ABSTRACT
@#Objective To investigate the effects of overexpression of OXA-48 on drug resistance,adaptability of bacterial strain and Toll-like receptor(TLR)signaling pathway of host cells. Methods The recombinant plasmid pET32a(+)-OXA-48was transformed into E.coli BL21(DE3),and the recombinant strain pET32a(+)-OXA-48-BL21(DE3)was identified by colony PCR and sequencing. Taking A_(600)(0. 3,0. 5 and 0. 7),IPTG final concentration(0. 4,0. 6 and 0. 8mmol/L)and induction time(2,4 and 6 h)as variables and mRNA transcription level as response value,an orthogonal experiment with three factors and three levels was designed to optimize the induced expression conditions of the plasmid. The drug resistance of recombinant strain pET32a(+)-OXA-48-BL21(DE3)to Imipenem(IPM),Meropenem(MEM),Ceftriaxone(CRO)and Cefepime(FEP)was detected by disk diffusion method;The adaptability was detected by biofilm formation test and serum resistance test. Mouse alveolar macrophages(MH-S)were infected with pET32a(+)-OXA-48-BL21(DE3),pET32a(+)-BL21(DE3)and E.coli BL21(DE3)strains,respectively. The mRNA transcription levels of TLR2,TLR4 and NF-кB(p65)genes were detected by qRT-PCR method,and the expressions of Interleukin-6(IL-6),IL-10,tumor necrosis factor-α(TNF-α)and transforming growth factor-β(TGF-β)were detected by ELISA. Results The recombinant strain pET32a(+)-OXA-48-BL21(DE3)was constructed correctly as identified by colony PCR and sequencing. The optimum induction conditions were as follows:A_(600)of 0. 3,IPTG final concentration of 0. 6 mmol/L and induction time of 2 h. Compared with pET32a(+)-BL21(DE3)strain,the resistance of recombinant strain pET32a(+)-OXA-48-BL21(DE3)to IPM,MEM,CRO and FEP significantly decreased(t = 7. 14～22. 32,P < 0. 05),the biofilm formed significantly increased(t = 15. 69,P < 0. 05),and the survival rate in serum significantly increased(t = 10. 60,P < 0. 05);The mRNA transcription level of TLR2 gene in MH-S cells infected with pET32a(+)-OXA-48-BL21(DE3)significantly increased 24 h after infection(t = 5. 77,P < 0. 05),while the mRNA transcription level of TLR4 and NF-кB(p65)genes(t = 3. 71～10. 06,P < 0. 05)and the expression level of IL-6 significantly increased 12 and 24 h after infection. Compared with the normal group,the expression of IL-6and TNF-α in MH-S cells infected with pET32a(+)-OXA-48-BL21(DE3)increased significantly at 6,12 and 24 h after infection(t = 7. 90 ～ 13. 44 and 5. 40～6. 32 respectively,each P < 0. 01),while the expression of IL-10 decreased significantly(t = 3. 15～4. 08,each P < 0. 05). There was no significant difference in the expression of TGF-β(t = 0. 013～1. 41,each P > 0. 05). The expression of IL-6 was significantly higher than that in pET32a(+)-BL21(DE3)group at 12 and 24 h after infection(t = 2. 92 and 3. 79 respectively,each P < 0.05) Conclusion Overexpression of OXA-48 can reduce bacterial drug resistance,improve bacterial adaptability and the transcription level of factors related to TLR signaling pathway in host cells,and affect the expression level of downstream cytokines in host cells.