Antibiotic Resistance Profiling of A. baumannii

Seventeen clinical isolates of A. baumannii were characterized in this study. Strains were chosen from diverse anatomical origin and from a wide range of disease presentations including urinary tract, respiratory, wound, intra-abdominal infections, and bacteremia. Strains were collected in this pilot study from January of 2010 through August of 2012. Antimicrobial susceptibility to ampicillin-sulbactam (A/S), amikacin (AK), ceftriaxone (CAX), ceftazidime (CAZ), cefotaxime (CFT), ciprofloxacin (CP), cefepime (CPE), gentamicin (GM), levofloxacin (LVX), meropenem (MER), piperacillin (PI), trimethoprim-sulfamethoxazole (T/S), tetracycline (TE), ticarcillin-K clavulanate (TIM), and tobramycin (TO) was determined at the Nashville General Hospital clinical laboratory and values of “susceptible”, “non-susceptible” or “intermediate” per International Organization for Standardization (ISO) 20776–1:2019 guidelines, was determined [18 (link)]. A bacterial strain was considered “susceptible” when it was inhibited in vitro by a concentration of drug that is associated with a high likelihood of therapeutic success. An “intermediate” designation indicated the strain had variable inhibition in vitro, or was inhibited by a concentration of drug that is associated with an uncertain therapeutic effect. And strains were designated resistant or “non-susceptible” to a given antibiotic when the strain was not inhibited in vitro by a concentration of drug that is associated with therapeutic success. Additionally, anatomical site source of culture were retrieved in a de-identified manner from the electronic medical record system. Approval to characterize the de-identified bacterial isolates was provided by the affiliated Meharry Medical College Institutional Review Board (IRB 081204AAH23119). Reference laboratory strains of A. baumannii including 17978 and the 19606 T type strain (ATCC, Manassas, Virginia) from patients with meningitis and urinary tract infection, respectively, were also evaluated for comparison. All bacterial strains were stored as glycerol stock at -80 °C until use. All isolates were grown in Luria-Bertani (LB) broth at 37 °C in room air under shaking conditions overnight at 180 rpm to an optical density of 600 nm (OD₆₀₀) between 0.8–1.0.