Real-Time PCR and MSRA From Positive Blood Culture Bottles
Real-Time PCR and MSRA From Positive Blood Culture Bottles
We developed, validated, and implemented real-time polymerase chain reaction (PCR) detection of the femA gene for Staphylococcus aureus and the mecA gene for methicillin resistance directly from BACTEC (Becton Dickinson, Sparks, MD) blood culture bottles showing gram-positive cocci in clusters. For the 332 positive blood cultures tested, the assay had 100% sensitivity and specificity for identifying methicillin-susceptible (n = 28) and methicillin-resistant (n = 28) S aureus, and overall was 98% sensitive and 94% specific, with 3 uninterpretable test results when identification of coagulase-negative staphylococci was included. PCR detection yields rapid (2-3 hours) results and accurate identification of S aureus directly from signal-positive blood culture bottle samples.
Staphylococcus aureus is an important cause of bloodstream infections and a leading cause of severe health care-associated infections. Infection results in significant morbidity and mortality and longer hospital stays if not treated early with effective antibiotics. The prevalence of methicillin resistance in S aureus causing infection now exceeds 49% in US hospitals and continues to increase. Thus, improved methods are needed for rapid detection and differentiation of methicillin-susceptible S aureus (MSSA) and methicillin-resistant S aureus (MRSA) bacteremia to ensure optimal treatment early in the infection.
Initial antimicrobial treatment for bacteremia often is based on the results of the Gram stain from a positive blood culture bottle. In 48 to 72 hours, results of conventional culture and susceptibility testing permit a change to pathogen-specific antimicrobial therapy. Although vancomycin remains the treatment of choice for MRSA bacteremia, unnecessary use should be avoided to prevent further emergence of resis-tance as well as colonization or infection by organisms such as vancomycin-resistant enterococci. In addition, treatment of MSSA infections with vancomycin might be inferior to treatment with antistaphylococcal penicillins. The earlier one knows whether the positive blood culture contains S aureus and whether it is methicillin-resistant or susceptible, the more quickly appropriate therapy can be initiated.
We developed, validated, and implemented real-time polymerase chain reaction (PCR) detection of the femA gene for Staphylococcus aureus and the mecA gene for methicillin resistance directly from BACTEC (Becton Dickinson, Sparks, MD) blood culture bottles showing gram-positive cocci in clusters. For the 332 positive blood cultures tested, the assay had 100% sensitivity and specificity for identifying methicillin-susceptible (n = 28) and methicillin-resistant (n = 28) S aureus, and overall was 98% sensitive and 94% specific, with 3 uninterpretable test results when identification of coagulase-negative staphylococci was included. PCR detection yields rapid (2-3 hours) results and accurate identification of S aureus directly from signal-positive blood culture bottle samples.
Staphylococcus aureus is an important cause of bloodstream infections and a leading cause of severe health care-associated infections. Infection results in significant morbidity and mortality and longer hospital stays if not treated early with effective antibiotics. The prevalence of methicillin resistance in S aureus causing infection now exceeds 49% in US hospitals and continues to increase. Thus, improved methods are needed for rapid detection and differentiation of methicillin-susceptible S aureus (MSSA) and methicillin-resistant S aureus (MRSA) bacteremia to ensure optimal treatment early in the infection.
Initial antimicrobial treatment for bacteremia often is based on the results of the Gram stain from a positive blood culture bottle. In 48 to 72 hours, results of conventional culture and susceptibility testing permit a change to pathogen-specific antimicrobial therapy. Although vancomycin remains the treatment of choice for MRSA bacteremia, unnecessary use should be avoided to prevent further emergence of resis-tance as well as colonization or infection by organisms such as vancomycin-resistant enterococci. In addition, treatment of MSSA infections with vancomycin might be inferior to treatment with antistaphylococcal penicillins. The earlier one knows whether the positive blood culture contains S aureus and whether it is methicillin-resistant or susceptible, the more quickly appropriate therapy can be initiated.
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