Checkerboard Method

Firstly, the minimum inhibitory concentration (MIC) of two different drugs to Helicobacter pylori should be determined by using agar dilution method respectively. Then, different drug combinations were designed as shown in Figure 1 to explore the combined bacteriostatic effect of the two drugs. Take point a in Figure 1 as an example, it contains 0.5×MIC of drug A and 0.25×MIC of drug B. 

Figure 2 shows the specific method for us to prepare the drug-containing plate. Briefly, 49.5 mL sterilized culture medium (5% sheep blood) was mixed with 0.25 mL of the two drugs (dissolved in DMSO), and the final concentration of each drug reaches to the appropriate concentration. There are 25 ml drug-containing culture medium in each plate.

After solidification for 24 h, about 1×10⁸ CFU/ml Helicobacter pylori suspension (in PBS) were flooded on the plate, and the growth of bacteria was observed in 4 days later. The result was judged according to the formula in Figure 3.

Figure 1

Figure 2

Figure 3

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