AUTHOR=Babouee Flury Baharak , Bösch Anja , Gisler Valentin , Egli Adrian , Seiffert Salome N. , Nolte Oliver , Findlay Jacqueline 

TITLE=Multifactorial resistance mechanisms associated with resistance to ceftazidime-avibactam in clinical Pseudomonas aeruginosa isolates from Switzerland

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1098944

DOI=10.3389/fcimb.2023.1098944

ISSN=2235-2988

ABSTRACT=<sec><title>Background</title><p>Increasing reports of multidrug resistance (MDR) in clinical <italic>Pseudomonas aeruginosa</italic> have led to a necessity for new antimicrobials. Ceftazidime-avibactam (CZA) is indicated for use against MDR <italic>P. aeruginosa</italic> across a broad range of infection types and particularly those that are carbapenem resistant. This study sought to determine the molecular mechanisms of CZA and imipenem (IPM)-resistance in clinical <italic>P. aeruginosa</italic> isolates obtained from Swiss hospitals.</p></sec><sec><title>Methods</title><p>Clinical <italic>P. aeruginosa</italic> isolates were obtained from inpatients in three hospitals in Switzerland. Susceptibility was determined by either antibiotic disc testing or broth microdilution according to EUCAST methodology. AmpC activity was determined using cloxacillin and efflux activity was determined using phenylalanine-arginine β-naphthylamide, in agar plates. Whole Genome Sequencing was performed on 18 clinical isolates. Sequence types (STs) and resistance genes were ascertained using the Centre for Genomic Epidemiology platform. Genes of interest were extracted from sequenced isolates and compared to reference strain <italic>P. aeruginosa</italic> PAO1.</p></sec><sec><title>Results</title><p>Sixteen different STs were identified amongst the 18 isolates in this study indicating a high degree of genomic diversity. No carbapenemases were detected but one isolate did harbor the ESBL <italic>bla</italic><sub>PER-1</sub>. Eight isolates were CZA-resistant with MICs ranging from 16-64 mg/L, and the remaining ten isolates had either low/wildtype MICs (n=6; 1-2 mg/L) or elevated, but still susceptible, MICs (n=4; 4-8 mg/L). Ten isolates were IPM-resistant, seven of which had mutations resulting in truncations of OprD, and the remaining nine IPM-susceptible isolates had intact <italic>oprD</italic> genes. Within CZA-R isolates, and those with reduced susceptibility, mutations resulting in <italic>ampC</italic> derepression, OprD loss, <italic>mexAB</italic> overexpression and ESBL (<italic>bla</italic><sub>PER-1</sub>) carriage were observed in various combinations and one harbored a truncation of the PBP4 <italic>dacB</italic> gene. Within the six isolates with wildtype-resistance levels, five had no mutations that would affect any antimicrobial resistance (AMR) genes of interest when compared to PAO1.</p></sec><sec><title>Conclusion</title><p>This preliminary study highlights that CZA-resistance in <italic>P. aeruginosa</italic> is multifactorial and could be caused by the interplay between different resistance mechanisms including ESBL carriage, increased efflux, loss of permeability and derepression of its intrinsic <italic>ampC</italic>.</p></sec>