ABSTRACT
Objective To investigate the inhibitory effects of aloin on the growth of Staphylococcus aureus and its virulence factors α-hemolysin in vitro.Methods Broth dilution was used to measure the minimum inhibitory concentration (MIC) of water-soluble aloin on S.aureus.Agar drilling method was used to observe the size of inhibition zone of aloin for S.aureus.Plasma coagulase test was used to detect the changes of S.aureus coagulase and absorbance was measured to detect the changes of hemolytic activity when S.aureus was exposed to aloin.Real time PCR was used to detect the effects of aloin on the expressions of hla and agrA mRNA.Results The soluble aloin inhibited the growth of S.aureus in a dose-dependent manner.The inhibition zone diameter of a standard strain of S.aureus (ATCC 25923) was 21.5 mm with MIC of 12.5 mg/mL and 17 mm for the clinical isolate SA1.5 with MIC of 15 mg/mL.After treated with soluble aloin,the coagulase titers of ATCC 25923 were 16,4 and 2 for 1/2 MIC,1 MIC and 2 MIC respectively compared with titer 32 of the control group without soluble aloin.The expression of α-hemolysin of S.aureus ATCC 25923 was down-regulated by soluble aloin and the hemolytic activity of S.aureus ATCC 25923 with 1/2 MIC,1 MIC and 2 MIC groups were (77.4 ±3.41) ％,(42.2 ± 2.4) ％ and (38.7 ± 2.4) ％ respectively.The expression levels of hla were 0.020 3 (0.019 6,0.028 8),0.011 6(0.010 6,0.013 1) and 0.033 7(0.020 2,0.042 9) respectively in the 1/2 MIC,1 MIC and 2 MIC group respectively,and there were significant differences among the three groups (H =16.807,P ＜ 0.05).The expression levels of agrA was 0.074 6 (0.066 2,0.098 2),0.020 8 (0.012 2,0.032 6) and 0.021 3 (0.010 2,0.029 6) in the 1/2 MIC,1 MIC and 2 MIC group respectively,and there were significant differences among the three groups (H =16.320,P ＜ 0.05).Conclusion Aloin may inhibit the growth of S.aureus and could effectively inhibit the expression of α-hemolysin.
ABSTRACT
In order to create a novel recombinant human interferon alpha2b (rh-IFN alpha2b) with higher biological activity, we subjected the rational designed sequence of rh-IFN alpha2b to direct evolution by strategy of the combinatorial mutagenesis. The amino acid residues at multiple sites of 52-53-55, 103-107, and 121-125 were simultaneously mutated. The resulted gene of the mutated rh-IFN a2b was cloned into the pET28a and expressed in E. coli BL21 Condon plus (RIL). The anti-virus activity of the novel interferon alpha2b was 9.3 x 10(7) IU/mg, 93 times higher than the wild type (1 x 10(6) IU/mg). The results showed that the multiple point mutation used in this study could effectively combine the site effects of rh-IFN alpha2b and increase its biological activity.