Functional characterization of biocide fitness determinants in the opportunistic pathogen Acinetobacter baumannii

Acinetobacter baumannii is a major multidrug resistant opportunistic pathogen. While antibiotic resistance mechanisms in A. baumannii are well-studied, resistance to biocides is much less characterized. A high-throughput genomic screen previously identified multiple genes that may play a role in biocide resistance. Growth assays confirmed that mutants of four of these genes, including AdeB efflux pump, showed increased susceptibility to various biocides. Furthermore, qRT-PCR analysis indicated that AdeB efflux pump and its cognate regulator, AdeRS may have a different ligand specificity, which was also evident in the same genomic screening data. A possible novel efflux pump, Neo1, was identified by the same high-throughput genomic screen. Unexpectedly, an in vivo functional assay of Neo1 and its ortholog, YccS, showed increased antibiotic sensitivity in Escherichia coli. For in vitro functional analysis, Neo1 was semi-purified using IMAC; however, preliminary ligand screening using nanoDSF did not identify potential ligands of Neo1. A separate qRT-PCR analysis established that spermine and spermidine induce the expression of the A. baumannii amvA multidrug efflux pump gene, suggesting these polyamines are its natural substrates. Together, the studies of this thesis provided insightful indications about the functions and regulations of multidrug efflux pumps and other biocide tolerant genes in A. baumannii.