Objective To investigate the effect of polymyxin B(PMB)combined with tigecycline(TGC)on delaying Klebsiella pneumoniae(KP)resistance to PMB,and to analyze the possible mechanisms involved in the induction and delay of resistance.Methods Six clinical isolates of KP strains from the Intensive Care Unit of First Affiliated Hospital of Army Medical University were subjected and then induced with PMB at 1/2 minimal inhibitory concentration(MIC)alone or combined with TGC at 1/2 and 1/4 MIC,respectively.The MIC changes of PMB in these strains were monitored over 14 consecutive passages.The strain 686K,which showed the most significant delay in resistance,was selected for further analysis.Differences in gene and protein expression were examined among the wild-type strain 686K,PMB-induced resistant strain(686K·R),and PMB combined with TGC delayed resistant strain(686K·DR)using transcriptome sequencing,qRT-PCR,and proteomics.Relevant target genes during the delay of resistance were analyzed through literature and bioinformatics analyses.Additionally,cpxR gene knockout strain 686K/ΔcpxR∷Apr and its complementation strain 686K/ΔcpxR∷Apr/pRK415-cpxR were constructed using homologous recombination technology to assess the expression levels of resistance-related genes and changes in MIC after induction in vitro.Results Under sub-MIC(1/2)PMB alone,resistance developed in all 6 KP strains within 2 d,while,the combination with TGC significantly delayed the development of resistance.Transcriptomic and proteomic analyses indicated that in strain 686K·R,the expression levels of the PhoP/Q two-component system,lipopolysaccharide(LPS)modification enzymes,and efflux pump systems were significantly up-regulated(|Log2FC|≥2,P<0.0001),while TGC co-administration markedly inhibited these expression changes.The cpxR deletion and complementation strains were successfully constructed.The expression levels of resistance-related genes phoP,pmrD,and acrA were decreased in the cpxR deletion strain(P<0.001),and the resistance was delayed until day 6 under PMB monotherapy,whereas the complementation strain restored the resistance phenotype by day 2.In the absence of cpxR,the effect of PMB when combined with TGC on delaying resistance did not differ from that observed with PMB monotherapy.Conclusion The combination of PMB and TGC can delay KP resistance to PMB.cpxR,as a critical regulatory factor,can impact PMB resistance by modulating LPS modifications and the expression of the AcrAB-TolC efflux pump,and plays an important regulatory role in the process of resistance induction.

Objective To investigate the effects of Epigallocatechin gallate(EGCG)on IL-1βinduced MIN6 cells apoptosis. M.Methods The experiment group was divided into control group,IL-1β group,IL-1β+ EGCG low concentration group and IL-1β+EGCG high concentration group.Cell activity was detected by CCK8.Insulin secretion was detected by ELISA.cell apoptosis was detected by flow cytometry.The mitochondrial membrane potential was detected by flow cytometry.ATP content and cell ac-tivity of ROS were detected by colorimetry and chemiluminescence method.Results Compared with normal group,IL-1β group showed much lower cell activity,insulin secretion,cell mitochondrial membrane potential and ATP content,and at the same time IL-1βgroup had significantly higher cell apoptosis and ROS activities.After given EGCG,both low concentration group and high con-centration group had higher cell activity,insulin secretion,cell mitochondrial membrane potential and ATP content,at the same time lower cell apoptosis and ROS activities was showed.And the IL-1β+EGCG high concentration group worked more powerful.Con-clusion EGCG has protective effects on IL-1βinduced MIN6 cells apoptosis.Its mechanism may be related to increasing the content of the ATP and mitochondrial membrane potential and protecting mitochondrial function as well reducing the activity of ROS.