Antimicrobial resistance is a growing problem that threatens treatment of infectious diseases and numerous medical procedures. It is well known that the introduction of new antibiotics is slow and costly. In consequence, this proposal concentrates on a critical aspect of the fight against the problem of bacterial resistance to antibiotics: the search for strategies aimed at preserving the effectiveness of currently available drugs. Our model system is the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib], the most clinically relevant acetyltransferase among gram-negative pathogens, which mediates resistance to amikacin (Ak) and other aminoglycosides. These antibiotics are an important component of the armamentarium against serious infections caused by several gram-negative pathogens. The long term goal of this research is to develop pharmacological tools that in combination with Ak overcome the presence of aac(6')-Ib and can be successfully used to treat Ak-resistant infections. We have identified oligoribonucleotide sequences, known as external guide sequences (EGSs), that elicit RNase P-mediated cleavage of aac(6')-Ib and ftsZ mRNA and result in a reduction of the levels of resistance to Ak and inhibition of cell division, respectively. Furthermore, we determined that nuclease resistant oligoribonucleotide analogs composed of locked nucleic acids and deoxyribonucleotide monomers (LNA/DNA) behave as EGSs.
One aim of this project is to generate efficient LNA/DNA EGSs that can penetrate the cells and inhibit expression of the resistance gene aac(6')-Ib. These compounds will be used in combination with Ak (LNA/DNA EGSaac/Ak) to achieve phenotypic conversion to susceptibility to Ak. However since a common problem of antisense strategies is that the inhibitory activity is not potent enough for an effective antimicrobial effect we will design compounds that act synergistically with the mix LNA/DNA EGSaac/Ak. We will identify inhibitors of AAC(6')-Ib that will eliminate the activity of any enzyme produced by residual expression of the resistance gene. We will also design LNA/DNA EGSs that will interfere with expression of the E. coli and A. baumannii essential cell division protein FtsZ by eliciting RNase P-cleavage of ftsZ mRNA genes. Combinations consisting of the mix LNA/DNA EGSaac/Ak plus an AAC(6')-Ib inhibitor and/or an LNA/DNA EGS targeting ftsZ will be tested to determine their ability to inhibit growth of E. coli and A. baumannii harboring aac(6')-Ib.

Public Health Relevance

Aminoglycosides are widely used antibiotics for treatment of serious bacterial infections but unfortunately the success rate of treatments with these antibiotics has gone down due to the appearance of multiresistant strains. Since introduction of new antibiotics is slow and costly, an option to deal with the problem of drug resistance is to develop strategies to prolong the effectiveness of currently available antibiotics. This project wil contribute to extend the useful life of clinically important aminoglycosides.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Academic Research Enhancement Awards (AREA) (R15)
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Special Emphasis Panel (ZRG1-IDM-B (81))
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Xu, Zuoyu
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California State University Fullerton
Schools of Arts and Sciences
United States
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Traglia, German M; Chua, Katherina; CentrĂ³n, Daniela et al. (2014) Whole-genome sequence analysis of the naturally competent Acinetobacter baumannii clinical isolate A118. Genome Biol Evol 6:2235-9
Reyes-Lamothe, Rodrigo; Tran, Tung; Meas, Diane et al. (2014) High-copy bacterial plasmids diffuse in the nucleoid-free space, replicate stochastically and are randomly partitioned at cell division. Nucleic Acids Res 42:1042-51
Lin, David L; Tran, Tung; Alam, Jamal Y et al. (2014) Inhibition of aminoglycoside 6'-N-acetyltransferase type Ib by zinc: reversal of amikacin resistance in Acinetobacter baumannii and Escherichia coli by a zinc ionophore. Antimicrob Agents Chemother 58:4238-41
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Lin, David L; Tran, Tung; Adams, Christina et al. (2013) Inhibitors of the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib] identified by in silico molecular docking. Bioorg Med Chem Lett 23:5694-8
Tran, Tung; Andres, Patricia; Petroni, Alejandro et al. (2012) Small plasmids harboring qnrB19: a model for plasmid evolution mediated by site-specific recombination at oriT and Xer sites. Antimicrob Agents Chemother 56:1821-7
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