Bacterial Cytological Profiling as a Tool To Study Mechanisms of Action of Antibiotics That Are Active against Acinetobacter baumannii.

An increasing number of multidrug-resistant Acinetobacter baumannii (MDR-AB) infections have been reported worldwide, posing a threat to public health. The establishment of methods to elucidate the mechanism of action (MOA) of A. baumannii-specific antibiotics is needed to develop novel antimicrobial therapeutics with activity against MDR-AB We previously developed bacterial cytological profiling (BCP) to understand the MOA of compounds in Escherichia coli and Bacillus subtilis Given how distantly related A. baumannii is to these species, it was unclear to what extent it could be applied. Here, we implemented BCP as an antibiotic MOA discovery platform for A. baumannii We found that the BCP platform can distinguish among six major antibiotic classes and can also subclassify antibiotics that inhibit the same cellular pathway but have different molecular targets. We used BCP to show that the compound NSC145612 inhibits the growth of A. baumannii via targeting RNA transcription. We confirmed this result by isolating and characterizing resistant mutants with mutations in the rpoB gene. Altogether, we conclude that BCP provides a useful tool for MOA studies of antibacterial compounds that are active against A. baumannii.