[Application of the BACspreader™ Microbe Dispersion Counter in drug susceptibility test on Mycobacterium tuberculosis].

Objective: To evaluate the application of the BACspreader™ Microbe Dispersion Counter in drug susceptibility test (DST) on Mycobacterium tuberculosis (MTB). Methods: The MTB strains were dispersed and diluted to 1.0 McFarland standard turbidity, by means of BACspreader™ Microbe Dispersion Counter and manual grinding method, respectively. The bacterial dispersion effect and bacterial activity were tested by microscope and colony counting method. During Jan. 2015 to June 2015, a total of 726 isolates of MTB were collected in all district tuberculosis hospitals of Shanghai. The bacterial suspension dispersed by instrument and manual grinding, were inoculated in slant medium for DST (Proportion Method), and then incubated in 37 ℃ incubator for 28 days and the DST results were reported. The effects of the 2 different bacterial dispersion methods were compared by comparing DST results and counting the bacterial colony which grew in high and low concentration control media. Paired chi-square test was used for statistical analysis, and the significance level was 0.05. Results: Compared to the manual grinding method, the MTB colony could be better dispersed by BACspreader™ Microbe Dispersion Counter, without reducing the bacterial activity. The DST results of 726 mycobacterial isolates were the same by different bacterial dispersion methods. The count of bacterial colony growing in high concentration control medium was significantly different between of the 2 dispersion methods (χ(2)=8.0, P<0.01). When counting the bacterial colony growing in low concentration control medium, the numerable rate was 97.7% by BACspreader™ Microbe Dispersion Counter, and 4.3% by manual grinding method; the difference being significant between the 2 dispersion methods (χ(2)=674, P<0.001). Conclusions: Compared to the manual grinding method, the slant medium inoculated with bacterial suspension obtained by BACspreader™ Microbe Dispersion Counter had better countability in low concentration control slants, and had more significant contrast between high and low concentration control slants, which was useful to determine the DST results. Introducing the BACspreader™ Microbe Dispersion Counter to MTB DST could automate the DST process, make the testing results objective and standardized, and reduce personal error in the tests.