Characterization of Pilin A and Thioredoxin A Mutant Strains of <i>Acinetobacter baumannii</i> , From a Transposon Insertion Library, for Pili Production and Virulence‐Associated Properties

Acinetobacter baumannii is a multi-drug resistant Gram-negative coccobacillus. It is responsible for high mortality among patients in the intensive care unit. Reported A. baumannii virulence factors include the thioredoxin system which plays a critical role in gene regulation and protein reduction. The Type IV pilus (T4P) is a well-known bacterial virulence factor that is associated with adhesion and molecular exchange. Previously, our laboratory revealed the role of A. baumannii thioredoxin A (TrxA) in pathogenesis by studying a trxA deletion mutant that downregulates T4P gene expression. TrxA, a potent disulfide bond reducer, might affect the assembly of pili by targeting T4P component proteins, including PilA, the major pilin protein of T4P which contains multiple cysteine residues required for disulfide bond formation. Using a transposon library derived from the AB5075 clinical isolate, we phenotypically characterized a pilA mutant strain and compared its pathogenesis to the wild type (WT) strain as well as another trxA mutant. Whole genome sequencing was conducted to confirm the disruption of trxA and pilA genes in the corresponding mutant strains of AB5075. Alteration of bacterial surface appendages in ΔtrxA and ΔpilA was visualized by Scanning electron microscopy. Like ΔtrxA, the T4P mutant ΔpilA had marked reduction of surface pili. Bacterial attachment to excised intestinal surfaces was greatly reduced for ΔtrxA and ΔpilA. Attenuation of ΔtrxA and ΔpilA in pathogenesis was further confirmed using a mouse sepsis model. Collectively, this characterized ΔpilA deficiency in A. baumannii resulted in attenuation of virulence making it a potential therapeutic target.