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

Abstract

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.Methicillin-resistant Staphylococcus aureus (MRSA) is a pathogen that is one of the most common causes of both community-acquired and nosocomial infections worldwide, especially in intensive care units (ICUs) (5,8,33,49). In the past two decades, the proportion of MRSA infections has increased dramatically, and up to 60% of S. aureus isolates from ICUs were reported to be methicillin resistant (26). Compared with cases of bacteremia caused by methicillin-susceptible S. aureus (MSSA) strains, cases of bacteremia caused by MRSA strains have been shown to be associated with more persistent infections, more recurrent episodes, longer hospital stays, and higher rates of mortality (3,6,11,13,14,27). Because of the high rates of mortality and the refractoriness of MRSA bacteremia to treatment, MRSA bacteremia has become a very challenging infectious disease (18,21,38,39,42).It has recently been demonstrated that high bacterial loads in blood correlate with disease severity in patients with infections caused by Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis (4,22,35,41), as well as in a murine model of Serratia marcescens infection (25). In the case of S. aureus-related infections, it was reported that positive blood cultures during follow-up and the persistence of fever were suggestive of a complicated course (6,15,37). However, the drastic decrease in the sen...

Combined Inhibition of Complement and CD14 Efficiently Attenuated the Inflammatory Response Induced byStaphylococcus aureusin a Human Whole Blood Model

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Improved Sensitivity for Molecular Detection of Bacterial and Candida Infections in Blood

“…In order to estimate the true concentration of pathogen DNA available in whole blood for molecular analysis from patients with bloodstream infections, we analyzed the data available in the literature. Organism-specific quantitative PCR has been used to measure the bacterial DNA present in whole-blood specimens from patients with sepsis, pneumonia, or suspected bloodstream infections (13,(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48). Each of these studies analyzed whole-blood specimens from patients with suspected or confirmed infections rather than spiked samples for which the genome-to-viable cell ratio is expected to be close to 1:1.…”

Vibrio vulnificus DNA Load and Mortality

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