MRSA and VISA strains continue to present serious challenge to the therapy of staphylococcal disease. Highly virulent and epidemic lineages have emerged among community acquired MRSA and treatment failure during vancomycin therapy continues to be reported in the clinical literature. As to the scientific challenges presented by drug resistant S. aureus: while several critical genetic determinants of the resistance mechanisms have been identified, the path leading from the resistant genes to the antibiotic resistant phenotype has remained an enigma in both MRSA and VISA strains. All clinical isolates of MRSA carry the same mecA gene encoding for the low antibiotic affinity protein PBP2a. Nevertheless, individual MRSA strains exhibit a vast range of oxacillin MIC values which can spread from a few micrograms up to the milligram range. Furthermore, the majority of MRSA isolates show a peculiar - heterogeneous - phenotype: such strains produce cultures in which the great majority of cells (99-99.9%) exhibit very low MIC values but the same cultures also contain one or more sub-populations of highly resistant bacteria which are present with low and unique frequencies. Besides presenting an intriguing scientific puzzle the phenomenon of hetero resistance may have important clinical implications as well, since selection of the highly resistant subpopulations in vivo may jeopardize the success of therapy. The mechanism by which these complex MRSA phenotypes are generated from the same mecA determinant is unknown. Similarly, genetic determinants associated with the acquisition of VISA type vancomycin resistance has been determined recently by full genome sequencing but the mechanism by which the increased vancomycin MIC value and the large number of phenotypic alterations are generated from the 33 specific mutations identified in the sequenced VISA strain JH9 [2] - remains to be determined. Thus, the common question posed for both the MRSA and VISA mechanisms in the new research program is this: how does one go from a resistance gene to the resistant phenotype? The studies in the new research program are organized into four major foci of activity. Project A. Genetic determinants of high level antibiotic resistance in heteroresistant MRSA clones. Project B. Genetic and environmental factors defining the antibiotic resistant phenotype in MRSA. Project C. Pathways of cell wall synthesis and antibiotic resistance level in MRSA. Project D. Genetic pathways to decreased vancomycin susceptibility.

Public Health Relevance

Multidrug resistant MRSA strains continue to spread both in hospitals and in the community and infections by these """"""""superbugs"""""""" were estimated to cause close to 19,000 deaths and billions of dollars in health care costs per year in the USA. Clinical treatment failures with vancomycin - often called the """"""""last resort"""""""" antibiotic - have also been described. We plan to use methods of modern science such as whole genome DNA sequencing to understand the mechanisms these dangerous pathogens have invented and to help develop new interventions that could reestablish control over multidrug resistant bacteria.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Drug Discovery and Mechanisms of Antimicrobial Resistance Study Section (DDR)
Program Officer
Huntley, Clayton C
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Rockefeller University
Other Domestic Higher Education
New York
United States
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Milheiriço, Catarina; de Lencastre, Hermínia; Tomasz, Alexander (2017) Full-Genome Sequencing Identifies in the Genetic Background Several Determinants That Modulate the Resistance Phenotype in Methicillin-Resistant Staphylococcus aureus Strains Carrying the Novel mecC Gene. Antimicrob Agents Chemother 61:
Hamilton, Stephanie M; Alexander, J Andrew N; Choo, Eun Ju et al. (2017) High-Level Resistance of Staphylococcus aureus to ?-Lactam Antibiotics Mediated by Penicillin-Binding Protein 4 (PBP4). Antimicrob Agents Chemother 61:
Rolo, Joana; Worning, Peder; Boye Nielsen, Jesper et al. (2017) Evidence for the evolutionary steps leading to mecA-mediated ?-lactam resistance in staphylococci. PLoS Genet 13:e1006674
Leinberger-Jabari, Andrea; Kost, Rhonda G; D'Orazio, Brianna et al. (2016) From the Bench to the Barbershop: Community Engagement to Raise Awareness About Community-Acquired Methicillin-Resistant Staphylococcus aureus and Hepatitis C Virus Infection. Prog Community Health Partnersh 10:413-423
Grilo, Inês R; Ludovice, Ana Madalena; Tomasz, Alexander et al. (2014) The glucosaminidase domain of Atl - the major Staphylococcus aureus autolysin - has DNA-binding activity. Microbiologyopen 3:247-56
Kim, Choonkeun; Mwangi, Michael; Chung, Marilyn et al. (2014) Correction: The Mechanism of Heterogeneous Beta-Lactam Resistance in MRSA: Key Role of the Stringent Stress Response. PLoS One 9:
Kim, Choonkeun; Mwangi, Michael; Chung, Marilyn et al. (2013) The mechanism of heterogeneous beta-lactam resistance in MRSA: key role of the stringent stress response. PLoS One 8:e82814
Mwangi, Michael M; Kim, Choonkeun; Chung, Marilyn et al. (2013) Whole-genome sequencing reveals a link between ?-lactam resistance and synthetases of the alarmone (p)ppGpp in Staphylococcus aureus. Microb Drug Resist 19:153-9
Vidaillac, Celine; Gardete, Susana; Tewhey, Ryan et al. (2013) Alternative mutational pathways to intermediate resistance to vancomycin in methicillin-resistant Staphylococcus aureus. J Infect Dis 208:67-74
Kim, Choonkeun; Milheiriço, Catarina; Gardete, Susana et al. (2012) Properties of a novel PBP2A protein homolog from Staphylococcus aureus strain LGA251 and its contribution to the ?-lactam-resistant phenotype. J Biol Chem 287:36854-63

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