The emergence of antibiotic resistant bacteria is one of the most challenging public health problems affecting humankind in the 21st century. Among these bacteria, vancomycin-resistant enterococci (VRE) are one of the most difficult organisms to treat in hospitals across the US. Only two antimicrobial compounds are currently FDA-approved for the treatment of VRE infections;namely, linezolid and quinupristin-dalfopristin (Q/D). However, the use of these two agents against VRE has been hampered by suboptimal therapeutic outcomes in severe infections, frequent occurrence of side effects and the emergence and widespread dissemination of linezolid- and Q/D-resistant VRE isolates. Daptomycin (DAP) is a lipopeptide antibiotic whose mechanism of killing involves the interaction with the bacterial cell membrane (CM) in a calcium-dependent manner. DAP is the only bactericidal antibiotic currently available with activity against VRE. Although DAP does not have an FDA-approved indication for the treatment of VRE infections, clinicians are often pushed to use DAP due to the lack of better alternatives to treat patients infected with VRE who are often severely ill and with important compromise of the immune system. The off-label use of DAP during VRE therapy has led in several instances to the development of DAP resistance (DAP-R), thus, worsening the clinical scenario even further. Our long- term goal for this grant application is to understand the molecular events that lead to the development of DAP- R during VRE therapy to be able to i) design improved therapeutic strategies to prevent the emergence of DAP-R, and ii) identify new potential targets for antimicrobial development in the future with the aim of protecting the efficacy of DAP against VRE. Based on the information gathered from the comparative whole- genome, CM and cell envelope ultrastructural analysis of VRE clinical strain pairs of DAP-susceptible and DAP-resistant Enterococcus faecalis (VREfs) and E. faecium (VREfm), we have identified two genes that are highly likely to be involved in the development of DAP-R: i) a gene (cls) encoding a cardiolipin synthase enzyme in both VREfs and VREfm, involved in cell membrane homeostasis and ii) a VREfs homolog of the liaF gene, which is part of a three-component gene system involved in the bacterial cell envelope response to antimicrobials and antimicrobial peptides. Thus, we aim to a) investigate the contribution of mutations in the above genes (cls in both VREfs and VREfm and liaF in VREfs) to DAP-resistance, and b) evaluate strategies to optimize the use of DAP for VRE by testing the effect of escalating doses of DAP and combination therapies of DAP with i) ampicillin (for VREfs), and ii) with tigecycline or rifampin (for VREfm), in preventing emergence of DAP-R using a murine model of infective endocarditis. We anticipate that these studies will contribute to a deeper understanding of the role of CM phospholipid homeostasis and cell envelope regulation in the development of antibiotic resistance and antimicrobial peptide action and will certainly facilitate the preservation of DAP as a useful antibiotic to treat VRE infections in the future.

Public Health Relevance

This proposal seeks to understand the molecular strategies used by vancomycin-resistant enterococci (VRE, a common hospital-associated pathogen) to develop resistance to the antibiotic daptomycin;a compound of last resource to treat VRE infections. We aim to design strategies to prevent the emergence of daptomycin resistance in VRE and potentially characterize novel targets for the development of antimicrobial agents with activity against enterococci and other multidrug resistant organisms.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI093749-02
Application #
8293053
Study Section
Drug Discovery and Mechanisms of Antimicrobial Resistance Study Section (DDR)
Program Officer
Huntley, Clayton C
Project Start
2011-07-01
Project End
2016-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
2
Fiscal Year
2012
Total Cost
$421,297
Indirect Cost
$96,168
Name
University of Texas Health Science Center Houston
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
800771594
City
Houston
State
TX
Country
United States
Zip Code
77225
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Diaz, Lorena; Tran, Truc T; Munita, Jose M et al. (2014) Whole-genome analyses of Enterococcus faecium isolates with diverse daptomycin MICs. Antimicrob Agents Chemother 58:4527-34
Munita, Jose M; Mishra, Nagendra N; Alvarez, Danya et al. (2014) Failure of high-dose daptomycin for bacteremia caused by daptomycin-susceptible Enterococcus faecium harboring LiaSR substitutions. Clin Infect Dis 59:1277-80
Chowdhury, Shahreen A; Nallapareddy, Sreedhar R; Arias, Cesar A et al. (2014) The majority of a collection of U.S. endocarditis Enterococcus faecalis isolates obtained from 1974 to 2004 lack capsular genes and belong to diverse, non-hospital-associated lineages. J Clin Microbiol 52:549-56
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Munita, Jose M; Murray, Barbara E; Arias, Cesar A (2014) Daptomycin for the treatment of bacteraemia due to vancomycin-resistant enterococci. Int J Antimicrob Agents 44:387-95
Davlieva, Milya; Zhang, Wanna; Arias, Cesar A et al. (2013) Biochemical characterization of cardiolipin synthase mutations associated with daptomycin resistance in enterococci. Antimicrob Agents Chemother 57:289-96
Diaz, Lorena; Kontoyiannis, Dimitrios P; Panesso, Diana et al. (2013) Dissecting the mechanisms of linezolid resistance in a Drosophila melanogaster infection model of Staphylococcus aureus. J Infect Dis 208:83-91
Tran, Truc T; Panesso, Diana; Gao, Hongyu et al. (2013) Whole-genome analysis of a daptomycin-susceptible enterococcus faecium strain and its daptomycin-resistant variant arising during therapy. Antimicrob Agents Chemother 57:261-8
Rincón, Sandra; Reyes, Jinnethe; Carvajal, Lina Paola et al. (2013) Cefazolin high-inoculum effect in methicillin-susceptible Staphylococcus aureus from South American hospitals. J Antimicrob Chemother 68:2773-8

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