Microscan walkaway analyzer

In the study, we used twenty clinical strains of antibiotic-resistant Enterobacter, which were isolated from patients with infections of the genitourinary system (n = 7); ears (n = 2); and wounds, ulcers, or purulent lesions (n = 11); who applied to qualify for experimental bacteriophage therapy at the Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences (HIIET PAS) in the years 2017–2021. The species of bacterial strains were determined using matrix-assisted laser desorption/ionization—time of flight (MALDI-TOF/TOF) mass spectrometry (Bruker Daltonics, Billerica, MA, USA). Antibiotic sensitivity was determined by the microdilution method using the MicroScan WalkAway analyzer (Beckman Coulter, Brea, CA, USA). All bacteria were grown on MacConkey agar (incubation at 37 °C, approximately 18 h), but were stored frozen in a 20% glycerol (Difco) solution at −70 °C prior to the experiments.

For the study, 137 strains belonging to Acinetobacter spp. (A. ursingii n = 1, A. pitti n = 2, A. johnsonii n = 2, and A. baumannii n = 132) and six other Gram-negative strains were used. Bacterial strains were collected from medical environments, thanks to cooperation with hospitals: Regional Specialist Hospital in Wroclaw, University Clinical Hospital in Wroclaw, Military Hospital with Polyclinic in Wroclaw, and Pomeranian Medical University in Szczecin, as well as from the collection of the Bacteriophage Laboratory in the years 2018–2022. Most of the strains showed the resistance to the currently used antibiotics. The species affiliation was determined by matrix-assisted laser desorption/ionization—time of flight (MALDI-TOF/TOF) mass spectrometry (Bruker Daltonics, Billerica, MA, USA). Antibiotic susceptibility was determined by the MicroScan WalkAway analyzer (Beckman Coulter, Brea, CA, USA). All bacterial strains were stored at −70 °C in 25% glycerol. After thawing, the strains were cultured on plates with McConkey agar (peptone 17 g, proteose peptone 3 g, lactose 10 g, bile salts 1.5 g, sodium chloride 5 g, neutral red 0.03 g, crystal violet 0.001 g, agar 13.5 g, water—added to make 1 liter; and pH adjusted to 7.1 +/− 0.2 sodium taurocholate) at 37 °C for 12 h.