A series of vectors for inducible gene expression in multidrug-resistant Acinetobacter baumannii

The continued emergence of antibiotic resistance among bacterial pathogens remains a significant challenge. Indeed, the enhanced antibiotic resistance profiles of contemporary pathogens often restrict the number of suitable molecular tools that are available. We have constructed a series of plasmids that confer resistance to two infrequently used antibiotics with variants of each plasmid backbone incorporating several regulatory control systems. The regulatory systems include both commonly used systems based on the lac- and arabinose-controlled promoters found in Escherichia coli, as well as less frequently used systems that respond to tetracycline/anhydrotetracycline and toluic acid. As a test case, we demonstrate the utility of these plasmids for regulated and tunable gene expression in a multidrug-resistant (MDR) isolate of Acinetobacter baumannii, strain AB5075-UW. The plasmids include derivatives of a freely replicating, broad-host-range plasmid allowing for inducible gene expression as well as a set of vectors for introducing genetic material at the highly conserved Tn7-attachment site. We also modified a set of CRISPR-interference plasmids for use in MDR organisms, thus allowing researchers to more readily interrogate essential genes in currently circulating clinical isolates. These tools will enhance molecular genetic analyses of bacterial pathogens in situations where existing plasmids cannot be used due to their antibiotic resistance determinants or lack of suitable regulatory control systems.

Clinical isolates of bacterial pathogens often harbor resistance to multiple antibiotics, with Acinetobacter baumannii being a prime example. The drug-resistance phenotypes associated with these pathogens represent a significant hurdle to researchers who wish to study modern isolates due to the limited availability of plasmid tools. Here, we present a series of freely replicating and Tn7-insertion vectors that rely on selectable markers to less frequently encountered antibiotics, apramycin, and hygromycin. We demonstrate the utility of these plasmid tools through a variety of experiments looking at a multidrug-resistant strain of A. baumannii, strain AB5075. Strain AB5075 is an established model strain for present-day A. baumannii, due in part to its genetic tractability and because it is a representative isolate of the globally disseminated multidrug-resistant clade of A. baumannii, global clone 1. In addition to the drug-selection markers facilitating use in strains resistant to more commonly used antibiotics, the vectors allow for controllable expression driven by several regulatory systems, including isopropyl β-D-1-thiogalactopyranoside (IPTG), arabinose, anhydrotetracycline, and toluic acid.