Staphylococcus aureus genotypic penicillin susceptibility using a blaZ qPCR directly on blood cultures shows high concordance with phenotype.

Staphylococcus aureus blood cultures were investigated geno- and phenotypically for penicillin susceptibility. A qPCR method detecting the blaZ gene was performed directly on positive blood culture vials and compared with routine disk diffusion results supplemented with the cloverleaf test. Among the collected vials, 100 were blaZ positive and 101 were blaZ negative. Full concordance was observed between genotypical and phenotypical penicillin susceptibility, however one penicillin resistant isolate was only weakly phenotypically positive.