Application of fnbA gene as new target for the species-specific and quantitative detection of Staphylococcus aureus directly from lower respiratory tract specimens by real time PCR.

Staphylococcus aureus is a significant cause of hospital-acquired pneumonia (HAP), particularly in mechanically ventilated patients. We used the fibronectin-binding protein A gene (fnbA) for the species-specific and quantitative detection of S. aureus directly from lower respiratory tract (LRT) specimens by a Taq Man real time PCR. For this reason, a total of 269 lower respiratory tract (LRT) specimens collected from patients with hospital-acquired pneumonia were assayed. Amplification of fnbA in serial dilutions ranged from 10(9) CFU/ ml to 10(2) CFU/ml. Standard curve of triplicate every dilution had slope 3.34±0.1 and R2>0.99 with SD 0.1. Based on these data, the sensitivity and specificity of the newly developed real time PCR targeting the fnbA gene were both 100%. The Cohen's Kappa test showed the Kappa value of 1.0. The fnbA gene is a potential marker for the species-specific detection of S. aureus and can be used to detect this bacterium in any clinical specimens by real time PCR. Moreover, this method reduces the time needed for quantitative detection of Staphylococcus aureus from LRT specimens to nearly 2 hours compared to 1 to 4 days for culture and provided sensitivity equal to or greater than culture.