OBJECTIVETo explore the effects of exogenous carbon monoxide-releasing molecules 2 (CORM-2) on the vitality and toxicity of E. coli ATCC 25922, and to analyze the potential mechanism.

METHODS(1) In vitro experiments. Standard strains of E. coli ATCC 25922 were divided into groups A (without addition), B, C, D, and E according to the random number table, and then the latter 4 groups were respectively cultured with 1.2 mmol/L CORM-2, 1.6 mmol/L CORM-2, 1.2 mmol/L inactive CORM-2 (iCORM-2), 1.6 mmol/L iCORM-2, with six samples in each group. After being cultured for 0, 3, 5, 8, 10, 12, 16, 20, 24, 27, 30, 48 hours, proliferative vitality of E. coli was examined (denoted as absorption value under 600 nm wavelength), and bacteria number was counted. Other standard strains of E. coli ATCC 25922 were divided into groups F (without addition) and G (cultured with 0.8 mmol/L CORM-2), the expressions of genes fliA, dnaK, marA, and waaQ related to E. coli were detected by quantitative real-time (qRT)-PCR. (2) In vivo experiments. Other standard strains of E. coli ATCC 25922 were grouped as A', B', C', D', and E' and treated with the same method as that in groups A, B, C, D, and E, and 0.5 mL bacterial liquid of each group were collected when the absorption value of bacterial liquid in group A' was equal to 0.4 (under 600 nm wavelength). Seventy-two C57BL/6 mice were divided into groups, namely blank control (without treatment), H, I, J, K, and L according to the random number table, with 12 mice in each group. The mice in the latter 5 groups were intraperitoneally injected with 0.5 mL bacterial suspension of groups A', B', C', D', and E' respectively. After injection, general condition of mice in groups H, I, J, K, and L was observed. The serum levels of TNF-α and IL-6 were determined at post injection hour (PIH) 6, 12. The liver and lung samples were harvested for determination of myeloperoxidase (MPO) activity at PIH 12. The same process was carried out in blank control group. Data were processed with repeated measure analysis of variance (ANOVA), factorial design ANOVA, one-way ANOVA, and t test.

RESULTS(1) In vitro experiments. Compared with those of groups A and D, the proliferative vitality and bacteria number of E. coli in group B were all decreased (with F values respectively 1170.80, 217.52, P values all below 0.01). Compared with those of groups A and E, the proliferative vitality and bacteria number of E. coli in group C were also obviously decreased (with F values respectively 7948.34, 14 432.85, P values all below 0.01). Compared with those in group F, the expression of fliA was downregulated, while the expressions of dnaK, marA, and waaQ were upregulated in group G (with t values 30.28, -165.54, -168.88, -187.28, P values all below 0.01). (2) In vivo experiments. Symptoms including listlessness and tachypnea were observed in mice in groups H, K, and L, and they were ameliorated or not obvious in groups I and J. At PIH 6, the serum levels of TNF-α and IL-6 in groups H and K were respectively (647.3 ± 3.8) pg/mL, (3.44 ± 0.22) ng/mL and (639.3 ± 0.8) pg/mL, (2.47 ± 0.32) ng/mL, which were obviously higher than those in group I [(124.6 ± 10.7) pg/mL, (1.03 ± 0.16) ng/mL, with t values from 15.22 to 84.03, P values all below 0.01]. The serum levels of TNF-α and IL-6 in group J at PIH 6, 12 were also obviously decreased as compared with those in groups H and L (with t values from 19.27 to 245.34, P values all below 0.01). MPO activity of liver and lung tissues were significantly attenuated in group I at PIH 12 as compared with those in groups H and K, and it was also attenuated in group J when compared with those in groups H and L (with t values respectively from 17.36 to 18.92 and 2.35 to 3.61, P values all below 0.01).

CONCLUSIONSCORM-2 can obviously inhibit the vitality and toxicity of E. coli, which might be attributable to regulation of expressions of genes fliA, dnaK, marA, and waaQ of E. coli.