Inhibition of silver ion on the frequency of bacterial integron trapping drug resistance gene cassette / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To analyze the effects of silver ion on the integration frequency of the class 1 integron in Escherichia coli ( E. coli) BL21(DE3) host. Methods:Two recombinant plasmids, pUCINT and pACINAD, were successively transformed into E. coli BL21 (DE3) to construct HS2 strains. Three experimental groups were set up using 0.3 μg/ml, 0.6 μg/ml and 0.8 μg/ml silver ion LB liquid medium, while control group used common LB liquid medium. Silver ion was supplied by silver nitrate and HS2 strains were cultured at 37℃ for 24 h. The copy number of cointegrates and the total copy number of integrons in each group were detected by real-time polymerase chain reaction (qPCR), and the ratio of them was the integration frequency. Changes in the integration frequency were analyzed by three independent phenotypic screening method and the protein expression in HS2 strains was analyzed by mass spectrometry. Results:The integration frequency in HS2 strains in the control group and three experimental groups (0.3 μg/ml, 0.6 μg/ml and 0.8 μg/ml silver ion) was 1.79×10 -5 (1.44×10 -5, 3.13×10 -5), 2.07×10 -5 (1.49×10 -5, 2.67×10 -5), 2.25×10 -6 (1.47×10 -6, 4.54×10 -6) and 1.69×10 -6 (0.22×10 -6, 3.08×10 -6), respectively. The integration frequency in the 0.6 μg/ml and 0.8 μg/ml silver ion groups was significantly lower than that in the control group ( P<0.01), but there was no significant difference between the 0.3 μg/ml silver ion group and the control group. Results of three independent phenotypic screening method were consistent with those obtained by qPCR. Mass spectrometry analysis showed that there were differences in protein expression in HS2 strains between the control group and the experimental groups. Conclusions:Silver ion at a certain concentration had an inhibitory effect on the frequency of drug resistance gene cassette captured by bacterial integron.