Densichek plus photometer

Susceptibility of all isolates was determined thrice by broth microdilution and gradient strip. Susceptibility tests were employed strictly according to the manufacturer’s instruction. From each isolate, a bacterial suspension in 0.9% saline solution was prepared. The suspension was adjusted to a McFarland value of between 0.48 and 0.52 using a DensiCHEK plus photometer (bioMerieux, Marcy-l’Etoile, France). For the gradient strip test, MIC Test Strips (Liofilchem, Roseto degli Abruzzi, Italy) were used (except for piperacillin-tazobactam (bioMerieux, Marcy-l’Etoile, France)) and were carried out on Mueller–Hinton agar plates (Becton Dickinson, Heidelberg, Germany). MIC was visually read from the gradient strip and was rounded up to the next standard upper two-fold serial dilution value. For the broth microdilution, MIC-Plates Micronaut-S MDR MRGN-Screening and Micronaut Sepsis GN (Merlin, Bornheim, Germany) were taken. Tests were performed with Mueller–Hinton broth (Merlin, Bornheim, Germany) and were visually read. All measurements were continuously supervised head-on by two medical doctors. Each sample was visually and independently read by three trained observers. MICs were interpreted according to EUCAST PK-PD breakpoints (version 10.0, 2020). Small colony variation was evaluated by daily subcultivating cultures over a two-week-long period.

Susceptibility was determined thrice by broth microdilution. Susceptibility tests were employed strictly according to the manufacturer’s instruction. From each strain, a bacterial suspension in 0.9% saline solution was prepared. The suspension was adjusted to a McFarland value of between 0.48 and 0.52 using a DensiCHEK plus photometer (bioMerieux, Marcy-l’Etoile, France). For each broth microdilution, MIC-Plates Micronaut STAPH (Merlin, Bornheim, Germany) were taken. Tests were performed with Mueller–Hinton broth (Merlin, Bornheim, Germany) and were visually and independently read by three trained observers. Minimal inhibitory concentrations (MIC) were interpreted according to EUCAST breakpoints 2022 v.12.

Antimicrobial susceptibility of all isolates after re-cultivation from cryo stocks was determined thrice by broth microdilution. Susceptibility tests were employed strictly according to the manufacturer’s instruction. From each isolate, a bacterial suspension in 0.9% saline solution was prepared. The suspension was adjusted to a McFarland value of between 0.48 and 0.52 using a DensiCHEK plus photometer (bioMerieux, Marcy-l’Etoile, France). For broth microdilution, Micronaut-S MDR MRGN-Screening MIC-Plates (Merlin, Bornheim, Germany) were utilized (tested antibiotics are listed in the legend of Table 2 in the “Results” section). Tests were performed with Mueller–Hinton broth (Merlin, Bornheim, Germany) and read with a BioTek ELx808 Absorbance Microplate Reader (now: Agilent Technologies Inc., Santa Clara, CA, USA). MICs were interpreted according to EUCAST 2022 v12 breakpoints (version 01.01.2022) for Enterobacterales and Pseudomonas, respectively.