High levels of mecA DNA detected by a quantitative real-time PCR assay are associated with mortality in patients with methicillin-resistant Staphylococcus aureus bacteremia

J Clin Microbiol. 2009 May;47(5):1443-51. doi: 10.1128/JCM.01197-08. Epub 2009 Mar 11.


Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is known to be a poor prognostic factor. While several PCR assays for the detection of MRSA in various clinical samples were recently reported, the possibility that a quantitative PCR assay could be used to quantify and monitor MRSA bacteremia has not been explored. In this study, we established a quantitative real-time PCR assay for the mecA gene using known copy numbers of a plasmid containing mecA DNA as a standard and the previously described mecA-specific primers and probe (P. Francois et al., J. Clin. Microbiol. 41:254-260, 2003). We employed this assay to examine 250 sequential whole-blood samples from 20 adult patients, including 13 survivors and 7 nonsurvivors, with culture-proven MRSA bacteremia at the intensive care units of National Taiwan University Hospital between 1 July 2006 and 31 January 2007. The levels of mecA DNA in the nonsurvivors were significantly higher than those in the survivors during the three periods of bacteremia examined (days 0 to 2, 3 to 5, and 6 to 8) (P = 0.003 by two-tailed Mann-Whitney U test). Moreover, the nonsurvivors had higher mecA DNA levels than the survivors after 3 days and 7 days of anti-MRSA therapy (medians for nonsurvivors and survivors at 3 days, 5.86 and 4.30 log copies/ml, respectively; medians for nonsurvivors and survivors at 7 days, 5.21 and 4.36 log copies/ml, respectively; P = 0.02 and P = 0.04, respectively, by two-tailed Mann-Whitney U test). Together, these findings suggest that the level of mecA DNA in blood could potentially be used to monitor MRSA bacteremia and evaluate responses to therapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Bacteremia / drug therapy
  • Bacteremia / microbiology*
  • Bacteremia / mortality
  • Bacterial Proteins / genetics*
  • DNA, Bacterial / blood*
  • Female
  • Humans
  • Male
  • Methicillin-Resistant Staphylococcus aureus / genetics*
  • Middle Aged
  • Penicillin-Binding Proteins
  • Polymerase Chain Reaction / methods*
  • Staphylococcal Infections / drug therapy
  • Staphylococcal Infections / microbiology*
  • Staphylococcal Infections / mortality
  • Taiwan
  • Time Factors
  • Treatment Outcome


  • Bacterial Proteins
  • DNA, Bacterial
  • Penicillin-Binding Proteins
  • mecA protein, Staphylococcus aureus