The ETGA AST method was successful in producing MICs that were in agreement with results obtained from the macrobroth dilution method using bacteria harvested directly from positive blood cultures. In contrast, gsPCR was less successful: MRSA versus oxacillin produced a very major

error at six hours, and MRSA versus vancomycin produced gsPCR reactions that were not always detected. A point of Acadesine nmr concern with these experiments is that the inoculation verification indicated that the bacterial input was much lower than 5E + 05 CFU/mL because the CFU were too dilute to be countable. It has been reported that a 0.5 McFarland standard, which is expected to be within 1-2E + 08 CFU/mL may be as low as 1E + 07 CFU/mL depending Caspase Inhibitor VI on the species being measured [3]. While this lower titer appeared not to affect the macrobroth or the ETGA results, it may have affected the gsPCR results. The procedure for harvesting the bacteria with a SST was followed as described by Beuving et al. [19, 20]. However, their manuscripts do not indicate whether the investigators verified their inoculation concentration performing their molecular AST assays. Harvesting

bacteria with SST from positive blood cultures GSK1210151A manufacturer was previously described by Funke and Funke-Kissling [13] for gram negative rods, and by Lupetti et al. [14] for gram positive cocci. In these reports, gram negative rods were harvested by applying positive blood culture directly into an SST, but gram positive cocci were first incubated in a 0.01% final concentration of saponin. The report from Beuving et al. harvests bacteria through an SST without any pre-treatment regardless of the gram status. If pre-treatment of the blood culture before serum separation is required for a more efficient bacterial yield, particularly for gram positive cocci, this could be a reason for some of the errors that we observed. Furthermore, we noticed that Phenylethanolamine N-methyltransferase transferring

bacteria from the gel plug to the saline solution can also lead to transferring some of the gel which could lead to overestimating the turbidity of the 0.5 McFarland standard. This observation presents an opportunity to further improve the sample preparation for increased bacterial yield harvested directly from positive blood cultures and ultimately improve the accuracy of molecular AST. Wiegard et al. [7] describe a microdilution AST method performed in a 96-well microtiter plate. The authors present a protocol in which a bacterium of interest is inoculated into a matrix of various antibiotics and concentrations. This plate is incubated for 16–20 hours prior to interpreting the results by visual observation. Utilizing this design, a high-throughput ETGA AST method could be developed. In this scenario, an AST matrix can be assembled (keeping a few wells available for the required ETGA controls), and allowed to incubate for four to six hours.