pseudomonas aeruginosa

“…In vitro studies revealed that the emergence of resistance occurs at lower frequency than with other agents, and it is linked to specific mutations leading to the structural modification of AmpC-or efflux-related mechanisms in the case of ceftazidimeavibactam (9,(27)(28)(29)(30). In this work, we describe one further mechanism for development of resistance to these new antibiotics, through the selection of extended-spectrum mutations from narrow-spectrum OXA ␤-lactamases, such as OXA-2, which is relatively frequent among P. aeruginosa isolates worldwide (31).…”