Isolation and Identification of Acinetobacter baumannii

Fecal specimens (rectal swab or stool) collected from patients upon admission or during hospitalization were sent to the microbiology laboratory of Queen Mary Hospital. The rectal swab or around 1 g of stool was incubated in 2 mL of brain heart infusion enrichment broth with 10 μg vancomycin (Sigma-Aldrich, St. Louis, MO, USA) and 0.5 μg meropenem (Hospira, Melbourne, Australia) at 35 °C for 18 h. Ten microliters of the enriched broth was further subcultured onto MacConkey agar with 2 μg meropenem and incubated aerobically at 35 °C for 48 h, as previously described [17 (link),24 (link)]. A. baumannii isolates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (Bruker Daltonics, Bremen, Germany). Antimicrobial susceptibility tests were performed using the Kirby–Bauer disk diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) recommendations or manufacturer’s instructions. Antimicrobial susceptibility was defined according to the CLSI recommendations [25 ].