Influence of antibiotic treatment on the detection of S. aureus in whole blood following pathogen enrichment

Early pathogendetection and identification are crucial for an effective and targeted antibiotic therapy in patients suffering from blood stream infection. Molecular diagnostic methods can accelerate pathogenidentification as compared to blood culture, but frequently suffer from the inhibition of polymerase chain reation (PCR) by sample matrix components, such as host DNA, anticoagulants, or plasma proteins. To overcome this limitation, molecular diagnostic methods commonly rely on pathogenenrichment by selective lysisof blood cells and pelleting of intact pathogensprior to analysis. Here, we investigated the impact of antibiotic treatment on the recovery of pathogenDNA using an established pathogenenrichment protocol. Based on the hypothesis that induction of bacterial cell walldisintegration following antibiotic administration leads to incomplete pelleting of pathogenDNA, S. aureus was grown in human whole blood with or without addition of cell wallactive (vancomycin, piperacillin) or non cell wallactive (ciprofloxacin, clindamycin) antibiotics at clinically relevant concentrations. Pathogendetection remained unaffected by non cell wallactive antibiotics or even increased in the presence of cell wallactive antibiotics, indicating improved accessibility of pathogenDNA. Likewise, mechanical lysisof S. aureus prior to pathogenenrichment resulted in increased recovery of pathogenDNA. Quantification of pathogenand human DNA after selective lysisof blood cells and pathogenenrichment confirmed partial depletion of human DNA, leading to a net enrichment of pathogenDNA over human DNA. Concurrent antibiotic administration does not reduce the recovery of pathogenDNA during pathogenenrichment by selective lysisand centrifugation. Leads to a 10-fold human DNA depletion as compared to pathogenDNA. Moreover, we confirm that the recovery of pathogenDNA after pathogenenrichment is not negatively influenced by concurrent antibiotic administration.