Staphylococcus aureus is a major human pathogen. It can cause rapidly fatal infections. A highly virulent clone of methicillin resistant S. aureus (MRSA), USA300, is epidemic in communities in the United States. MRSA is resistant to all antibiotics chemically related to penicillin, thus emergence of this clone is a serious public health issue. Our research objective is to identify genes that contribute to virulence of USA300. Emergence of USA300 is associated with acquisition of certain mobile genetic elements, which we suspect carry genes that impact virulence. To test this hypothesis, mutants of USA300 in which suspected virulence genes have been deleted will be tested in rabbit infection models and in vitro assays to determine if their virulence is reduced compared to the normal strain. Polymorphonuclear neutrophils (PMNs) are the first line of innate host defense against S. aureus infection and are critical for bacterial clearance. PMN function will be assayed in vitro to determine whether virulence factors affect human PMN chemotaxis, phagocytosis, or bacterial killing.
Specific aims are: 1) To identify virulence determinants in the arginine catabolic mobile element (ACME), which is unique to USA300. Deletion of ACME reduces virulence. Three """"""""likely suspect virulence genes, arcA, opp-3A and opp-3DF, will be deleted and each mutant tested to determine which impact virulence. 2) To determine whether SOS response induced by non-lethal exposure to beta-lactam antibiotic generates adaptive mutations offering a survival advantage to MRSA. 3) To determine if disruption of PVL genes attenuates virulence in a rabbit pneumonia model. PVL (Panton-Valentine leukocidin) is generally assumed to be the most important virulence factor in USA300, but this is highly controversial. The rabbit as a species is sensitive to PVL and lung may be target organ. Results from this model should help resolve the controversy as to whether PVL is a major virulence factor. 4) To determine whether genes within two other elements, (Sa3 prophage and SaPI5 pathogenicity island, encode virulence determinants. Relevance: Emergence of virulent, drug-resistant strains of S. aureus in the community is a public problem second only to AIDS in scope and importance. Defining genes contributing to the special virulence of USA300 strains is a critical first step for developing new drugs and approaches for treatment of severe infections caused by community-associated MRSA strains.

Public Health Relevance

Antibiotic resistant strains of Staphylococcus aureus, an important human pathogen, are on the rise. One particular clone, USA300, seems to be especially virulent. Several genes that could be important for virulence are uniquely present in USA300. By knocking each of these genes out and testing for loss of virulence, we hope to learn which genes code for virulence. Once these genes are identified, strategies to block their effects may be developed. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
1R01AI070289-01A2
Application #
7461989
Study Section
Drug Discovery and Mechanisms of Antimicrobial Resistance Study Section (DDR)
Program Officer
Perdue, Samuel S
Project Start
2008-04-01
Project End
2011-03-31
Budget Start
2008-04-01
Budget End
2009-03-31
Support Year
1
Fiscal Year
2008
Total Cost
$382,675
Indirect Cost
Name
University of California San Francisco
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Tattevin, Pierre; Schwartz, Brian S; Graber, Christopher J et al. (2012) Concurrent epidemics of skin and soft tissue infection and bloodstream infection due to community-associated methicillin-resistant Staphylococcus aureus. Clin Infect Dis 55:781-8
Malachowa, Natalia; Whitney, Adeline R; Kobayashi, Scott D et al. (2011) Global changes in Staphylococcus aureus gene expression in human blood. PLoS One 6:e18617
DeLeo, Frank R; Otto, Michael; Kreiswirth, Barry N et al. (2010) Community-associated meticillin-resistant Staphylococcus aureus. Lancet 375:1557-68
Diep, Binh An; Chan, Liana; Tattevin, Pierre et al. (2010) Polymorphonuclear leukocytes mediate Staphylococcus aureus Panton-Valentine leukocidin-induced lung inflammation and injury. Proc Natl Acad Sci U S A 107:5587-92
Chambers, Henry F (2009) Pathogenesis of staphylococcal infection: a manner of expression. J Infect Dis 199:291-3
Miragaia, Maria; de Lencastre, Herminia; Perdreau-Remington, Francoise et al. (2009) Genetic diversity of arginine catabolic mobile element in Staphylococcus epidermidis. PLoS One 4:e7722
Li, Min; Diep, Binh An; Villaruz, Amer E et al. (2009) Evolution of virulence in epidemic community-associated methicillin-resistant Staphylococcus aureus. Proc Natl Acad Sci U S A 106:5883-8
Tattevin, Pierre; Basuino, Li; Chambers, Henry F (2009) Subinhibitory fluoroquinolone exposure selects for reduced beta-lactam susceptibility in methicillin-resistant Staphylococcus aureus and alterations in the SOS-mediated response. Res Microbiol 160:187-92
DeLeo, Frank R; Chambers, Henry F (2009) Reemergence of antibiotic-resistant Staphylococcus aureus in the genomics era. J Clin Invest 119:2464-74
Chambers, Henry F; Deleo, Frank R (2009) Waves of resistance: Staphylococcus aureus in the antibiotic era. Nat Rev Microbiol 7:629-41

Showing the most recent 10 out of 11 publications