Occurrence of cefiderocol (CFDC) heteroresistance in carbapenem-resistant Acinetobacter baumannii (CRAB) cells after exposure to human fluids

ESCALANTE, JENNY (CO-FIRST AUTHOR); NISHIMURA, BRENT (CO-FIRST AUTHOR); MEZCORD, VYANKA; TRAGLIA, GERMAN MATIAS; QUENTIN, VALLE; TUTTOBENE, MARISEL ROMINA; SUBILS, TOMAS; PASTERAN, FERNANDO; TOLMASKY, MARCELO E.; BONOMO, ROBERT A.; RAO, GAURI; RAMÍREZ, MARÍA SOLEDAD

Copenhagen

Congreso; 33nd ECCMID; 2023

ECCMID

BackgroundInfections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) are among themost difficult to treat. Cefiderocol (CFDC) is the only drug recently approved by the FDAthat is active against CRAB. CFDC treatment failures may be due to heteroresistance, aphenotype characterized by the survival of a small proportion of cells in a populationseemingly isogenic. Adding human fluids to CRAB cultures can lead toCFDC heteroresistance. To better understand the nature of this phenomenon, we carried outmolecular and phenotypic analyses of CRAB heteroresistant bacterial subpopulations.MethodsCRAB strain AMA40 and two CFDC heteroresistant variants (AMA40 IHC_1 and IHC_2)generated by culturing strain AMA40 in human serum albumin containing fluids. Cultureswere made using iron-depleted cation-adjusted Mueller-Hinton (ID-CA-MH) broth. All threestrains were subjected to whole genome sequencing and transcriptomic analysis to identifythe mutations and transcriptomic changes responsible for the development of CFDCresistance. The impact of mutations on the activity of CFDC was assessed by susceptibilitytesting, EDTA acid inhibition analysis, biofilm formation, and static time-kill assays.ResultsVariants AMA40 IHC_1 and IHC_2 had 53 mutations, forty of which were common to bothheteroresistant strains. None of the mutations are located inside genes associated with ironuptakesystems or β-lactam resistance. However, pipA, a gene associated with ironhomeostasis in other species, was altered in heteroresistant strains. Transcriptomic analysesrevealed modifications in levels of expression of genes associated with antibiotic resistance.The blaNDM-1, blaADC-2, pbp3, and pbp1 were expressed at higher levels. At the sametime, the carO and ompA genes expression was reduced (Fig. 1A). Resistance to CFDC andcollateral resistance to amikacin were higher (Fig. 1B). Static time-kill assays showed thatwhen CA-MHB was supplemented with HSA, CFDC killing activity was considerablyreduced in all three strains.ConclusionsWe conclude that heteroresistance to CFDC in CRAB, when exposed to fluids containinghigh HSA, is caused by mutations and modifications in the expression of genes associatedwith resistance to β-lactams. We describe for the first time the possible contributionof pipA in heteroresistance to CFDC that deserves to be further explored.