New rapid screen for the detection of imipenem-resistant Acinetobacter baumanii

A rapid screen was developed for the detection of imipenem-resistant Acinetobacter baumanii (IRAb) following a recent outbreak in the Surgical Intensive Care Unit (SICU) of a hospital in Singapore. Antimicrobial solutions of imipenem ranging from 16 mg/L to 64 mg/L were prepared in-house. Each of the antimicrobial solutions was then incorporated singularly into MacConkey agar plates by two different methods. One of the methods involved preparing MacConkey agar plates in-house and then adding the antimicrobial solution before the agar solidified (AS method). In the second method, 1 ml of the antimicrobial solution was poured onto the surface of the agar plate (LAS method). Fifty hand-nutrient broth washes of medical staff working in the SICU, Medical Intensive Care Unit, Medical Rehabilitation Ward, and Surgical Rehabilitation Ward were inoculated onto the two types of agar media. Two strains of IRAb were isolated from the hands. The LAS plates showed faster bacterial growth of resistant pathogens by about 24 h, and their detection was easier because susceptible bacteria were inhibited by the antimicrobial. The LAS method incorporating imipenem at 32 mg/L is recommended for the rapid screening of resistant pathogens in the routine clinical laboratory.