The PI is interested in studying fluoroquinolone resistance in Staphylococcus spp. for three reasons. First, staphylococci are important pathogens and are growing more and more resistant to fluoroquinolones and other antibiotics. Understanding the mechanism of quinolone resistance, which appears to be different from that seen in the gram-negative bacteria, is thus an important goal. A second reason is that topoisomerase IV seems to be the main fluoroquinolone target in the gram positive bacteria rather than DNA gyrase, and this makes it possible to investigate the function and regulation of topoisomerases in ways not possible in the gram-negative bacteria. Finally, the PI is interested in the mechanism and regulation of multidrug efflux transporters that provide yet another mechanism of fluoroquinolone resistance in addition to alterations in topoisomerase itself. More specifically, the PI proposes the following: 1. To determine how mutations in the two topoisomerase IV subunits, ParC and ParD, make the topoisomerase less susceptible to fluoroquinolone action. To this end, the PI will purify and characterize mutant topoisomerases to determine if their binding of the antibiotic is reduced or affect the catalytic activity of the enzyme. Results of this analysis should indicate not only how the resistance mechanism works but whether quinolones act by reducing enzyme activity or more indirectly by stabilizing enzyme-DNA complexes. 2. To determine the location of topoisomerase IV relative to the DNA replication complex. Topoisomerase IV is thought to act by decatenation of newly replicated daughter chromosomes to allow segregation. Fluoroquinolones can be used to trap enzyme-DNA complexes and thus determine the sites where topoisomerase acts. Sites preferentially used by topo IV will be identified. The PI will also determine how rapidly the antibiotic stops new DNA synthesis, an indication of whether the topo IV acts near or far from the replication complex. The PI has isolated a new type of resistance-producing mutation that he hopes may shed light on the involvement of topo IV in DNA replication. These mutants will be characterized in detail. 3. To characterize the regulation and function of NorA, a multidrug efflux pump that mediates fluoroquinolone resistance. Gene fusions will be used to follow expression and the effect of various known global regulators will be determined. The promoter of norA will be located. NorA function will be assessed by purifying NorA protein and incorporating it in liposomes. 4. To characterize factors affecting the evolution of fluoroquinolone resistance. It has been noted that methicillin-resistant S. aureus strains are far more likely to become resistant to fluoroquinolones than methicillin-sensitive strains. The PI has evidence suggesting that this might be due to linkage of the methicillin resistance gene, mecA, to gyrA genes that have already started on the mutation pathway to detectable resistance. The PI will also determine whether the induction of fibronectin-binding proteins by quinolones in MSSA strains is responsible for the tendency of the MSSA that become quinolone resistant to spread clonally, in contrast to MRSA.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI023988-14
Application #
6510357
Study Section
Bacteriology and Mycology Subcommittee 2 (BM)
Project Start
1986-09-01
Project End
2003-03-31
Budget Start
2002-04-01
Budget End
2003-03-31
Support Year
14
Fiscal Year
2002
Total Cost
$368,744
Indirect Cost
Name
Massachusetts General Hospital
Department
Type
DUNS #
City
Boston
State
MA
Country
United States
Zip Code
02199
Hooper, David C; Jacoby, George A (2016) Topoisomerase Inhibitors: Fluoroquinolone Mechanisms of Action and Resistance. Cold Spring Harb Perspect Med 6:
Hooper, David C; Jacoby, George A (2015) Mechanisms of drug resistance: quinolone resistance. Ann N Y Acad Sci 1354:12-31
Jacoby, George; Cattoir, Vincent; Hooper, David et al. (2008) qnr Gene nomenclature. Antimicrob Agents Chemother 52:2297-9
Truong-Bolduc, Que Chi; Hooper, David C (2007) The transcriptional regulators NorG and MgrA modulate resistance to both quinolones and beta-lactams in Staphylococcus aureus. J Bacteriol 189:2996-3005
Strahilevitz, Jacob; Onodera, Yoshikuni; Hooper, David C (2006) An improved expression plasmid for affinity purification of Staphylococcus aureus gyrase A subunit. Protein Expr Purif 47:10-5
Strahilevitz, Jacob; Robicsek, Ari; Hooper, David C (2006) Role of the extended alpha4 domain of Staphylococcus aureus gyrase A protein in determining low sensitivity to quinolones. Antimicrob Agents Chemother 50:600-6
Truong-Bolduc, Que Chi; Strahilevitz, Jacob; Hooper, David C (2006) NorC, a new efflux pump regulated by MgrA of Staphylococcus aureus. Antimicrob Agents Chemother 50:1104-7
Strahilevitz, Jacob; Hooper, David C (2005) Dual targeting of topoisomerase IV and gyrase to reduce mutant selection: direct testing of the paradigm by using WCK-1734, a new fluoroquinolone, and ciprofloxacin. Antimicrob Agents Chemother 49:1949-56
Strahilevitz, Jacob; Truong-Bolduc, Que Chi; Hooper, David C (2005) DX-619, a novel des-fluoro(6) quinolone manifesting low frequency of selection of resistant Staphylococcus aureus mutants: quinolone resistance beyond modification of type II topoisomerases. Antimicrob Agents Chemother 49:5051-7
Hooper, David C (2005) Efflux pumps and nosocomial antibiotic resistance: a primer for hospital epidemiologists. Clin Infect Dis 40:1811-7

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